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SDG 14

The origins of marine mites: Interpreting geographical and ecological patterns
28 March 2007
Stellenbosch University

Marshall, DJ;Procheş, Ş

Hypotheses are advanced concerning the origins of non-halacarid mites in the marine environment. The hypothesis that oribatid (ameronothroid) and astigmatid (hyadesioid) taxa have had longer marine associations than their prostigmatid and mesostigmatid counterparts, is supported by contrasting geographical, ecological and taxonomic patterns among these mite groups, in particular by the high species to genus ratios, the general lack of generic representation in the terrestrial environment, and well-established marine trophic links of ameronothroid and hyadesioid mites. A second hypothesis that polar and subpolar genera of marine ameronothroid mites (and possibly hyadesioid mites) originated independently of the tropical genera, is suggested by three distinct latitudinal distributions of the major genera of these groups. A third hypothesis that marine origins were caused by glaciation events in the polar regions and competition in the tropics, is supported by species richness patterns across global latitudes, and the apparent habitat separation between rock-dwelling Antarctic and sedimentbased tropical marine mites. A final hypothesis concerns the basis for the return to land by the Antarctic ameronothroid genus Halozetes.
Temperature- and body mass-related variation in cyclic gas exchange characteristics and metabolic rate of seven species: Broader implications
29 March 2007
Stellenbosch University

Klock, CJ;Chown, SL

The influence of temperature on metabolic rate and characteristics of the gas exchange patterns of flightless, sub-Antarctic Ectemnorhinus-group species from Heard and Marion islands was investigated. All of the species showed cyclic gas exchange with no Flutter period, indicating that these species are not characterized by discontinuous gas exchange cycles. Metabolic rate estimates were substantially lower in this study than in a previous one of a subset of the species, demonstrating that open-system respirometry methods provide more representative estimates of standard metabolic rate than do many closed-system methods. We recommend that the latter, and especially constant-pressure methods, either be abandoned for estimates of standard metabolic rate in insects, or have their outputs subject to careful scrutiny, given the wide availability of the former. V˙ CO2 increase with an increase in temperature (range: 0–15 1C) was modulated by an increase in cycle frequency, but typically not by an increase in burst volume. Previous investigations of temperature-related changes in cyclic gas exchange (both cyclic and discontinuous) in several other insect species were therefore substantiated. Interspecific mass-scaling of metabolic rate (ca. 0.466–0.573, excluding and including phylogenetic non-independence, respectively) produced an exponent lower than 0.75 (but not distinguishable from it or from 0.67). The increase of metabolic rate with mass was modulated by an increase in burst volume and not by a change in cycle frequency, in keeping with investigations of species showing discontinuous gas exchange. These findings are discussed in the context of the emerging macrophysiological metabolic theory of ecology.
An exploratory analysis of geographic genetic variation in southern African nyala (Tragelaphus angasii)
13 April 2007
Stellenbosch University

Grobler, JP;Pretorius, DM;Botha, K;Kotze, A;Hallerman, EM;Jansen van Vuuren, B

We report patterns of genetic variation based on microsatellite, allozyme and mitochondrial control region markers in nyala from geographic locations sampled in South Africa, Mozambique, Malawi and Zimbabwe. Highly significant differences were observed among allele frequencies at three microsatellite loci between populations from KwaZulu-Natal, Limpopo and Malawi, with the Malawi and KwaZulu-Natal groupings showing the highest differentiation ðRST ¼ 0:377Þ: Allozyme frequencies showed minor, non-statistically significant regional differences among the South African populations, with maximum FST values of 0.048–0.067. Mitochondrial DNA analyses indicated a unique haplotype in each location sampled. Since none of these indices of population differentiation showed significant correlation to absolute geographic distance, we conclude that geographic variation in this species is probably a function of a distribution pattern stemming from habitat specificity. It is suggested that translocations among geographically distant regional populations be discouraged at present, pending a more elaborate investigation. Transfer of native individuals among local populations may, however, be required for minimizing the likelihood of inbreeding depression developing in small captive populations.
Biological invasions in the Antarctic: extent, impacts and implications
13 April 2007
Stellenbosch University

Frenot, Y.;Chown, S.L.;Whinam, J.;Selkirk, P.M.;Convey, P.;Skotnici, M.;Bergstrom, D.M.

Alien microbes, fungi, plants and animals occur on most of the sub-Antarctic islands and some parts of the Antarctic continent. These have arrived over approximately the last two centuries, coincident with human activity in the region. Introduction routes have varied, but are largely associated with movement of people and cargo in connection with industrial, national scientific program and tourist operations. The large majority of aliens are European in origin. They have both direct and indirect impacts on the functioning of species-poor Antarctic ecosystems, in particular including substantial loss of local biodiversity and changes to ecosystem processes. With rapid climate change occurring in some parts of Antarctica, elevated numbers of introductions and enhanced success of colonization by aliens are likely, with consequent increases in impacts on ecosystems. Mitigation measures that will substantially reduce the risk of introductions to Antarctica and the sub-Antarctic must focus on reducing propagule loads on humans, and their food, cargo, and transport vessels.
Nestedness of Southern Ocean island biotas: ecological perspectives on a biogeographical conundrum
13 April 2007
Stellenbosch University

Greve, M.;Gremmen, N.J.M.;Gaston, K.J.;Chown, S.L.

Aim To use patterns of nestedness in the indigenous and non-indigenous biotas of the Southern Ocean islands to determine the influence of dispersal ability on biogeographical patterns, and the importance of accounting for variation in dispersal ability in their subsequent interpretation, especially in the context of the Insulantarctic and multi-regional hypotheses proposed to explain the biogeography of these islands. Location Southern Ocean islands. Methods Nestedness was determined using a new metric, d1 (a modification of discrepancy), for the indigenous and introduced seabirds, land birds, insects and vascular plants of 26 Southern Ocean islands. To assess the possible confounding effects of spatial autocorrelation on the results, islands were assigned to 11 major island groups and each group was treated as a single island in a following analysis. In addition, nestedness of the six Southern Ocean islands comprising the South Pacific Province (New Zealand islands) was analysed. All analyses were conducted for species and genera, for each of the taxa on its own, and for the complete data sets. Results Statistically significant nestedness was found in all of the taxa examined, with nestedness declining in the order seabirds > land birds > vascular plants > insects for the indigenous species. Vagility had a marked influence on nestedness and the biogeographical patterns shown by the indigenous species. This influence was borne out by additional analyses of marine taxa and small-sized terrestrial species, both of which were more nested than the most nested group examined here, the seabirds. Assemblages of non-indigenous species also showed nestedness, and nestedness was generally more pronounced than in the indigenous species. Surprisingly, vagility had a significant effect on nestedness in these assemblages too. Main conclusions Nestedness analyses provide a quantitative means of comparing biogeographical patterns for groups differing in vagility. These comparisons revealed that vagility has a considerable influence on biogeographical patterns and should be taken into account in analyses. Here, investigations of more vagile taxa support hypotheses for a single origin of the Southern Ocean island biota (the Insulantarctica scenario), whilst those of less mobile taxa support the more commonly held, multi-regional hypothesis. All biogeographical analyses across the Southern Ocean (and elsewhere) will be influenced by the effects of dispersal ability, with composite analyses dominated by sedentary groups likely to favour multi-regional scenarios, and those dominated by mobile groups favouring single origins. Mechanisms underlying nestedness in the region range from nested physiological tolerances in more mobile groups to colonization ability and patterns of speciation in less vagile taxa. Considerable nestedness in the non-indigenous assemblages is largely a consequence of the fact that many of these species are European weedy species.
Human impacts, energy availability and invasion across Southern Ocean Islands
13 April 2007
Stellenbosch University

Chown, SL;Hull, B;Gaston, KJ

Aim Ongoing biological invasions will enhance the impacts of humans on biodiversity. Nonetheless, the effects of exotic species on diversity are idiosyncratic. Increases in diversity might be a consequence of similar responses by species to available energy, or because of positive relationships between human density, energy and propagule pressure. Here we use data from the Southern Ocean island plants and insects to investigate these issues. Location The Southern Ocean Islands ranging from Tristan da Cunha to Heard Island and South Georgia. Methods Generalized linear models are used to explore the relationships between indigenous and exotic species richness for plants and insects on two different islands. Similar models are used to examine interactions between indigenous and exotic species richness, energy availability and propagule pressure at the regional scale. Results Positive relationships were found between indigenous and exotic species richness at local scales, although for plants, the relationship was partially triangular. Across the Southern Ocean Islands, there was strong positive covariation between indigenous and exotic plant species richness and insect species richness, even taking spatial autocorrelation into account. Both exotic and indigenous plant and insect species richness covaried with energy availability, as did human visitor frequency. When two islands with almost identical numbers of human visits were contrasted, it was clear that energy availability, or perhaps differences in climate-matching, were responsible for differences in the extent of invasion. Conclusion In plants and insects, there are positive relationships between indigenous and exotic diversity at local and regional scales across the Southern Ocean islands. These relationships are apparently a consequence of similar responses by both groups and by human occupants to available energy. When visitor frequency is held constant, energy availability is the major correlate of exotic species richness, though the exact mechanistic cause of this relationship requires clarification.
Constraint and competition in assemblages: A cross-continental and modeling approach for ants
16 April 2007
Stellenbosch University

Parr, CL;Sinclair, BJ;Andersen, AN;Gaston, KJ;Chown, SL

The mechanisms leading to structure in local assemblages are controversial. On the one hand, assemblage structure is thought to be the outcome of local interactions determined by the properties of species and their responses to the local environment. Alternatively, this structure has been shown to be an emergent property of assemblages of identical individuals or of random sampling of a regional assemblage. In ants at baits, a combination of environmental stress and interspecific competition is widely held to lead to a unimodal relationship between the abundance of dominant ants and species richness. It is thought that in comparatively adverse environments, both abundance and richness are low. As habitats become more favorable, abundance increases until the abundance of dominant ants is so high that they exclude those that are subordinate and so depress richness. Here we demonstrate empirically that this relationship is remarkably similar across three continents. Using a null model approach, we then show that the ascending part of the relationship is largely constrained to take this form not simply as a consequence of stress but also as a result of the shape of abundance frequency distributions. While the form of the species-abundance frequency distribution can also produce the descending part of the relationship, interspecific competition might lead to it too. Scatter about the relationship, which is generally not discussed in the literature, may well be a consequence of resource availability and environmental patchiness. Our results draw attention to the significance of regional processes in structuring ant assemblages.
Marine alien species of South Africa - status and impacts
16 April 2007
Stellenbosch University

Robinson, TB;Griffiths, CL;McQuaid, CD;Ruis, M

The current status of marine alien species along the South African coast is reviewed and the ecological and economic impacts of these invasions are discussed. In all, 10 confirmed extant alien and 22 cryptogenic species are recorded from the region. All 10 alien species support well-established populations and the majority of these remain restricted in distribution to sheltered bays, estuaries and harbours. Only one species, the Mediterranean mussel Mytilus galloprovincialis, has spread extensively along the coast and caused significant ecological impacts. These include the competitive displacement of indigenous species and a dramatic increase in intertidal mussel biomass. These changes have also increased available habitat for many infaunal species and resulted in enhanced food supply for intertidal predators. Considerable economic benefits have also resulted from this invasion because M. galloprovincialis forms the basis of the South African mussel culture industry.
Biogeographical patterns in the fauna associated with southern African mussel beds
17 April 2007
Stellenbosch University

Hammond, W;Griffiths, CL

Macrofauna communities colonizing intertidal mussel beds were sampled at seven sites between Swakopmund (Namibia) and Salt Rock (KwaZulu-Natal). Mean mussel cover, length, biomass and bed depth were all low in the southeast (former Transkei). Faunal abundance and biomass were minimal along the south coast, increasing up both west and east coasts. Species diversity and richness showed the reverse trends, peaking at south coast sites and dropping off to the west and east. Multivariate analysis grouped the faunal communities into four distinct clusters, corresponding to the recognized Namib, Namaqua, Agulhas and Natal biogeographical provinces. The low mussel biomass and cover in the Eastern Cape can be attributed to intense human exploitation, but the low faunal abundance and biomass along the south coast was unexpected, as was the negative correlation between faunal abundance and diversity. Over recent decades intense exploitation has resulted in marked declines in mussel cover along the east coast, while the M. galloprovincialis invasion has resulted in dramatic increases in mussel cover to the west. The results given here indicate how these changes might have affected the wider intertidal communities in these regions.
Molecular and morphometric assessment of the taxonomic status of Ectemnorhinus weevil species (Coleoptera : Curculionidae, Entiminae) from the sub-Antarctic Prince Edward Islands
19 April 2007
Stellenbosch University

Grobler, G.C.;Janse van Rensburg, L.B.;Bastos, A.D.S.;Chimimba, C.T.;Chown, S.L.

