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SDG 13

Climatic variability and hemispheric differences in insect cold tolerance: support from southern Africa
29 March 2007
Stellenbosch University

Sinclair, BJ;Chown, SL

1. Insects generally survive subzero temperatures by utilizing either freeze tolerance or freeze avoidance. Comparative analyses from a limited data set have indicated that freeze tolerance may be predominant among species at temperate latitudes in the southern hemisphere, while freeze avoidance dominates in the north. 2. We investigated the cold tolerance strategies of cockroaches and beetles from cold regions in southern Africa, including the Cederberg mountains, the Karoo desert and the Drakensberg mountains. 3. We found that 8 of 11 species are freeze tolerant. 4. Overall, 77% of species investigated in the southern hemisphere (n = 27) were freeze tolerant, which is significantly different from the 29% (n = 258) in the north (P < 0·001). 5. There are regular, unpredictable subzero temperature events in the southern African habitats; such variability appears to be a general feature of many cold habitats in the southern hemisphere, which may lead to the observed interhemispheric discrepancies in cold-tolerance strategies.
Niche-based modelling as a tool for predicting the risk of alien plant invasions at a global scale
16 April 2007
Stellenbosch University

Thuiller, W;Richardson, DM;Pysek, P;Midgley, GF;Hughes, GO;Rouget, M

Predicting the probability of successful establishment of plant species by matching climatic variables has considerable potential for incorporation in early warning systems for the management of biological invasions. We select South Africa as a model source area of invasions worldwide because it is an important exporter of plant species to other parts of the world because of the huge international demand for indigenous flora from this biodiversity hotspot. We first mapped the five ecoregions that occur both in South Africa and other parts of the world, but the very coarse definition of the ecoregions led to unreliable results in terms of predicting invasible areas. We then determined the bioclimatic features of South Africa's major terrestrial biomes and projected the potential distribution of analogous areas throughout the world. This approach is much more powerful, but depends strongly on how particular biomes are defined in donor countries. Finally, we developed bioclimatic niche models for 96 plant taxa (species and subspecies) endemic to South Africa and invasive elsewhere, and projected these globally after successfully evaluating model projections specifically for three well-known invasive species (Carpobrotus edulis, Senecio glastifolius, Vellereophyton dealbatum) in different target areas. Cumulative probabilities of climatic suitability show that high-risk regions are spatially limited globally but that these closely match hotspots of plant biodiversity. These probabilities are significantly correlated with the number of recorded invasive species from South Africa in natural areas, emphasizing the pivotal role of climate in defining invasion potential. Accounting for potential transfer vectors (trade and tourism) significantly adds to the explanatory power of climate suitability as an index of invasibility. The close match that we found between the climatic component of the ecological habitat suitability and the current pattern of occurrence of South Africa alien species in other parts of the world is encouraging. If species' distribution data in the donor country are available, climatic niche modelling offers a powerful tool for efficient and unbiased first-step screening. Given that eradication of an established invasive species is extremely difficult and expensive, areas identified as potential new sites should be monitored and quarantine measures should be adopted.
The effect of fire season, fire frequency, rainfall and management on fire intensity in savanna vegetation in South Africa
17 April 2007
Stellenbosch University

Govender, N;Trollope, WSW;van Wilgen, BW

1. Fire is important for the maintenance and conservation of African savanna ecosystems. Despite the importance of fire intensity as a key element of the fire regime, it is seldom measured or included in fire records. 2. We estimated fire intensity in the Kruger National Park, South Africa, by documenting fuel loads, fuel moisture contents, rates of fire spread and the heat yields of fuel in 956 experimental plot burns over 21 years. 3. Individual fires were conducted in five different months (February, April, August, October and December) and at five different return intervals (1, 2, 3, 4 and 6 years). Estimated fire intensities ranged from 28 to 17 905 kW m(-1). Fire season had a significant effect on fire intensity. Mean fire intensities were lowest in summer fires (1225 kW m(-1)), increased in autumn fires (1724 kW m(-1)) and highest in winter fires (2314 kW m(-1)); they were associated with a threefold difference between the mean moisture content of grass fuels in winter (28%) and summer (88%). 4. Mean fuel loads increased with post-fire age, from 2964 kg ha(-1) on annually burnt plots to 3972 kg ha(-1) on biennial, triennial and quadrennial burnt plots (which did not differ significantly), but decreased to 2881 kg ha(-1) on sexennial burnt plots. Fuel loads also increased with increasing rainfall over the previous 2 years. 5. Mean fire intensities showed no significant differences between annual burns and burns in the biennial, triennial and quadrennial categories, despite lower fuel loads in annual burns, suggesting that seasonal fuel moisture effects overrode those of fuel load. Mean fire intensity in sexennial burns was less than half that of other burns (638 vs. 1969 kW m(-1)). 6. We used relationships between season of fire, fuel loads and fire intensity in conjunction with the park's fire records to reconstruct broad fire intensity regimes. Changes in management from regular prescribed burning to 'natural' fires over the past four decades have resulted in a decrease in moderate-intensity fires and an increase in high-intensity fires. 7. The highest fire intensities measured in our study (11 000 - > 17 500 kW m(-1)) were significantly higher than those previously reported for African savannas, but were similar to those in South American cerrado vegetation. The mean fire intensity for late dry season (winter) fires in our study was less than half that reported for late dry season fires in savannas in northern Australia. 8. Synthesis and applications. Fire intensity has important effects on savanna vegetation, especially on the dynamics of the tree layer. Fire intensity varies with season (because of differences in fuel moisture) as well as with fuel load. Managers of African savannas can manipulate fire intensity by choosing the season of fire, and further by burning in years with higher or lower fuel loads. The basic relationships described here can also be used to enhance fire records, with a view to building a long-term data set for the ongoing assessment of the effectiveness of fire management.
Home away from home - objective mapping of high-risk source areas for plant introductions
01 August 2007
Stellenbosch University

Richardson, DM;Thuiller, W

Prevention is the best way to slow the escalation of problems associated with biological invasions. Screening of potential introductions is widely applied for assessing the risk of species becoming invasive. Despite advances in the understanding of the determinants of invasiveness, screening still relies heavily on assessments of the potential of species to 'fit in' to the broad environmental conditions of a target region. Most screening systems ask whether species are native to, or are known to be naturalized or invasive in, regions with 'similar' climatic/environmental conditions to the target region. The level of similarity required to make the species a high-risk introduction is generally not specified. This paper describes a protocol for making such assessments more objective, using South Africa as a test case. Using nonparametric niche-based modelling (generalized additive model; GAM) calibrated on the current distribution of each South African biome, we mapped regions of the world that are climatically similar to South African biomes. Lists were produced of countries with the largest areas climatically similar to South Africa overall, and to each biome separately. Validation of the usefulness of the approach was sought by evaluating whether the main invasive plant species in South African biomes occur naturally, or have adventive ranges, in regions mapped as analogous to South African biomes. A very large part of the world is climatically similar to South Africa, with eight countries having larger areas of land classified as climatically similar to South African biomes than the total area of South Africa. Almost all the most prominent invasive species in South African biomes occur naturally or are invasive outside their natural range in areas with similar climates to those that occur in parts of South Africa. This confirms the value of objective climate matching in screening protocols. We examined climatic conditions for a representative sample of major invasive plants from other parts of the world. The analysis identified several species that are already invasive in regions that have matched climates in South Africa but that are not yet introduced or, if already present, have not yet invaded large areas. For example, the following known invasive species should be considered high-risk species in South African grasslands: Alliaria petiolata, Cytisus scoparius, Gleditsia triacanthos, Heracleum mantegazzianum, Hieracium pilosella, Juniperus communis, Pinus contorta, P. monticola, P. ponderosa, P. sylvestris, Prunus laurcerasus, and P. serotina. Objectively matched climatic regions are also useful as a first-cut assessment when evaluating species with no invasive history.
Ensemble models predict Important Bird Areas in southern Africa will become less effective for conserving endemic birds under climate change
27 May 2010
Stellenbosch University

Coetzee, B.W.T.;Robertson, M.;Erasmus, B.;van Rensburg, B.J.;Thuiller, W.

Aim: To examine climate change impacts on endemic birds, which are of global significance for conservation, on a continent with few such assessments. We specifically assess projected range changes in relation to the Important Bird Areas (IBAs) network and assess the possible consequences for conservation. Location: South Africa, Lesotho and Swaziland. Methods: The newly emerging ensemble modelling approach is used with 50 species, four climate change models for the period 2070-2100 and eight bioclimatic niche models in the statistical package BIOMOD. Model evaluation is done using the Receiver Operating Characteristic and the recently introduced True Skill Statistic. Future projections are made considering two extreme assumptions: species have full dispersal ability and species have no dispersal ability. A consensus forecast is identified using Principal Components Analysis. This forecast is interpreted in terms of the IBA network. An irreplaceability analysis is used to highlight priority IBAs for conservation attention in terms of climate change. Results: The majority of species (62%) are predicted to lose climatically suitable space. Five species lose at least 85% of their climatically suitable space. Many IBAs lose species (41%; 47 IBAs) and show high rates of species turnover of more than 50% (77%; 95 IBAs). Highly irreplaceable regions for endemic species become highly localised under climate change, meaning that the endemic species analysed here experience similar range contractions to maintain climate niches. Main conclusions: The South African IBAs network is likely to become less effective for conserving endemic birds under climate change. The irreplaceability analysis identified key refugia for endemic species under climate change, but many of these areas are not currently IBAs. In addition, many of these high priority areas that are IBAs fall outside of the current formal protected areas network.
Population responses within a landscape matrix:a macrophysiological approach to understanding climate change impacts
01 June 2010
Stellenbosch University

Chown, S.L.;Gaston, K.J.;van Kleunen, M.;Clusella-Trullas, S.

Global environmental change (GEC) is a significant concern. However, forecasting the outcomes of this change for species and ecosystems remains a major challenge. In particular, predicting specific changes in systems where initial conditions, instabilities, and model errors have large impacts on the outcome is problematic. Indeed, predictive community ecology has been deemed unworthy of pursuit or an unreachable goal. However, new developments in large-scale biology provide ways of thinking that might substantially improve forecasts of local and regional impacts of climate change. Most notably, these are the explicit recognition of the regional and landscape contexts within which populations reside, the matrix approach that can be used to investigate the consequences of population variation across space and within assemblages, and the development of macrophysiology, which explicitly seeks to understand the ecological implications of physiological variation across large spatial and temporal scales. Here we explore how a combination of these approaches might promote further understanding and forecasting of the effects of global climate change and perhaps other GEC drivers on biodiversity. We focus on the population level, examining the ways in which environmental variation might be translated through performance and its plasticity to variation in demography.
Conserving pattern and process in the Southern Ocean: designing a Marine Protected Area for the Prince Edward Islands
14 October 2010
Stellenbosch University

Lombard, A.T.;Reyers, B.;Schonegevel, L.Y.;Cooper, J.;Smith-Adao, L.B.;Nel, D.C.;Froneman, P.W.;Ansorge, I.J.;Bester, M.N.;Tosh, C.A.;Strauss, T.;Akkers, T.;Gon, O.;Leslie, R.W.;Chown, S.L.

South Africa is currently proclaiming a Marine Protected Area (MPA) in the Exclusive Economic Zone (EEZ) of its sub-Antarctic Prince Edward Islands. The objectives of the MPA are to: 1) contribute to a national and global representative system of MPAs, 2) serve as a scientific reference point to inform future management, 3) contribute to the recovery of the Patagonian toothfish (Dissostichus eleginoides), and 4) reduce the bird bycatch of the toothfish fishery, particularly of albatrosses and petrels. This study employs systematic conservation planning methods to delineate a MPAwithin the EEZ that will conserve biodiversity patterns and processes within sensible management boundaries, while minimizing conflict with the legal toothfish fishery. After collating all available distributional data on species, benthic habitats and ecosystem processes, we used C-Plan software to delineate a MPA with three management zones: four IUCN Category Ia reserves (13% of EEZ); two Conservation Zones (21% of EEZ); and three Category IV reserves (remainder of EEZ). Compromises between conservation target achievement and the area required by the MPA are apparent in the final reserve design. The proposed MPA boundaries are expected to change over time as new data become available and as impacts of climate change become more evident.
Monitoring effects of anthropogenic climate change on ecosystems: A role for systematic ecological observation?
18 October 2010
Stellenbosch University

Midgley, G.F.;Chown, S.L.;Kgope, B.S.

We consider here the opportunities and challenges for South Africa in long-termecological research (LTER) to detect the impacts of anthropogenic climate change on biota (as one of several competing objectives of long-term monitoring). The LTER approach has high potential for this purpose in SouthAfrica because of a wealth of historical climate data relative to much of the African continent, and good representation of many African ecosystem types. However, there are substantial challenges to the identification and attribution of climate change impacts on African ecosystems. These are posed by climate variability at a range of time scales, the importance of rainfall rather than temperature as an ecological driver, and the significance of fire as a stochastic disturbance. An awareness of environmental and climate history will be crucial to interpreting data on trends, and sites with established historical data should be preferred for this reason. The placement of LTER sites to provide representivity of ecosystem types may unintentionally limit the detectability of climate change impacts, because change might best be detected in ecotonal or azonal environments. This could be overcome by additional experimental manipulations at LTER sites to ‘force’ anticipated changes and characterize species and ecosystem responses.Afocus on the detection of climate change would sharpen an LTER programme’s emphasis over time and provide policy advice, and science training rationales for the long term. It should especially interpret key information to decision-makers as a priority.
Ground-dwelling beetle assemblages in the northern Cape Floristic Region: Patterns, correlates and implications
20 October 2010
Stellenbosch University

Botes, A.;McGeoch, M.A.;Chown, S.L.

Recent studies have both shown and predicted that global climate change will have a substantial influence on biodiversity.This is true especially of a global biodiversity hotspot, the Cape Floristic Region. Although the effects of predicted changes have been widely assessed for plants, little is known about how insect diversity in the region might be affected. In particular, patterns in and the correlates of diversity in the region are poorly understood, and therefore the likely affects of a changing abiotic environment on this significant group of organisms are not clear.Therefore, we investigate patterns in, and correlates of, epigaeic beetle (Tenebrionidae and Carabidae) diversity in one of the most climate change-sensitive areas in the Cape Floristic Region, the Cederberg. In particular, we determine whether epigaeic beetle assemblage structure differs between the main vegetation types in the Cederberg (Strandveld, Mountain Fynbos and Succulent Karoo), how restricted these beetles are to specific vegetation types, and which environmental variables might be associated with site-related differences in beetle richness and abundance. Sampling was undertaken during October 2002 and 2003 across an altitudinal gradient ranging from sea level (Lambert’s Bay) to approximately 2000 m above sea level (Sneeukop, Cederberg) and down again to 500 m above sea level (Wupperthal) using pitfall traps. The environmental correlates of abundance and species density in the epigaeic beetles were similar to those identified previously for ants across the transect, with both taxa being positively related to several temperature variables. Several species showed habitat specificity and fidelity, and clear distinctions existed between the vegetation types across the transect. A larger proportion of the variance in tenebrionid species density was explained by environmental variables and spatial factors than for carabids.The most likely explanation for this difference is that the correlates might well reflect collinear historical processes, rather than a causal relationship between contemporary environmental variables and species density. If this is the case, it suggests that caution should be exercised when interpreting environmental correlates of species density, and making climate change predictions based on these correlates.
The decline of water hyacinth on Lake Victoria was due to biological control by Neochetina spp.
25 October 2010
Stellenbosch University

Wilson, J.R.U.;Ajuonu, O.;Center, T.D.;Hill, M.P.;Julien, M.H.;Katagira, F.F.;Neuenschwander, P.;Njoka, S.W.;Ogwang, J.;Reeder, R.H.;Van, T.

There has been some debate recently about the cause of the decline of water hyacinth on Lake Victoria. While much of this evidence points to classical biological control as the major factor, the El Niño associated weather pattern of the last quarter of 1997 and the first half of 1998 has confused the issue.We argue first that the reductions in water hyacinth on Lake Victoria were ultimately caused by the widespread and significant damage to plants by Neochetina spp., although this process was increased by the stormy weather associated with the El Niño event; second that increased waves and current on Lake Victoria caused by El Niño redistributed water hyacinth plants around the lake; and third that a major lakewide resurgence of water hyacinth plants on Lake Victoria has not occurred and will not occur unless the weevil populations are disrupted. We conclude that the population crash of water hyacinth on Lake Victoria would not have occurred in the absence of the weevils, but that it may have been hastened by stormy weather associated with the El Niño event.
Fire season effects on the recruitment of non-sprouting serotinous Proteaceae in the eastern (bimodal rainfall) fynbos biome, South Africa
03 November 2010
Stellenbosch University

Heelemann, S.;Proches, S.;Rebelo, A.G.;van Wilgen, B.W.;Porembski, S.;Cowling, R.M.

Research in Mediterranean-climate shrublands in both South Africa and Australia shows that recruitment of proteoid shrubs (non-sprouting, serotinous Proteaceae) is best after warm-season (summer and autumn) fires and worst after cool-season (winter and spring) ones. This pattern has been attributed to post-dispersal seed attrition as well as size of pre-dispersal seed reserves. Here we investigate patterns of post-fire recruitment for four proteoid species in the eastern part of South Africa’s fynbos biome, which has a bimodal (spring and autumn) rainfall regime. Despite the lack of significant differences in recruitment between cool- and warm-season burns, we find some evidence for favourable recruitment periods following fires in spring and autumn, immediately before, and coinciding with, the bimodal rainfall peaks. This suggests that enhanced recruitment is associated with conditions of high soil moisture immediately after the fire, and that rapid germination may minimize post-dispersal seed attrition. In two of the species, we also find a shift from peak flowering in winter and spring in the Mediterranean-climate part of the fynbos biome, to summer and autumn flowering in the eastern part. Because these two species are only weakly serotinous, warm-season flowering would result in maximal seed banks in spring, which could explain the spring recruitment peak, but not the autumn one.We conclude that eastern recruitment patterns differ significantly from those observed in the western and central parts of the biome, and that fire management protocols for the east, which are currently based on data and experience from the winter-rainfall fynbos biome, need to be adjusted accordingly. Fire managers in the eastern fynbos biome should be less constrained by requirements to burn within a narrow seasonal range, and should therefore be in a better position to apply the required management burns.
An assessment of the implementation and outcomes of recent changes to fire management in the Kruger National Park
03 November 2010
Stellenbosch University

van Wilgen, B.W.;Govender, N.;MacFadyen, S.

This paper reviews recent changes in fire management in the Kruger National Park, and assesses the resulting fire patterns against thresholds of potential concern. In 2002, a lightning-driven approach was replaced by an approach that combined point ignitions with unplanned and lightning fires. The approach aimed to burn an annual target area, determined by rainfall and fuel conditions, in point-ignition fires of different sizes. Most of the original fire-related thresholds of potential concern (TPCs) were incorporated into the new approach. The annual target area to be burnt ranged from 12 to 24% of the park between 2002 and 2006. The total area burnt generally exceeded the targets each year, and management fires accounted for less than half of the total area burnt. The fire regime was dominated by very large fires (> 5 000 ha) which accounted for 77% of the total area burnt. New TPCs were developed to assess whether the fire regime encompassed a sufficient degree of variability, in terms of fire intensity and the spatial distribution of burnt areas. After assessment and adjustment, it appears that these TPCs have not yet been exceeded. The point-ignition approach, and its evaluation in terms of variability and heterogeneity, is based on the untested assumption that a diverse fire regime will promote biodiversity. This assumption needs to be critically assessed. We recommend that the practice of point ignitions be continued, but that greater efforts be made to burn larger areas earlier in the season to reduce large and intense dry-season fires.
Rapid range expansion and community reorganization in response to warming
03 November 2010
Stellenbosch University

le Roux, P.C.;McGeoch, M.A.

Species ranges are expected to expand along their cooler boundaries in response to rising temperatures associated with current global climate change. However, this ‘fingerprint’ of climate change is yet to be assessed for an entire flora. Here, we examine patterns of altitudinal range change in the complete native vascular flora of sub-Antarctic Marion Island. We demonstrate a rapid mean upslope expansion in the flora since 1966, in response to 1.2˚C warming on the island. The 3.4 ±0.8myr-1 (mean ±SE) upslope expansion rate documented is amongst the highest estimates from partial floras. However, less than half of the species in the flora were responsible for the expansion trend, demonstrating that the global fingerprint of warming may be driven by a highly responsive subset of the species pool. Individual range expansion rates varied greatly, with species-specific niche requirements explaining some of this variation. As a result of the idiosyncratic expansion rates, altitudinal patterns of species richness and community composition changed considerably, with the formation of no-analog communities at high and intermediate altitudes. Therefore, both species- and community-level changes have occurred in the flora of Marion Island over a relatively short period of rapid warming, demonstrating the sensitivity of high latitude communities to climate change. Patterns of change within this flora illustrate the range of variation in species responses to climate change and the consequences thereof for species distributions and community reorganization.
What limits fire? An examination of drivers of burnt area in Southern Africa
08 November 2010
Stellenbosch University

Archibald, S.;Roy, D.P.;van Wilgen, B.W.;Scholes, R.J.