There are long-standing controversies on the taxonomic status of Ectemnorhinus weevil species occurring on the sub-Antarctic Prince Edward Islands. Since the two islands that constitute the Prince Edward Islands archipelago (PEIA), Marion Island (MI) and Prince Edward Island (PEI), differ in terms of alien invasive species such as the introduced house mouse Mus musculus and conservation management strategies, it is important to consider inter-island dynamics when investigating inter-specific relationships. Using a combined molecular phylogenetic and morphometric approach, we attempted to resolve the taxonomic status of the PEIA Ectemnorhinus weevil species. A COI gene phylogeny was inferred following the genetic characterization of 52 Ectemnorhinus weevils from both islands, and morphometric assessment using a set of 15 linear, external measurements was used to differentiate between the two currently recognized species, Ectemnorhinus similis and Ectemnorhinus marioni. Analyses revealed the presence of two genetically and morphometrically distinct species on PEI, whilst evidence for a single species, comprising diverse genetically discrete populations was found on MI. Based on these results, the species unique to PEI has been designated Ectemnorhinus kuscheli n. sp. whilst we confirm the synonymy between E. similis and E. marioni, the two species originally described from MI. E. kuscheli appears to be restricted to PEI, whereas E. similis occurs on both MI and PEI.
Testing the beneficial acclimation hypothesis and its alternatives for locomotor performance
19 April 2007
Stellenbosch University

Deere, JA;Chown, SL

The beneficial acclimation hypothesis ( BAH) is controversial. While physiological work all but assumes that the BAH is true, recent studies have shown that support for the BAH is typically wanting. The latter have been criticized for assessing the benefits of developmental plasticity rather than acclimation. Here we examine the BAH within a strong inference framework for five congeneric species of ameronothroid oribatid mites that occupy marine to terrestrial habitats. We do so by assessing responses of maximum speed, optimum temperature, and performance breadth, measured from - 10 degrees C to 35 degrees C, to four treatment temperatures ( 0 degrees, 5 degrees, 10 degrees, and 15 degrees C). We show that the BAH and its alternatives often make similar empirical predictions. Weak beneficial acclimation is characteristic of one of the more marine species. In the other two upper-shore and marine species, evidence exists for deleterious acclimation and the colder-is-better hypothesis. In the two fully terrestrial species, there is no plasticity. Lack of plasticity is beneficial when cue reliability is low or costs of plasticity are high, and the former seems plausible in terrestrial habitats. However, weak plasticity in the uppershore/marine species and the absence of plasticity in the terrestrial species might also be a consequence of phylogenetic constraint.
Novel ecosystems: theoretical and management aspects of the new ecological world order
20 April 2007
Stellenbosch University

Hobbs, RJ;Arico, S;Aronson, S;Baron, JS;Bridgewater, P;Cramer, VA;Epstein, PR;Ewel, JJ;Klink, CA;Lugo, AE;Norton, D;Ojima, D;Richardson, DM

We explore the issues relevant to those types of ecosystems containing new combinations of species that arise through human action, environmental change, and the impacts of the deliberate and inadvertent introduction of species from other regions. Novel ecosystems (also termed 'emerging ecosystems') result when species occur in combinations and relative abundances that have not occurred previously within a given biome. Key characteristics are novelty, in the form of new species combinations and the potential for changes in ecosystem functioning, and human agency, in that these ecosystems are the result of deliberate or inadvertent human action. As more of the Earth becomes transformed by human actions, novel ecosystems increase in importance, but are relatively little studied. Either the degradation or invasion of native or 'wild' ecosystems or the abandonment of intensively managed systems can result in the formation of these novel systems. Important considerations are whether these new systems are persistent and what values they may have. It is likely that it may be very difficult or costly to return such systems to their previous state, and hence consideration needs to be given to developing appropriate management goals and approaches.
A global indicator for biological invasion
20 April 2007
Stellenbosch University

McGeoch, MA;Chown, SL;Kalwij, JM

"Trends in invasive alien species' is one of only two indicators of threat to biodiversity that form part of the Convention on Biological Diversity's (CBD) framework for monitoring progress toward its "2010 target" (ie., the commitment to achieve by 2010 a significant reduction in the current rate of biodiversity loss). To date, however, there is no fully developed indicator for invasive alien species (JAS) that combines trends, derived from a standard set of methods, across species groups, ecosystems, and regions. Here we provide a rationale for the form and characteristics of an indicator of trends in MS that will meet the 2010 framework goal and targets for this indicator We suggest single and composite indicators that include problem-status and inanagement-status measures that are designed to be flexible, readily disaggregated, and as far as possible draw on existing data. The single indicators at national and global scales are number of IAS and numbers of operational management plans for MS. Global trends in IAS are measured as the progress of nations toward the tat-gets of stabilizing JAS numbers and the implementation of MS management plans. The proposed global indicator thus represents a minimum information set that most directly addresses the indicator objective and simultaneously aims to maximize national participation. This global indicator now requires testing to assess its accuracy, sensitivity and tractability. Although it may not be possible to achieve the desired objective for a global indicator of biological invasion by 2010 as comprehensively as desired, it seems possible to obtain trend estimates for a component of the taxa, ecosystems, and regions involved. Importantly, current indicator development initiatives will. also contribute to developing the mechanisms necessary for monitoring global trends in MS beyond 2010.
Caterpillars benefit from thermal ecosystem engineering by wandering albatrosses on sub-Antarctic Marion Island
20 April 2007
Stellenbosch University

Sinclair, BJ;Chown, SL

Wandering albatrosses (Diomedea exulans) nest on Southern Ocean islands, building elevated nests upon which they incubate eggs and raise chicks, and which the chicks occupy through winter. The nests support high invertebrate biomass, including larvae of the flightless moth Pringleophaga marioni. Here we argue that high biomass of P marioni in the nests is not associated with nutrient loading as previously suspected, but that higher temperatures in the nests increase growth and feeding rate, and decrease deleterious repeated cold exposure, providing fitness advantages for P marioni. Thus, wandering albatrosses may be serving as thermal engineers, modifying temperature and therefore enabling better resource use by P marioni.
Effects of experimental harvesting on recruitment of an alien mussel Mytilus galloprovincialis
24 April 2007
Stellenbosch University

Robinson, TB;Branch, GM;Griffiths, CL;Govender, A

Successful fisheries management is underpinned by an understanding of the processes that underlie the population dynamics of exploited stocks. This study considered the effects of experimental harvesting on recruitment of Mytilus galloprovincialis along the west coast of South Africa, where harvesting of this alien species is being contemplated. In particular, the role of settlement habitat availability in the form of adult mussels was analysed. To track the effects of a spectrum of harvesting intensities, five treatments were implemented: F = 0 (i.e. a control), F = 0.3, F = 0.6, F = 0.9 and F = 1. At these harvesting intensities 0%, 30%, 60%, 90% or 100% of mussel biomass was removed respectively at the outset of the experiment. A significant negative exponential relationship (p < 0.01) was found between M. galloprovincialis recruit density and harvesting intensity, with intensities greater than F = 0.3 dramatically reducing recruitment. This pattern was recorded throughout the intertidal zone and remained temporally constant over 2 years. Significant positive linear relationships (p < 0.01) between recruit density and adult mussel biomass or density indicate a strong correlation between availability of settlement habitat and recruitment. It is likely that the high recruit density recorded at low harvesting intensities (2000–20 000 per 0.01 m2) exceeds the level required for population maintenance. However, if settlement habitat is eliminated or significantly reduced, as was achieved by F = 0.3 or above, recruitment may become limiting. Thus, to protect stock replenishment, harvesting of M. galloprovincialis in this region should take place at intensities less than F = 0.3.
Tourists' willingness to pay to view otters along the Wild Coast, South Africa: a potential for increased ecotourism
25 April 2007
Stellenbosch University

Dumasile, L.;Somers, M.J.;Walters, M.;Nel, J.A.J.

This article reports on tourists’ willingness to pay to view Cape clawless otters Aonyx capensis along the Eastern Cape Wild Coast, South Africa. We collected data from a survey carried out using a structured, selfadministered questionnaire. We analyzed 67 completed questionnaires, of which 60 respondents (89.5%) indicated that they would be interested in viewing otters and would be prepared to pay an extra fee, over and above the normal entrance fees, for a trained guide to show them otters. The remaining 7 (10.4%) respondents indicated that they would reconsider and pay if this would create jobs for members of the local community. Most (98.4% and 91.8%) of the respondents also indicated that they would still pay even if there was only a 50% or 25% chance of seeing otters. Most of the respondents were willing to pay either less than R50.00 (ca US$8.00) or R50.00- R100.00 to view otters regardless of the chances of seeing them. We conclude from our results that otters do have the potential to increase ecotourism in the area, and also to contribute financially to the poverty stricken local Dwesa community.
Distribution and habitat choice of Cape clawless otters Aonyx capensis in South Africa
25 May 2007
Stellenbosch University

Nel, J;Somers, MJ

Cape clawless otters, Aonyx capensis,are widely distributed in South Africa, as elsewhere on the continent. They occur in a wide variety of environments and most aquatic habitats, from freshwater lakes to the marine littoral,and even in episodic rivers in arid areas, provided freshwater sources are adequate and sufficient food is available. This animal is not much affected by turbid water as it locates prey by touch, and usually forages close to shores or banks. Evidence of presence in given localities and habitats, distributed over a large area of the Northern,Western, and Eastern Cape provinces, was deduced from signs (faecal deposits or distinctive tracks) on land. Accepting the inherent pitfalls of this approach we nevertheless feel using it is acceptable for a first approximation of habitat preferences over a large geographical area. Results point to areas with dense reed beds and a rocky substrate on banks being used most intensively, probably on account of a localized high food biomass.
Shell availability and use by the hermit crab Clibanarius virescens along the Eastern Cape coast, South Africa
21 August 2007
Stellenbosch University

Nakin, MD;Somers, MJ

Patterns of shell availability and use of the intertidal yellow-banded hermit crab Clibanarius virescens were studied by means of field sampling. Data were collected at three sites (Dwesa, Nqabara and Mendwana) along the Eastern Cape coast, South Africa. The most striking result was that at all three sites there was a difference between observed frequencies of shells used compared to that which was expected from their availability as live animals or empty shells on the rocks and the strandline. This suggests selection by the crabs. Crabs commonly used shells of Burnupena cincta and Burnupena pubescens and amongst other types, rarely used the shells of Cymatium dolarium and Stramonita capensis. Fewer types of shells were used than were available. A wider diversity of shell species were occupied at Dwesa (N = 11) and Nqabara (N = 10) than at Mendwana (N = 6). The diversity of shells used by the hermit crabs in this study falls within the globally predicted levels given body size of the study species and the latitude of the studied population.
Environmental factors, regional body size distributions, and spatial variation in body size of local avian assemblages
05 November 2008
Stellenbosch University

Greve, M.;Gaston, K.J.;van Rensburg, B.J.;Chown, S.L.

Aim To determine how well variation in median body size of avian assemblages is predicted by (1) the environmental models usually employed in analyses of Bergmann’s rule and (2) random sampling from the regional body size frequency distribution. If body size frequency distributions of local assemblages represent a random sample of a regional frequency distribution, then geographic variation in body sizes of assemblages might be a consequence of the determinants of spatial variation in species richness rather than direct influences on body size per se. Location Southern Africa. Methods Median body masses (as a measure of body size) of avian assemblages were calculated for quarter degree grid cells across South Africa and Lesotho. The relationship between median body mass and four environmental variables (minimum and maximum monthly temperatures, precipitation, and seasonality in the normalized difference vegetation index, as a measure of seasonality in productivity) was examined using general linear models first without taking spatial autocorrelation into account, and accounting for it by fitting an exponential spatial covariance structure. Model fit was assessed using the Akaike Information Criterion and Akaike weights. At each species richness value, random assemblages were sampled by either drawing species randomly from the regional body mass frequency distribution, or drawing species from the regional body mass frequency distribution with a probability proportional to their geographic distribution in the area. The ability of randomizations to predict actual body masses was examined using two-tailed Fisher exact tests. Results: Seasonality in productivity was the only environmental variable that remained a significant predictor of body mass variation in spatially explicit models, though the positive relationship was weak. When species richness was included in the models it remained the only significant predictor of size variation. Randomizations predicted median body mass poorly at low species richness, but well at high richness. Main conclusions: Environmental models that have previously been proposed explain little of the variation in body mass across avian assemblages in South Africa. However, much of the variation in median mass of assemblages could be predicted by randomly drawing species from the regional body mass frequency distribution, particularly using randomizations in which all species were drawn from the regional body mass frequency distribution with equal probability and at high species richness values. This outcome emphasizes the need to consider null expectations in investigations of the geographic variation in body size together with the likely environmental mechanisms underlying spatial variation in average size. Moreover, it suggests that in the South African avifauna, spatial variation in the body sizes of assemblages may be determined indirectly by the factors that influence geographic variation in species richness.
Diversity and depletions in continental carnivore guilds: implications for prioritizing global carnivore conservation
28 January 2009
Stellenbosch University

Dalerum, Fredrik;Cameron, Elissa Z.;Kunkel, Kyran;Somers, Michael J.

Large carnivores are important ecosystem components but are extinction prone due to small populations, slow growth rates and large area requirements. Consequently, there has been a surge of carnivore conservation efforts. Such efforts typically target local populations, with limited attention to the effects on the ecosystem function of predator guilds. Also, there is no framework for prioritizing these efforts globally. We compared taxonomic and functional diversity of continental carnivore guilds, compared them with the corresponding guilds during the Late Pleistocene and synthesized our results into suggestions for global prioritizations for carnivore conservation. Recent extinctions have caused taxonomically and functionally depleted carnivore guilds in Europe and North and South America, contrasting with guilds in Africa and Asia, which have retained a larger proportion of their carnivores. However, Asia is at higher risk of suffering further extinctions than other continents. We suggest three priorities of contrasting urgency for global carnivore conservation: (i) to promote recovery of the threatened Asian species, (ii) to prevent species in the depleted guilds in Europe and North and South America from becoming threatened, and (iii) to reconstruct functionally intact sympatric guilds of large carnivores at ecologically effective population sizes.
How does the spatial structure of habitat loss affect the eco-epidemic dynamics?
15 August 2009
Stellenbosch University

Su, Min;Hui, Cang;Zhang, Yanyu;Li, Zizhen

Habitat loss is considered as one of the primary causes of species extinction, especially for a species that also suffers from an epidemic disease. Little attention has been paid to the combined effect of habitat loss and epidemic transmission on the species spatiotemporal dynamics. Here, a spatial model of the parasite–host/prey–predator eco-epidemiological system with habitat loss was studied. Habitat patches in the model, instead of undergoing a random loss, were spatially clustered by different degrees. Not only the quantity of habitat loss but also its clustering degree was shown to affect the equilibrium of the system. The infection rate and the probability of successful predation were keys to determine the spatial patterns of species. The epidemic disease is more likely to break out if only a small amount of suitable patches were lost. Counter-intuitively, infected preys are more sensitive to habitat loss than predators if the lost patches are highly clustered. This result is new to eco-epidemiology and implies a possibility of using spatial arrangement of suitable (or unsuitable) patches to control the spread of epidemics in the ecological system.
The effect of migration on the spatial structure of intraguild predation in metapopulations
15 August 2009
Stellenbosch University

Su, Min;Zhang, Yanyu;Hui, Cang;Li, Zizhen

We consider the effects of migration on intraguild predation (IGP) via lattice models and pair approximation. The following results can be found: there exists asymmetry between two consumers’ migration effects on the spatial structure of IGP; migration of each consumer reduces its own clumping degree; the spatial structure is influenced by the ecological neighborhood.
Spatiotemporal dynamics of the epidemic transmission in a predator-prey system
15 August 2009
Stellenbosch University

Su, Min;Hui, Cang;Zhang, Yanyu;Li, Zizhen

Epidemic transmission is one of the critical density-dependent mechanisms that affect species viability and dynamics. In a predator-prey system, epidemic transmission can strongly affect the success probability of hunting, especially for social animals. Predators, therefore, will suffer from the positive density-dependence, i.e., Allee effect, due to epidemic transmission in the population. The rate of species contacting the epidemic, especially for those endangered or invasive, has largely increased due to the habitat destruction caused by anthropogenic disturbance. Using ordinary differential equations and cellular automata, we here explored the epidemic transmission in a predator-prey system. Results show that a moderate Allee effect will destabilize the dynamics, but it is not true for the extreme Allee effect (weak or strong). The predator-prey dynamics amazingly stabilize by the extreme Allee effect. Predators suffer the most from the epidemic disease at moderate transmission probability. Counter-intuitively, habitat destruction will benefit the control of the epidemic disease. The demographic stochasticity dramatically influences the spatial distribution of the system. The spatial distribution changes from oil-bubble-like (due to local interaction) to aggregated spatially scattered points (due to local interaction and demographic stochasticity). It indicates the possibility of using human disturbance in habitat as a potential epidemic-control method in conservation.
Ambient, productive and wind energy, and ocean extent predict global species richness of procellariiform seabirds
15 December 2009
Stellenbosch University

Davies, R.G.;Irlich, U.M.;Chown, S.L.;Gaston, K.J.

Aims Tests of the energy hypothesis for the large-scale distribution of species richness have largely been concerned with the influence of two alternative forms of environmental energy, temperature and energy from primary productivity, both of which (at least in terrestrial systems) peak within the tropics. Taxa showing extratropical diversity peaks present a potential challenge to the generality of species– energy theory. One such group are pelagic seabirds of the order Procellariiformes that show not only an extra-tropical diversity peak but one confined to the Southern Ocean, hence a highly asymmetric one. They are distinct in being exceptionally adapted to take advantage of wind energy, which theymay rely on for long-distance ocean foraging for the patchy resources needed to meet their energetic needs.Wind represents a readily available source of kinetic energy, shows a strong latitudinal gradient, and has been largely omitted from species–energy theory. Moreover, maximal benefits of wind are likely to be afforded in areas of greatest available contiguous ocean extent.We compare the relative importance of wind speed, ocean productivity (chlorophyll concentration), air temperature and available ocean extent (distance) in explaining large-scale global distribution of procellariiform species richness across the world’s oceans. Location Global, oceanic. Methods Hierarchical partitioning, model selection, ordinary least squares (OLS) and spatial generalized least squares (GLS) regression. Results Hierarchical partitioning of non-spatial regression models indicates that ocean distance is the most important predictor of procellariiform species richness followed by wind speed and then temperature. In contrast, that of spatial regression models indicates the roughly equal importance of ocean distance and temperature, followed by wind speed. Although contributing additional model fit, ocean productivity is consistently the weakest predictor. Best-fit models include all four predictors and explain 67% of observed variation. The species–productivity relationship is negative overall, while the species–temperature relationship is humpshaped. In contrast, ocean distance and wind speed are positively associated with species richness. Conclusions Large-scale procellariiform species richness distribution may represent a trade-off in the use of different energy forms, being highest in Southern Ocean areas where productive energy and temperature are relatively low, but where available ocean foraging extent and wind energy required to utilize it are near-maximal.
Physiological tolerances account for range limits and abundance structure in an invasive slug.
03 February 2010
Stellenbosch University

Lee, J.E.;Janion, C.;Marais, E.;Jansen van Vuuren, B.;Chown, S.L.

Despite the importance of understanding the mechanisms underlying range limits and abundance structure, few studies have sought to do so. Here we use a terrestrial slug species, Deroceras panormitanum, that has invaded a remote, largely predator-free, Southern Ocean island as a model system to do so. Across Marion Island, slug density does not conform to an abundant centre distribution. Rather, abundance structure is characterized by patches and gaps. These are associated with this desiccation-sensitive species’ preference for biotic and drainage line habitats that share few characteristics except for their high humidity below the vegetation surface. The coastal range margin has a threshold form, rapidly rising from zero to high density. Slugs do not occur where soil-exchangeable Na values are higher than 3000 mg kgK1, and in laboratory experiments, survival is high below this value but negligible above it. Upper elevation range margins are a function of the inability of this species to survive temperatures below an absolute limit of K6.48C, which is regularly exceeded at 200 m altitude, above which slug density declines to zero. However, the linear decline in density from the coastal peak is probably also a function of a decline in performance or time available for activity. This is probably associated with an altitudinal decline in mean annual soil temperature. These findings support previous predictions made regarding the form of density change when substrate or climatic factors set range limits.
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.
Mytilus on the move: transport of an invasive bivalve to the Antarctic
18 October 2010
Stellenbosch University

Lee, J.E.;Chown, S.L.

Increasing numbers of scientific and tourist vessels are entering the Antarctic region and have the potential to bring with them a range of organisms that are not currently found in the region. Little is known about the frequency of such introductions or the identity and survivorship of the species associated with them. In this study, we report the findings of an inspection of the sea chests of the South African National Antarctic Programme supply vessel, the SA ‘Agulhas’, while the vessel was in dry dock in June 2006. Large populations of a known invasive mussel, Mytilus galloprovincialis (Lamarck), were found. By extrapolating from shell length, the age of individuals was estimated, the results of which suggest that some specimens have survived transportation to the Antarctic region on multiple occasions. These findings are cause for concern and demonstrate that Antarctic research and supply vessels are important vectors for marine non-indigenous species into the region.
Why Carcinus maenas cannot get a grip on South Africa’s wave-exposed coastline
18 October 2010
Stellenbosch University

Hampton, S.L.;Griffiths, C.L.

The European green crab Carcinus maenas has established considerable breeding populations in harbours and sheltered bays in the South-Western Cape, South Africa, but appears unable to flourish on the waveexposed coastline. This study compares the abilities of C. maenas and those of an indigenous rocky-shore crab, Plagusia chabrus, to resist hydrodynamic forces. C. maenas had less than half the vertical tenacity of P. chabrus (371.5g and 780.5g respectively) and was unable to grip against as fast a unidirectional flow (0.23m s¯¹ vs 0.53m s¯¹) as P. chabrus. C. maenas also has significantly shorter and lighter limbs than P. chabrus and the dactyls of its walking legs are poorly adapted to grip onto rocky substrata. We conclude that C. maenas is poorly adapted to survive in wave-swept conditions and hence unlikely to displace indigenous crab species along the open wave-exposed coastline of South Africa. However, it may invade other sheltered locations, particularly Saldanha Bay and False Bay.
Experimental harvesting of Mytilus galloprovincialis: Can an alien mussel support a small-scale fishery?
18 October 2010
Stellenbosch University

Robinson, T.B.;Govender, A.;Griffiths, C.L.;Branch, G.M.

In an effort to stimulate new fisheries and address historic imbalances in access to fishing rights, there has been a recent focus on the development of small-scale fisheries in South Africa. To assess the biological viability of a fishery for the alien mussel Mytilus galloprovincialis, an experimental fishery operated by two impoverished coastal communities was initiated. Harvesting took place on a rotational basis at three sites, nested within four locations. At each of these 12 sites, 5 treatments were undertaken to span a spectrum of harvesting intensities (F = 0, 0.3, 0.6, 0.9 and a once-off total removal). A dynamic biomass-based fisheries model was developed to predict changes in exploited populations over time. Monthly maximum sustainable yield (MSY) estimates peaked at 1560 kg per 100m of shore in March–April and September–October, but dropped by two orders of magnitude to 15 kg per 100m of shore during the remainder of the year. The two peaks in MSY corresponded to the peak spawning periods of M. galloprovincialis along the South African west coast. Consequently, harvesting will only be viable if focused within two seasons spanning the peaks in MSY. Under these conditions, a range of harvesting intensities between F = 0.1 and 0.3 would permit long-term biological sustainability of a fishery. If implemented, this would represent the first instance of a marine invasive species being utilised to achieve socio-economic goals in South Africa.
The invasion and subsequent die-off of Mytilus galloprovincialis in Langebaan Lagoon, South Africa: effects on natural communities
18 October 2010
Stellenbosch University

Robinson, T.B.;Griffiths, C.L.;Branch, G.M.;Govender, A.

The alien mussel Mytilus galloprovincialis invaded sand banks in Langebaan Lagoon on the west coast of South Africa in the mid-1990s. However, by 2001 these beds had completely died off, with only empty shells and anoxic sand remaining. In an effort to prevent the re-settlement of this aggressive invader, all dead mussel shells were then cleared. This study considered the impacts of the invasion and subsequent die-off on natural benthic communities. Community composition differed significantly between non-invaded and invaded areas (ANOSIM,R = 0.685 and P 0.05). Invasion thus dramatically altered natural communities and although the subsequent removal of the dead mussel shells appears to have aided recovery, community composition remained different from the pre-invasion state after 5 months.
Changes in South African rocky intertidal invertebrate community structure associated with the invasion of the mussel Mytilus galloprovincialis
19 October 2010
Stellenbosch University

Robinson, T.B.;Branch, G.M.;Griffiths, C.L.;Govender, A.;Hockey, P.A.R.

Since the establishment of the alien mussel Mytilus galloprovincialis in South Africa, several authors have studied its interactions with individual indigenous species. However, the broader implications of this invasion on the intertidal zone remain undocumented. This paper analyses the impacts of this mussel on the rocky-shore invertebrate community structure at Marcus Island on the west coast of South Africa. The effects of the invasion were linked to 3 key elements and were not consistently spread across the intertidal zone, but were focused within the mid-to-low shore. Firstly, physical stress in the mid-intertidal zones was ameliorated by the presence of M. galloprovincialis beds. Secondly, habitat complexity was increased where M. galloprovincialis replaced bare rock or less complex secondary habitat. Thirdly, habitat became less patchy as mussel beds blanketed the shore. Consequently, invertebrate density and species richness increased substantially, and community composition changed significantly in the mid-shore. Lower on the shore, significant changes in invertebrate community structure were driven by a switch from mono-layered beds of the small indigenous mussel Aulacomya ater to multilayered beds of M. galloprovincialis, despite no change in total species richness.
Fine-scale temporal and spatial dynamics of epigaeic ants in Fynbos: sampling implications
20 October 2010
Stellenbosch University

Boonzaaier, C.;McGeoch, M.A.;Parr, C.L.

Conservation and management strategies are dependent on reliable species richness information. Accurate species richness counts, especially for invertebrates, are almost impossible to obtain from sampling alone, due to the high costs and effort involved. Therefore, there is a great need to optimize sampling effort to gain maximum information from minimum sampling duration and intensity. Reliable species richness information is particularly critical for under-studied, high diversity regions, such as the Cape Floristic Region (CFR), where biodiversity is threatened by agricultural practices and urbanization. Ants (Formicidae) form an important part of the fauna of the CFR, especially as seed dispersers. This study investigated sampling effort options for maximizing ant species representivity in the region. The specific aims were to determine (i) whether a doubling in the sample duration significantly increased the number of species captured (ii) the effect of increased spatial versus temporal sampling effort on diversity estimates and (iii) the effect of adding an additional trapping method. Sampling was conducted at Elandsberg, Western Cape Province, from 20 February to 1 March 2004. Pitfall trapping was conducted in two five-day sessions and tuna-baits were used once. Species rarefaction curves were drawn and compared using EstimateS. A total of 42 species were captured and asymptotes to species richness were reached. Doubling of sample duration yielded no significant increase in species richness and was equally affected in terms of number of species as was doubling the sampling intensity. However, increasing the number of spatial replicates yielded a higher turnover in species. Baiting added no additional species to pitfall catches. Therefore, when sampling ant diversity in theCFR, investing sampling effort within seasons in spatial replication is likely to be more effective than increasing sampling duration.
Conservation of Southern Ocean Islands: invertebrates as exemplars
27 October 2010
Stellenbosch University

Chown, S.L.;Lee, J.E.;Shaw, J.D.