The factors controlling the extent of fire in Africa south of the equator were investigated using moderate resolution (500 m) satellite-derived burned area maps and spatial data on the environmental factors thought to affect burnt area. A random forest regression tree procedure was used to determine the relative importance of each factor in explaining the burned area fraction and to address hypotheses concerned with human and climatic influences on the drivers of burnt area. The model explained 68% of the variance in burnt area. Tree cover, rainfall in the previous 2 years, and rainfall seasonality were the most important predictors. Human activities – represented by grazing, roads per unit area, population density, and cultivation fraction – were also shown to affect burnt area, but only in parts of the continent with specific climatic conditions, and often in ways counter to the prevailing wisdom that more human activity leads to more fire. The analysis found no indication that ignitions were limiting total burnt area on the continent, and most of the spatial variation was due to variation in fuel load and moisture. Split conditions from the regression tree identified (i) low rainfall regions, where fire is rare; (ii) regions where fire is under human control; and (iii) higher rainfall regions where burnt area is determined by rainfall seasonality. This study provides insights into the physical, climatic, and human drivers of fire and their relative importance across southern Africa, and represents the beginnings of a predictive framework for burnt area.
A quantitative climate-match score for risk-assessment screening of reptile and amphibian introductions
08 November 2010
Stellenbosch University

van Wilgen, N.J.;Roura-Pascual, N.;Richardson, D.M.

Assessing climatic suitability provides a good preliminary estimate of the invasive potential of a species to inform risk assessment. We examined two approaches for bioclimatic modeling for 67 reptile and amphibian species introduced to California and Florida. First, we modeled the worldwide distribution of the biomes found in the introduced range to highlight similar areas worldwide from which invaders might arise. Second, we modeled potentially suitable environments for species based on climatic factors in their native ranges, using three sources of distribution data. Performance of the three datasets and both approaches were compared for each species. Climate match was positively correlated with species establishment success (maximum predicted suitability in the introduced range was more strongly correlated with establishment success than mean suitability). Data assembled from the Global Amphibian Assessment through NatureServe provided the most accurate models for amphibians, while ecoregion data compiled by the World Wide Fund for Nature yielded models which described reptile climatic suitability better than available point-locality data. We present three methods of assigning a climate-match score for use in risk assessment using both the mean and maximum climatic suitabilities. Managers may choose to use different methods depending on the stringency of the assessment and the available data, facilitating higher resolution and accuracy for herpetofaunal risk assessment. Climate-matching has inherent limitations and other factors pertaining to ecological interactions and life-history traits must also be considered for thorough risk assessment.
Fine scale variability in soil frost dynamics surrounding cushions of the dominant vascular plant species (Azorella Selago) on Sub-Antarctic Marion Island
09 November 2010
Stellenbosch University

Haussmann, N.S.;Boelhouwers, J.C.;McGeoch, M.A.

Through changing soil thermal regimes, soil moisture and affecting weathering and erosion processes plants can have an important effect on the physical properties and structure of soils. Such physical soil changes can in turn lead to biological facilitation, such as vegetation-banked terrace formation or differential seedling establishment. We studied the fine scale variability in soil temperature and moisture parameters, specifically focusing on frost cycle characteristics around cushions of the dominant, vascular plant species, Azorella selago, on sub-Antarctic Marion Island. The frost season was characterised by numerous low intensity and very shallow frost cycles. Soils on eastern cushion sides were found to have lower mean and maximum temperatures in winter than soils on western cushion sides. In addition, lower variability in temperature was found on eastern cushion sides in winter than on western cushion sides, probably as a result of higher wind speeds on western cushion sides and/or eastern, leeside snow accumulation. Despite the mild frost climate, extensive frost heave occurred in the study area, indicating that needle ice forms at temperatures above –2°C. Our results demonstrate the effectiveness of frost pull as a heave mechanism under shallow frost conditions. The results highlight the importance of Azorella cushions in modifying site microclimates and of understanding the consequences of these modifications, such as potentially providing microhabitats. Such potential microhabitats are particularly important in light of current climate change trends on the island, as continued warming and drying will undoubtedly increase the need for thermal and moisture refugia.
The extent and impacts of ungulate translocations: South Africa in a global context
23 November 2010
Stellenbosch University

Spear, D.;Chown, S.L.

Despite the apparent risks of the introduction of non-indigenous ungulates to biodiversity, relatively little is known globally about the pathways of introduction, propagule pressure and realized impacts of ungulate introductions. These issues were examined here by investigating ungulate introductions to South Africa within a global context. Across countries globally, introduced ungulate richness is not related to indigenous ungulate richness, and several countries are clear outliers. South Africa is second only to the USA in the number of ungulate species introduced to date. Zoos have traded more ungulate species and individuals to non-zoo recipients than to other zoos, highlighting the tensions that exist between in situ and ex situ conservation goals. Introductions to, and extralimital introductions within South Africa have increased through time, with propagule pressure being highest in areas with high human population density. The long distances ungulates have been translocated raise concerns for genetic homogenization. Translocations of indigenous ungulate species extralimitally have significantly altered range sizes, typically to a greater extent than is expected from range shifts associated with global climate change. Although ungulate introductions and translocations are likely to have impacts on biodiversity, evidence for such impacts in South Africa, and elsewhere, is limited. Whilst arguments may be made for a precautionary approach to ungulate introductions, an evidence-based one is much more likely to deliver efficient and convincing conservation decision-making.
Thermal benefits of melanism in cordylid lizards: a theoretical and field test
23 November 2010
Stellenbosch University

Clusella-Trullas, S.;Van Wyk, J.H.;Spotila, J.R.

The hypothesis that low skin reflectance (melanism) provides an advantage for thermoregulation under cold conditions has received mixed support in ectothermic vertebrates. We selected a model system, three allopatric closely related species of cordylid lizards that differ in skin reflectance, to test this hypothesis. Cordylus niger and Cordylus oelofseni are melanistic and inhabit peninsular and montane areas, respectively, whereas Cordylus cordylus is more widespread and inhabits low inland areas. By combining theoretical, experimental, and field data on these species, we demonstrate that the difference in body temperature (Tb) between melanistic and non-melanistic lizards under ecologically relevant climate variation ranged from 0° to 2°C. Despite its small magnitude, however, the faster heating rate and higher Tb of melanistic species relative to non-melanistic species conferred an advantage under cold conditions. Comparison of habitat thermal quality (de) and thermal accuracy (db) across species indicated that, in winter, melanism conferred the greatest advantage during small windows of thermal opportunity. This finding was most pronounced for C. oelofseni, which is most constrained by cold temperatures in its habitat. By contrast, due to their rock-dwelling habits, melanistic and non-melanistic species benefited from rock refugia in summer, giving similar levels of thermoregulatory effectiveness across species, regardless of skin reflectance. This study therefore demonstrates that skin reflectance variation across cordylids has significant effects on their thermal balance. Furthermore, studies investigating the role of varying skin reflectance in field populations and species should incorporate fine and broad temporal scales (daily, monthly, and seasonal), environmental variability, and cost–benefit trade-offs of thermoregulation.
Accommodating scenarios of climate change and management in modelling the distribution of the invasive tree Schinus molle in South Africa
31 May 2011
Stellenbosch University

Richardson, D.M.;Iponga, D.M.;Roura-Pascual, N.;Krug, R.M.;Milton, S.J.;Hughes, G.O.;Thuiller, W.

Determining the potential range of invasive alien species under current conditions is important. However, we also need to consider future distributions under scenarios of climate change and different management interventions when formulating effective long-term intervention strategies. This paper combines niche modelling and fine-scale processbased modelling to define regions at high risk of invasion and simulate likely dynamics at the landscape scale. Our study species is Schinus molle (Peruvian pepper tree; Anacardiaceae), a native of central South America, introduced to South Africa in about 1850 where it was widely planted along roads. Localities of planted and naturalized trees were mapped along 5380 km of roads - a transect that effectively samples a large part of western South Africa. Correlative modelling was used to produce profiles of present and future environmental conditions characterizing its planted and naturalized ranges. A cellular-automata simulation model was used to estimate the dynamics of S. molle under future climates and different management scenarios. The overall potential range of S. molle in the region is predicted to shrink progressively with predicted climate change. Some of the potential range of S. molle defined based on current conditions (including areas where it is currently highly invasive) is likely to become less favourable. The species could persist where it is well established long after conditions for recruitment have deteriorated. Some areas where the species is not widely naturalized now (notably the fynbos biome) are likely to become more favourable. Our modelling approach allows for the delineation of areas likely to be invaded in future by considering a range of factors at different scales that mediate the interplay of climatic variables and other drivers that define the dimensions of human intervention such as distance from planted trees and the density of planted plants, both of which affect propagule pressure.
Interaction intensity and importance along two stress gradients: adding shape to the stress-gradient hypothesis
01 June 2011
Stellenbosch University

Le Roux, P.C.;McGeoch, M.A.

The stress-gradient hypothesis (SGH) predicts that the community-wide prevalence of positive interactions, relative to negative interactions, is greater under more severe environmental conditions. Because the frequency of positive and negative interactions within a community is the aggregate of multiple pair-wise interactions, one approach to testing the SGH is to examine how pair-wise interactions vary along severity gradients. While the SGH suggests that the net outcome of an interaction should monotonically become more positive with increasing environmental severity, recent studies have suggested that the severity-interaction relationship (SIR) may rather be unimodal. We tested which of the proposed shapes of the SIR best fits the variation in the interaction between two species along two types of severity gradients on sub-Antarctic Marion Island. This was done by comparing the performance of the grass Agrostis magellanica in the presence and absence of the cushion plant Azorella selago, along both species’ entire altitudinal ranges (transects spanning 4–8 km), and along a shorter (transect = 0.4 km) wind exposure gradient. Along the altitudinal transects the relative intensity, but not the absolute intensity or the importance, of the Azorella selago–Agrostis magellanica interaction increased with altitude, consistently forming a plateau-shaped SIR with a positive symptote. Thus, while the performance of Agrostis magellanica was negatively affected by Azorella selago at low altitudes, the grass benefited from growing on the cushion plant under greater environmental severity. Along the wind exposure gradient the intensity of the interaction also became more positive with increasing environmental severity for most performance measures. This suggests that the switch from a net negative to a net positive interaction can occur across both short and long distances. Therefore, this study provides strong evidence for a plateau-shaped SIR, and confirms that the SIR is unimodal along the particular non-resource severity gradients of this study.
Leaf miner and plant galler species richness on Acacia: relative importance of plant traits and climate
01 June 2011
Stellenbosch University

Bairstow, K.A.;Clarke, K.L.;McGeoch, M.A.;Andrew, N.R.

Diversity patterns of herbivores have been related to climate, host plant traits, host plant distribution and evolutionary relationships individually. However, few studies have assessed the relative contributions of a range of variables to explain these diversity patterns across large geographical and host plant species gradients. Here we assess the relative influence that climate and host plant traits have on endophagous species (leaf miners and plant gallers) diversity across a suite of host species from a genus that is widely distributed and morphologically variable. Forty-six species of Acacia were sampled to encapsulate the diversity of species across four taxonomic sections and a range of habitats along a 950 km climatic gradient: from subtropical forest habitats to semi-arid habitats. Plant traits, climatic variables, leaf miner and plant galler diversity were all quantified on each plant species. In total, 97 leaf mining species and 84 plant galling species were recorded from all host plants. Factors that best explained leaf miner richness across the climatic gradient (using AIC model selection) included specific leaf area (SLA), foliage thickness and mean annual rainfall. The factor that best explained plant galler richness across the climatic gradient was C:N ratio. In terms of the influence of plant and climatic traits on species composition, leaf miner assemblages were best explained by SLA, foliage thickness, mean minimum temperature and mean annual rainfall, whilst plant gall assemblages were explained by C:N ratio, %P, foliage thickness, mean minimum temperature and mean annual rainfall. This work is the first to assess diversity and structure across a broad environmental gradient and a wide range of potential key climatic and plant trait determinants simultaneously. Such methods provide key insights into endophage diversity and provide a solid basis for assessing their responses to a changing climate.
Biocapacity supply and demand in Northwestern China: a spatial appraisal of sustainability
03 October 2011
Stellenbosch University

Yue, D.;Xu, X.;Hui, C.;Xiong, Y.;Han, X.;Ma, J.

Integrating spatial analysis with the supply and demand of biocapacity is critical for the sustainable development of regional eco-economic systems. Previous studies have focused on the temporal analysis of biocapacity at broad geographical scales, but lacked the systematic spatial realization at fine scales. An improvement is proposed of this conventional methodology of the ecological footprint by incorporating landuse data derived from high-resolution remote-sensing images into the calculation of biocapacity supply at regional, provincial and county levels in Northwestern China in 2000. The spatial heterogeneity and its effect on the biocapacity supply were systematically revealed for this region. First, the biocapacity supply declined from the east (the Guanzhong Basin and the Loess Plateau) to the middle (the Qaidam Basin and the Turpan Basin), and turned to rise from the middle to the west (the northwest of the Xinjiang Uygur Autonomy). Second, although the gap between biocapacity supply and demand resulted in a small ecological deficit at the regional level, a large ecological deficit was observed at the provincial and county levels, highlighting an unsustainable situation for some of the sub-regions. Importantly, a power law relationship was unveiled between the biocapacity supply and population density, suggesting that (i) the biocapacity supply as a critical indicator could reflect the intensity of human exploitation on local biophysical resources and (ii) humans tend to have a preference to inhabit those areas with high biological productivity. These results provide opportunities to enhance policy development by central and local governments as part of the long-term Great Western Development Strategy of China.
Water loss in insects: An environmental change perspective
24 November 2011
Stellenbosch University

Chown, S.L.;Sorensen, J.G.;Terblanche, J.S.

In the context of global environmental change much of the focus has been on changing temperatures. However, patterns of rainfall and water availability have also been changing and are expected to continue doing so. In consequence, understanding the responses of insects to water availability is important, especially because it has a pronounced influence on insect activity, distribution patterns, and species richness. Here we therefore provide a critical review of key questions that either are being or need to be addressed in this field. First, an overview of insect behavioural responses to changing humidity conditions and the mechanisms underlying sensing of humidity variation is provided. The primary sensors in insects belong to the temperature receptor protein superfamily of cation channels. Temperature-activated transient receptor potential ion channels, or thermoTRPs, respond to a diverse range of stimuli and may be a primary integrator of sensory information, such as environmental temperature and moisture. Next we touch briefly on the components of water loss, drawing attention to a new, universal model of the water costs of gas exchange and its implications for responses to a warming, and in places drying, world. We also provide an overview of new understanding of the role of the sub-elytral chamber for water conservation, and developments in understanding of the role of cuticular hydrocarbons in preventing water loss. Because of an increasing focus on the molecular basis of responses to dehydration stress we touch briefly on this area, drawing attention to the role of sugars, heat shock proteins, aquaporins, and LEA proteins. Next we consider phenotypic plasticity or acclimation responses in insect water balance after initial exposures to altered humidity, temperature or nutrition. Although beneficial acclimation has been demonstrated in several instances, this is not always the case. Laboratory studies show that responses to selection for enhanced ability to survive water stress do evolve and that genetic variation for traits underlying such responses does exist in many species. However, in others, especially tropical, typically narrowly distributed species, this appears not to be the case. Using the above information we then demonstrate that habitat alteration, climate change, biological invasions, pollution and overexploitation are likely to be having considerable effects on insect populations mediated through physiological responses (or the lack thereof) to water stress, and that these effects may often be non-intuitive.
The development and application of strategic adaptive management within South African National Parks
28 November 2011
Stellenbosch University

Roux, D.J.;Foxcroft, L.C.

Adaptive management is an appealing approach to deal with inherent uncertainty in complex and interactive social-ecological systems (Holling 2001; Rogers 2003). In short, adaptive management is about learning-by-doing in a scientific way, adapting behaviour and overall direction as new information becomes available. It provides a structured way for improving our incomplete understanding through an iterative process of setting objectives, implementing policy decisions and evaluating the implications of their outcomes for future decision making. In essence, adaptive management is: the process of treating natural resource management as an experiment such that the practicality of trial and error is added to the rigour and explicitness of the scientific experiment, producing learning that is both relevant and valid. (Meffe et al. 2002)
Human-mediated introductions of Australian acacias – a global experiment in biogeography
12 December 2011
Stellenbosch University

Richardson, D.M.;Carruthers, J.;Hui, C.;Impson, F.A.C.;Miller, J.T.;Robertson, R.P.;Rouget, M.;Le Roux, J.J.;Wilson, J.R.U.

Aim Australian acacias (1012 recognized species native to Australia, which were previously grouped in Acacia subgenus Phyllodineae) have been moved extensively around the world by humans over the past 250 years. This has created the opportunity to explore how evolutionary, ecological, historical and sociological factors interact to affect the distribution, usage, invasiveness and perceptions of a globally important group of plants. This editorial provides the background for the 20 papers in this special issue of Diversity and Distributions that focusses on the global cross-disciplinary experiment of introduced Australian acacias. Location Australia and global. Methods The papers of the special issue are discussed in the context of a unified framework for biological invasions. Distributions of species were mapped across Australia, their representation in bioclimatic zones examined and the potential global distribution of the group modelled. By collating a variety of different lists, we determined which Australian acacias have reached different stages in the introduction-naturalization-invasion continuum in different parts of the world. Paradigms and key research questions relating to barriers to invasion, stages of invasion and management perceptions are sketched. Results According to our global database of Australian acacia records, 386 species have been moved outside Australia by human agency, 71 species are naturalized or weedy, and 23 are unequivocally invasive. Climatic models suggest that about a third of the world’s land surface is climatically suitable for Australian acacias. Many species are commercially important crops or are useful for other purposes and have been extensively planted, and many different human perceptions of Australian acacias exist in different parts of the world. The papers in the special issue cover all the barriers, stages and processes that define biological invasions and touch on many aspects: history and the human dimension; aspects of the species pool; species traits; biotic interactions; climate and niche; and management. Main conclusions Australian acacias are an excellent model group for examining interactions between evolutionary, ecological and socio-economic drivers of species introductions. New insights have emerged on the biological, ecological and evolutionary correlates of naturalization and invasion, but human usage factors permeate all explanatory models. Understanding and managing introduced Australian acacias requires a fundamental and integrative appreciation of both intrinsic (e.g. species traits) and extrinsic (e.g. human usage and perceptions) aspects.
Life on the edge: rare and restricted episodes of a pan-tropical mutualism adapting to drier climates
12 December 2011
Stellenbosch University

McLeish, M.;Guo, D.;van Noort, S.;Midgley, G.

• The fig tree–fig wasp obligate pollination mutualism has strong ancestral affinities with tropical communities, but is present in much drier contemporary biomes, especially at higher latitudes at the edge of their range. The extent to which adaptation to environmental variables is evolutionarily conserved and whether environmental differences function in ecological speciation of the mutualism are unknown. • Here we use climate models and phylogenetic reconstructions to test whether the Ficus–fig wasp mutualism has adapted and radiated into drier climates and led to ecological speciation in both plant and insect. • The results showed phylogenetic correspondence between closely related Ficus species with either savanna, forest, or riparian habitat categories, were most strongly explained by both climate and environmental variables. Rare episodes of adaptation to dry apotypic conditions have resulted in substantial radiations into savanna. • Inferences were consistent with predictions of niche conservatism and support the postulate that ecological speciation of the mutualism occurs, but under contrasting and intertwined circumstances among plant-pollinator adaptation and tolerance to the environment.
Modelling horses for novel climate courses: insights from projecting potential distributions of native and alien Australian acacias with correlative and mechanistic models
12 December 2011
Stellenbosch University

Webber, B.L.;Yates, C.J.;Le Maitre, D.C.;Scott, J.K.;Kriticos, D.J.;Ota, N.;McNeill, A.;Le Roux, J.J.;Midgley, G.F.

Aim Investigate the relative abilities of different bioclimatic models and data sets to project species ranges in novel environments utilizing the natural experiment in biogeography provided by Australian Acacia species. Location Australia, South Africa. Methods We built bioclimatic models for Acacia cyclops and Acacia pycnantha using two discriminatory correlative models (MaxEnt and Boosted Regression Trees) and a mechanistic niche model (CLIMEX). We fitted models using two training data sets: native-range data only (‘restricted’) and all available global data excluding South Africa (‘full’). We compared the ability of these techniques to project suitable climate for independent records of the species in South Africa. In addition, we assessed the global potential distributions of the species to projected climate change. Results All model projections assessed against their training data, the South African data and globally were statistically significant. In South Africa and globally, the additional information contained in the full data set generally improved model sensitivity, but at the expense of increased modelled prevalence, particularly in extrapolation areas for the correlative models. All models projected some climatically suitable areas in South Africa not currently occupied by the species. At the global scale, widespread and biologically unrealistic projections by the correlative models were explained by open-ended response curves, a problem which was not always addressed by broader background climate space or by the extra information in the full data set. In contrast, the global projections for CLIMEX were more conservative. Projections into 2070 indicated a polewards shift in climate suitability and a decrease in model interpolation area. Main conclusions Our results highlight the importance of carefully interpreting model projections in novel climates, particularly for correlative models. Much work is required to ensure bioclimatic models performed in a robust and ecologically plausible manner in novel climates. We explore reasons for variations between models and suggest methods and techniques for future improvements.
The ecology of Bactrocera tryoni (Diptera: Tephritidae): what do we know to assist pest management?
13 December 2011
Stellenbosch University

Clarke, A.R.;Powell, K.S.;Weldon, C.W.;Taylor, P.W.

The distribution, systematics and ecology of Bactrocera tryoni, the Queensland fruit fly, are reviewed. Bactrocera tryoni is a member of the B. tryoni complex of species, which currently includes four named species, viz. B. tryoni ssp., B. neohumeralis, B. melas and B. aquilonis. The species status of B. melas and B. aquilonis is unclear (they may be junior synonyms of B. tryoni) and their validity, or otherwise, needs to be confirmed as a matter of urgency. While Queensland fruit fly is regarded as a tropical species, it cannot be assumed that its distribution will spread further south under climate change scenarios. Increasing aridity and hot dry summers, as well as more complex, indirect interactions resulting from elevated CO2, make predicting the future distribution and abundance of B. tryoni difficult. The ecology of B. tryoni is reviewed with respect to current control approaches (with the exception of sterile insect technique (SIT) which is covered in a companion paper). We conclude that there are major gaps in the knowledge required to implement most noninsecticide-based management approaches. Priority areas for future research include host–plant interactions, protein and cue-lure foraging and use, spatial dynamics, development of new monitoring tools, investigating the use of natural enemies and better integration of fruit flies into general horticultural IPM systems.
Discontinuous gas exchange: new perspectives on evolutionary origins and ecological implications
16 August 2012
Stellenbosch University

Chown, S.L.

1. When at rest, many insects and some other arthropods exchange gasses discontinuously. Whether or not discontinuous gas exchange (DGE) is adaptive has long been controversial. Several competing evolutionary hypotheses exist, none of which enjoy unequivocal support. This Gordian knot seems now to have been cut. 2. Discontinuous gas exchange appears to arise as a consequence of energy-saving, metabolic downregulation. Moreover, many ecological circumstances, such as quiescence during daily inactivity and during seasonal resource shortages, are likely to have favoured such downregulation. 3. Once the brain relinquishes control of gas exchange to the segmental ganglia, an interaction between peripheral CO2 sensing and central O2 sensing sets in, leading to the discontinuous pattern. 4. The evolution of DGE may thus be readily explained, with the primary evolutionary hypothesis incorporating a non-adaptive mechanistic component and an adaptive energy savings one. 5. Paradoxically, though, DGE results in a comparatively high water loss for a given metabolic rate in insects compared with other organisms. Thus, the pattern itself may not have evolved to limit water loss under xeric conditions. Rather, variation in the components of the DGE cycle, which has formed the foundation for much debate concerning the ecological and evolutionary advantages of this gas exchange pattern, may have evolved to do so, accounting for associations between these components and environmental conditions. 6. The relatively high respiratory water loss of insects may spell ecological trouble given increasing metabolic rates of ectotherms associated with rising global temperatures and global change– type drought in many regions.
Continent-wide risk assessment for the establishment of nonindigenous species in Antarctica
20 February 2013
Stellenbosch University

Chown, S.L.;Huiskes, A.H.L.;Gremmen, N.J.M.;Lee, J.E.;Terauds, A.;Crosbie, K.;Frenot, Y.;Hughes, K.A.;Imura, S.;Kiefer, K.;Lebouvier, M.;Raymond, B.;Tsujimoto, M.;Ware, C.;van de Vijver, B.;Bergstrom, D.M.

Invasive alien species are among the primary causes of biodiversity change globally, with the risks thereof broadly understood for most regions of the world. They are similarly thought to be among the most significant conservation threats to Antarctica, especially as climate change proceeds in the region. However, no comprehensive, continent-wide evaluation of the risks to Antarctica posed by such species has been undertaken. Here we do so by sampling, identifying, and mapping the vascular plant propagules carried by all categories of visitors to Antarctica during the International Polar Year’s first season (2007–2008) and assessing propagule establishment likelihood based on their identity and origins and on spatial variation in Antarctica’s climate. For an evaluation of the situation in 2100, we use modeled climates based on the Intergovernmental Panel on Climate Change’s Special Report on Emissions Scenarios Scenario A1B [Nakic´enovic´ N, Swart R, eds (2000) Special Report on Emissions Scenarios: A Special Report of Working Group III of the Intergovernmental Panel on Climate Change (Cambridge University Press, Cambridge, UK)]. Visitors carrying seeds average 9.5 seeds per person, although as vectors, scientists carry greater propagule loads than tourists. Annual tourist numbers (∼33,054) are higher than those of scientists (∼7,085), thus tempering these differences in propagule load. Alien species establishment is currently most likely for the Western Antarctic Peninsula. Recent founder populations of several alien species in this area corroborate these findings. With climate change, risks will grow in the Antarctic Peninsula, Ross Sea, and East Antarctic coastal regions. Our evidence-based assessment demonstrates which parts of Antarctica are at growing risk from alien species that may become invasive and provides themeans tomitigate this threat now and into the future as the continent’s climate changes.
The roles of climate, phylogenetic relatedness, introduction effort, and reproductive traits in the establishment of non-native reptiles and amphibians
01 March 2013
Stellenbosch University

van Wilgen, N.J.;Richardson, D.M.

We developed a method to predict the potential of non-native reptiles and amphibians (herpetofauna) to establish populations. This method may inform efforts to prevent the introduction of invasive non-native species. We used boosted regression trees to determine whether nine variables influence establishment success of introduced herpetofauna in California and Florida. We used an independent data set to assess model performance. Propagule pressure was the variable most strongly associated with establishment success. Species with short juvenile periods and species with phylogenetically more distant relatives in regional biotas were more likely to establish than species that start breeding later and those that have close relatives. Average climate match (the similarity of climate between native and non-native range) and life form were also important. Frogs and lizards were the taxonomic groups most likely to establish, whereas a much lower proportion of snakes and turtles established. We used results from our best model to compile a spreadsheet-based model for easy use and interpretation. Probability scores obtained from the spreadsheet model were strongly correlated with establishment success as were probabilities predicted for independent data by the boosted regression tree model. However, the error rate for predictions made with independent data was much higher than with cross validation using training data. This difference in predictive power does not preclude use of the model to assess the probability of establishment of herpetofauna because (1) the independent data had no information for two variables (meaning the full predictive capacity of the model could not be realized) and (2) the model structure is consistent with the recent literature on the primary determinants of establishment success for herpetofauna. It may still be difficult to predict the establishment probability of poorly studied taxa, but it is clear that non-native species (especially lizards and frogs) that mature early and come from environments similar to that of the introduction region have the highest probability of establishment.
The ecology, biogeography, history and future of two globally important weeds: Cardiospermum halicacabum Linn. and C. grandiflorum Sw.
04 June 2014
Stellenbosch University

Gildenhuys, E.;Ellis, A.G.;Carroll, S.P.;Le Roux, J.J.

Members of the balloon vine genus, Cardiospermum, have been extensively moved around the globe as medicinal and horticultural species, two of which are now widespread invasive species; C. grandiflorum and C. halicacabum. A third species, C. corindum, may also have significant invasion potential. However, in some regions the native status of these species is not clear, hampering management. For example, in South Africa it is unknown whether C. halicacabum and C. corindum are native, and this is a major constraint to on-going biological control programmes against invasive C. grandiflorum. We review the geography, biology and ecology of selected members of the genus with an emphasis on the two most widespread invaders, C. halicacabum and C. grandiflorum. Specifically, we use molecular data to reconstruct a phylogeny of the group in order to shed light on the native ranges of C. halicacabum and C. corindum in southern Africa. Phylogenetic analyses indicate that southern African accessions of these species are closely related to South American taxa indicating human-mediated introduction and/or natural long distance dispersal. Then, on a global scale we use species distribution modelling to predict potential suitable climate regions where these species are currently absent. Native range data were used to test the accuracy with which bioclimatic modelling can identify the known invasive ranges of these species. Results show that Cardiospermum species have potential to spread further in already invaded or introduced regions in Australia, Africa and Asia, underlining the importance of resolving taxonomic uncertainties for future management efforts. Bioclimatic modelling predicts Australia to have highly favourable environmental conditions for C. corindum and therefore vigilance against this species should be high. Species distribution modelling showed that native range data over fit predicted suitable ranges, and that factors other than climate influence establishment potential. This review opens the door to better understand the global biogeography of the genus Cardiospermum, with direct implications for management, while also highlighting gaps in current research.
Stable and fluctuating temperature effects on the development rate and survival of two malaria vectors, Anopheles arabiensis and Anopheles funestus
04 June 2014
Stellenbosch University

Lyons, C.L.;Coetzee, M.;Chown, S.L.

Background: Understanding the biology of malaria vector mosquitoes is crucial to understanding many aspects of the disease, including control and future outcomes. The development rates and survival of two Afrotropical malaria vectors, Anopheles arabiensis and Anopheles funestus, are investigated here under conditions of constant and fluctuating temperatures. These data can provide a good starting point for modelling population level consequences of temperature change associated with climate change. For comparative purposes, these data were considered explicitly in the context of those available for the third African malaria vector, Anopheles gambiae. Methods: Twenty five replicates of 20–30 eggs were placed at nine constant and two fluctuating temperatures for development rate experiments and survival estimates. Various developmental parameters were estimated from the data, using standard approaches. Results: Lower development threshold (LDT) for both species was estimated at 13-14°C. Anopheles arabiensis developed consistently faster than An. funestus. Optimum temperature (Topt) and development rate at this temperature (μmax) differed significantly between species for overall development and larval development. However, Topt and μmax for pupal development did not differ significantly between species. Development rate and survival of An. funestus was negatively influenced by fluctuating temperatures. By contrast, development rate of An. arabiensis at fluctuating temperatures either did not differ from constant temperatures or was significantly faster. Survival of this species declined by c. 10% at the 15°C to 35°C fluctuating temperature regime, but was not significantly different between the constant 25°C and the fluctuating 20°C to 30°C treatment. By comparison, previous data for An. gambiae indicated fastest development at a constant temperature of 28°C and highest survival at 24°C. Conclusions: The three most important African malaria vectors all differ significantly in development rates and survival under different temperature treatments, in keeping with known distribution data, though differences among M and S molecular forms of An. gambiae likely complicate the picture. Increasing temperatures associated with climate change favour all three species, but fluctuations in temperatures are detrimental to An. funestus and may also be for An. gambiae. This may have significant implications for disease burden in areas where each species is the main malaria vector.
Human-mediated drivers of change - impacts on coastal ecosystems and marine biota of South Africa
12 June 2014
Stellenbosch University

Mead, A.;Griffiths, C.L.;Branch, G.M.;McQuaid, C.D.;Blamey, L.K.;Bolton, J.J.;Anderson, R.J.;Dufois, F.;Rouault, M.;Froneman, P.W.;Whitfield, A.K.;Harris, L.R.;Nel, R.;Pillay, D.;Adams, J.B.

Coastal ecosystems are highly vulnerable to human-mediated drivers of global change because they are located at the land–ocean interface and often host centres of urbanisation and development. The South African coastline comprises several distinct coastal ecoregions that support a wide range of coastal (inshore) ecosystems, including rocky, sandy and mixed shores, kelp beds, estuaries and seagrass communities. A growing body of evidence indicates that local air and sea temperatures, wind patterns, ocean current speed and upwelling regimes are all being affected by human-mediated climate change. In addition, anthropogenic activities, such as shipping (introducing coastal bioinvasives), exploitation of coastal marine resources, industry (releasing pollutants) and urban development, act synergistically with climate change to place pressure on coastal ecosystems and their biota. The aim of this review was primarily to synthesise and update research into causes of direct and indirect human-mediated global change and their effects on South African coastal systems. It incorporates both historic and the latest regional research on climate change and anthropogenic threats across the ecosystems listed above, much of which was supported by the South African Network for Coastal and Oceanic Research (SANCOR), specifically the SEAChange programme in recent years. It is evident that all these ecosystems are vulnerable to all the drivers considered, albeit to differing degrees, depending on their location on the coast. Whereas some bioinvasives have had a dramatic impact on rocky shore systems on the West Coast, their impact has been moderate on the South Coast and minimal on the East Coast; exploitation shows the reverse pattern. Furthermore, the impacts of human-mediated drivers on coastal ecosystems are synergistic. Of major interest is the fact that the West Coast and parts of the South Coast are exhibiting cooling trends in offshore sea surface temperatures, rather than warming. Correspondingly, a geographical spread of organisms associated with West and South-West Coast rocky shores and kelp beds has tended to be eastwards around Cape Point, rather than northwards along the West Coast as would have been expected with warming sea temperatures. Overall, significant progress has been made toward a better understanding of the combined pressures on each ecosystem and knowledge gaps have been identified, thus helping to direct future research themes.
Historical fire regimes in a poorly understood, fire-prone ecosystem: eastern coastal fynbos
30 July 2014
Stellenbosch University

Kraaij, T.;Baard, J.A.;Cowling, R.M.;van Wilgen, B.W.;Das, S.

Wecharacterised the historical fire regime (1900–2010) in eastern coastal fynbos shrublands, which occur in a poorly studied part of the Cape Floral Kingdom (CFK). Natural (lightning-ignited) fires dominated the fire regime. Fire seasonality decreased from west (Outeniqua region) to east (Tsitsikamma region) within the study area, and between the study area and further west in the CFK. This is consistent with a west–east climatic gradient in the CFK, where rainfall is concentrated in winter in the west, and evenly distributed across months in the east. Median fire return intervals (FRIs) (1980–2010) were broadly comparable to other fynbos areas but estimates varied widely depending on whether or not the data were censored (16–26 years with and 8–13 years without censoring). FRIs appeared to be shorter in the Tsitsikamma, where rainfall and plant growth rates are higher, than in the Outeniqua. The total area burnt annually has increased significantly since 1980, coinciding with an increase in weather conducive to fires, suggesting that fire regimes may be responding to climate change. Frequent recurrence of very large fires and the virtual absence of vegetation in older postfire age classes are potential causes for concern in achieving fynbos conservation objectives.
Fire regimes in eastern coastal fynbos: Imperatives and thresholds in managing for diversity
30 July 2014
Stellenbosch University

Kraaij, T.;Cowling, R.M.;van Wilgen, B.W.

Until recently, fire ecology was poorly understood in the eastern coastal region of the Cape Floral Kingdom (CFK), South Africa. Rainfall in the area is aseasonal and temperatures are milder than in the winter-rainfall and drier inland parts of the CFK, with implications for the management of fire regimes. We synthesised the findings of a research programme focused on informing ecologically sound management of fire in eastern coastal fynbos shrublands and explored potential east–west trends at the scales of study area and CFK in terms of fire return interval (FRI) and fire season. FRIs (8–26 years; 1980–2010) were comparable to those elsewhere in the CFK and appeared to be shorter in the eastern Tsitsikamma than in the western Outeniqua halves of the study area. Proteaceae juvenile periods (4–9 years) and postfire recruitment success suggested that for biodiversity conservation purposes, FRIs should be ≥ 9 years in eastern coastal fynbos. Collectively, findings on the seasonality of actual fires and the seasonality of fire danger weather, lightning and post-fire proteoid recruitment suggested that fires in eastern coastal fynbos are not limited to any particular season. We articulated these findings into ecological thresholds pertaining to the different elements of the fire regime in eastern coastal fynbos, to guide adaptive management of fire in the Garden Route National Park and elsewhere in the region. Conservation implications: Wildfires are likely to remain dominant in eastern coastal fynbos, whilst large-scale implementation of prescribed burning is unattainable. Fires occurring in any season are not a reason for concern, although other constraints remain: the need for sufficient fire intensity, safety requirements, and integration of fire and invasive alien plant management.
Long-term effects of fire frequency and season on herbaceous vegetation in savannas of the Kruger National Park, South Africa
30 July 2014
Stellenbosch University

Smith, M.D.;van Wilgen, B.W.;Burns, C.E.;Govender, N.;Potgieter, A.L.F.;Andelman, S.;Biggs, H.C.;Botha, J.;Trollope, W.S.W.

Aims: The long-termeffects of changing fire regimes on the herbaceous component of savannas are poorly understood but essential for understanding savanna dynamics. We present results from one of the longest running (>44 years) fire experiments in savannas, the experimental burn plots (EBPs), which is located in the Kruger National Park (South Africa) and encompasses four major savanna vegetation types that span broad spatial gradients of rainfall (450–700mm) and soil fertility. Methods: Herbaceous vegetation was sampled twice in the EBPs using a modified step-point method, once prior to initiation of the experiment (1954) and again after 44–47 years. Different combinations of three fire frequency (1-, 2- and 3-year return intervals) and five season (before the first spring rains, after the first spring rains, mid-summer, late summer and autumn) treatments, as well as a fire exclusion treatment, were applied at the plot level (;7 ha each), with each treatment (n = 12 total) replicated four times at each of the four sites (n = 192 plots total). The effects of long-term alterations to the fire regime on grass community structure and composition were analyzed separately for each site. Important Findings: Over the 44+ years duration of the experiment, fires were consistently more intense on sites with higher mean annual rainfall (>570 mm), whereas fires were not as intense or consistent for sites with lower and more variable rainfall (<510 mm) and potentially higher herbivory due to greater soil fertility. Because the plots were open to grazing, the impacts of herbivory along with more variable rainfall regimes likely minimized the effects of fire for the more arid sites. As a consequence, fire effects on grass community structure and composition were most marked for the higher rainfall sites and generally not significant for the more arid sites. For the high-rainfall sites, frequent dry season fires (1- to 3-year return intervals) resulted in high grass richness, evenness and diversity, whereas fire exclusion and growing season fires had the lowest of these measures and diverged the most in composition as the result of increased abundance of a few key grasses. Overall, the long-term cumulative impacts of altered fire regimes varied across broad climatic and fertility gradients, with fire effects on the grass community decreasing in importance and herbivory and climatic variability likely having a greater influence on community structure and composition with increasing aridity and soil fertility.
Phenology predicts the native and invasive range limits on common ragweed
30 July 2014
Stellenbosch University

Chapman, D.S.;Haynes, T.;Beal, S.;Essl, F.;Bullock, J.M.

Accurate models for species’ distributions are needed to forecast the progress and impacts of alien invasive species and assess potential range-shifting driven by global change. Although this has traditionally been achieved through data-driven correlative modelling, robustly extrapolating these models into novel climatic conditions is challenging. Recently, a small number of process-based or mechanistic distribution models have been developed to complement the correlative approaches. However, tests of these models are lacking, and there are very few process-based models for invasive species. We develop a method for estimating the range of a globally invasive species, common ragweed (Ambrosia artemisiifolia L.), from a temperature- and photoperiod-driven phenology model. The model predicts the region in which ragweed can reach reproductive maturity before frost kills the adult plants in autumn. This aligns well with the poleward and high-elevation range limits in its native North America and in invaded Europe, clearly showing that phenological constraints determine the cold range margins of the species. Importantly, this is a ‘forward’ prediction made entirely independently of the distribution data. Therefore, it allows a confident and biologically informed forecasting of further invasion and range shifting driven by climate change. For ragweed, such forecasts are extremely important as the species is a serious crop weed and its airborne pollen is a major cause of allergy and asthma in humans. Our results show that phenology can be a key determinant of species’ range margins, so integrating phenology into species distribution models offers great potential for the mechanistic modelling of range dynamics.
Invasion trajectory of alien trees: the role of introduction pathway and planting history
31 July 2014
Stellenbosch University

Donaldson, J.E.;Hui, C.;Richardson, D.M.;Robertson, M.P.;Webber, B.L.;Wilson, J.R.U.