The Southern Ocean Islands (SOI) have an exceptionally high conservation status, and human activity on the islands is low by comparison with more tropical islands. In consequence, overexploitation, pollution and habitat destruction have had little influence on the invertebrate biotas of the islands, although overexploitation of pelagic species has the potential for an indirect influence via reduction of nutrient inputs to the terrestrial systems. By contrast, invasive alien species, the local effects of global climate change, and interactions between them are having large impacts on invertebrate populations and, as a consequence, on ecosystem functioning. Climate change is not only having direct impacts on indigenous invertebrates, but also seems to be promoting the ease of establishment of new alien invertebrate species. It is also contributing to population increases of invertebrate alien species already on the islands, sometimes with pronounced negative consequences for indigenous species and ecosystem functioning. Moreover, alien plants and mammals are also affecting indigenous invertebrate populations, often with climate change expected to exacerbate the impacts. Although the conservation requirements are reasonably well-understood for terrestrial systems, knowledge of freshwater and marine near-shore systems is inadequate. Nonetheless, what is known for terrestrial, freshwater and marine systems suggests that ongoing conservation of SOI invertebrates requires intervention from the highest political levels internationally, to slow climate change, to local improvements of quarantine measures to reduce the rates and impacts of biological invasions.
Mean mass-specific metabolic rates are strikingly similar across life’s major domains: Evidence for life’s metabolic optimum
27 October 2010
Stellenbosch University

Makarieva, A.M.;Gorshkov, V.G.;Li, B.-L.;Chown, S.L.;Reich, P.B.;Gavrilov, V.M.

A fundamental but unanswered biological question asks how much energy, on average, Earth’s different life forms spend per unit mass per unit time to remain alive. Here, using the largest database to date, for 3,006 species that includes most of the range of biological diversity on the planet—from bacteria to elephants, and algae to sapling trees—we show that metabolism displays a striking degree of homeostasis across all of life. We demonstrate that, despite the enormous biochemical, physiological, and ecological differences between the surveyed species that vary over 1020-fold in body mass, mean metabolic rates of major taxonomic groups displayed at physiological rest converge on a narrow range from 0.3 to 9 W kg-1. This 30-fold variation among life’s disparate forms represents a remarkably small range compared with the 4,000- to 65,000-fold difference between the mean metabolic rates of the smallest and largest organisms that would be observed if life as a whole conformed to universal quarterpower or third-power allometric scaling laws. The observed broad convergence on a narrow range of basal metabolic rates suggests that organismal designs that fit in this physiological window have been favored by natural selection across all of life’s major kingdoms, and that this range might therefore be considered as optimal for living matter as a whole.
Influence of largemouth bass, Micropterus salmoides, on abundance and habitat selection of Cape galaxias, Galaxias zebratus, in a mountain streamin the Cape Floristic Region, South Africa
28 October 2010
Stellenbosch University

Shelton, J.M.;Day, J.A.;Griffiths, C.L.

Predatory alien fishes have been widely introduced into streams in the Cape Floristic Region (CFR), South Africa, but little is known about their effect on native fishes. Results from this 2006 study suggest that the presence of alien predatory largemouth bass, Micropterus salmoides, may have influenced abundance and habitat selection of the native Galaxias zebratus at one location in a small CFR mountain stream. Numbers of adults, but not of juveniles, were significantly lower where M. salmoides was present, suggesting a size-specific influence on G. zebratus abundance. Because other studies have found the influence of a predator to be affected by prey size and the diel activity of predator and prey, we measured microhabitat use by adult and juvenile G. zebratus by day and by night. Galaxias zebratus selected deeper, faster-flowing microhabitats more strongly where M. salmoides was present than where it was absent. This suggests that G. zebratus adjusts its habitat use in the presence of M. salmoides, although differences in available habitat, or in interactions with other indigenous species, could be partly responsible for the observed differences. In-stream vegetation presence was strongly positively related to depth and strongly negatively related to velocity at positions where G. zebratus was observed, suggesting that the deeper, slower-flowing microhabitats occupied by G. zebratus were structurally more complex than the shallower, faster-flowing ones.
Animal introductions to southern systems: lessons for ecology and for policy
03 November 2010
Stellenbosch University

Chown, S.L.;Spear, D.;Lee, J.E.;Shaw, J.D.

Numerous animal species have been introduced to areas from which they were previously absent, and many of these have become invasive, with substantial impacts. However, in other cases, impacts are assumed from theory. Empirical demonstrations are uncommon, making evidence-based conservation policy difficult to achieve. Here we review the broader ecological and conservation lessons from recent work on non-indigenous species in two southern systems, the policy implications thereof, and the subsequent changes to policy as a result of this work. First, we discuss invasions in the Antarctic region. Strong relationships exist between numbers of animal invasions and numbers of human visitors to Southern Ocean Islands, abiotic factors are often limiting for introduced species, homogenization across islands differs among taxonomic groups, and control actions can rapidly result in unintended consequences. This knowledge has influenced national policy and decisions within the Antarctic Treaty System. Second, we discuss ungulate introductions and translocations, both in South Africa and elsewhere. We show that substantial homogenization has resulted from both processes. However, firm evidence for impacts of ungulate introductions and translocations is sometimes difficult to find, despite the theoretical likelihood thereof. Such a lack of information may have profound consequences for the effective implementation of policy.
Present distribution and abundance of the introduced barnacle Balanus glandula Darwin in South Africa
03 November 2010
Stellenbosch University

Laird, M.C.;Griffiths, C.L.

The date of first introduction of the North-East Pacific acorn barnacle Balanus glandula to South Africa is unknown, but it is depicted in photographic records dating back to at least 1992. Its present range and population density were determined by surveying 24 sites on the west and south coasts of South Africa. B. glandula occurred over approximately 400 km of coastline, from Elands Bay in the north-west to Misty Cliffs on the west coast of the Cape Peninsula. The abundance of B. glandula was affected by site, zone, prevalence of upwelling, and orientation of the shore. Its distribution was very patchy, both on macro- and microscales, with Bloubergstrand and Moullie Point having the highest abundances of 28 445 and 24 500 individuals m–2 respectively. B. glandula was the dominant barnacle at all West Coast sites where it was recorded, comprising 78.49% of all barnacles found. The successful invasions of B. glandula in South Africa, Argentina and Japan suggest that this species poses a potential threat to intertidal communities in cool, temperate waters.
Resilience and elasticity of intertidal communities in response to harvesting of the alien mussel Mytilus galloprovincialis
03 November 2010
Stellenbosch University

Robinson, T.B.;Branch, G.M.;Griffiths, C.L.;Govender, A.

Besides the direct impacts of exploitation on target species, indirect effects on non-target species are unavoidable and find expression in changes in community structure. We quantified the effects of experimental harvesting of Mytilus galloprovincialis on intertidal communities on the South African west coast. In the mid- and low-shore, four months of harvesting at intensities greater than F=0.3 and F=0.6 respectively, resulted in significant changes in community composition. These changes were driven by progressively greater spatial dominance by the macroalgae Cladophora flagelliformis, Porphyra capensis and Ulva species as harvesting intensity increased. Four months after cessation of harvesting, community structure had not recovered and even areas subjected to as little as F=0.3 supported significantly altered communities in both zones. The fact that substantial community changes were induced by even low-intensity exploitation is indicative of low resilience to harvesting. The densities and cover of the dominant taxa returned to a pre-harvest state 16 months after the cessation of harvesting, but multivariate analyses indicated that the overall community composition required 32 months for Cover Letter full recovery. Although these communities displayed elasticity within three years, it is recommended that should a M. galloprovincialis fishery be established in the region, harvesting be implemented at a maximum intensity of F=0.3. This approach would maximise yields and protect associated intertidal communities.
Effects of time-lagged niche construction on metapopulation dynamics and environmental heterogeneity
15 November 2010
Stellenbosch University

Han, X.;Hui, C.;Zhang, Y.

Time-delayed responses to environmental changes and disturbance can beget profound effects on the spatiotemporal dynamics of metapopulations. Here, we first examined the effect of three forms of time-lag (that is, equal-weight, recency and primacy effects) on population dynamics, using a spatially structured lattice model. The time-lag was incorporated in the niche construction process of the system (an organism–environment feedback). Using bifurcations diagrams and numerical simulations, we found that the time-lag can form a phase-locked oscillation. Three typical spatial patterns emerged: spiral wave, spiral-broken wave and circular wave. These spatial patterns gradually become immobile as a result of the self-organized ecological imprinting due to niche construction. Therefore, the phase-locked oscillation and the ecological imprinting process together determine the spatial structure of metapopulations and the environmental heterogeneity.
Conserving the fishes of the Twee River, Western Cape, South Africa: revisiting the issues
15 November 2010
Stellenbosch University

Marr, S.M.;Sutcliffe, L.M.E.;Day, J.A.;Griffiths, C.L.;Skelton, P.H.

The Twee River catchment contains two endemic fish species — the Twee River redfin and the Twee River galaxias — which are threatened by water abstraction, habitat degradation, and the presence of introduced fishes. Fyke nets were used to determine the current distribution ranges of fish in the catchment to update a 1997 survey and to provide key information for the compilation of a conservation strategy for the Twee River redfin, Barbus erubescens. Population estimates from 1997 placed their total number at 8 400, but population size could not be estimated from the present surveys. A number of small populations of Twee River redfin and Twee River galaxias, which are restricted to two short stretches of tributary rivers, were identified. Their long-term survival remains uncertain. Conservation action, including the eradication of alien fish and the creation of a dedicated sanctuary for the endemic populations, is recommended.
A brief histoty of marine bio-invasions in South Africa
15 November 2010
Stellenbosch University

Griffiths, C.L.;Mead, A.;Robinson, T.B.

Marine species have been introduced continuously into South Africa for more than 400 years, since the arrival of the first European explorers. Various waves of introduction can be identified over this period, each associated with a different mix of vectors. Early wooden vessels carried specialized wood-boring species, a rich external fouling community, plus semi-terrestrial species associated with dry ballast. Modem steel vessels continue to import fouling species, despite the use of anti-fouling paints, and may ply new routes, bringing additional introductions from novel locations. More modern waves of introduction are associated with use of ballast water and with marine aquaculture. Research on marine bio-invasions in South Africa has a short history, marked by a rapid rate of discovery of introductions. Some 86 marine species are currently regarded as introduced to the region, virith a further 39 considered cryptogenic, but this number is increasing rapidly. Moreover, many taxa and regions still remain inadequately explored, indicating that the current list remains far from complete. The reasons for under-reporting of introduced populations are discussed and include lack of sample coverage, misidentification of aliens as native species and erroneous redescriptions of aliens as new, indigenous species. However, the lack of taxonomic expertise across large sections of the biota remains the greatest impediment to progress.
Temporal development of hull-fouling assemblages associated with an Antarctic supply vessel
22 November 2010
Stellenbosch University

Lee, J.E.;Chown, S.L.

Introduction of non-native species poses one of the greatest, but least understood threats to marine biodiversity. Whilst considerable research effort has focused on vectors such as ballast water, hull fouling remains poorly understood and there is a notable lack of data concerning the temporal development of fouling communities. Here we use remote video capture techniques to assess the development and change of fouling assemblages on an Antarctic supply vessel over a 2 yr period. Assemblages were dominated by cosmopolitan species, some of which are known to be invasive. We demonstrate that whilst areas surrounded by sea-ice are at low risk of introductions from this pathway, substantial fouling assemblages are routinely transported to sub-Antarctic islands where the thermal conditions may allow their establishment. Extent of fouling assemblages, and thus the threat of invasion, may be reduced by changing the dry docking regime and minimising port layover times and in-water cleaning of submerged hull surfaces.
Breaching the dispersal barrier to invasion: quantification and management
23 November 2010
Stellenbosch University

Lee, J.E.;Chown, S.L.

Globalization has resulted in unprecedented movements of people, goods, and alien species across the planet. Although the impacts of biological invasions are widely appreciated, a bias exists in research effort to post-dispersal processes because of the difficulties of measuring propagule pressure. The Antarctic provides an ideal model system in which to investigate propagule movements because of the region’s isolation and small number of entry routes. Here we investigated the logistics operations of the South African National Antarctic Programme (SANAP) and quantified the initial dispersal of alien species into the region. We found that over 1400 seeds from 99 taxa are transported into the Antarctic each field season in association with SANAP passenger luggage and cargo. The first ever assessment of propagule drop-off indicated that 30–50% of these propagules will enter the recipient environment. Many of the taxa include cosmopolitan weeds and known aliens in the Antarctic, indicating that logistics operations form part of a globally self-perpetuating cycle moving alien species between areas of human disturbance. In addition, propagules of some taxa native to the Antarctic region were also found, suggesting that human movements may be facilitating intra-regional homogenization. Several relatively simple changes in biosecurity policy that could significantly reduce the threat of introduction of nonnative species are suggested.
Indirect effects of invasive species removal devastate World Heritage Island
23 November 2010
Stellenbosch University

Bergstrom, D.M.;Lucieer, A.;Kiefer, K.;Wasley, J.;Belbin, L.;Pedersen, T.K.;Chown, S.L.