Global change is driving a massive rearrangement of the world’s biota. Trajectories of distributional shifts are shaped by species traits, the recipient environment and driving forces with many of the driving forces directly due to human activities. The relative importance of each in determining the distributions of introduced species is poorly understood. We consider 11 Australian Acacia species introduced to South Africa for different reasons (commercial forestry, dune stabilization and ornamentation) to determine how features of the introduction pathway have shaped their invasion history. Projections from species distribution models (SDMs) were developed to assess how the reason for introduction influences the similarity between climatic envelopes in native and alien ranges. A lattice model for an idealized invasion was developed to assess the relative contribution of intrinsic traits and introduction dynamics on the abundance and extent over the course of simulated invasions. SDMs show that alien populations of ornamental species in South Africa occupy substantially different climate space from their native ranges, whereas species introduced for forestry occupy a similar climate space in native and introduced ranges. This may partly explain the slow spread rates observed for some alien ornamental plants. Such mismatches are likely to become less pronounced with the current drive towards ‘eco gardens’ resulting in more introductions of ornamental species with a close climate match between native and newly introduced regions. The results from the lattice model showed that the conditions associated with the introduction pathway (especially introduction pressure) dominate early invasion dynamics. The placement of introduction foci in urban areas limited the extent and abundance of invasive populations. Features of introduction events appear to initially mask the influence of intrinsic species traits on invasions and help to explain the relative success of species introduced for different purposes. Introduction dynamics therefore can have long-lasting influences on the outcomes of species redistributions, and must be explicitly considered in management plans.
Forestry trial data can be used to evaluate climate-based species distribution models in predicting tree invasions
31 July 2014
Stellenbosch University

Motloung, R.F.;Robertson, M.P.;Rouget, M.;Wilson, J.R.U.

Climate is frequently used to predict the outcome of species introductions based on the results from species distribution models (SDMs). However, despite the widespread use of SDMs for pre- and post-border risk assessments, data that can be used to validate predictions is often not available until after an invasion has occurred. Here we explore the potential for using historical forestry trials to assess the performance of climate-based SDMs. SDMs were parameterized based on the native range distribution of 36 Australian acacias, and predictions were compared against both the results of 150 years of government forestry trials, and current invasive distribution in southern Africa using true skill statistic, sensitivity and specificity. Classification tree analysis was used to evaluate why some Australian acacias failed in trials while others were successful. Predicted suitability was significantly related to the invaded range (sensitivity = 0.87) and success in forestry trials (sensitivity = 0.80), but forestry trial failures were under-predicted (specificity = 0.35). Notably, for forestry trials, the success in trials was greater for species invasive somewhere in the world. SDM predictions also indicate a considerable invasion potential of eight species that are currently naturalized but not yet widespread. Forestry trial data clearly provides a useful additional source of data to validate and refine SDMs in the context of risk assessment. Our study identified the climatic factors required for successful invasion of acacias, and accentuates the importance of integration of status elsewhere for risk assessment.
Antagonistic effects of biological invasion and temperature change on body size of island ectotherms
31 July 2014
Stellenbosch University

Treasure, A.M.;Chown, S.L.

Aim Despite their potentially profound consequences, little is known about the impacts of interactions among environmental change drivers on indigenous species. For biological invasions, much theoretical prominence has been given to additive or synergistic interactions with temperature change. However, empirical investigations are sparse. Here, we investigate the outcomes of interactions between temperature change and biological invasions on ectotherm body size in a temperate system. Location The sub-Antarctic Prince Edward Island group (46°54′ S, 37°45′ E). Methods We use long-term (24 years) body size data on weevil species from Marion and Prince Edward Islands. Invasive house mice, which prey on four of the five weevil species, are present on Marion Island, while the neighbouring Prince Edward Island is mouse free. Theory predicts that with higher temperatures, body size should decline across all species, and previous work suggests that size-selective predation by mice should enhance this effect on the invaded island. Generalized linear models were used to determine the relative effects of sex, island, altitude and mean annual temperature on body size for each of the species. Results Temperature change and biological invasions interact to affect body size in an antagonistic fashion. In weevil species not preyed on by invasive house mice, body size and declining size with increasing temperature are consistent across adjacent invaded and non-invaded islands. By contrast, species preyed on by mice are smaller on the invaded island and show opposite size-temperature relationships on the invaded and mouse-free islands. Main conclusions Size declines on the non-invaded island are in keeping with theoretical expectations of declining size with increasing temperatures. By contrast, this expectation is not met on the island invaded by mice, largely owing to what appears to be increased energetic demand of predators in colder years. These results emphasize that interactions among change drivers will take a range of forms, and that humans may have substantial influences on fundamental ecological patterns.
Natural hazards in a changing world: A case for ecosystem-based management
18 August 2014
Stellenbosch University

Nel, J.L.;Le Maitre, D.C.;Nel, D.C.;Reyers, B.;Archibald, S.;van Wilgen, B.W.;Forsyth, G.G.;Theron, A.K.;O'Farrell, P.J.;Kahinda, J.M.M.;Engelbrecht, F.A.;Kapangaziwiri, E.;van Niekerk, L.;Barwell, L.

Communities worldwide are increasingly affected by natural hazards such as floods, droughts, wildfires and storm-waves. However, the causes of these increases remain underexplored, often attributed to climate changes or changes in the patterns of human exposure. This paper aims to quantify the effect of climate change, as well as land cover change, on a suite of natural hazards. Changes to four natural hazards (floods, droughts, wildfires and storm-waves) were investigated through scenario-based models using land cover and climate change drivers as inputs. Findings showed that human-induced land cover changes are likely to increase natural hazards, in some cases quite substantially. Of the drivers explored, the uncontrolled spread of invasive alien trees was estimated to halve the monthly flows experienced during extremely dry periods, and also to double fire intensities. Changes to plantation forestry management shifted the 1:100 year flood event to a 1:80 year return period in the most extreme scenario. Severe 1:100 year storm-waves were estimated to occur on an annual basis with only modest human-induced coastal hardening, predominantly from removal of coastal foredunes and infrastructure development. This study suggests that through appropriate land use management (e.g. clearing invasive alien trees, re-vegetating clear-felled forests, and restoring coastal foredunes), it would be possible to reduce the impacts of natural hazards to a large degree. It also highlights the value of intact and well-managed landscapes and their role in reducing the probabilities and impacts of extreme climate events.
Range expansions across ecoregions: interactions of climate change, physiology and genetic diversity
19 August 2014
Stellenbosch University

Rius, M.;Clusella-Trullas, S.;McQuaid, C.D.;Navarro, R.A.;Griffiths, C.L.;Matthee, C.A.;von der Heyden, S.;Turon, X.

Aim Climate change is expected to drive range shifts among a wide array of organisms. Non-indigenous species (NIS) provide a unique opportunity to observe the establishment of range boundaries in a way that cannot be directly seen for native species. Recent studies have indicated that climate change facilitates biological invasions at local scales. However, the generality of these effects is unclear, as there is a dearth of comparative studies that assess how rapid environmental change affects species ranges across taxa and biogeographic provinces. Location The South African coast and other coastlines across the world. Methods We first studied the distribution of shallow-marine benthic organisms along the South African coastline and analysed the global distribution of NIS. We then obtained DNA sequence data from a suite of co-occurring NIS from along the studied coastline and compared these data with available genetic information from other regions of the world. Subsequently, we conducted physiological experiments to assess how thermal tolerance was related to species distribution. Finally, we analysed ship-based seawater temperature records and compared these with past changes in the range size and abundance of NIS. These records were used to estimate shipping intensity and NIS propagule pressure. Results We found that NIS with a variety of thermal tolerances and distributions have expanded their ranges and increased in abundance as seawater temperature regimes have changed. We found little interannual variation in shipping transport intensity. Most haplotypes of the studied NIS in South Africa were shared with other regions. Main conclusions This study provides empirical evidence that NIS, regardless of their thermal tolerance, range size and genetic variability, are expanding their ranges and increasing in abundance. This trend is uncorrelated with levels of human-mediated NIS transport but concurrent with changes in seawater temperature, which suggests that climate change fosters the spread and abundance of NIS across multiple spatial scales.
Lack of coherence in the warming responses of marine crustaceans
25 August 2014
Stellenbosch University

Faulkner, K.T.;Clusella-Trullas, S.;Peck, L.S.;Chown, S.L.

1. Understanding the extent to which organisms are affected by climate change and are capable of adapting to warming is essential for managing biodiversity. Recent macrophysiological analyses suggest that range-related responses to warming may be more coherent (less variable) and predictable in marine than in terrestrial systems. 2. To examine this generalization, we investigate basal upper thermal tolerances (measured as CTmax), the extent of their phenotypic plasticity and the impacts of different rates of temperature change on these tolerances, in five species of intertidal crustaceans from three distinct thermal regimes, incorporating South African (RSA) shores and sub-Antarctic Marion Island (MI). 3. For all species, lower rates of change resulted in lower CTmax, while acclimation resulted in varied responses depending on the rate of temperature change. At fast rates of temperature change, higher temperature acclimation resulted in elevated CTmax, while at slow rates of change, acclimation had no effect or resulted in a decline in CTmax. 4. Maximum habitat temperatures recorded at the organisms’ microsites were lower than the CTmax for the MI populations but were above CTmax at slow rates of change for RSA populations. Thus, populations from more equatorward locations have a lower tolerance of extremes than those from cooler regions. In addition to reduced warming tolerance, RSA populations had a lower acclimation capacity than their sub-Antarctic counterparts. 5. We find substantial differences in long-term responses among groups in different areas as a consequence of spatial variation in the interactions among basal tolerance, phenotypic plasticity and thermal environments. These outcomes emphasize the significance of examining forecasts using a range of data and approaches so that their certainty can be established to inform key policy decisions in a spatially appropriate context.
Solving the puzzle of Pringleophaga – threatened, keystone detritivores in the sub-Antarctic
26 March 2015
Stellenbosch University

Haupt, T.M.;Crafford, J.E.;Chown, S.L.

1. In the globally significant, lowland terrestrial systems of the sub-Antarctic’s South Indian Ocean Province Islands, caterpillars of the flightless moth genus Pringleophaga (Lepidoptera: Tineidae) are typically responsible for much nutrient turnover. 2. On Marion Island, Pringleophaga marioni is a keystone species for this reason. 3. Rising temperatures have led to increasing populations of introduced house mice, which, in turn, feed extensively on Pringleophaga caterpillars. 4. Because of the caterpillars’ keystone role, predation by mice is leading to changes in the functioning of the terrestrial system. 5. Given the estimates of an extended life cycle duration for P. marioni (and its congeners), that is, two to more than 5 years, an ongoing puzzle is why the species has not shown greater population declines on Marion Island than have been recorded (in some habitats 40–97% in 20 years), given extremely high estimates of predation (c. 1% of standing biomass per day). 6. One reason may be inaccurate previous estimates of life cycle duration for the species. 7. Here, we provide a new, quantitative estimate, by rearing caterpillars at different temperature regimes (5, 10, 15 and 5–15 °C), and combining these results with additional data from a prior study, to demonstrate that the life cycle duration for this species is approximately 1 year – half the previous minimum estimate. 8. The new quantitative data provide grounds for improved models for estimating population persistence of this species, and information for models assessing the costs and benefits of conservation interventions such as the eradication of invasive house mice.
Beyond climate: disturbance niche shifts in invasive species
04 September 2015
Stellenbosch University

González-Moreno, P.;Diez, J.M.;Richardson, D.M.;Vilà, M.

Aim Analysing how species niches shift between native and introduced ranges is a powerful tool for understanding the determinants of species distributions and for anticipating range expansions by invasive species. Most studies only consider the climatic niche, by correlating widely available presence-only data with regional climate.However, habitat characteristics and disturbance also shape species niches, thereby potentially confounding shifts attributed only to differences in climate. Here we used presence and abundance data for Oxalis pes-caprae, a species native to South Africa and invading areas globally, to understand how niche shifts may be influenced by disturbance at habitat and landscape scales in addition to climate. Locality Mediterranean climate areas world-wide. Methods We used available presence-only data and also conducted extensive surveys of the abundance of Oxalis (c. 11,000 plots) across different habitats in South Africa and in the introduced range in the Mediterranean Basin.We extended principal component analysis methods for measuring niche shifts by using Bayesian generalized linear models to identify climatic and disturbance niche shifts. Results We found a large climatic niche expansion towards stronger seasonality and lower temperature in the introduced range, but this expansion was greatly reduced when considering only conditions available in both ranges. Oxalis occupied more natural landscapes in the native range that remained unoccupied in the introduced range (‘niche unfilling’). In contrast to the similar abundances in natural and disturbed habitats in its native range, Oxalis was more abundant in disturbed habitats in the introduced range. Conclusions The large climatic niche expansion most likely reflects significant plasticity of Oxalis rather than rapid evolution. Furthermore, the unfilling of its disturbance niche in the introduced range suggests high potential for further invasion of natural areas. Together, these findings suggest that the potential for future spread of invasive species may be underestimated by approaches that characterize species niches based only on climate or partial information about their distributions.
Biological Flora of the British Isles: Ambrosia artemisiifolia
08 September 2015
Stellenbosch University

Essl, F.;Biró, K.;Brandes, D.;Broennimann, O.;Bullock, J.M.;Chapman, D.S.;Chauvel, B.;Dullinger, S.;Fumanal, B.;Guisan, A.;Karrer, G.;Kazinczi, G.;Kueffer, C.;Laitung, B.;Lavoie, C.;Leitner, M.;Mang, T.;Moser, D.;Müller-Schärer, H.;Petitpierre, B.;Richter, R.;Schaffner, U.;Smith, M.;Starfinger, U.;Vautard, R.;Vogl, G.;von der Lippe, M.;Follak, S.

1. This account presents information on all aspects of the biology of Ambrosia artemisiifolia L. (Common ragweed) that are relevant to understanding its ecology. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, and history, conservation, impacts and management. 2. Ambrosia artemisiifolia is a monoecious, wind-pollinated, annual herb native to North America whose height varies from 10 cm to 2.5 m, according to environmental conditions. It has erect, branched stems and pinnately lobed leaves. Spike-like racemes of male capitula composed of staminate (male) florets terminate the stems, while cyme-like clusters of pistillate (female) florets are arranged in groups in the axils of main and lateral stem leaves. 3. Seeds require prolonged chilling to break dormancy. Following seedling emergence in spring, the rate of vegetative growth depends on temperature, but development occurs over a wide thermal range. In temperate European climates, male and female flowers are produced from summer to early autumn (July to October). 4. Ambrosia artemisiifolia is sensitive to freezing. Late spring frosts kill seedlings and the first autumn frosts terminate the growing season. It has a preference for dry soils of intermediate to rich nutrient level. 5. Ambrosia artemisiifolia was introduced into Europe with seed imports from North America in the 19th century. Since World War II, it has become widespread in temperate regions of Europe and is now abundant in open, disturbed habitats as a ruderal and agricultural weed. 6. Recently, the North American ragweed leaf beetle (Ophraella communa) has been detected in southern Switzerland and northern Italy. This species appears to have the capacity to substantially reduce growth and seed production of A. artemisiifolia. 7. In heavily infested regions of Europe, A. artemisiifolia causes substantial crop-yield losses and its copious, highly allergenic pollen creates considerable public health problems. There is a consensus among models that climate change will allow its northward and uphill spread in Europe.
Climate change expected to drive habitat loss for two key herbivore species in an alpine environment
08 September 2015
Stellenbosch University

Parida, M.;Hoffmann, A.A.;Hill, M.P.

Aim Our first aim was to determine the environmental factors associated with two native Australian Lepidoptera species, Lomera caespitosae and Oncopera alpina, key herbivores of alpine and subalpine Poa grasses. Both species have been associated with areas of extensive grass death in Australian alpine regions, possibly affecting vegetation succession and recovery. Our second aim was to generate and evaluate potential distributional changes for both these moths and their host plants under scenarios of climate change. Location Alpine regions in south-eastern Australia. Methods We surveyed alpine regions in south-eastern Australia to compile presence–absence datasets for both moth species. We constructed ecological niche models from our survey data, in addition to predicting distributions of suitable host-plant species for the moths. Grass damage sites attributed to the moths were used additionally as independent test datasets to validate model performance. Future effects on species distributions under climate change scenarios were then investigated. Results The environmental factors affecting distributions differed between the moth species; for example, precipitation variables appeared to be important for L. caespitosae, while low winter–spring temperatures were expected to limit O. alpina. The findings were related to the presence of grass damage, which was greater in areas where species distributions overlapped. A declining trend in suitability was predicted for both herbivore species under climate change, while Poa spp. distributions were expected to be less influenced by climate change. Main conclusions The distributions of both moth species are more likely to be restricted by climate than host-plant availability. Predicted climate change effects are likely to put L. caespitosae under greater immediate risk of local extinction than O. alpina as a result of large areas of habitat loss by 2050.
Climate mediates the effects of disturbance on ant assemblage structure
09 September 2015
Stellenbosch University

Gibb, H.;Sanders, N.J.;Dunn, R.R.;Watson, S.;Photakis, M.;Abril, S.;Andersen, A.N.;Angulo, E.;Armbrecht, I.;Arnan, X.;Baccaro, F.B.;Bishop, T.R.;Boulay, R.;Castracani, C.;Del Toro, I.;Delsinne, T.;Diaz, M.;Donoso, D.A.;Enriquez, M.L.;Fayle, T.M.;Feener Jr, D.H.;Fitzpatrick, M.C.;Gomez, C.;Grasso, D.A.;Groc, S.;Heterick, B.;Hoffmann, B.D.;Lach, L.;Lattke, J.;Leponce, M.;Lessard, J.P.;Longino, J.;Lucky, A.;Majer, J.;Menke, S.B.;Mezger, D.;Mori, A.;Munyai, T.C.;Paknia, O.;Pearce-Duvet, J.;Pfeiffer, M.;Philpott, S.M.;de Souza, J.L.P.;Tista, M.;Vasconcelos, H.L.;Vonshak, M.;Parr, C.L.

Many studies have focused on the impacts of climate change on biological assemblages, yet little is known about how climate interacts with other major anthropogenic influences on biodiversity, such as habitat disturbance. Using a unique global database of 1128 local ant assemblages, we examined whether climate mediates the effects of habitat disturbance on assemblage structure at a global scale. Species richness and evenness were associated positively with temperature, and negatively with disturbance. However, the interaction among temperature, precipitation and disturbance shaped species richness and evenness. The effect was manifested through a failure of species richness to increase substantially with temperature in transformed habitats at low precipitation. At low precipitation levels, evenness increased with temperature in undisturbed sites, peaked at medium temperatures in disturbed sites and remained low in transformed sites. In warmer climates with lower rainfall, the effects of increasing disturbance on species richness and evenness were akin to decreases in temperature of up to 98°C. Anthropogenic disturbance and ongoing climate change may interact in complicated ways to shape the structure of assemblages, with hot, arid environments likely to be at greatest risk.
Global trade will accelerate plant invasions in emerging economies under climate change
26 October 2015
Stellenbosch University

Seebens, H.;Essl, F.;Dawson, W.;Fuentes, N.;Moser, D.;Pergl, J.;Pysek, P.;van Kleunen, M.;Weber, E.;Winter, M.;Blasius, B.

Trade plays a key role in the spread of alien species, and has arguably contributed to the recent enormous acceleration of biological invasions, thus homogenizing biotas world-wide. Combining data on 60-year trends of bilateral trade, as well as on biodiversity and climate, we modeled the global spread of plant species among 147 countries. The model results were compared with a recently compiled unique global data set on numbers of naturalized alien vascular plant species representing the most comprehensive collection of naturalized plant distributions currently available. The model identifies major source regions, introduction routes and hotspots of plant invasions that agree well with observed naturalized plant numbers. In contrast to common knowledge, we show that the Imperialist Dogma’, stating that Europe has been a net exporter of naturalized plants since colonial times, does not hold for the past 60 years, when more naturalized plants were being imported to than exported from Europe. Our results highlight that the current distribution of naturalized plants is best predicted by socio-economic activities 20 years ago. We took advantage of the observed time lag and used trade developments until recent times to predict naturalized plant trajectories for the next two decades. This shows that particularly strong increases in naturalized plant numbers are expected in the next 20 years for emerging economies in megadiverse regions. The interaction with predicted future climate change will increase invasions in northern temperate countries and reduce them in tropical and (sub)tropical regions, yet not by enough to cancel out the trade-related increase.
Plasticity of thermal tolerance and metabolism but not water loss in an invasive reed frog
04 November 2015
Stellenbosch University

Davies, S.J.;McGeoch, M.A.;Clusella-Trullas, S.