1. Owing to the detrimental impacts of invasive alien species, their control is often a priority for conservation management. Whereas the potential for unforeseen consequences of management is recognized, their associated complexity and costs are less widely appreciated. 2. We demonstrate that theoretically plausible trophic cascades associated with invasive species removal not only take place in reality, but can also result in rapid and drastic landscape-wide changes to ecosystems. 3. Using a combination of population data from of an invasive herbivore, plot-scale vegetation analyses, and satellite imagery, we show how a management intervention to eradicate a mesopredator has inadvertently and rapidly precipitated landscape-wide change on sub-Antarctic Macquarie Island. This happened despite the eradication being positioned within an integrated pest management framework. Following eradication of cats Felis catus in 2001, rabbit Oryctolagus cuniculus numbers increased substantially although a control action was in place (Myxoma virus), resulting in island-wideecosystem effects. 4.Synthesis and applications. Our results highlight an important lesson for conservation agencies working to eradicate invasive species globally; that is, risk assessment of management interventions must explicitly consider and plan for their indirect effects, or face substantial subsequent costs. On Macquarie Island, the cost of further conservation action will exceed AU$24 million.
Oxygen limitation and thermal tolerance in two terrestrial arthropod species
16 May 2011
Stellenbosch University

Stevens, M.M.;Jackson, S.;Bester, S.A.;Terblanche, J.S.;Chown, S.L.

Recent studies of marine invertebrates and fish have suggested that lower and upper critical temperatures (CTmin and CTmax) are coupled by a common mechanism: oxygen and capacity limitation of thermal tolerance (OCLT). Using thermolimit respirometry, we tested the predictions of this theory for terrestrial arthropods by measuring maxima and minima for both critical temperatures and metabolic rate in two arthropods, the isopod Porcellio scaber and the beetle Tenebrio molitor, at 40%, 21%, 10% and 2.5% ambient O2. Critical temperatures were identified as particular points on both activity and CO2 traces in four ways. In the first two instances, we identified the inflection points in regressions of absolute difference sum (ADS) residuals calculated for activity (aADS) and CO2 (VI), respectively. In the third, we visually identified the lowest point before the post-mortal peak in CO2 release (PMV). Finally, we pinpointed the sudden drop in CO2 at death, where CO2 fell outside the 95% confidence intervals of the 5 min period immediately preceding the drop-off (CI). Minimum and maximum metabolic rates were determined using CO2 traces, and the temperatures corresponding to these identified as TMetMin and TMetMax. For both species, ambient oxygen concentration did not influence CTmin, minimum metabolic rate, or TMetMin. By contrast, severe hypoxia (2.5% O2) caused a 6.9°C decline in activity-based CTmax for T. molitor and a 10.6°C decline for P. scaber, relative to normoxia (21% O2). The magnitude of this decrease differed between methods used to estimated critical thermal limits, highlighting the need for a standard method to determine these endpoints during thermolimit respirometry. Maximum metabolic rate also declined with decreasing ambient oxygen in both species. The combination of increasing metabolic rate and oxygen limitation affected upper thermal limits in these arthropods only in severe hypoxia (2.5% O2). In both species, CTmin and CTmax responded differently to oxygen limitation, suggesting that this is not a common mechanism coupling upper and lower limits in terrestrial arthropods.
Body size variation in insects: a macroecological perspective
16 May 2011
Stellenbosch University

Chown, S.L.;Gaston, K.J.

Body size is a key feature of organisms and varies continuously because of the effects of natural selection on the size-dependency of resource acquisition and mortality rates. This review provides a critical and synthetic overview of body size variation in insects from a predominantly macroecological (large-scale temporal and spatial) perspective. Because of the importance of understanding the proximate determinants of adult size, it commences with a brief summary of the physiological mechanisms underlying adult body size and its variation, based mostly on findings for the model species Drosophila melanogaster and Manduca sexta. Variation in nutrition and temperature have variable effects on critical weight, the interval to cessation of growth (or terminal growth period) and growth rates, so influencing final adult size. Ontogenetic and phylogenetic variation in size, compensatory growth, scaling at the intra- and interspecific levels, sexual size dimorphism, and body size optimisation are then reviewed in light of their influences on individual and species body size frequency distributions. Explicit attention is given to evolutionary trends, including gigantism, Cope’s rule and the rates at which size change has taken place, and to temporal ecological trends such as variation in size with succession and size-selectivity during the invasion process. Large-scale spatial variation in size at the intraspecific, interspecific and assemblage levels is considered, with special attention being given to the mechanisms proposed to underlie clinal variation in adult body size. Finally, areas particularly in need of additional research are identified.
Metabolic rate, genetic and microclimate variation among springtail populations from sub-Antarctic Marion Island
16 May 2011
Stellenbosch University

McGaughran, A.;Convey, P.;Stevens, M.I.;Chown, S.L.

Measurement of metabolic rates (made at 10°C) of individuals of the springtail Cryptopygus antarcticus travei from six geographically distinct populations on sub-Antarctic Marion Island were combined with mitochondrial DNA (COI) haplotype analysis to examine in parallel both physiological and genetic variation of distinct populations. We found evidence of genetic diVerentiation among populations and a general indication of long-term isolation with limited gene Xow. While we found support for an overall pattern of metabolic rate structure among populations from diVerent geographic locations on the island (mean rate = 0.0009–0.0029μl O2 μg-1 h-1 for populations of a mean individual mass of 8–26 μg), we were unable to demonstrate a coherent common pattern between this and genetic variation. However, spatial structure in metabolic rate variation was strongly related to the extent of variability in microclimate among sites, and also showed some indication of a phylogeographic signal. Thus, over the relatively short timescale of Marion Island’s history (<1 million years), the periodic geographic barriers that have driven population diVerentiation from a molecular perspective may also have resulted in some physiological diVerentiation of populations.
Measuring the effectiveness of regional conservation assessments at representing biodiversity surrogates at a local scale: A case study in Réunion Island (Indian Ocean)
16 May 2011
Stellenbosch University

Payet, K.;Rouget, M.;LaGabrielle, E.;Esler, K. J.

In a context of scarce financial and human resources, the allocation of conservation efforts needs to be optimized. Our analysis attempts to draw conclusions on the integration of regional and local conservation assessments, specifically, with regard to the acquisition of fine-scale data to complement the regional assessment. This study undertaken in Réunion Island (Indian Ocean) assessed how biodiversity surrogates targeted at a regional scale represented other biodiversity surrogates at a local scale. Biodiversity surrogates at both scales consisted of species, habitats and processes. Habitats and processes at regional scale were defined using a coarser scale of thematic resolution than at local scale.The surrogacy was tested in terms of incidental representation of local-scale features in the regional assessments, and correlation of irreplaceability values between scales. Near-minimum sets and irreplaceability values were generated using MARXAN software. Our results revealed that conservation targets for processes at local scale were never met incidentally, while threatened species and fragmented habitats were also usually under-represented. More specifically, requiring only 12% of the local planning domain, the application of species as surrogates at regional scale was the least effective option at representing biodiversity features at local scale. In contrast, habitats at a coarse scale of thematic resolution achieved a significant proportion of conservation targets incidentally (67%) and their irreplaceability values were well correlated with the irreplaceability values of surrogates at local scale. The results highlighted that all three types of biodiversity surrogates are complementary for assessing overall biodiversity. Because of the cost of data acquisition, we recommended that the most efficient strategy to develop nested regional/local conservation plans is to apply habitats and processes at a coarse scale of thematic resolution at regional scale, and threatened species and degraded habitats at local scale, with their fine-scale mapping limited to highly transformed areas.
The history and status of oyster exploitation and culture in South Africa
23 May 2011
Stellenbosch University

Haupt, T.M.;Griffiths, C.L.;Robinson, T.B.;Tonin, A.F.G.;De Bruyn, P.A.

Both wild and cultivated oysters are consumed in South Africa. Edible wild oysters include Striostrea margaritacea, Saccostrea cucullata, Ostrea atherstonei, and O. algoensis, all of which occur along the south and east coasts, but not on the west coast. Wild oysters are exploited commercially, recrcationally, and by subsistence fishers, with S. margaritacea being by far the most intensively targeted species. Commercial harvesting of S. margaritacea takes place along the southern Cape coast and in KwaZulu-Natal (KZN), with the southern Cape hosting 102 of the 145 commercial pickers. Data on total annual commercial catch of oysters in the various harvesting areas are presented, but these are minimum estimates, because collectors do not always comply with harvesting regulations or fully report catches. Subsistence harvesting remains largely unmanagcd, except in KZN, and is particularly prevalent in the eastern Cape Province. The culture of oysters is dependent on imported Crassostrea gigas spat, mostly from Chile. Accurate annual oyster production statistics arc only available since 1985, although approximately 2 million C. gigas oysters are known to have been cultured annually throughout the 1970s and early '80s. Since then, production increased steadily from 1985 to 1991, peaking at some 8 million individuals, then declined to 2–4 million individuals from the mid 1990s onward. Although the market for oysters has grown, production has not kept up with demand, largely because of a lack of suitable locations for oyster culture. Finding suitable sites for cultivation along the northern Cape Province coast and establishing local oyster hatcheries for C. gigas are suggested as future priorities for the industry.
Freshwater fish introductions in mediterranean-climate regions: are there commonalities in the conservation problem?
23 May 2011
Stellenbosch University

Marr, S.M.;Marchetti, M.P.;Olden, J.D.;García-Berthou, E.;Morgan, D.L.;Arismendi, I.;Day, J.A.;Griffiths, C.L.;Skelton, P.H.

Aim To compare patterns and drivers of freshwater fish introductions across five climatically similar regions and evaluate similarities and differences in the nonnative species introduced. Location Five mediterranean-climate regions: California (USA), central Chile, south-western Australia, the Iberian peninsula (Spain and Portugal) and the south-western Cape (South Africa). Methods Species presence–absence for native and non-native fishes were collated across the regions, and patterns of faunal change were examined using univariate and multivariate statistical approaches. Taxonomic patterns in freshwater fish introductions were evaluated by comparing the number of species introduced by order to the numbers expected from binomial probabilities. Factors influencing multiple introductions of freshwater fish species in mediterranean regions were determined using generalized linear modelling. Results High levels of endemism (70–90%) were revealed for south-western Cape, south-western Australia and Chile. Despite their high rates of endemism, all regions currently have more non-native species than endemic species. Taxonomic selection was found for five orders, although this was only significant for Salmoniformes across regions. The average increase in regional compositional similarity of fish faunas resulting from non-native fish introductions was 8.0%. Important factors predicting multiple introductions of a species include previous introduction success and mean latitude of its distribution Main conclusions The mediterranean-climate regions of the world, separated by vast distances, originally had a few fish species in common but are now more similar, owing to species introductions, illustrating the extent and importance of taxonomic homogenization. Introductions are largely driven by taxonomically biased human interests in recreational fisheries, aquaculture and ornamental pet species.
Larval settlement behaviour in six gregarious ascidians in relation to adult distribution
23 May 2011
Stellenbosch University

Rius, M.;Branch, G.M.;Griffiths, C.L.;Turon, X.

Settlement influences the distribution and abundance of many marine organisms, although the relative roles of abiotic and biotic factors influencing settlement are poorly understood. Species that aggregate often owe this characteristic to larval behaviour, and we investigated whether this predisposes ascidians to becoming invasive, by increasing their capacity to maintain their populations. We explored the interactive effects of larval phototaxis and geotaxis and conspecific adult extracts on settlement rates of a representative suite of 6 species of ascidians that form aggregations in the field, including 4 aliens with global distributions, and how they relate to adult habitat characteristics. In the laboratory, the larvae were (1) held in light or dark, (2) offered the choice of settling in the light or dark, or (3) held in the presence or absence of adult extract. When confined in either light or dark conditions, all species settled equally in dark and light. Four showed strong geotaxis, 3 settling preferentially on the bottom of experimental chambers, and one on the top. Offered a choice between dark and light, 2 species settled preferentially in the dark with no geotactic preferences and another 2 showed an interaction between light and geotaxis. For 4 of the species, the responses of settlers accorded with, and may contribute to, adult orientation patterns in the field. Adult extracts inhibited settlement of 3 species and failed to influence settlement of the other 3, arguing against conspecific attraction being a cause of aggregation and an explanation of the propensity of ascidians to become invasive.
Marine biodiversity in South Africa: An evaluation of current states of knowledge
23 May 2011
Stellenbosch University

Griffiths, C.L.;Robinson, T.B.;Lange, L.;Mead, A.