Phenotypic plasticity may buffer the selection pressures on organisms that inhabit novel or rapidly-changing environments. We investigated plasticity of thermal tolerance, energetic and water loss traits and their interaction with behaviour in a small-bodied, arboreal anuran (Hyperoliusmarmoratus Rapp, Hyperoliidae) undergoing rapid range expansion into the winter rainfall region of South Africa. After short-term exposure to three temperatures (acclimation treatments) commonly encountered in their historical and novel ranges, frogs exhibited a broad thermal tolerance range (mean ±s.d.: 42.1±2.9 °C) and higher plasticity in CTmax than in CTmin. Resting metabolic rate was lowest in cold-acclimated animals, while active metabolic rates were lowest in warm-acclimated frogs, likely reflecting compensation towards energy conservation. Evaporative water loss was not significantly altered by the acclimation treatments in either resting or active animals, indicating limited plasticity in this trait compared to metabolism. Our results suggest that plasticity of temperature limits and metabolism may benefit this species in variable environments such as those encountered in its expanded range. Lack of plasticity in water loss during resting and activity suggests that these frogs rely on their high cutaneous resistance and behavioural means to buffer climate variation. This study highlights the importance of synergistic interactions between physiology and behaviour in determining amphibian responses to temperature variation.
Early eclosion of overwintering cotton bollworm moths from warming temperatures accentuates yield loss in wheat
27 January 2016
Stellenbosch University

Ouyang, F.;Hui, C.;Men, X.Y.;Zhang, Y.S.;Fan, L.;Shi, P.;Zhao, Z.;Ge, F.

Understanding and predicting the impact of climate change on population demography, biotic interactions and ecosystem service is central to ecology. Long-term time series analysis of insect populations is crucial for analyzing the effect of climate change on plant–insect interactions in agro-ecological systems; yet such data are often lacking. Here, based on field experiments and the long-term time series of the overwintering adult cotton bollworm Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) collected since 1975, we investigate the dynamic trend of H. armigera, as well as its driving forces and effects on the recruitment of H. armigera and crop yield. Results illustrated a shift to early eclosion of diapausing pupae due to global warming, extending the duration and abundance of adults in the overwintering generation. This then led to more larvae recruited in the first generation, and consequently damages the wheat at early growing stages. Our results suggest that the asynchronous effects of rising global surface temperature on the relative growth rate of spring crops and insect pests could intensify in the future, causing accentuated crop yield loss. To mitigate the adverse herbivore-mediated effect on crop yield in a warming climate, efficient cultivation measures and pest management are necessary, such as planting precocious crops with short growth period and timely control of insect pests.
Determinants of the Fynbos/Succulent Karoo biome boundary: Insights from a reciprocal transplant experiment
27 January 2016
Stellenbosch University

Esler, K.J.;von Staden, L.;Midgley, G.F.

Boundaries between Fynbos and Succulent Karoo vegetation in the Greater Cape Floristic Region are frequently characterised by sharp transitions from sandy, dystrophic to loamy, mesotrophic soils, together with a more gradual climate transition from cooler, wetter conditions typical of Fynbos at higher elevations to warmer, drier conditions at lower elevations typical of Succulent Karoo. There is very high species turnover across these boundaries, providing an opportunity to disentangle the relative roles of climate and soil type in determining the biome boundary. A fully reciprocal transplant approach was employed here to investigate this question, using three species from each biome occurring naturally in close proximity at Jonaskop, Western Cape. Greenhouse-germinated and established seedlings of all species were planted into both sandy, dystrophic and loamy, mesotrophic soils typical of each biome at four sites along an elevational transect (elevations 545 m, 744 m, 953 m, 1303 m) at Jonaskop, and their growth and survivorship monitored for 7 months. At least one site on the elevation gradient represented annual climate rainfall and temperature conditions during the experimental period typical of the range edge for each of the selected species, this typically being the lowest elevation site (warm × dry) for Fynbos species (Protea humiflora, P. magnifica and P. amplexicaulis), and the highest elevation site (cool × wet) for Succulent Karoo species (Ruschia lineolata, Drosanthemum speciosum and Pteronia incana). Fynbos species showed significant adverse responses to loamy mesotrophic soil, with highly significant reductions in growth and high and rapid rates of mortality relative to their native soil. Fynbos species showed somewhat reduced growth and survival at the lowest elevation when grown in native soils, but demonstrated significant interaction between soil type and elevation with much lower growth and survival at the lowest elevation on the loamy soils. Surprisingly, all the Fynbos species showed reductions in growth and survival at the highest elevation, with significant reductions in two of the three species. Succulent Karoo species, by contrast, showed very few significant performance differences between soil types and few significant soil × elevation interactive effects, but did show significant growth and survival responses to elevation, with high growth and survival at mid-level elevations, far higher than their natural extent at the site. These results suggest that the selected Succulent Karoo species are neither edaphically nor climatically constrained from establishing and growing in sandy dystrophic soils and cool climates typical of the Fynbos vegetation along this elevation gradient, but that Fynbos species are strongly limited both edaphically and climatically from growing under conditions typical of the Succulent Karoo.We propose that Succulent Karoo elements may be excluded competitively or through disturbance from colonising sandy dystrophic soils at higher elevations in Fynbos vegetation, with fire regime most likely responsible for maintaining the sharply delineated boundaries between these biomes. This is because fire would strongly exclude non-fire adapted Succulent Karoo species at and above the biome boundary, while loamy soils and climate together would strongly exclude Fynbos species from the heavier soils of the Succulent Karoo. The relative climate and soil affinities of these biomes, accentuated by the role of fire, could therefore provide a coherent explanation for biome boundaries in the Greater Cape Floristic Region. We note however that the limited species selection in this study precludes a conclusive general result, and that several interesting questions remain about soil, climate and disturbance determinants across this biome boundary.
Rising temperatures and changing rainfall patterns in South Africa’s national parks
14 March 2016
Stellenbosch University

van Wilgen, N.J.;Goodall, V.;Holness, S.;Chown, S.L.;McGeoch, M.A.

Air temperatures have increased globally over the past decades, while rainfall changes have been more variable, but are taking place. In South Africa, substantial climate-related impacts are predicted, and protected area management agencies will need to respond actively to impacts. It is critical for management agencies to understand the way in which climate is changing locally to predict impacts and respond appropriately. Here, for the first time, we quantify observable changes in temperature and rainfall in South African national parks over the past five to ten decades. Our results show significant increases in temperatures in most parks, with increases being most rapid in the arid regions of the country. Increases in the frequency of extreme high temperature events were also most pronounced in these regions. These results are consistent with other climate studies conducted in these areas. Similar increases were identified for both minimum and maximum temperatures, though absolute minimum temperatures increased at greater rates than absolute maxima. Overall, rainfall trends were less obvious, but a decrease in rainfall was observed for the southern Cape (in three parks), and an increase was detected in one park. The observed temperature changes over the last 20–50 years have in several instances already reached those predicted for near future scenarios (2035), indicating that change scenarios are conservative. These results provide individual parks with evidence-based direction for managing impacts under current and projected changes in local climate. They also provide the management agency with sub-regional information to tailor policy and impact monitoring. Importantly, our results highlight the critical role that individual weather stations play in informing local land management and the concerns for parks that have no local information on changes in climate.
Predicted decrease in global climate suitability masks regional complexity of invasive fruit fly species response to climate change
18 May 2016
Stellenbosch University

Hill, M.P.;Bertelsmeier, C.;Clusella-Trullas, S.;Garnas, J.;Robertson, M.P.;Terblanche, J.S.

Climate change affects the rate of insect invasions as well as the abundance, distribution and impacts of such invasions on a global scale. Among the principal analytical approaches to predicting and understanding future impacts of biological invasions are Species Distribution Models (SDMs), typically in the form of correlative Ecological Niche Models (ENMs). An underlying assumption of ENMs is that species–environment relationships remain preserved during extrapolations in space and time, although this is widely criticised. The semi-mechanistic modelling platform, CLIMEX, employs a top-down approach using species ecophysiological traits and is able to avoid some of the issues of extrapolation, making it highly applicable to investigating biological invasions in the context of climate change. The tephritid fruit flies (Diptera: Tephritidae) comprise some of the most successful invasive species and serious economic pests around the world. Here we project 12 tephritid species CLIMEX models into future climate scenarios to examine overall patterns of climate suitability and forecast potential distributional changes for this group. We further compare the aggregate response of the group against species-specific responses. We then consider additional drivers of biological invasions to examine how invasion potential is influenced by climate, fruit production and trade indices. Considering the group of tephritid species examined here, climate change is predicted to decrease global climate suitability and to shift the cumulative distribution poleward. However, when examining species-level patterns, the predominant directionality of range shifts for 11 of the 12 species is eastward. Most notably, management will need to consider regional changes in fruit fly species invasion potential where high fruit production, trade indices and predicted distributions of these flies overlap.
Fostering collaboration for knowledge and action in disaster management in South Africa
26 July 2016
Stellenbosch University

Sitas, N.;Reyers, B.;Cundill, G.;Prozesky, H.E.;Nel, J.L.;Esler, K.J.

Engaging diverse stakeholders in collaborative processes to integrate environmental information into decision making is important, but challenging. It requires working at and across the boundaries between knowledge types — a complex milieu of different value systems, norms, and mental models — and multiple stakeholder-engagement processes which facilitate knowledge exchange and co-production. Using a qualitative, inductive approach, we analysed perceptions and outputs of a transdisciplinary project which aimed to generate new knowledge, awareness and action for ecosystem-based disaster management in South Africa. Several obstacles that could potentially undermine the project’s objectives were identified, including: preconceived assumptions; entrenched disciplinary thinking; and confusing terminology. Enabling factors included efforts to ensure project cocreation and the use of knowledge brokers in promoting systems thinking that is grounded in practice.
A novel bioenergy feedstock in Latin America? Cultivation potential of Acrocomia aculeate under current and future climate conditions
27 October 2016
Stellenbosch University

Plath, M.;Moser, C.;Bailis, R.;Brandt, P.;Hirsch, H.;Klein, A.M.;Walmsley, D.;von Wehrden, H.

Plant oil is a key commodity in the global economy, particularly for food and bioenergy markets. However, current production practices often impair smallholder livelihoods, cause land use changes, and compete for food production. The neotropical palm Acrocomia aculeata is currently being promoted as a novel sustainable biomass feedstock, particularly for bioenergy, but only little is known about the palm’s ecological requirements. Based on a comprehensive literature and database search for recorded occurrences of A. aculeata in Latin America, we computed an ecological niche modeling to determine the palm’s potential distribution area based on climatic and soil variables. We subsequently considered current land cover and predicted future climate change scenarios to discuss the cultivation potential of A. aculeata within its possible distribution area. The results revealed a large potential to cultivate A. aculeata in Latin America under current abiotic environmental conditions. The two core distribution regions identified were (1) Central America including the Caribbean, northern Colombia and Venezuela, and (2) southern Brazil and eastern Paraguay. A considerable proportion of the medium to highly suitable growing areas were found to be currently used for agricultural production or covered by land types with high conservation and carbon sequestration value. Applying the model under the IPCC’s A2A ‘business as usual’ emission scenario suggested that by 2080 the vast majority of suitable growing areas severely decline in extent or disappear entirely. Our ecological niche modeling thus shows that despite the palm’s high cultivation potential, a sustainable deployment of A. aculeata requires a precautious, evidence-based approach.
Ecological research and conservation manangement in the Cape Floristic Region between 1945 and 2015: History, current understanding and future challenges
02 November 2016
Stellenbosch University

van Wilgen, B.W.;Carruthers, J.;Cowling, R.M.;Esler, K.J.;Forsyth, A.T.;Gaertner, M.;Hoffman, M.T.;Kruger, F.J.;Midgley, G.F.;Palmer, G.;Pence, G.Q.K.;Raimondo, D.C.;Richardson, D.M.;van Wilgen, N.J.;Wilson, J.R.U.

In 1945, the Royal Society of South Africa published a wide-ranging report, prepared by a committee led by Dr C.L. Wicht, dealing with the preservation of the globally unique and highly diverse vegetation of the south-western Cape. The publication of the Wicht Committee’s report signalled the initiation of a research programme aimed at understanding, and ultimately protecting, the unique and diverse ecosystems of the Cape Floristic Region. This programme has continued for over 70 years, and it constitutes the longest history of concerted scientific endeavour aimed at the conservation of an entire region and its constituent biota. This monograph has been prepared to mark the 70th anniversary of the Wicht Committee report. It provides a detailed overview of the circumstances that led up to the Wicht Committee’s report, and the historical context within which it was written. It traces the development of new and substantial scientific understanding over the past 70 years, particularly with regard to catchment hydrology, fire ecology, invasive alien plant ecology, the harvesting of plant material and conservation planning. The Wicht Committee’s report also made recommendations about ecosystem management, particularly with regard to the use of fire and the control of invasive alien plants, as well as for the establishment of protected areas. Subsequently, a combination of changing conservation philosophies and scientific conservation planning led to the creation and expansion of a network of protected areas that now covers nearly 19% of the Cape Floristic Region. We also review aspects of climate change, most of which could not have been foreseen by the Wicht Committee. We conclude that those responsible for the conservation of these ecosystems will face many challenges in the 21st century. These will include finding ways for effectively managing invasive alien plants and fires, as foreseen by the Wicht Committee. While the protected area network has expanded beyond the modest targets proposed by the Wicht Committee, funding has not kept pace with this expansion, with consequences for the ability to effectively manage protected areas. The research environment has also shifted away from long-term research conducted by scientists embedded in management agencies, to short-term studies conducted largely by academic institutions. This has removed a significant benefit that was gained from the long-term partnership between research and management that characterised the modis operandus of the Department of Forestry. Growing levels of illegal resource use and a changing global climate also pose new challenges that were not foreseen by the Wicht Committee.
Cost-effective monitoring of biological invasions under global change: a model-based framework
26 January 2017
Stellenbosch University

Vicente, J.R.;Alagador, D.;Guerra, C.;Alonso, J.M.;Kueffer, C.;Vaz, A.S.;Fernandes, R.F.;Cabral, J.A.;Araujo, M.B.;Honrado, J.P.

1. Ecological monitoring programmes are designed to detect and measure changes in biodiversity and ecosystems. In the case of biological invasions, they can contribute to anticipating risks and adaptively managing invaders. However, monitoring is often expensive because large amounts of data might be needed to draw inferences. Thus, careful planning is required to ensure that monitoring goals are realistically achieved. 2. Species distribution models (SDMs) can provide estimates of suitable areas to invasion. Predictions from these models can be applied as inputs in optimization strategies seeking to identify the optimal extent of the networks of areas required for monitoring risk of invasion under current and future environmental conditions. A hierarchical framework is proposed herein that combines SDMs, scenario analysis and cost analyses to improve invasion assessments at regional and local scales. We illustrate the framework with Acacia dealbata Link. (Silver-wattle) in northern Portugal. The framework is general and applicable to any species. 3. We defined two types of monitoring networks focusing either on the regional-scale management of an invasion, or management focus within and around protected areas. For each one of these two schemes, we designed a hierarchical framework of spatial prioritization using different information layers (e.g. SDMs, habitat connectivity, protected areas). We compared the performance of each monitoring scheme against 100 randomly generated models. 4. In our case study, we found that protected areas will be increasingly exposed to invasion by A. dealbata due to climate change. Moreover, connectivity between suitable areas for A. dealbata is predicted to increase. Monitoring networks that we identify were more effective in detecting new invasions and less costly to management than randomly generated models. The most cost-efficient monitoring schemes require 18% less effort than the average networks across all of the 100 tested options. 5. Synthesis and applications. The proposed framework achieves cost-effective monitoring networks, enabling the interactive exploration of different solutions and the combination of quantitative information on network performance with orientations that are rarely incorporated in a decision support system. The framework brings invasion monitoring closer to European legislation and management needs while ensuring adaptability under rapid climate and environmental change.
Microclimates mitigate against hot temperatures in dryland ecosystems: termite mounds as an example
20 February 2017
Stellenbosch University

Joseph, G.S.;Seymour, C.L.;Coetzee, B.W.T.;Ndlovu, M.;De La Torre, A.;Suttle, R.;Hicks, N.;Oxley, S.;Foord, S.H.

Termite mounds have recently been shown to protect against drought by providing refuges for plants and foci for revegetation, but whether mounds modulate temperature remains untested. Organisms tend to experience climate at finer scales than those captured by models predicting how distributions alter with global change, so microclimates represent important “climate refuges.” Using data we collected from African savanna sites, generalized linear mixed-effects models and linear quantile regression analysis confirm for the first time that the woody species associated with large termite mounds establish microclimates that are significantly cooler than surrounding savannas, a cooling effect that is even greater at warmer extremes. As air temperatures approached 40°C, a cooling effect of up to 4°C occurred, representing a doubling from that observed at 34°C. African savannas encompass 10 million km2, and much of this harbors evenly dispersed termitaria. The temperature-modulating effect of mounds facilitates agricultural and conservation decision-making as global change begins to impact the integrity of both human well-being and ecological processes.
Lizards paid a greater opportunity cost to thermoregulate in a less heterogeneous environment
03 May 2017
Stellenbosch University

Basson, C.H.;Levy, O.;Angilletta Jr, M.J.;Clusella-Trullas, Susana

1. The theory of thermoregulation has developed slowly, hampering efforts to predict how individuals can buffer climate change through behaviour. Mixed results of field and laboratory experiments underscore the need to test hypotheses about thermoregulation explicitly, while measuring costs and benefits in different thermal landscapes. 2. We simulated body temperature and energy expenditure of a virtual lizard that either thermoregulates optimally or thermoconforms in a landscape of either low or high quality (one or four basking sites, respectively). We then compare the predicted values in each landscape with the observed values for real lizards in experimental arenas. 3. Lizards thermoregulated more accurately in the high-quality landscape than they did on the low-quality landscape, albeit only slightly so, but spent similar amounts of energy in these landscapes. Basking, rather than shuttling between heat sources, accounted for the majority of the energy consumed in both landscapes. 4. These results did not support the predictions of our model. In the low-quality landscape, real lizards thermoregulated intensely despite the potential to save energy by thermoconforming. In the high-quality landscape, lizards moved more than expected, suggesting that lizards explored their surroundings despite being able to thermoregulate without doing so. 5. Our results suggest that non-energetic benefits drive thermoregulatory behaviour in costly environments, despite the missed opportunities arising from thermoregulation. We propose that energetic costs associated with thermoregulatory movement will become substantial in homogeneous environments such as flat plains and dense forests. The theory of thermoregulation should incorporate these aspects if biologists wish to predict responses of ectotherms to changing climates and habitats.
Multi-site generalised dissimilarity modelling: using zeta diversity to differentiate drivers of turnover in rare and widespread species
24 May 2017
Stellenbosch University

Latombe, G.;Hui, C.;McGeogh, M.A.

1. Generalised dissimilarity modelling (GDM) applies pairwise beta diversity as a measure of species turnover with the purpose of explaining changes in species composition under changing environments or along environmental gradients. Beta diversity only captures turnover across pairs of sites and, therefore, disproportionately represents turnover in rare species across communities. By contrast, zeta diversity, the average number of shared species across multiple sites, captures the full spectrum of rare, intermediate and widespread species as they contribute differently to compositional turnover. 2. We show how integrating zeta diversity into GDMs (which we term multi-site generalised dissimilarity modelling, MS-GDM), provides a more information rich approach to modelling how communities respond to environmental variation and change. We demonstrate the value of including zeta diversity in biodiversity assessment and modelling using BirdLife Australia Atlas data. Zeta diversity values for different numbers of sites (the order of zeta) are regressed against environmental differences and distance using two kinds of regressions: shape constrained additive models and a combination of I-splines and generalised linear models. 3. Applying MS-GDM to different orders of zeta revealed shifts in the importance of environmental variables in explaining species turnover, varying with the order of zeta and thus with the level of co-occurrence of the species and, by extension, their commonness and rarity. In particular, precipitation gradients emerged as drivers in the turnover of rare species, whereas temperature gradients were more important drivers of turnover in widespread species. 4. Appreciation of the factors that drive compositional turnover across multiple sites is necessary for accommodating the full spectrum of compositional turnover across rare to common species. This extends beyond understanding drivers for pairwise beta diversity only. MS-GDM provides a valuable addition to the toolkit of GDM, with further potential for survey gap analysis and prediction of species composition in unsampled sites.
Climate constrains the establishment and proliferation of Anthonomus santacruzi, a flower-feeding biological control agent of the invasive weed Solanum mauritianum in South Africa
01 August 2017
Stellenbosch University

Singh, D.;Olckers, T.

The flowerbud-feeding weevil Anthonomus santacruzi Hustache (Coleoptera: Curculionidae) was released in South Africa in 2008 for the biological control of the invasive tree Solanum mauritianum Scopoli (Solanaceae). The weevil was widely deployed throughout KwaZulu-Natal province, which supports large S. mauritianum infestations, and has become well established in its warmer coastal regions. The aim of this study was to provide field evidence that climate is constraining the weevil’s distribution in South Africa. Solanum mauritianum populations were sampled at 23 sites across an altitudinal gradient in KwaZulu-Natal to determine A. santacruzi densities in relation to food availability and climatic variables. Despite significantly higher amounts of floral material on S. mauritianum at the higher altitude inland sites, A. santacruzi numbers were significantly higher at the lower altitude coastal sites. There was thus a significant negative relationship between A. santacruzi numbers and altitude and significant positive relationships between A. santacruzi numbers and both temperature and humidity. Neither rainfall nor food availability influenced A. santacruzi numbers, although lower amounts of floral material at the coastal sites may well have been caused by higher weevil densities at these sites. Anthonomus santacruzi was absent at only three sites, all at higher altitudes, further demonstrating that conditions in coastal or low-altitude regions are favourable for establishment and population proliferation. Future release efforts in KwaZulu-Natal, but also in other South African provinces, should thus be focused on coastal regions and inland regions that are below 1000 m above sea level.
Ranking of invasive spread through urban green areas in the world’s 100 most populous cities
19 December 2017
Stellenbosch University

Hui, C.;Richardson, D.M.;Visser, V.