Continental South Africa has a coastline of some 3,650 km and an Exclusive Economic Zone (EEZ) of just over 1 million km2. Waters in the EEZ extend to a depth of 5,700 m, with more than 65% deeper than 2,000 m. Despite its status as a developing nation, South Africa has a relatively strong history of marine taxonomic research and maintains comprehensive and wellcurated museum collections totaling over 291,000 records. Over 3 million locality records from more than 23,000 species have been lodged in the regional AfrOBIS (African Ocean Biogeographic Information System) data center (which stores data from a wider African region). A large number of regional guides to the marine fauna and flora are also available and are listed. The currently recorded marine biota of South Africa numbers at least 12,914 species, although many taxa, particularly those of small body size, remain poorly documented. The coastal zone is relatively well sampled with some 2,500 samples of benthic invertebrate communities have been taken by grab, dredge, or trawl. Almost none of these samples, however, were collected after 1980, and over 99% of existing samples are from depths shallower than 1,000 m—indeed 83% are from less than 100 m. The abyssal zone thus remains almost completely unexplored. South Africa has a fairly large industrial fishing industry, of which the largest fisheries are the pelagic (pilchard and anchovy) and demersal (hake) sectors, both focused on the west and south coasts. The east coast has fewer, smaller commercial fisheries, but a high coastal population density, resulting in intense exploitation of inshore resources by recreational and subsistence fishers, and this has resulted in the overexploitation of many coastal fish and invertebrate stocks. South Africa has a small aquaculture industry rearing mussels, oysters, prawns, and abalone—the latter two in land-based facilities. Compared with many other developing countries, South Africa has a well-conserved coastline, 23% of which is under formal protection, however deeper waters are almost entirely excluded from conservation areas. Marine pollution is confined mainly to the densely populated KwaZulu-Natal coast and the urban centers of Cape Town and Port Elizabeth. Over 120 introduced or cryptogenic marine species have been recorded, but most of these are confined to the few harbors and sheltered sites along the coast.
Oysters as vectors of marine aliens, with notes on four introduced species associated with oyster farming in South Africa
23 May 2011
Stellenbosch University

Haupt, T.M.;Griffiths, C.L.;Robinson, T.B.;Tonin, A.F.G.

Translocated oysters are well known to act as vectors of marine alien species, but to date this topic has received scant attention in South Africa, despite the fact that oysters have been imported into this region since 1894. Surveys of oyster farms in South Africa revealed four newly-recorded alien species: the black sea urchin, Tetrapygus niger, from Chile; the European flat oyster, Ostrea edulis (thought to be extinct since its intentional introduction in 1946); Montagu's crab, Xantho incisus, from the North Eastern Atlantic seas of Europe, and the brachiopod Discinisca tenuis from Namibia. Oyster imports are the most likely vector of all these species. The biological attributes of each species, the possible threats posed by their introduction, and the needs for additional control measures to limit or prevent further introduction and spread of alien species via oyster culture are discussed.
Semi-submersible rigs: a vector transporting entire marine communities around the world
23 May 2011
Stellenbosch University

Wanless, R. M.;Scott, S.;Sauer, W.H.H.;Andrew, T.G.;Glass, J.P.;Godfrey, B.;Griffiths, C.L.;Yeld, E.

A virtually intact subtropical reef community (14 phyla, 40 families and 62 non-native taxa) was associated with a rig under tow from Brazil that became stranded on the remote island of Tristan da Cunha. This exposes rigs as a significant vector spreading alien marine organisms, and includes the first records of free-swimming marine finfish populations becoming established after unintentional movement. With relatively trivial effort, a pre-tow clean would have obviated the need to salvage and dispose of the rig (undertaken largely to address concerns about invasive species), at a cost of ~US$20 million. Our findings show that towing biofouled structures across biogeographic boundaries present unexcelled opportunities for invasion to a wide diversity of marine species. Better control and management of this vector is required urgently. Simultaneous, unintentional introductions of viable populations of multiple marine organisms are rare events, and we develop a basic framework for rapid assessment of invasion risks.
Western Zambian sable: Are they a geographic extension of the giant sable antelope?
31 May 2011
Stellenbosch University

Jansen van Vuuren, B.;Robinson, T.J.;VazPinto, P.;Estes, R.;Matthee, C.A.

The giant sable {Hippotragus niger variant) is one of Africa's most spectacular large antelope. Years of civil unrest in Angola, a highly localized distribution and interbreeding with its congener the roan antelope (H. equinus)has led to this subspecies being considered as critically endangered. Sable antelope occurring -600 km to the east in western Zambia superficially resemble giant sable in phenotype, prompting speculation in the popular media that the distribution of giant sable may be larger than currently documented. Our aim here was to investigate the evolutionary placement of western Zambian sable using mitochondrial DNA control region data. Phylogenetic analyses (maximum likelihood and Bayesian analyses) supported the monophyly of H. n. varían/(Bayesian posterior probability of >0.95,bootstrap support >80%) and nested the western Zambian sable within H. n. niger. This finding was supported by an analysis of molecular variance that discretely grouped western Zambian sable from giant sable (φST = 0.645, P= 0.001 ). Significant genetic structure was also found across the range of H. n. niger as indicated by our phylogenetic analyses and analysis of molecular variance (φST = 0.418, P = 0.001). We conclude that although the western Zambian sable antelope and those of H. n. variani resemble one another in morphology, particularly with respect to facial markings, significant genetic differences underpin these two evolutionary lineages. Our findings hold implications for the conservation of sable and highlight the need for active management intervention.
House mouse colonization patterns on the sub-Antarctic Kerguelen Archipelago suggest singular primary invasions and resilience against re-invasion
31 May 2011
Stellenbosch University

Hardouin, E.A.;Chapuis, J.-L.;Stevens, M.I.;Jansen van Vuuren, B.;Quillfeldt, P.;Scavetta, R.J.;Teschke, M.;Tautz, D.

Background: Starting from Western Europe, the house mouse (Mus musculus domesticus) has spread across the globe in historic times. However, most oceanic islands were colonized by mice only within the past 300 years. This makes them an excellent model for studying the evolutionary processes during early stages of new colonization. We have focused here on the Kerguelen Archipelago, located within the sub-Antarctic area and compare the patterns with samples from other Southern Ocean islands. Results: We have typed 18 autosomal and six Y-chromosomal microsatellite loci and obtained mitochondrial D-loop sequences for a total of 534 samples, mainly from the Kerguelen Archipelago, but also from the Falkland Islands, Marion Island, Amsterdam Island, Antipodes Island, Macquarie Island, Auckland Islands and one sample from South Georgia. We find that most of the mice on the Kerguelen Archipelago have the same mitochondrial haplotype and all share the same major Y-chromosomal haplotype. Two small islands (Cochons Island and Cimetière Island) within the archipelago show a different mitochondrial haplotype, are genetically distinct for autosomal loci, but share the major Y-chromosomal haplotype. In the mitochondrial D-loop sequences, we find several single step mutational derivatives of one of the major mitochondrial haplotypes, suggesting an unusually high mutation rate, or the occurrence of selective sweeps in mitochondria. Conclusions: Although there was heavy ship traffic for over a hundred years to the Kerguelen Archipelago, it appears that the mice that have arrived first have colonized the main island (Grande Terre) and most of the associated small islands. The second invasion that we see in our data has occurred on islands that are detached from Grande Terre and were likely to have had no resident mice prior to their arrival. The genetic data suggest that the mice of both primary invasions originated from related source populations. Our data suggest that an area colonized by mice is refractory to further introgression, possibly due to fast adaptations of the resident mice to local conditions.
Alien invaders and reptile traders: what drives the live animal trade in South Africa?
01 June 2011
Stellenbosch University

van Wilgen, N.J.;Wilson, J.R.U.;Elith, J.;Wintle, B.A.;Richardson, D.M.

The global trade in reptiles for pets has grown rapidly in recent decades. Some species introduced by the pet trade have established and become invasive, for example the Burmese python in Florida. Although there are currently no invasive alien reptiles in South Africa, the last 30 years has seen an exponential increase in the number of introductions of an increasing number of species from an increasing number of countries. We determine and analyse the presence and abundance of species in the South African reptile trade. This serves as a background to efforts to overhaul the management and regulation of this trade, particularly given the need for increasingly objective risk-assessment protocols. We show that introduced species tend to come from specific families including Boidae, Chameleonidae, Elapidae, Pythonidae, Testudinidae and Viperidae. Moreover, within specific families (e.g. chameleons), species of larger body size are more likely to be introduced. As the risk of a species becoming invasive may be increased by higher propagule pressure, it is also important to characterize the volume of trade.Here we analyse data on the abundance of reptiles in South Africa using generalized, additive models and show that venomous and expensive species are traded in low numbers, whereas species that are easy to breed and handle or are large, colourful or patterned are preferred. These human imposed preferences have the potential to cause significant taxonomic changes to the reptile fauna of South Africa, which still largely reflects natural biogeographic and evolutionary processes. Elucidation of import and trade patterns enables us to estimate the probable propagule pressure of any particular species. Because the dispersal pathway defined by trade influences the likelihood of invasion, this information is important for informing policy development and directing management efforts.
Parasite-specific variation and the extent of male-biased parasitism; an example with a South African rodent and ectoparasitic arthropods
01 June 2011
Stellenbosch University

Matthee, S.;McGeoch, M.A.;Krasnov, B.R.

We asked whether the occurrence and the extent of host gender-biased parasitism vary among higher parasite taxa, among individual species within these taxa and within parasite species among localities. To answer this question, we studied prevalence, abundance, species richness and the level of aggregation of ectoparasites (ticks, mites, lice and fleas) collected from male and female striped mice (Rhabdomys pumilio) in 9 localities of the Western Cape Province of South Africa. We used meta-analyses to compare parasitological variables between male and female hosts across localities for individual parasite species and higher taxa as well as across parasite species within a higher taxon. Whenever gender-biased parasitism was found, it indicated higher infestation of male than female hosts (except 1 low abundant mite species). We found that the occurrence and extent of gender-biased infestation varied mainly within a parasite species among localities and among parasite species within a higher taxon but not among parasite taxa. Our results suggest that the extent of a gender-biased pattern of parasite infestation of the same host may not only involve host-related mechanisms but also depends on biological features of a particular parasite species.
The effect of predation on the prevalence and aggregation of pathogens in prey
03 October 2011
Stellenbosch University

Su, M.;Hui, C.

Although pathogens and predators have been widely used as bio-control agents against problematic prey species, little has been done to examine the prevalence and aggregation of pathogens in spatially structured eco-epidemiological systems. Here, we present a spatial model of a predator–prey/host–parasite system based on pair approximation and spatially stochastic simulations, with the predation pressure indicated by predator abundance and predation rates. Susceptible prey can not only be infected by contacting adjacent infected individuals but also by the global transmission of pathogens. The disease prevalence was found to follow a hump-shaped function in response to predation pressure. Moreover, predation pressure was not always negatively correlated with pathogen aggregation as proposed from empirical studies, but depending on the level of predation pressure. Highly connected site network facilitated the parasites infection, especially under high predation pressure. However, the connectivity of site network had no effect on the prevalence and aggregation of pathogens that can infect health prey through global transmission. It is thus possible to better design biological control strategies for target species by manipulating predation pressure and the range of pathogen transmission.
Effects of density-dependent dispersal behaviours on the speed and spatial patterns of range expansion in predator-prey metapopulations
03 October 2011
Stellenbosch University

Ramanantoanina, A;Hui, C;Ouhinou, A

Dispersal can strongly affect the spatiotemporal dynamics of a species (its spread, spatial distribution and persistence). We investigated how two dispersal behaviours, namely prey evasion (PE) and predator pursuit (PP), affect the dynamics of a predator–prey system. PE portrays the tendency of prey avoiding predators by dispersing into adjacent patches with fewer predators, while PP describes the tendency of predators to pursue the prey by moving into patches with more prey. Based on the Beddington predation model, a spatially explicit metapopulation model was built to incorporate PE and PP. Numerical simulations were run to investigate the effects of PE and PP on the rate of spread, spatial synchrony and the persistence of populations. Results show that both PE and PP can alter spatial synchrony although PP has a weaker desynchronising effect than PE. The predator–prey system without PE and PP expanded in circular waves. The effect of PE can push the prey to distribute in a circular ring front, whereas the effect of PP can change the circular waves to anisotropic expansion. Furthermore, weak PE and PP can accelerate the spread of prey while strong and disproportionate intensities slow down the range expansion. The effects of PE and PP further enhance the population size, break down the spatial synchrony and promote the persistence of populations.
Cryptic species, biogeographic complexity and the evolutionary history of the Ectemnorhinus group in the sub-Antarctic, including a description of Bothrometopus huntleyi, n. sp.
24 November 2011
Stellenbosch University

Grobler, G.C.;Bastos, A.D.S.;Treasure, A.M.;Chown, S.L.

The biogeography of the South Indian Ocean Province (SIP) biotas has long been controversial. Much of the discussion has been based on interpretation of species distributions, based on morphological or anatomical delimitations. However, molecular phylogenetic approaches elsewhere have recently shown that interpretations based solely on morphological data may be misleading. Nonetheless, few studies have employed molecular phylogenetic approaches to understand the biogeography of the SIP biotas. We do so here for the Ectemnorhinus group of genera, a monophyletic unit of weevils endemic to the region. We use mitochondrial cytochrome oxidase I DNA sequence data to reconstruct relationships among 13 species and 22 populations in the genera Palirhoeus, Bothrometopus and Ectemnorhinus. On the basis of this analysis we find little support for separating the genus Palirhoeus from Bothrometopus, and little support for the morphologically-based species groups currently recognized within Bothrometopus. Using a molecular clock we show that dispersal among islands probably took place against the prevailing wind direction. These data also support a previous hypothesis of radiation of the epilithic genera Bothrometopus and Palirhoeus during the Pliocene/early Pleistocene, but reject the hypothesis that the genus Ectemnorhinus radiated following the last glacial maximum. We show that Bothrometopus parvulus (C.O. Waterhouse) on the Prince Edward Islands comprises two species that are not sister taxa.We name the second species Bothrometopus huntleyi n. sp. and provide a description thereof.
Non-indigenous microorganisms in the Antarctic: assessing the risks
24 November 2011
Stellenbosch University

Cowan, D.A.;Chown, S.L.;Convey, P.;Tuffin, M.;Hughes, K.;Pointing, S.;Vincent, W.F.