Urban landscapes are highly fragmented (leading to the extinction of native species) as well as transformed and disturbed (creating novel environments). Such conditions provide non-native species with opportunities to establish and spread through ‘‘urban green areas’’ (UGAs). UGAs can serve as stepping stones for many alien species to recruit and may become sources of propagules to launch invasions in adjoining natural ecosystems. There is great diversity in the spatial structures of UGAs worldwide; these are determined by the city’s level of development, human density, urban planning policy, and history. We explore the invasion risks of, and the potential of invasive spread in, UGAs in the world’s 100 most populous cities (in 40 countries). Based on maps of enhanced vegetation index at 250 m resolution over the extent of 25 by 25 km for each city centre, we simulate the invasion and spread of a reference species (a virtual ruderal invasive species) from the city centre into surrounding urban or rural areas. Doing so allowed us to provide an objective baseline for comparing urban susceptibility to such invasions across diverse cultures, histories and societies. We derive the global ranking of invasive spread potential for each city based on the rate of spread of the reference species, and the ranking of 40 countries, based on the average rate of spread in their cities. We explore correlates of spread rates after 100 time steps (years) by examining the roles of climate (mean annual temperature and rainfall), human demography (city population size and growth rate), and socio-economic indicators [human footprint, human development index and gross domestic product (GDP) per capita]. Small city population size and high GDP per capita are the only significant predictors of high potential for invasive spread. Among the G20 countries, Canada, South Korea, South Africa, France, USA and Brazil all feature in the top-10 countries, and Atlanta, Washington, D.C. and Dallas in the USA, Chittagong in Bangladesh, Toronto in Canada and Brasilia in Brazil are listed among the top 10 cities overall. Our results can serve as a global baseline assessment of invasive spread risks through UGAs, and call for improved protocols for monitoring, planning and management of UGAs.
Naturalization of ornamental plant species in public green spaces and private gardens
19 December 2017
Stellenbosch University

Mayer, K.;Haeuser, E.;Dawson, W.;Essl, F.;Kreft, H.;Pergl, J.;Pysek, P.;Weigelt, P.;Winter, M.;Lenzner, B.;van Kleunen, M.

Ornamental horticulture is the most important pathway for alien plant introductions worldwide, and consequently, invasive spread of introduced plants often begins in urban areas. Although most introduced ornamental garden-plant species are locally not naturalized yet, many of them have shown invasion potential elsewhere in the world, and might naturalize when climate changes. We inventoried the planted flora of 50 public and 61 private gardens in Radolfzell, a small city in southern Germany, to investigate whether local naturalization success of garden plants is associated with their current planting frequency, climatic suitability (as assessed with climatic niche modelling) and known naturalization status somewhere in the world. We identified 954 introduced garden-plant species, of which 48 are already naturalized in Radolfzell and 120 in other parts of Germany. All currently naturalized garden plants in Radolfzell have a climatic suitability probability of C 0.75 and are naturalized in C 13 out of 843 regions globally. These values are significantly higher than those of garden plants that have not become locally naturalized yet. Current planting frequencies, however, were not related to current naturalization success. Using the identified local naturalization thresholds of climatic suitability and global naturalization frequency, and climate projections for the years 2050 and 2070, we identified 45 garden-plant species that are currently not naturalized in Radolfzell but are likely to become so in the future. Although our approach cannot replace a full risk assessment, it is well-suited and applicable as one element of a screening or horizon scanning-type approach.
Managing consequences of climate-driven species redistribution requires intergration of ecology, conservation and social science
06 March 2018
Stellenbosch University

Bonebrake, T.C.;Brown, C.J.;Bell, J.D.;Blanchard, J.L.;Chauvenet, A.;Champion, C.;Chen, I.-C.;Clark, T.D.;Colwell, R.K.;Danielsen, F.;Dell, A.I.;Donelson, J.M.;Evengard, B.;Ferrier, S.;Frusher, S.;Garcia, R.A.;et al.

Climate change is driving a pervasive global redistribution of the planet’s species. Species redistribution poses new questions for the study of ecosystems, conservation science and human societies that require a coordinated and integrated approach. Here we review recent progress, key gaps and strategic directions in this nascent research area, emphasising emerging themes in species redistribution biology, the importance of understanding underlying drivers and the need to anticipate novel outcomes of changes in species ranges.We highlight that species redistribution has manifest implications across multiple temporal and spatial scales and from genes to ecosystems. Understanding range shifts from ecological, physiological, genetic and biogeographical perspectives is essential for informing changing paradigms in conservation science and for designing conservation strategies that incorporate changing population connectivity and advance adaptation to climate change. Species redistributions present challenges for human well-being, environmental management and sustainable development. By synthesising recent approaches, theories and tools, our review establishes an interdisciplinary foundation for the development of future research on species redistribution. Specifically, we demonstrate how ecological, conservation and social research on species redistribution can best be achieved by working across disciplinary boundaries to develop and implement solutions to climate change challenges. Future studies should therefore integrate existing and complementary scientific frameworks while incorporating social science and human-centred approaches. Finally, we emphasise that the best science will not be useful unless more scientists engage with managers, policy makers and the public to develop responsible and socially acceptable options for the global challenges arising from species redistributions.
Timing of cherry tree blooming: Contrasting effects of rising winter low temperatures and early spring temperatures
03 April 2018
Stellenbosch University

Shi, P.;Chen, Z.;Reddy, G.V.P.;Hui, C.;Huang, J.;Xiao, M.

Phenology reflects the interplay of climate and biological development. Early spring phenological phenomena are particularly important because the end of diapause or dormancy is related not only to heat accumulation in the early spring but also probably to winter low temperatures. Although a warmer winter can reduce overwintering mortality in many insects and plants, it also reduces the accumulation of chilling time that often triggers the end of diapause or dormancy. We examined a continuous 67-year time series of the first flowering date of cherry trees and compared three phenological models based on the temperature-dependent developmental rate: (i) the accumulated degree days (ADD) method, (ii) the number of days transferred to a standardized temperature (DTS) method, and (iii) the accumulated developmental progress (ADP) method. The ADP method performed the best but only slightly better than the DTS method. We further explained the residuals from the ADP method by an additive model using the mean winter minimum daily temperatures, the number of days with low temperatures (represented by daily minimum temperature) below a critical low temperature, and the minimum annual extreme temperature. These three temperature variables explained more than 57.5% deviance of the ADP model residuals. Increased mean winter low temperatures can delay the blooming of cherry trees by reducing the accumulation of chilling time, whereas reduced numbers of cold days can shift the blooming to become earlier. Overall, rising winter low temperatures will delay the flowering time, while rising early spring temperatures directly shift earlier the flowering time. The flowering time has been shifted to earlier, and the balance from the opposing effects of rising winter low temperatures and early spring temperatures explains this shift.
Achieving the national development agenda and the Sustainable Development Goals(SDGs) through investment in ecological infrastructure: A case study of South Africa
04 April 2018
Stellenbosch University

Cumming, T.L.;Shackleton, R.T.;Forster, J.;Dini, J.;Khan, A.;Gumula, M.;Kubiszewski, I.

Ecological infrastructure (EI) refers to ecosystems that deliver services to society, functioning as a nature-based equivalent of, or complement to, built infrastructure. EI is critical for socio-economic development, supporting a suite of development imperatives at local, national and international scales. This paper presents the myriad of ways that EI supports sustainable development, using South Africa and the South African National Development Plan as a case study, linking to the Sustainable Development Goals on a global level. We show the need for EI across numerous development and sustainability issues, including food security, water provision, and poverty alleviation. A strategic and multi-sectoral approach to EI investment is essential for allocating scarce public and private resources for achieving economic and social-ecological priorities. Opportunities to unlock investment in EI, both internationally and on the national level, are identified. This includes leveraging private sector investment into landscape management and integrating the costs of managing EI into public sectors that benefit directly from ecosystem services, such as the water sector and infrastructure development. Additionally, investing in EI also aligns well with international development and climate change funds. Investment in EI from a range of innovative sources supports global and national development, while complementing other development investments.
Collaborative learning to unlock investments for functional ecological infrastructure: Bridging barriers in social-ecological systems in South Africa
04 April 2018
Stellenbosch University

Angelstam, P.;Barnes, G.;Elbakidze, M.;Marais, C.;Marsh, A.;Polonsky, S.;Richardson, D.M.;Rivers, N.;Shackleton, R.T.;Stafford, W.

Maintenance of functional ecological (or green) infrastructure is threatened by habitat conversion, fragmentation and loss, water scarcity, invasive species, climate change, resource extraction, poor policy implementation and societal inequity. Using South Africa as a case study, our transdisciplinary team identified actions likely to be effective in scaling up research and development projects that support implementation of policy about ecological infrastructure by active adaptive management. Based on expert knowledge at three scales, we analysed South Africa's opportunity to active adaptive management and to unlock investments that enhance functional ecological infrastructure. Barriers included lack of trust among actors, limited collaborative governance and integrated planning, including local partnerships; as well as a poor inclusion of evidence based knowledge based on monitoring of landscape restoration efforts and its social and ecological consequences. Bridges include practicing transdisciplinary knowledge production, enhancing social learning among actors and stakeholders, and advocacy based on improved understanding. We propose a portfolio of place-based actions that could help to facilitate unlocking investments for functional ecological infrastructure by prioritising conservation, management and restoration through integrated cross-scale, collaborative and multi-sector spatial planning. Understanding the structure and dynamics of social-ecological systems, identifying champions, framing key messages for different audiences, and sharing failures and success stories internationally, are crucial requirements to unlock investments.
Developing a framework of minimum standards for the risk assessment of alien species.
16 April 2018
Stellenbosch University

Roy, H.E.;Rabitsch, W.;Scalera, R.;Stewart, A.;Gallardo, B.;Genovesi, P.;Essl, F.;Adriaens, T.;Bacher, S.;Booy, O.;Branquart, E.;Brunel, S.;Copp, G.H.;Dean, H.;D'hondt, B.;Josefsson, M.;Kenis, M.;Kettunen, M.;Linnamagi, M.;Lucy, F.;Martinou, A.;Moore, N.;Nentwig, W.;Nieto, A.;Pergl, J.;Peyton, J.;Roques, A.;Schindler, S.;Schönrogge, K.;Solarz, W.;Stebbing, P.D.;Trichkova, T.;Vanderhoeven, S.;van Valkenburg, J.;Zenetos, A.

1. Biological invasions are a threat to biodiversity, society and the economy. There is an urgent need to provide evidence-based assessments of the risks posed by invasive alien species (IAS) to prioritize action. Risk assessments underpin IAS policies in many ways: informing legislation; providing justification of restrictions in trade or consumer activities; prioritizing surveillance and rapid response. There are benefits to ensuring consistency in content of IAS risk assessments globally, and this can be achieved by providing a framework of minimum standards as a checklist for quality assurance. 2. From a review of existing risk assessment protocols, and with reference to the requirements of the EU Regulation on IAS (1143/2014) and international agreements including the World Trade Organisation, Convention on Biological Diversity and International Plant Protection Convention, coupled with consensus methods, we identified and agreed upon 14 minimum standards (attributes) a risk assessment scheme should include. 3. The agreed minimum standards were as follows: (1) basic species description; (2) likelihood of invasion; (3) distribution, spread and impacts; (4) assessment of introduction pathways; (5) assessment of impacts on biodiversity and ecosystems; (6) Assessment of impact on ecosystem services; (7) assessment of socio-economic impacts; (8) consideration of status (threatened or protected) of species or habitat under threat; (9) assessment of effects of future climate change; (10) completion possible even when there is a lack of information; (11) documents information sources; (12) provides a summary in a consistent and interpretable form; (13) includes uncertainty; (14) includes quality assurance. In deriving these minimum standards, gaps in knowledge required for completing risk assessments and the scope of existing risk assessment protocols were revealed, most notably in relation to assessing benefits, socio-economic impacts and impacts on ecosystem services but also inclusion of consideration of climate change. 4. Policy implications. We provide a checklist of components that should be within invasive alien species risk assessments and recommendations to develop risk assessments to meet these proposed minimum standards. Although inspired by implementation of the European Union Regulation on invasive alien species, and as such developed specifically within a European context, the derived framework and minimum standards could be applied globally.
Reduced mobility but high survival: thermal tolerance and locomotor response of the specialist herbivore, Pareuchaetes insulate (Walker) (Lepidoptera: Erebidae), to low temperatures
04 May 2018
Stellenbosch University

Uyi, O.O.;Zachariades, C.;Marais, E.;Hill, M.P.

Disentangling the responses of insects to variations in their thermal environment is central to our understanding of the evolution of temperature-dependent performance in these species.Here,we report results of experiments examining the effects of high(upper lethal temperature = ULT) and low (lower lethal temperature = LLT) temperature and exposure time on the survival of larvae and adults of a multivoltine, nocturnal moth species, Pareuchaetes insulata, a biological control agent whose impact on an invasive weed, Chromolaena odorata has been variable in South Africa. The influence of temperature and acclimation on locomotion performance of the moth was also investigated. Temperature and duration of exposure significantly affected survival of both adults and larvae of P. insulata with more extreme temperatures and/or longer durations proving to be more lethal. Third instar larvae and adults are both freeze intolerant and had LT50 of −5.9 and −4.7°C, respectively, after a 2 h exposure. Although cold acclimation was beneficial to the nocturnal larvae, temperatures below 10°C significantly reduce their locomotion activities. The average daily minimum temperatures in the coldest months at three locations in South Africa are over 5°C lower than those of Fort Lauderdale, Florida, USA, where P. insulate was originally collected. Our results suggest that lethal high or low temperatures at short timescales are trivial in explaining the variable performance of P. insulata, but reduced locomotion at sub-lethal temperatures may be and important driver of the population dynamics of the biocontrol agent (especially in winter months) and may consequently explain the low population levels of the moth because of possible reduced feeding by larvae during night-time low temperatures.
Climate warming drives invasion history of Ambrosia artemisiifolia in central Europe
02 August 2018
Stellenbosch University

Mang, T.;Essl, F.;Moser, D.;Dullinger, S.

It is thought that future climate change is likely to foster biological invasions, but effects of climate warming on invasions in recent decades are little explored. In this paper, we analyse the history of the spread of Ambrosia artemisiifolia (common ragweed) in central Europe in order to determine the effects of climate warming. In addition, we infer the likely history of this species’ spread and current distribution from incomplete documentation. The area studied in central Europe includes Austria, the Czech Republic, Germany, Hungary, Liechtenstein, Slovakia, Slovenia and Switzerland. These countries were represented by a lattice of grid cells of size 5' × 3' (~ 6 × 6 km2), and we modelled this species’ increase in range in this grid from 1900 to 2010 at an annual resolution. The spread was modelled to be driven by the spatio-temporal variation in environmental suitability of grid cells as determined by climatic conditions and land use, propagule production and dispersal from invaded cells, and ‘background’ introductions from unknown sources. A hierarchical Bayesian modelling approach accounted for lagged and incomplete records of occurrence and spatio-temporal variation in sampling intensity.We fitted models with different representations of climate variation over time, and further contrasted the hierarchical model to a simplified model, which assumed that records accurately reflected the species’ actual spread. Climatic conditions were the most important determinants of environmental suitability for invasion, and suitability also increased with increase in the proportion of urban area and length of railways in grid cells. Temperature was, on average, 2.7 °C higher in the environmentally more suitable cells than in the less suitable cells. The pattern in the spread was determined by local range expansion frommultiple, spatially scattered points of introduction. Assuming a linear trend in climate warming over the modelling period provided a better model fit than using annual weather conditions or the long-term average of the climate. The model estimated that by 2010 only about 60% of the actually invaded grid cells were recorded, and records lagged behind actual colonizations by years up to decades. Inferences of the hierarchical and simplified models differed quantitatively.We conclude that by using our modelling framework it is possible to separate spatial effects of climate on the spread of non-native species from temporal effects, and that climate warming has already promoted the spread of Ambrosia artemisiifolia in central Europe. The recorded distribution reflects only a part of this species’ actual distribution. Properly accounting for incomplete records hence improves inferences about the dynamics of spread.
An assessment of climate, weather, and fuel factors influencing a large, destructive wildfire in the Knysna region, South Africa
01 October 2018
Stellenbosch University

Kraaij, T.;Baard, J.A.;Arndt, J.;Vhengani, L.;van Wilgen, B.W.

Background: In June 2017, wildfires burned 15 000 ha around the town of Knysna in the Western Cape, destroying > 800 buildings, > 5000 ha of forest plantations, and claiming the lives of seven people. We examined the factors that contributed to making this one of the worst fires on record in the region. Results: One third of the area that burned was in natural vegetation (mainly fynbos shrublands), and more than half was in plantations of invasive alien (non-native) pine trees, or in natural vegetation invaded by alien trees. We used satellite imagery to assess burn severity in different land cover types by comparing pre- and post-fire images to estimate biomass consumed. We used daily weather data from two weather stations to calculate fire danger and drought indices over 70 years, and compared the fire weather conditions during the 2017 Knysna fires to the long-term weather record. The amount of biomass consumed was significantly higher in plantations of invasive alien trees, and in fynbos invaded by alien trees, than in uninvaded fynbos, providing support for the contention that invasion by alien trees increases the impact and difficulty of control of wildfires. Fire danger indices on the days of the fires were in the top 0.1 to 0.2% of days in the historic record, indicating that fire weather conditions were extreme but not unprecedented. The fires were preceded by a prolonged drought, and 18-month running means for two drought indices were the highest on record. Conclusion: The severity of the fires was exacerbated by very high fire danger conditions, preceded by an unprecedented drought, and further worsened by the conversion of natural fynbos vegetation to plantations, and invasion of vegetation by alien trees. Historical fire suppression also resulted in fuel buildups, further aggravating the problem of fire control, while residential development within and adjacent to fire-prone areas increased the risks faced by residents. Our results support calls to control invasive alien plants, reduce commercial planting of invasive alien trees, strictly regulate development in areas of high fire risk, and maintain awareness of the need for fire-wise practices.
Climate change vulnerability assessment of species
24 January 2019
Stellenbosch University

Foden, W.B.;Young, B.E.;Akcakaya, H.R.;Garcia, R.A.;Hoffmann, A.A.;Stein, B.A.;Thomas, C.D.;Wheatley, C.J.;Bickford, D.;Carr, J.A.;Hole, D.G.;Martin, T.G.;Pacifici, M.;Pearce-Higgins, J.W.;Platts, P.J.;Visconti, P.;Watson, J.E.M.;Huntley, B.

Assessing species' vulnerability to climate change is a prerequisite for developing effective strategies to conserve them. The last three decades have seen exponential growth in the number of studies evaluating how, how much, why, when, and where species will be impacted by climate change. We provide an overview of the rapidly developing field of climate change vulnerability assessment (CCVA) and describe key concepts, terms, steps and considerations. We stress the importance of identifying the full range of pressures, impacts and their associated mechanisms that species face and using this as a basis for selecting the appropriate assessment approaches for quantifying vulnerability. We outline four CCVA assessment approaches, namely trait-based, correlative, mechanistic and combined approaches and discuss their use. Since any assessment can deliver unreliable or even misleading results when incorrect data and parameters are applied, we discuss finding, selecting, and applying input data and provide examples of open-access resources. Because rare, small-range, and declining-range species are often of particular conservation concern while also posing significant challenges for CCVA, we describe alternative ways to assess them. We also describe how CCVAs can be used to inform IUCN Red List assessments of extinction risk. Finally, we suggest future directions in this field and propose areas where research efforts may be particularly valuable.
Phenotypic plasticity in locomotor performance of a monophyletic group of weevils accords with the ‘warmer is better’ hypothesis
23 May 2019
Stellenbosch University

Treasure, A.M.;Chown, S.L.

Ectotherms may respond to variable environmental conditions by altering their phenotypes. Phenotypic plasticity was initially thought to be beneficial to an organism’s physiological fitness but several alternative hypotheses have been proposed with growing empirical support. In this study, we tested the full suite of hypotheses by investigating acclimation responses of locomotor performance for nine populations of five species of sub-Antarctic weevils, using static and fluctuating temperatures. Species showed typical locomotion thermal performance curves with temperature of the maximum speed (Topt) ranging between 22.3±1.7°C (mean±s.e.m.) and 31.1±0.7°C. For most species, Topt was not affected by acclimation. For maximum speed (Umax), significant, positive effects of acclimation were found for all species except a supralittoral one. Individuals acclimated to 0°C showed much lower values than the other two acclimation treatments (15°C and fluctuating 0–15°C). Performance breadth (the index of the breadth of the curve, Tbr) typically showed little response to acclimation. None of the traits of the supralittoral species was affected by acclimation treatment. Responses to stable and fluctuating temperature treatments were similar. Our findings also revealed that the mean estimated activation energy 0.40±0.015 eV (mean ± s.e.m.) was lower than for other herbivores, the category to which these weevils belong, suggesting that some form of compensation in the rate–temperature relationship may be evident. Thus, we typically found support for the ‘warmer is better’ hypothesis for acclimation of locomotor performance, although some compensation was evident.
Climatic controls of decomposition drive the global biogeography of forest-tree symbioses
05 June 2019
Stellenbosch University

Steidinger, B.S.;Crowther, T.W.;Liang, J.;van Nuland, M.E.;Werner, G.D.A.;Reich, P.B.;Nabuurs, G.;de-Miguel, S.;Zhou, M.;Picard, N.;Herault, B.;Zhao, X.;Zhang, C.;Routh, D.;GFBI consortium;Peay, K.G.

The identity of the dominant root-associated microbial symbionts in a forest determines the ability of trees to access limiting nutrients from atmospheric or soil pools, sequester carbon and withstand the effects of climate change. Characterizing the global distribution of these symbioses and identifying the factors that control this distribution are thus integral to understanding the present and future functioning of forest ecosystems. Here we generate a spatially explicit global map of the symbiotic status of forests, using a database of over 1.1 million forest inventory plots that collectively contain over 28,000 tree species. Our analyses indicate that climate variables—in particular, climatically controlled variation in the rate of decomposition—are the primary drivers of the global distribution of major symbioses. We estimate that ectomycorrhizal trees, which represent only 2% of all plant species7, constitute approximately 60% of tree stems on Earth. Ectomycorrhizal symbiosis dominates forests in which seasonally cold and dry climates inhibit decomposition, and is the predominant form of symbiosis at high latitudes and elevation. By contrast, arbuscular mycorrhizal trees dominate in aseasonal, warm tropical forests, and occur with ectomycorrhizal trees in temperate biomes in which seasonally warm-and-wet climates enhance decomposition. Continental transitions between forests dominated by ectomycorrhizal or arbuscular mycorrhizal trees occur relatively abruptly along climate-driven decomposition gradients; these transitions are probably caused by positive feedback effects between plants and microorganisms. Symbiotic nitrogen fixers—which are insensitive to climatic controls on decomposition (compared with mycorrhizal fungi)—are most abundant in arid biomes with alkaline soils and high maximum temperatures. The climatically driven global symbiosis gradient that we document provides a spatially explicit quantitative understanding of microbial symbioses at the global scale, and demonstrates the critical role of microbial mutualisms in shaping the distribution of plant species.
Cointroductions of Australian acacias and their rhizobial mutualists in the Southern Hemisphere
19 July 2019
Stellenbosch University

Warrington, S.;Ellis, A.;Novoa, A.;Wandrag, E.M.;Hulme, P.E.;Duncan, R.P.;Valentine, A.;Le Roux, J.J.

Aim Mutualisms are often disrupted for plants introduced to new ranges, yet many of these plants have managed to obtain effective mutualistic associations in their new ranges. There are two potential pathways for non-native plants to reassemble mutualisms: cointroduction (i.e. familiar associations with cointroduced mutualists) or ecological fitting (i.e. forming or adapting novel associations with resident native mutualists). We assessed the importance of each pathway for mutualist reassembly in four Australian Acacia species (A. baileyana, A. dealbata, A. decurrens and A. melanoxylon) and their associated nitrogen-fixing rhizobial symbionts in two non-native locations. Location Native ranges of acacias in south-eastern Australia and two non-native ranges in New Zealand and South Africa. Methods Rhizobia associated with each acacia species in each country were isolated and identified based on DNA sequencing of the housekeeping recA gene and the symbiotic nodA gene. Separate phylogenies were reconstructed for each gene region to infer biogeographic histories of acacia-associated rhizobia. Selected rhizobial strains for each acacia species by country combination were used as inocula in a glasshouse experiment and early growth kinetics and nitrogen fixation efficiency of acacia seedlings were compared between inoculum treatments to determine symbiotic effectiveness. Results All isolated rhizobial strains belonged to the genus Bradyrhizobium. Phylogenetic analyses revealed almost no country- or species-specific clusters of these strains for either gene region and indicated that most acacia-associated bradyrhizobia in New Zealand and South Africa were cointroduced from Australia. These results were supported by little variation in the growth performances of acacia seedlings, irrespective of inoculum treatment. Main conclusions This study revealed that cointroduction of Australian acacias and their rhizobia may be more prevalent than previously thought. Additionally, a single rhizobium cointroduction event may be sufficient to facilitate the establishment of effective mutualisms in numerous Acacia species, potentially leading to an invasion meltdown.
Opportunities for behavioral rescue under rapid environmental change
18 October 2019
Stellenbosch University

Fey, S.B.;Vasseur, D.A.;Alujević, K.;Kroeker, K.J.;Logan, M.L.;O'Connor, M.I.;Rudolf, V.H.W.;DeLong, J.P.;Peacor, S.;Selden, R.L.;Sih, A.;Clusella-Trullas, S.

Laboratory measurements of physiological and demographic tolerances are important in understanding the impact of climate change on species diversity; however, it has been recognized that forecasts based solely on these laboratory estimates overestimate risk by omitting the capacity for species to utilize microclimatic variation via behavioral adjustments in activity patterns or habitat choice. The complex, and often context-dependent nature, of microclimate utilization has been an impediment to the advancement of general predictive models. Here, we overcome this impediment and estimate the potential impact of warming on the fitness of ectotherms using a benefit/cost trade-off derived from the simple and broadly documented thermal performance curve and a generalized cost function. Our framework reveals that, for certain environments, the cost of behavioral thermoregulation can be reduced as warming occurs, enabling behavioral buffering (e.g., the capacity for behavior to ameliorate detrimental impacts) and “behavioral rescue” from extinction in extreme cases. By applying our framework to operative temperature and physiological data collected at an extremely fine spatial scale in an African lizard, we show that new behavioral opportunities may emerge. Finally, we explore large-scale geographic differences in the impact of behavior on climate‐impact projections using a global dataset of 38 insect species. These multiple lines of inference indicate that understanding the existing relationship between thermal characteristics (e.g., spatial configuration, spatial heterogeneity, and modal temperature) is essential for improving estimates of extinction risk.
Thermal tolerance patterns across latitude and elevation
12 December 2019
Stellenbosch University

Sunday, J.;Bennett, J.M.;Calosi, P.;Clusella-Trullas, S.;Gravel, S.;Hargreaves, A.L.;Leiva, F.P.;Verberk, W.C.E.P.;Olalla-Tárraga, M.A.;Morales-Castilla, I.

Linking variation in species' traits to large-scale environmental gradients can lend insight into the evolutionary processes that have shaped functional diversity and future responses to environmental change. Here, we ask how heat and cold tolerance vary as a function of latitude, elevation and climate extremes, using an extensive global dataset of ectotherm and endotherm thermal tolerance limits, while accounting for methodological variation in acclimation temperature, ramping rate and duration of exposure among studies. We show that previously reported relationships between thermal limits and latitude in ectotherms are robust to variation in methods. Heat tolerance of terrestrial ectotherms declined marginally towards higher latitudes and did not vary with elevation, whereas heat tolerance of freshwater and marine ectotherms declined more steeply with latitude. By contrast, cold tolerance limits declined steeply with latitude in marine, intertidal, freshwater and terrestrial ectotherms, and towards higher elevations on land. In all realms, both upper and lower thermal tolerance limits increased with extreme daily temperature, suggesting that different experienced climate extremes across realms explain the patterns, as predicted under the Climate Extremes Hypothesis. Statistically accounting for methodological variation in acclimation temperature, ramping rate and exposure duration improved model fits, and increased slopes with extreme ambient temperature. Our results suggest that fundamentally different patterns of thermal limits found among the earth's realms may be largely explained by differences in episodic thermal extremes among realms, updating global macrophysiological ‘rules’.
Rethinking the scale and formulation of indices assessing organism vulnerability to warmer habitats
11 February 2020
Stellenbosch University

Garcia, R.A.;Allen, J.L.;Clusella-Trullas, S.

Ecologists often use indices or proxies to communicate complex ecological entities. Indices commonly known as thermal safety margin, habitat thermal quality and hours of restriction describe species’ vulnerability to climate change by comparing organisms’ thermal limits or preferences to available habitat temperatures. Ready access to temperature data, from global gridded datasets or limited in situ measurements, has made these indices popular for vulnerability assessments across taxonomic groups and regions. However, such coarse descriptions of thermal landscape mask the spatio‐temporal heterogeneity that organisms experience, compromising the value of these indices. Full understanding of how scale affects index estimates is lacking, leaving ecologists and conservation managers with little guidance for applying or interpreting indices. Here, we show that incomplete temperature sampling, in space or time, provides erroneous assessments of vulnerability. Gradually sub‐sampling a long‐term, fine‐scale dataset of operative environmental temperature altered the index estimates for a lizard. Uncertainty associated with the selection of data increased with coarser scales, often leading to contrasting interpretations about the species’ vulnerability to climate change when different data subsets were used. Compressing the environmental temperature data into central or extreme tendencies, as traditionally done to compute these indices, further masked the thermal variation that animals exploit to buffer warming. We suggest the use of improved index formulations that better describe temperature availability at scales that are appropriate to the study organism.
Wildfire management in Mediterranean-type regions: paradigm change needed
03 March 2020
Stellenbosch University

Moreira, F.;Ascoli, D.;Safford, H.;Adams, M.;Moreno, J.M.;Pereira, J.C.;Catry, F.;Armesto, J.;Bond, W.J.;Gonzalez, M.;Curt, T.;Koutsias, N.;McCaw, L.;Price, O.;Pausas, J.;Rigolot, E.;Stephens, S.;Tavsanoglu, C.;Vallejo, R.;van Wilgen, B.;Xanthopoulos, G.;Fernandes, P.

During the last decades, climate and land use changes led to an increased prevalence of megafires in Mediterranean-type climate regions (MCRs). Here, we argue that current wildfire management policies in MCRs are destined to fail. Focused on fire suppression, these policies largely ignore ongoing climate warming and landscape-scale buildup of fuels. The result is a "firefighting trap" that contributes to ongoing fuel accumulation precluding suppression under extreme fire weather, and resulting in more severe and larger fires. We believe that a "business as usual" approach to wildfire in MCRs will not solve the fire problem, and recommend that policy and expenditures be rebalanced between suppression and mitigation of the negative impacts of fire. This requires a paradigm shift: policy effectiveness should not be primarily measured as a function of area burned (as it usually is), but rather as a function of avoided socio-ecological damage and loss.
Malaria patterns across altitudinal zones of Mount Elgon following intensified control and prevention programs in Uganda
10 July 2020
Stellenbosch University

Siya, A.;Kalule, B.J.;Ssentongo, B.;Lukwa, A.T.;Egeru, A.

Background Malaria remains a major tropical vector-borne disease of immense public health concern owing to its debilitating effects in sub-Saharan Africa. Over the past 30 years, the high altitude areas in Eastern Africa have been reported to experience increased cases of malaria. Governments including that of the Republic of Uganda have responded through intensifying programs that can potentially minimize malaria transmission while reducing associated fatalities. However, malaria patterns following these intensified control and prevention interventions in the changing climate remains widely unexplored in East African highland regions. This study thus analyzed malaria patterns across altitudinal zones of Mount Elgon, Uganda. Methods Times-series data on malaria cases (2011-2017) from five level III local health centers occurring across three altitudinal zones; low, mid and high altitude was utilized. Inverse Distance Weighted (IDW) interpolation regression and Mann Kendall trend test were used to analyze malaria patterns. Vegetation attributes from the three altitudinal zones were analyzed using Normalized Difference Vegetation Index (NDVI) was used to determine the Autoregressive Integrated Moving Average (ARIMA) model was used to project malaria patterns for a 7 year period. Results Malaria across the three zones declined over the study period. The hotspots for malaria were highly variable over time in all the three zones. Rainfall played a significant role in influencing malaria burdens across the three zones. Vegetation had a significant influence on malaria in the higher altitudes. Meanwhile, in the lower altitude, human population had a significant positive correlation with malaria cases. Conclusions Despite observed decline in malaria cases across the three altitudinal zones, the high altitude zone became a malaria hotspot as cases variably occurred in the zone. Rainfall played the biggest role in malaria trends. Human population appeared to influence malaria incidences in the low altitude areas partly due to population concentration in this zone. Malaria control interventions ought to be strengthened and strategically designed to achieve no malaria cases across all the altitudinal zones. Integration of climate information within malaria interventions can also strengthen eradication strategies of malaria in such differentiated altitudinal zones.
Realised rather than fundamental thermal niches predict site occupancy: implications for climate change forecasting
02 February 2021
Stellenbosch University

Braschler, B.;Duffy, G.A.;Nortje, E.;Kritzinger-Klopper, S.;du Plessis, D.;Karenyi, N.;Leihy, R.I.;Chown, S.L.

Thermal performance traits are regularly used to make forecasts of the responses of ectotherms to anthropogenic environmental change, but such forecasts do not always differentiate between fundamental and realised thermal niches. Here we determine the relative extents to which variation in the fundamental and realised thermal niches accounts for current variation in species abundance and occupancy and assess the effects of niche-choice on future-climate response estimations. We investigated microclimate and macroclimate temperatures alongside abundance, occupancy, critical thermal limits, and foraging activity of 52 ant species (accounting for > 95% individuals collected) from a regional assemblage from across the Western Cape Province, South Africa, between 2003 and 2014. Capability of a species to occupy sites experiencing the most extreme temperatures, coupled with breadth of realised niche, explained most deviance in occupancy (up to 75%), while foraging temperature range and body mass explained up to 50.5% of observed variation in mean species abundance. When realised niches are used to forecast responses to climate change, large positive and negative effects among species are predicted under future conditions, in contrast to the forecasts of minimal impacts on all species that are indicated by fundamental niche predictions.
The evolution of insect body coloration under changing climates
04 February 2021
Stellenbosch University

Clusella-Trullas, S.;Nielsen, M.

nsects have been influential models in research on color variation, its evolutionary drivers and the mechanistic basis of such variation. More recently, several studies have indicated that insect color is responding to rapid climate change. However, it remains challenging to ascertain drivers of color variation among populations and species, and across space and time, as multiple biotic and abiotic factors can interact and mediate color change. Here, we describe some of the challenges and recent advances made in this field. First, we outline the main alternative hypotheses that exist for insect color variation in relation to climatic factors. Second, we review the existing evidence for contemporary adaptive evolution of insect color in response to climate change and then discuss factors that can promote or hinder the evolution of color in response to climate change. Finally, we propose future directions and highlight gaps in this research field. Pigments and structures producing insect color can vary concurrently or independently, and may evolve at different rates, with poorly understood effects on gene frequencies and fitness. Disentangling multiple competing hypotheses explaining insect coloration should be key to assign color variation as an evolutionary response to climate change.
Levers and leverage points for pathways to sustainability
04 February 2021
Stellenbosch University

Chan, K.M.A.;Boyd, D.R.;Gould, R.K.;Jetzkowitz, J.;Liu, J.;Muraca, B.;Naidoo, R.;Olmsted, P.;Satterfield, T.;Selomane, O.;Singh, G.G.;Sumaila, R.;Ngo, H.T.;Boedhihartono, A.K.;Agard, J.;de Aguiar, A.P.D.;Armenteras, D.;Balint, L.;Barrington-Leigh, C.;Cheung, W.W.L.;Díaz, S.;Driscoll, J.;Esler, K.J.;Eyster, H.;Gregr, E.J.;Hashimoto, S.;Hernández Pedraza, G.C.;Hickler, T.;Kok, M.;Lazarova, T.;Mohamed, A.A.A.;Murray-Hudson, M.;O'Farrell, P.;Palomo, I.;Saysel, A.K.;Seppelt, R.;Settele, J.;Strassburg, B.;Xue, D.;Brondízio, E.S.

Humanity is on a deeply unsustainable trajectory. We are exceeding planetary boundaries and unlikely to meet many international sustainable development goals and global environmental targets. Until recently, there was no broadly accepted framework of interventions that could ignite the transformations needed to achieve these desired targets and goals. As a component of the IPBES Global Assessment, we conducted an iterative expert deliberation process with an extensive review of scenarios and pathways to sustainability, including the broader literature on indirect drivers, social change and sustainability transformation. We asked, what are the most important elements of pathways to sustainability? Applying a social–ecological systems lens, we identified eight priority points for intervention (leverage points) and five overarching strategic actions and priority interventions (levers), which appear to be key to societal transformation. The eight leverage points are: (1) Visions of a good life, (2) Total consumption and waste, (3) Latent values of responsibility, (4) Inequalities, (5) Justice and inclusion in conservation, (6) Externalities from trade and other telecouplings, (7) Responsible technology, innovation and investment, and (8) Education and knowledge generation and sharing. The five intertwined levers can be applied across the eight leverage points and more broadly. These include: (A) Incentives and capacity building, (B) Coordination across sectors and jurisdictions, (C) Pre‐emptive action, (D) Adaptive decision-making and (E) Environmental law and implementation. The levers and leverage points are all non-substitutable, and each enables others, likely leading to synergistic benefits. Transformative change towards sustainable pathways requires more than a simple scaling-up of sustainability initiatives—it entails addressing these levers and leverage points to change the fabric of legal, political, economic and other social systems. These levers and leverage points build upon those approved within the Global Assessment's Summary for Policymakers, with the aim of enabling leaders in government, business, civil society and academia to spark transformative changes towards a more just and sustainable world.
Quantification of oxygen capture in mineral matter during gasification
17 November 2009
North West University

Van Dyk, J.C.;Waanders, F.B.;Van Heerden, J.H.P.

It has been observed that during the transformation of minerals at higher temperatures (>1000 °C), mineral species are formed containing a high number of oxygen molecules, i.e. gehlenite (Ca2Al2SiO7), mullite (Al6Si3O15), margarite (CaAl4Si2O10(OH)2) and almandine (Fe3Al2Si3O12). Results of the coal sources evaluated in this investigation indicated significant differences in mineral elemental composition, i.e. the CaO content varied between 5 mass % and 10 mass %, the Fe2O3 content varied between 1.6 mass % to more than 5 mass %, as well as differences in the TiO2, P2O5 and MgO content. The coal sources producing the highest concentration of Ca–Al–Si species (CaAl2Si2O8 anorthite and CaAl4Si2O10(OH)2 margarite), which crystallized from the slag-liquid phase during the combustion stage, also contained the highest amount of acidic components or highest percentage of kaolinite. The highest concentration of mullite and free SiO2 after the gasification reaction (before the combustion zone), also resulted in the highest concentration of Ca–Al–Si compounds forming during the oxidation phase. The free-SiO2 in the mineral structure of the coal sources resulted then in the formation of mineral structures with Mg, Na or Ca when present in the mineral structure, to form new mineral compounds such as KAl3Si3O10(OH)2 (muscovite), Mg5Al2Si3O10(OH)8 (clinochlore), or other high oxygen molecule-containing mineral compounds. Thus, if free-SiO2 was not present after the gasification phase, and mostly taken up in the form of anorthite (due to high or higher CaO contents or Fe-contents in high Fe-containing coal sources), the concentration of Si-oxygen capture compounds are relatively low. An acceptable linear correlation between oxygen capture tendencies (increase in mineral matter content during the combustion phase) versus CaO-content was obtained with the South African coal sources evaluated. This confirmed the observations obtained based on HT-XRD and FactSage modelling. It can be concluded that the linear model to predict oxygen capture behavior from CaO-content is acceptable and can be used as a predictive tool. The SiO2 content, for example, has an inverse affect on oxygen trends up to a specific concentration of CaO in the coal. However, this model is only valid for the coal types tested (South African Highveld coal sources), and additional test work will have to be conducted for other coal types, i.e. northern hemisphere coal
Investigation of the multiple-component structure of the 20 January 2005 cosmic ray ground level enhancement
25 November 2009
North West University

McCracken, K.G.;Moraal, H.;Stoker, P.H.