The Antarctic continent is frequently cited as the last pristine continent on Earth. However, this view is misleading for several reasons. First, there has been a rapid increase in visitors to Antarctica, with large increases at research bases and their environs and to sites of major tourist interest (e.g. historical sites and concentrations of megafauna). Second, although substantial efforts are made to avoid physical disturbance and contamination by chemical, human and other wastes at these sites, little has been done to prevent the introduction of non-indigenous microorganisms. Here, we analyse the extent and significance of anthropogenic introduction of microbial ‘contaminants’ to the Antarctic continent. We conclude that such processes are unlikely to have any immediate gross impact on microbiological community structure or function, but that increased efforts are required to protect the unique ecosystems of Antarctica from microbial and genetic contamination and homogenisation.
Spatial scale and species identity influence the indigenous–alien diversity relationship in springtails
24 November 2011
Stellenbosch University

Terauds, A.;Chown, S.L.;Berstrom, D.M.

Although theory underlying the invasion paradox, or the change in the relationship between the richness of alien and indigenous species from negative to positive with increasing spatial scale, is well developed and much empirical work on the subject has been undertaken, most of the latter has concerned plants and to a lesser extent marine invertebrates. Here we therefore examine the extent to which the relationships between indigenous and alien species richness change from the local metacommunity to the interaction neighborhood scales, and the influences of abundance, species identity, and environmental favorability thereon, in springtails, a significant component of the soil fauna. Using a suite of modeling techniques, including generalized least squares and geographically weighted regressions to account for spatial autocorrelation or nonstationarity of the data, we show that the abundance and species richness of both indigenous and alien species at the metacommunity scale respond strongly to declining environmental favorability, represented here by altitude. Consequently, alien and indigenous diversity covary positively at this scale. By contrast, relationships are more complex at the interaction neighborhood scale, with the relationship among alien species richness and/or density and the density of indigenous species varying between habitats, being negative in some, but positive in others. Additional analyses demonstrated a strong influence of species identity, with negative relationships identified at the interaction neighborhood scale involving alien hypogastrurid springtails, a group known from elsewhere to have negative effects on indigenous species in areas where they have been introduced. By contrast, diversity relationships were positive with the other alien species. These results are consistent with both theory and previous empirical findings for other taxa, that interactions among indigenous and alien species change substantially with spatial scale and that environmental favorability may play a key role in explaining the larger scale patterns. However, they also suggest that the interactions may be affected by the identity of the species concerned, especially at the interaction neighborhood scale.
Revealing the scale of marine bioinvasions in developing regions: a South African re-assessment
12 December 2011
Stellenbosch University

Mead, A.;Carlton, J.T.;Griffiths, C.L.;Rius, M.

As recently as 2009 the number of introductions recorded for South Africa comprised 22 marine and estuarine species. This review aims to reassess the diversity and scale of introduced marine and estuarine species in the region. Accurate taxonomic and systematic work, broad review of historical records and new sampling surveys across selected marine habitats conducted by a team of local and international experts has effectively revealed the presence of previously misidentified, overlooked, or new introductions. A total of 86 introduced and 39 cryptogenic species are recognized, increasing known numbers four and twofold respectively within 1 year, although the current assessment is far from fully comprehensive. Additional species were revealed within the historic literature (76%), from surveys conducted post-2005 (11%) and following taxonomic resolution (13%). Temporal analyses confirmed discovery rates were increasing over time. Ship fouling and ballast water were the dominant vector pathways, accounting for 48 and 38% respectively. Spatial analyses revealed patterns of bioinvasion to be significantly higher on the west coast compared to the other coastal regions. Overall, 53% of introductions were concentrated within harbour areas with only 4 opencoast invaders detected at present. Introduced species found in the cool and warm-temperate provinces of the west and south coast mainly originated from the northern hemisphere (65%). In contrast, introductions located in the sub-tropical and tropical provinces of the east coast mainly originated from the southern hemisphere (18%), with the remaining 17% of introduced species being of unknown origin. The research approach described has proven pivotal, contributing massively toward revealing the true scale and patterns of bioinvasion for a developing region within a relatively short period of time.
Introduced and cryptogenic marine and estuarine species of South Africa
12 December 2011
Stellenbosch University

Mead, A.;Carlton, J.T.;Griffiths, C.L.;Rius, M.

The introduction history, systematics, transport vectors and distribution patterns of 85 introduced and 39 cryptogenic marine or estuarine animals and plants of South Africa are presented. This represents an addition of 93 species compared with previous lists. Taxa covered include protists, dinoflagellates, sponges, cnidarians, annelids, crustaceans, pycnogonids, insects, molluscs, brachiopods, bryozoans, echinoderms, ascidians, fish, algae and higher plants. For each species a justification motivating its inclusion as an introduction into South African shores or its cryptogenic status, is provided. Challenges associated with this type of inventory work are explored and major patterns of bioinvasion within the region are summarized briefly.
“Nested” cryptic diversity in a widespread marine ecosystem engineer: a challenge for detecting biological invasions
12 December 2011
Stellenbosch University

Teske, P.R.;Rius, M.;McQuaid, C.D.;Styan, C.A.;Piggott, M.P.;Benhissoune, S.;Fuentes-Grünewald, C.;Walls, K.;Page, M.;Attard, C.R.M.;Cooke, G.M.;McClusky, C.F.;Banks, S.C.;Baker, N.P.;Beheregaray, L.B.

Background: Ecosystem engineers facilitate habitat formation and enhance biodiversity, but when they become invasive, they present a critical threat to native communities because they can drastically alter the receiving habitat. Management of such species thus needs to be a priority, but the poorly resolved taxonomy of many ecosystem engineers represents a major obstacle to correctly identifying them as being either native or introduced. We address this dilemma by studying the sea squirt Pyura stolonifera, an important ecosystem engineer that dominates coastal communities particularly in the southern hemisphere. Using DNA sequence data from four independently evolving loci, we aimed to determine levels of cryptic diversity, the invasive or native status of each regional population, and the most appropriate sampling design for identifying the geographic ranges of each evolutionary unit. Results: Extensive sampling in Africa, Australasia and South America revealed the existence of “nested” levels of cryptic diversity, in which at least five distinct species can be further subdivided into smaller-scale genetic lineages. The ranges of several evolutionary units are limited by well-documented biogeographic disjunctions. Evidence for both cryptic native diversity and the existence of invasive populations allows us to considerably refine our view of the native versus introduced status of the evolutionary units within Pyura stolonifera in the different coastal communities they dominate. Conclusions: This study illustrates the degree of taxonomic complexity that can exist within widespread species for which there is little taxonomic expertise, and it highlights the challenges involved in distinguishing between indigenous and introduced populations. The fact that multiple genetic lineages can be native to a single geographic region indicates that it is imperative to obtain samples from as many different habitat types and biotic zones as possible when attempting to identify the source region of a putative invader. “Nested” cryptic diversity, and the difficulties in correctly identifying invasive species that arise from it, represent a major challenge for managing biodiversity.
A revision of the Pyura stolonifera species complex (Tunicata, Ascidiacea), with a description of a new species from Australia
12 December 2011
Stellenbosch University

Rius, M.;Teske, P.R.

Pyura stolonifera is a large solitary ascidian found in Africa, Australasia and South America. The taxonomic status of different populations of this species is disputed, especially since there is evidence for several distinct morphological and genetic units that point towards the existence of multiple cryptic species. While some researchers still recognize P. stolonifera as a single species, others treat the different populations as distinct species. Here, we present a revision of the P. stolonifera species complex based on the examination of samples from all regions where there are reliable reports of this taxon. We recognize four species that are both morphologically and genetically distinct, one of which is new to science and is formally described here. This species is morphologically distinct from the other three members of the species complex in terms of the colour and texture of the tunic, the arrangement of the gonads within the gut and the shape of the dorsal tubercle, among other characters. We name the new species Pyura dalbyi after Dr. J.E. Dalby Jr., whose research on its ecology and distribution provided the incentive for examining this species more closely.
Revalidation of Hepsetus cuvieri (Castelnau, 1861) (Characiformes: Hepsetidae) from the Quanza, Zambezi and southern part of the Congo ichthyofaunal provinces
13 December 2011
Stellenbosch University

Zengeya, T.A.;Decru, E.;Vreven, E.

Hepsetus cuvieri (Castelnau, 1861), originally described from “lac N’gami” (Botswana) and synonymized with H. odoe (Bloch, 1794) by Roberts (1984), is revalidated. Hepsetus cuvieri can be readily distinguished from H. odoe based on a lower total number of gill rakers (8–13 versus 14–21); a generally higher number of scales between the dorsal fin and the lateral line (101/2–111/2 versus 71/2–101/2) and a higher number of scales between the adipose fin and the lateral line (61/2–71/2 versus 41/2–61/2) and other characters. A neotype is designated, as the holotype of this nominal species is apparently lost. Hepsetus cuvieri is restricted to the Quanza, Zambezi ichthyofaunal provinces and the southern part of the Congo Basin, i.e. the Congo ichthyofaunal province.
Eco-Evolutionary Feedback and the Invasion of Cooperation in Prisoner’s Dilemma Games
23 January 2012
Stellenbosch University

Zhang, Feng;Hui, Cang

Unveiling the origin and forms of cooperation in nature poses profound challenges in evolutionary ecology. The prisoner’s dilemma game is an important metaphor for studying the evolution of cooperation. We here classified potential mechanisms for cooperation evolution into schemes of frequency- and density-dependent selection, and focused on the density-dependent selection in the ecological prisoner’s dilemma games. We found that, although assortative encounter is still the necessary condition in ecological games for cooperation evolution, a harsh environment, indicated by a high mortality, can foster the invasion of cooperation. The Hamilton rule provides a fundamental condition for the evolution of cooperation by ensuring an enhanced relatedness between players in low-density populations. Incorporating ecological dynamics into evolutionary games opens up a much wider window for the evolution of cooperation, and exhibits a variety of complex behaviors of dynamics, such as limit and heteroclinic cycles. An alternative evolutionary, or rather succession, sequence was proposed that cooperation first appears in harsh environments, followed by the invasion of defection, which leads to a common catastrophe. The rise of cooperation (and altruism), thus, could be much easier in the density-dependent ecological games than in the classic frequency-dependent evolutionary games.
RS & GIS-based Spatialtemporal Analysis of Ecological Footprint and Biocapacity Pattern of Jinghe River Watershed in China: Does Supply Meet Demand?
23 January 2012
Stellenbosch University

Yue, Dongxia;Ma, Jinhui;Guo, Jianjun;Zhang, Jiajing;Du, Jun;Song, Yajie;Hui, Cang

The Ecological Footprint methodology is a framework that tracks Ecological Footprint (humanity’s demands on the biosphere) by comparing human demand against the regenerative capacity (Biocapacity) of the planet (WWF, 2010) to advance the science of sustainability. As such, the spatiotemporal dynamics of the Ecological Footprint (EF) and Biocapacity (BC) in a given watershed are important topics in the field of sustainability research based on remote sensing (RS) data and geographic information system (GIS) techniques．This paper reports on a case study of the Jinghe River Watershed using improved EF methodology with the help of GIS and high resolution remote sensing data, to quantitatively estimate the relationship between EF demand and BC supply and analyze their spatial distribution patterns at multiple spatial scales for four periods (1986, 1995, 2000 and 2008). We predict the future BC both overall, and of six categories of biological productivity area for the next four decades using the Markov Chain Method．The results showed that the spatial distribution of EF demand and BC supply were significantly uneven in the region, in which the per-capita EF of all counties located in the watershed increased continually from 1986 to 2008, and the EF per person of counties in the middle and lower reaches area was markedly greater than that in the upper reaches over time. On the supply side, the per-capita BC of all counties decreased gradually from 1986 to 2008, and the per-capita BC of counties in the upper reaches area was greater than that in the middle and lower reaches during the period, causing the uneven spatial distribution of Ecological budget-the gap between supply and demand, showed that the Jinghe River Watershed on the whole has begun to be unsustainable since 2008, with each county exhibiting differential temporal patterns. The prediction results showed that the total BC will increase continually from 2020 to 2050, and the BC of six categories will reduce, indicating that unsustainability in the region will escalate. As a whole, The EF demand has exceeded the BC supply, and the gap was widening in the Jinghe Watershed. This paper provided an in-depth portrait of the spatiotemporal dynamics of EF and BC, as well as their interactions with humanity and ecosystems.
Alien species in South Africa's national parks
01 February 2012
Stellenbosch University

Spear, D.;McGeoch, M.A.;Foxcroft, L.C.;Bezuidenhout, H.