Worldwide observations of the cosmic ray ground level enhancement (GLE) of 20 January 2005 are used to investigate a commonly observed but poorly understood feature of this class of event. It is argued that the GLE comprised two distinctly different cosmic ray populations. The first resulted in an impulsive, highly anisotropic, field-aligned pulse with a relatively hard rigidity spectrum and significant velocity dispersion. The characteristics of the anisotropy were almost identical to those for similar impulsive increases observed during GLEs in 1960, 1978, and 1989. The p 0 g ray observations from the RHESSI and CORONAS-F spacecraft and Type III radio emissions yield a path length of 1.76 ± 0.1 AU to Earth for the first pulse. After the highest energies in the initial anisotropic pulse had passed Earth, another field-aligned but mildly anisotropic cosmic ray pulse developed slowly worldwide, exhibiting the characteristics of the conventional GLE. The risetime and anisotropy of this second population indicate substantial scattering, apparently at variance to the essentially scatter-free nature of the initial pulse. We show that the coexisting scatter-free initial impulsive increase and the diffusive character of the second pulse are consistent with the standard quasi-linear theory of pitch angle diffusion. Throughout the GLE, the anisotropy remained field-aligned, and a third maximum, seen by some stations, is shown to be due to changes in the direction of the heliospheric magnetic field (HMF). Examination of 22 large (>20%) GLEs in the historical record shows that the impulsive pulse never occurs after the commencement of the P2 pulse, indicating that the impulsive-gradual combination is not due to a chance sampling of differing scattering regions of the HMF. It is further shown that impulsive pulses, or their equivalents, have been observed in 13 out of the 15 GLEs associated with solar activity in the solar longitude range 24° –98°W, leading us to propose that the event of 20 January 2005 should be regarded as the defining example of the GLE. The observations lead us to propose two separate acceleration episodes in the typical GLE: (1) acceleration directly associated with the flare itself and located in the lower corona and (2) acceleration by a supercritical shock driven by the associated coronal mass ejection, located at 3–5 solar radii and farther in the upper corona. A one-to-one association with so-called impulsive and gradual solar energetic particle events at lower energies is proposed. On the basis of these observations, a generic model for the GLE is proposed
Discovery of a VHE gamma-ray source coincident with the supernova remnant CTB 37A
17 December 2009
North West University

Aharonian, F.;Büsching, I.;De Jager, O.C.;Holleran, M.;Raubenheimer, B.C.;Venter, C.;H.E.S.S. Collaboration

Aims. The supernova remnant (SNR) complex CTB 37 is an interesting candidate for observations with very high energy (VHE) γ-ray telescopes such as HESS. In this region, three SNRs are seen. One of them is potentially associated with several molecular clouds, a circumstance that can be used to probe the acceleration of hadronic cosmic rays. Methods. This region was observed with the HESS Cherenkov telescopes and the data were analyzed with standard HESS procedures. Recent X-ray observations with Chandra and XMM-Newton were used to search for X-ray counterparts. Results. The discovery of a new VHE γ-ray source HESS J1714-385 coincident with the remnant CTB 37A is reported. The energy spectrum is well described by a power-law with a photon index of Γ = 2.30 ± 0.13 and a differential flux at 1 TeV of cm-2 s-1 TeV-1. The integrated flux above 1 TeV is equivalent to 3% of the flux of the Crab nebula above the same energy. This VHE γ-ray source is a counterpart candidate for the unidentified EGRET source 3EG J1714-3857. The observed VHE emission is consistent with the molecular gas distribution around CTB 37A; a close match is expected in a hadronic scenario for γ-ray production. The X-ray observations reveal the presence of thermal X-rays from the NE part of the SNR. In the NW part of the remnant, an extended non-thermal X-ray source, CXOU J171419.8-383023, is discovered as well. Possible connections of the X-ray emission to the newly found VHE source are discussed
Simultaneous HESS and Chandra observations of Sagitarius A* during an X-ray flare
18 January 2010
North West University

Aharonian, F.;Büsching, I.;De Jager, O.C.;Holleran, M.;Raubenheimer, B.C.;Venter, C.;H.E.S.S. Collaboration

The rapidly varying (~10 min timescale) non-thermal X-ray emission observed from Sgr A implies that particle acceleration is occuring close to the event horizon of the supermassive black hole. The TeV γ-ray source HESS J1745-290 is coincident with Sgr A and may be closely related to its X-ray emission. Simultaneous X-ray and TeV observations are required to elucidate the relationship between these objects. We report on joint HESS/Chandra observations performed in July 2005, during which an X-ray flare was detected. Despite a factor of ≈9 increase in the X-ray flux of Sgr A, no evidence is found for an increase in the TeV γ-ray flux from this region. We find that an increase in the γ-ray flux of a factor of 2 or greater can be excluded at a confidence level of 99%. This finding disfavours scenarios in which the keV and TeV emission are associated with the same population of accelerated particles and in which the bulk of the γ-ray emission is produced within ~1014 cm (~100) of the supermassive black hole
Chandra and HESS observations of the supernova remnant CTB 37B
09 February 2010
North West University

Aharonian, F.;Büsching, I.;De Jager, O.C.;Holleran, M.;Raubenheimer, B.C.;Venter, C.;H.E.S.S. Collaboration

We discovered the >100 GeV γ-ray source, HESS J1713−381, apparently associated with the shell-type supernova remnant (SNR) CTB37B, using HESS in 2006. In 2007 we performed X-ray follow-up observations with Chandra with the aim of identifying a synchrotron counterpart to the TeV source and/or thermal emission from the SNR shell. These new Chandra data, together with additional TeV data, allow us to investigate the nature of this object in much greater detail than was previously possible. The new X-ray data reveal thermal emission from a ∼4 region in close proximity to the radio shell of CTB37B. The temperature of this emission implies an age for the remnant of ∼5000 years and an ambient gas density of ∼0.5 cm−3. Both these estimates are considerably uncertain due to the asymmetry of the SNR and possible modifications of the kinematics due to efficient cosmic ray (CR) acceleration. A bright (≈7× 10−13 erg cm−2 s−1) and unresolved (<1 ) source (CXOUJ171405.7−381031), with a soft (Γ ≈ 3.3) non-thermal spectrum is also detected in coincidence with the radio shell. Absorption indicates a column density consistent with the thermal emission from the shell, suggesting a genuine association rather than a chance alignment. The observed TeV morphology is consistent with an origin in the complete shell of CTB37B. The lack of diffuse non-thermal X-ray emission suggests an origin of the γ-ray emission via the decay of neutral pions produced in interactions of protons and nuclei, rather than inverse Compton (IC) emission from relativistic electrons
Discovery of very high energy gamma-ray emission coincident with molecular clouds in the W 28 (G6.4-0.1) field
16 February 2010
North West University

Aharonian, F.;Büsching, I.;De Jager, O.C.;Holleran, M.;Raubenheimer, B.C.;Venter, C.;H.E.S.S. Collaboration

Aims. Observations of shell-type supernova remnants (SNRs) in the GeV to multi-TeV γ-ray band, coupled with those at millimetre radio wavelengths, are motivated by the search for cosmic-ray accelerators in our Galaxy. The old-age mixed-morphology SNRW28 (distance ∼2 kpc) is a prime target due to its interaction with molecular clouds along its northeastern boundary and other clouds situated nearby. Methods. We observed theW28 field (for ∼40 h) at very high energy (VHE) γ-ray energies (E > 0.1 TeV) with the HESS. Cherenkov telescopes. A reanalysis of EGRET E > 100 MeV data was also undertaken. Results from the NANTEN 4 m telescope Galactic plane survey and other CO observations were used to study molecular clouds. Results. We have discovered VHE γ-ray emission (HESS J1801−233) coincident with the northeastern boundary of W 28 and a complex of sources (HESS J1800−240A, B and C) ∼0.5◦ south of W 28 in the Galactic disc. The EGRET source (GRO J1801−2320) is centred on HESS J1801−233 but may also be related to HESS J1800−240 given the large EGRET point spread function. The VHE differential photon spectra are well fit by pure power laws with indices Γ ∼ 2.3 to 2.7. The spectral indices of HESS J1800−240A, B, and C are consistent within statistical errors. All VHE sources are ∼10 in intrinsic radius except for HESS J1800−240C, which appears pointlike. The NANTEN 12CO(J = 1−0) data reveal molecular clouds positionally associating with the VHE emission, spanning a ∼15 km s−1 range in local standard of rest velocity. Conclusions. The VHE/molecular cloud association could indicate a hadronic origin for HESS J1801−233 and HESS J1800−240, and several cloud components in projection may contribute to the VHE emission. The clouds have components covering a broad velocity range encompassing the distance estimates forW28 (∼2 kpc) and extending up to ∼4 kpc. Assuming hadronic origin and distances of 2 and 4 kpc for cloud components, the required cosmic-ray density enhancement factors (with respect to the solar value) are in the range ∼10 to ∼30. If situated at 2 kpc distance, such cosmic-ray densities may be supplied by SNRs like W 28. Additionally and/or alternatively, particle acceleration may come from several catalogued SNRs and SNR candidates, the energetic ultra compact HII region W 28A2, and the HII regions M 8 and M 20, along with their associated open clusters. Further sub-mm observations would be recommended to probe in detail the dynamics of the molecular clouds at velocites >10 km s−1 and their possible connection to W 28
Identification of the reaction zones occurring in a commercial-scale Sasol-Lurgie FBDB gasifier
14 April 2010
North West University

Bunt, J.R.;Waanders, F.B.

Gasification behaviour is particle dependent, whilst gasifier (reactor) behaviour is an averaging process of individual responses of each particle. It was hypothesized, that if it were possible to extract and analyze particles from different reaction zones within a gasifier, it may be likely to enhance the understanding of the contribution that these particles make towards gasification. This better understanding of the particle-type compositional responses could act as an enabler to further manipulate and improve gasifier performance. The primary focus of this study was to evaluate a sequential (axial) sampling “turn-out” methodology of a quenched fixed-bed commercial-scale Sasol–Lurgi gasifier, in order to present samples that accurately describe operational aspects occurring in the reaction zones within the reactor. Characterization of the chemical properties of the sample increments were expected to deliver distinct profiles of the drying, pyrolysis, reduction and combustion (ash-bed) zones, which could be used to advance the kinetic modeling capability of the process. In order to interpret the coal property transformational behaviour occurring within the commercial-scale gasifier, the proximate, Fischer tar, ultimate, and coal char CO2 reactivity analysis were conducted. The pyrolysis zone was found to be the largest reaction zone situated below the drying zone within the gasifier, followed by the reduction zone, and combustion (ash-bed) zones. Whilst the boundaries of the pyrolysis zone were very clearly defined by the residual volatile matter distribution profile, distinctive regional overlap with a “slow pyrolysis with gasification” region was observed in the bottom half of the pyrolysis zone, above which a “rapid de-volatilization” region existed. The reduction zone was found to also exhibit an overlap in zonal fronts, i.e. a gasification region occurred below the pyrolysis zone and co-existed in equal proportions, with an oxidation frontal region occurring above the combustion zone. The combustion zone was found to be very shallow, below which the ash-bed region existed. The findings clearly suggest that text book pictures showing axially-depicted reaction zones occurring within the fixed-bed gasifier, i.e. drying, pyrolysis, gasification and combustion, inadequately describe the “real” situation and in practice, overlap of reaction regions within zones indeed also transpire
Indonesia and Africa: questioning the origins of some of Africa’s most famous icons
07 January 2011
North West University

Dick-Read, Robert

In the author’s opinion there have been three far-reaching gaps in the study of Africa’s history: 1) Indonesian involvement in East and Central Africa; 2) Links between Madagascar and Eastern and South/Central Africa; and 3) Extension of Indonesian interest to West Africa, particularly Nigeria. He contends that Indonesians (the term applies to ‘Insular Southeast Asians’) may have begun regular trading to Africa when Greek and Roman demand for oriental spices developed several centuries BCE. The East African ‘Zanj’ were, in his view, an Afro/Indonesian race linked with the people of ‘Zabag’ - Sumatra and Java – later with Srivijaya in particular, whose interest in the gold, copper, iron and other products of Africa were extensive. Madagascar was only ever of secondary importance to Indonesians compared with mineral-rich Africa. But for centuries the Austronesian-speaking, Afro-Indonesian people of Madagascar maintained regular contact with the mainland giving rise to mixed societies, particularly in the Mozambique-Zimbabwe region. He believes the ancient Zimbabwe culture was in several ways linked with that of Madagascar, and that the vast ruin area of Nyanga was also connected. These cross-channel associations were gradually eclipsed by the domination of Arab-Shirazi colonisation down the East African Coast. There is a wealth of evidence that Indonesians rounded the Cape and sailed to West Africa. Several elements of Nigerian culture generally attributed to East-West overland movements or trans-Saharan Arab traders, are more likely to have reached the lower Niger regions by sea from Indonesia. Among these was the technology enabling the iconic ‘bronze’ artwork for which Nigeria is famous.
From disaster relief to disaster risk reduction: a consideration of the evolving international relief mechanism
19 January 2011
North West University

Van Niekerk, D

Disaster risk reduction is an ever-growing concept and finds its application within various disciplines. This article investigates the development of disaster risk reduction and some of the most important aspects which shaped it. The early years of international disaster relief are discussed and it is shown how a change in this system was necessitated by a variety of factors and international disasters, which exposed its weakness. The article argues that disaster relief and development aid were inextricably linked and it is this linkage which provided a catalyst for questioning the manner in which relief, and development assistance, were provided. The later emphasis on disaster preparedness and management is discussed, and international policies and mechanisms, which contributed to a gradual shift in focus towards disaster risk reduction, enjoy attention. The article concludes that solutions to disaster risks lie within a rigorous transdisciplinary focus.
Slow-onset disaster and sustainable livelihoods: the Vaal River in the vicinity of Parys
19 January 2011
North West University

Van Riet, G;Tempelhoff, J W N

This article is based on data gathered during a research project commissioned by the Fezile Dabi District Municipality in the northern part of South Africa’s Free State Province. The research team (which included the authors) was asked to investigate allegations of pollution of tap water, as well as sewage from the local wastewater treatment plant flowing into the Vaal River in the town of Parys on the banks of the Vaal River. The authors adopt a sustainable livelihoods approach in analysing data gathered by way of unstructured interviews in and around Parys in June–July 2008. They argue that actual and perceived levels of pollution are eroding various local livelihood assets and it is posited that the situation constitutes an unfolding slow-onset disaster. It is imperative that shocks such as sewerage spills and rumours of polluted potable water are addressed to ensure that these do not become long-term negative trends.
The role of good environmental governance in the sustainable development of South Africa
29 March 2011
North West University

Feris, Loretta

This article seeks to analyse good governance decision-making in the environmental context through an understanding and interpretation of the relationship between good environmental governance (evidenced inter alia by decision-making by public authorities) and sustainable development in South Africa. It critically assesses recent case law in an attempt to understand the way in which our courts are evaluating authorities’ environmental decisions. In reaching its objectives, this article considers also how environmental decisions are made in the first place and asks the question: what are the value choices underlying government’s decisions and what role does sustainable development play in informing decisions for good environmental governance.
Parallel planning mechanisms as a "Recipe for disaster"
30 March 2011
North West University

Van Wyk, J

This note offers a critical reflection of the recent landmark decision in City of Johannesburg Metropolitan Municipality v Gauteng Development Tribunal which lay to rest the negative consequences of employing the DFA procedures of the Development Facilitation Act 67 of 1995 (DFA) alongside those of the provincial Ordinances to establish townships (or to use DFA parlance, “land development areas”). The welcome and timely decision in City of Johannesburg Metropolitan Municipality v Gauteng Development Tribunal has declared invalid chapters V and VI of the DFA. Moreover, it has formalised planning terminology in South Africa, delineated the boundaries of “municipal planning” and “urban planning and development” as listed in Schedules 4 and 5 of the Constitution of the Republic of South Africa, 1996 and, in the process, clarified the structure of planning law. This note examines the decision of the SCA and focus on the role it will clearly have in reforming some of the law relating to planning. It considers the facts of the case, uncertainties around terminology, the structure of planning in South Africa, the content of municipal planning, the role of the DFA and the consequences of the declaration of invalidity by the SCA.
Micro credit and the transforming of uncertainty since 1976: international lessons for South Africa.
13 January 2012
North West University

Mashigo, Polly;Schoeman, Christie

• Summary: The formal banking system plays a pivotal role in the delivery of financial services, particularly credit. However, the delivery of credit to poor households in South Africa by the formal banking system is hampered by the existence of irreducible uncertainty. The article analyses a sample of successful practices in different countries to determine the genotype structure in these cases that support specific social technology and the minimalist solidarity group lending method, to transform financial uncertainty that cannot be solved by the market mechanism and even brokerage institutions like banks. Based on the findings, this article recommends that existing social technology can be developed in an environment created and conditioned by a proposed system of constituents or principles, to give the poor access to low-cost credit in South Africa.
Innovation opportunities in irrigation technology for using virtual water in 21st century South Africa: reflections from the past to the present.
13 January 2012
North West University

Nyandoro, Mark

• Summary: In 21st century South Africa, new and old technological innovations in agriculture can be employed to protect existing and future water supplies that are increasingly becoming vulnerable to encroaching global warming trends. The purpose of this article is to identify irrigation technology, the impact on irrigative farming of a polluted water environment through mining and other baneful industrial activities in the Republic. It also aims to discuss innovation opportunities in irrigation technology for using virtual water – a concept commonly associated with the Middle East. South Africa possesses arguably the most sophisticated engineering technology in irrigation in southern Africa. In this article, reflections on irrigation from the past to the present will be complemented by a historical focus of the context in which this farming enterprise evolved. A brief historical synopsis of irrigation shows that this activity which became more technologically advanced in the colonial and post-independence eras was also practiced in the pre-colonial period for food security and as an insurance against drought. Irrigation was practised in South Africa before and after the colonisation of the Cape by the Dutch in 1652. Irrigation technology in the seventeenth century tended to lack the sophistication and modernisation of the contemporary world. Innovative improvements became imperative as the state increasingly became more involved in agriculture from the 1920s and 1930s largely as part of a process leading to the evolution of settler irrigation policy which was premised on capital accumulation and the deprivation of Africans of land ownership rights. This policy orientation clearly changed from the advent of independence to the 21st century in favour of a policy that aimed at economically empowering the Black smallholder sector farmers without necessarily neglecting the largescale commercial producers. Irrigation farming is not a novel phenomenon to the region. Since the turn of the new millennium, technological innovation has been prioritised because South Africa is situated in a predominantly hot arid zone of the sub-region. Total evaporation creates endemic water shortages. It is therefore imperative that water resources are well managed in a country which thrives largely on mining, industrial and agricultural pursuits. Due to South Africa’s geophysical location in one of the world’s arid terrains, irrigation has been identified as an essential corollary to dry land farming and other economic endeavours. Nevertheless, in spite of advances that have been made in centre-pivot manufacturing, South Africa has generally tended to ignore cheaper irrigation methodologies such as the drip, terracing and flood systems which seem more suitable and appropriate in arid conditions. It has also ignored the fact that using large volumes of both riparian and imported water from Lesotho to irrigate a crop like maize in the Eastern Free State Province, for example, is not only unviable but it is also unsustainable. A major rethink of how food supply can be boosted on the basis of irrigated agriculture, utilising more advanced and peculiarly suitable technology in hot and arid or water deficient areas is vital. This is more so because industrial demand for water – a large quantity of which is expensively procured or transferred from Lesotho through the Vaal River system - is in direct competition with the demand for water to produce surplus food under irrigation. Most industrial and farming activities in Gauteng, Free State and Mpumalanga provinces, to name a few, are dependent on this water which is under threat of depletion. Given South Africa’s arid conditions, the adoption of the virtual water concept, following the Saudi Arabian experience, would be a possible conservationist measure. This article also argues that because water is limited, mining and air pollution which eventually ends up in the water should be controlled to ensure safe drinking and irrigation water.
Contradictions of community within local government in the 1950s with reference to municipal beer trading.
19 January 2012
North West University

Atkinson, Doreen

• Opsomming: Hierdie artikel beskryf die etiese dilemmas waarin munisipale amptenare in die 1950s hulleself bevind het, veral rakende die munisipale bierbrouery in die swart woongebiede. Hierdie ervarings illustreer die patriargale verhoudings tussen swart en blanke gemeenskappe, en die paternalistiese politieke denke van hierdie era. Die onderliggende probleem was dat blanke amptenare probeer het om swart inwoners se reg om bier te gebruik binne ’n konteks van inheemse gemeenskapsreg verstaan het, en nie as ’n vorm van moderne, indiwiduele regte nie. Drie hooftemas word hier geanaliseer: bierbrouery as ’n teenvoeter vir probleme van moderniteit en sosiale dissipline; die rol van kulturele verskille wat patriargale sisteme van beheer aangemoedig het; en die morele probleme van winste as gevolg van bierbrouery, in ’n konteks van paternalisme. Die artikel beskryf hoe die munisipale amptenare hulle morele besware uiteindelik oorkom het, in ’n konteks van Verwoerdiaanse voorskrifte op munisipale segregasie en rassedominasie.

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