Invasive alien species (IAS) are one of the major threats to biodiversity in protected areas, and pose a significant management challenge (e.g. Pyšek et al. 2002, Allen, Brown & Stohlgren 2009). One of the first steps towards managing IAS in protected areas is establishing which alien species are present, followed by on-going surveillance and prevention efforts to combat new introductions (Foxcroft et al. 2009). Information on the identity of alien species is also needed to conduct risk assessments to prioritize species for control, as well as to monitor management effectiveness in preventing introductions and containing alien species expansion (McGeoch et al. 2010). Here we provide lists of alien plant and animal species for South Africa’s 19 national parks (including marine protected areas). These lists are intended to serve as a baseline (i) against which future improvements in knowledge of the alien fauna and flora in SANParks may be compared, and (ii) for future monitoring of the success of alien species prevention 31 and control (Foxcroft 2009, McGeoch et al. in press).
Paradoxical reproduction and body size in the rock lizard, Agama atra atra, in Namaqualand, South Africa
07 August 2012
Stellenbosch University

Mouton, P. le F.N.;Herselman, Y.M.

The rock lizard Agama atra atra from Namaqualand differs in both body size and reproduction from other populations of this species occurring elsewhere in southern Africa. Both sexes from Namaqualand are significantly larger than their counterparts in the south-western Cape. While reproduction in this species is strongly seasonal elsewhere, it is apparently continuous in Namaqualand. Females with vitellogenic ovarian follicles and/or oviducal eggs were collected during the winter months, a time when females are typically reproductively quiescent in other populatlons. Aseasonal reproduction and large body size of this species in Namaqualand do not correlate with prevailing environmental conditions in the area.T he presence of at least one other species with continuous reproduction and two others with tropical affinities in the same general area, suggests that the Namaqualand population of A. a. atra may be a tropical relict.
Spatial and temporal variation in cadmium body loads of four intertidal invertebrates from False Bay, South Africa
07 August 2012
Stellenbosch University

Reinecke, A.J.;Mdzeke, N.P.;Reinecke, S.A.

Increasing urbanization and industrialization along the coastal areas of False Bay in South Africa can endanger coastal ecosystems because of increasing metal pollution. To obtain baseline data on contamination levels in the intertidal zone, cadmium (Cd) body loads of four invertebrate species were measured seasonally over a period of 15 months from different sites within the bay. Specimens of Tetraclita serrata (barnacle), Oxystele sinenses (periwinkle), Cymbula oculus (limpet) and Choromytilus meridionalis (mussel) were collected and analysed to determine temporal changes in Cd body burdens. Cd concentrations were also measured in water and sediments. Cd concentrations in the intertidal animals varied considerably between sampling sites and between seasons and also occasionally between species. All four species accumulated Cd in their bodies to levels several times higher than environmental concentrations. No significant difference could be shown between the Cd concentrations in the gastropod grazers and the filter-feeders. The highest mean body load of Cd (70.67 μg/g dry weight) for a single sampling occasion was measured in the sessile barnacles (T. serrata) collected at Rooi-Els. The highest mean Cd concentration (11.95 μg/g) for the bay as a whole was measured in the limpet C. oculus. Two-way analysis of variance indicated that spatial (location) rather than temporal (seasonal) factors affected Cd concentrations in the invertebrates. Cd concentrations in False Bay sometimes exceeded the norms or water quality standards.
Trophic interrelationships between the exotic Nile tilapia, Oreochromis niloticus and indigenous tilapiine cichlids in a subtropical African river system (Limpopo River, South Africa)
16 August 2012
Stellenbosch University

Zengeya, T.A.;Booth, A.J.;Bastos, A.D.S.;Chimimba, C.T.

The stable isotope ratio and seasonal changes in diet of two indigenous (Oreochromis mossambicus, Tilapia rendalli) and one exotic (Oreochromis niloticus) tilapiine cichlids in the subtropical Limpopo River, South Africa were investigated to determine patterns of resource partitioning. Stomach contents of O. niloticus and O. mossambicus indicated high dietary overlap across size class, habitat and season, with both species primarily feeding on vegetative detritus. However, stable isotope analysis revealed that the two Oreochromis species had different stable isotope ratios derived from different food sources. The relatively δ13C-depleted O. niloticus indicates a phytoplanktonbased diet, while the δ13C-enriched O. mossambicus indicates a macrophagous diet dominated by vegetative detritus and periphyton. The high similarity in stomach contents and the interspecific differences in isotopic composition reveal fine-scale patterns of food resource partitioning that could be achieved through selective feeding. Tilapia rendalli was largely macrophagous and fed mainly on aquatic macrophytes and had a low dietary overlap with both O. niloticus and O. mossambicus. In the Limpopo River, detritus and algae are probably the most abundant food resources and the causal factors responsible for the observed patterns of resource partitioning among the tilapiines are usually difficult to ascertain. Fish may be able to perceive food resources in terms of the dynamics that determine their availability. Detailed studies of variation in food resource availability and fish habitat use within the system are needed to evaluate this hypothesis.
Importance of primary metabolites in canola in mediating interactions between a specialist leaf-feeding insect and its specialist solitary endoparasitoid
28 January 2013
Stellenbosch University

Soufbaf, M;Fathipour, Y;Zalucki, MP;Hui, C

The role of primary plant chemistry on trophic interactions is not well studied. We examined the effect of primary plant metabolites, focusing on nitrogen, on several biological indices of second and third trophic level insects in a model tritrophic system, consisting of two strains of the crucifer, Brassica napus (canola) (SLM046 and RGS003), the specialist insect herbivore Plutella xylostella (L.) (Lepidoptera: Plutellidae), and its specialist koinobiont larval-pupal parasitoid Diadegma semiclausum (Helle´n) (Hymenoptera: Ichneumonidae). In particular, we measured relative growth rate of the herbivore in relation to an index for plant quality (nitrogen content of leaf tissues), developmental time of the herbivore (sum of second, third, and fourth larval instars durations), and intrinsic rate of increase (rm) of the herbivore and the parasitoid. Tritrophic studies were conducted on development, survivorship curve analysis, reproductive potential, life history, parasitism, and several other fitness correlates of the parasitoid. The life table parameters of D. semiclausum were determined under laboratory conditions. The intrinsic rate of increase (rm) of the parasitoid was significantly higher on RGS003 than SLM046. In this tritrophic model, the results indicated that the bottom-up direct effect on the herbivore population growth rate was marginally as strong as the direct effect of top-down force due to the parasitoid population growth rate; but it was higher than its indirect counterpoint mediated with the parasitoid population growth rate. Consequently, D. semiclausum performed better on RGS003, which was the most inferior host to P. xylostella in comparison with another plant cultivar and had the lowest content of nitrogen in its leaves.
Precision control of an invasive ant on an ecologically sensitive tropical island: a principle with wide applicability
19 February 2013
Stellenbosch University

Gaigher, R.;Samways, M.J.;Jolliffe, K.G.;Jolliffe, S.-M.

Effective management of invasive ants is an important priority for many conservation programs but can be difficult to achieve, especially within ecologically sensitive habitats. This study assesses the efficacy and nontarget risk of a precision ant baiting method aiming to reduce a population of the invasive big-headed ant Pheidole megacephala on a tropical island of great conservation value. Area-wide application of a formicidal bait, delivered in bait stations, resulted in the rapid decline of 8 ha of P. megacephala. Effective suppression remained throughout the succeeding 11-month monitoring period. We detected no negative effects of baiting on nontarget arthropods. Indeed, species richness of nontarget ants and abundance of other soil-surface arthropods increased significantly after P. megacephala suppression. This bait station method minimized bait exposure to nontarget organisms and was cost effective and adaptable to target species density. However, it was only effective over short distances and required thorough bait placement. This method would therefore be most appropriate for localized P. megacephala infestations where the prevention of nontarget impacts is essential. The methodology used here would be applicable to other sensitive tropical environments.
Antarctic marine biodiversity and deep-sea hydrothermal vents
20 February 2013
Stellenbosch University

Chown, S.L.

The diversity of many marine benthic groups is unlike that of most other taxa. Rather than declining from the tropics to the poles, much of the benthos shows high diversity in the Southern Ocean. Moreover, many species are unique to the Antarctic region. Recent work has shown that this is also true of the communities of Antarctic deep-sea hydrothermal vents. Vent ecosystems have been documented from many sites across the globe, associated with the thermally and chemically variable habitats found around these, typically high temperature, streams that are rich in reduced compounds and polymetallic sulphides. The animal communities of the East Scotia Ridge vent ecosystems are very different to those elsewhere, though the microbiota, which form the basis of vent food webs, show less differentiation. Much of the biological significance of deep-sea hydrothermal vents lies in their biodiversity, the diverse biochemistry of their bacteria, the remarkable symbioses among many of the marine animals and these bacteria, and the prospects that investigations of these systems hold for understanding the conditions that may have led to the first appearance of life. The discovery of diverse and unusual Antarctic hydrothermal vent ecosystems provides opportunities for new understanding in these fields. Moreover, the Antarctic vents south of 60uS benefit from automatic conservation under the Convention on the Conservation of Antarctic Marine Living Resources and the Antarctic Treaty. Other deep-sea hydrothermal vents located in international waters are not protected and may be threatened by growing interests in deep-sea mining.
TEASIng apart alien-species risk assessments: A framework for best practices
27 February 2013
Stellenbosch University

Leung, B.;Roura-Pascual, N.;Bacher, S.;Heikkilä, J.;Brotons, L.;Burgman, M.A.;Dehnen-Schmutz, K.;Essl, E.;Hulme, P.E.;Richardson, D.M.;Sol, D.;Vilà, M.

Some alien species cause substantial impacts, yet most are innocuous. Given limited resources, forecasting risks from alien species will help prioritise management. Given that risk assessment (RA) approaches vary widely, a synthesis is timely to highlight best practices. We reviewed quantitative and scoring RAs, integrating > 300 publications into arguably the most rigorous quantitative RA framework currently existing, and mapping each study onto our framework, which combines Transport, Establishment, Abundance, Spread and Impact (TEASI). Quantitative models generally measured single risk components (78% of studies), often focusing on Establishment alone (79%). Although dominant in academia, quantitative RAs are underused in policy, and should be made more accessible. Accommodating heterogeneous limited data, combining across risk components, and developing generalised RAs across species, space and time without requiring new models for each species may increase attractiveness for policy applications. Comparatively, scoring approaches covered more risk components (50% examined > 3 components), with Impact being the most common component (87%), and have been widely applied in policy (> 57%), but primarily employed expert opinion. Our framework provides guidance for questions asked, combining scores and other improvements. Our risk framework need not be completely parameterised to be informative, but instead identifies opportunities for improvement in alien species RA.
Reproductive photoresponsiveness in male spiny mice from South Africa
28 February 2013
Stellenbosch University

Medger, K.;Chimimba, C.T.;Bennett, N.C.

Many seasonally breeding mammals use changes in photoperiod as a reliable cue to time reproduction. Photoperiodic timing assists an animal in predicting annual environmental changes in its habitat and therefore, enables it to accurately time reproductive events to the most favourable conditions. Changes in day length are more pronounced in the temperate regions and photoperiod is used as a cue for reproduction by most mammals above 30° latitude; however, a number of subtropical species also use this proximate factor to regulate their reproductive cycle. We investigated the reproductive photoresponsiveness of 14 male spiny mice (Acomys spinosissimus) from southern Africa to short-day (SD; 8 h light : 16 h dark) and long-day (LD; 16 h light : 8 h dark) photoperiods. Testicular mass and volume, seminiferous tubule diameter and plasma testosterone concentrations significantly increased in animals subjected to LD and they were regressed when the males were kept under SD. Body mass of the males was not significantly affected by the photoperiodic conditions. Although male A. spinosissimus appear to use photoperiod as a proximate factor to regulate reproduction seasonally, other environmental factors, such as rainfall, food quantity and quality as well as temperature, may regulate reproduction in A. spinosissimus in concert with photoperiod. In conclusion, the present study demonstrates the significance of photoperiodic time-measuring systems in the regulation of seasonal reproduction in a subtropical rodent.
Phylogeography of a mite, Halozetes fulvus, reflects the landscape history of a young volcanic island in the sub-Antarctic
01 March 2013
Stellenbosch University

Mortimer, E.;Jansen van Vuuren, B.;Meiklejohn, K.I.;Chown, S.L.

Previous studies of the microarthropods of Marion Island, Southern Ocean, documented high mitochondrial COI (cytochrome c oxidase subunit I) haplotype diversity and significant genetic structure, which were ascribed to landscape subdivision. In this paper we revisit these ideas in light of new geomorphological evidence indicating a major lineament orientated along N26.5°E. Using the microarthropod Halozetes fulvus, we test the hypothesis that the eastern and western sides of the island show different population genetic patterns, corresponding to the previously unrecognized geological separation of these regions, and perhaps also with differences in climates across the island and further landscape complexity. Mitochondrial COI data were collected for 291 H. fulvus individuals from 30 localities across the island. Notwithstanding our sampling effort, haplotype diversity was under-sampled as indicated by rarefaction analyses. Overall, significant genetic structure was found across the island as indicated by FST analyses. Nested clade phylogeographical analyses suggested that restricted gene flow (with isolation-bydistance) played a role in shaping current genetic patterns, as confirmed by Mantel tests. At the local scale, coalescent modelling revealed two different genetic patterns. The first, characterizing populations on the southwestern corner of the island, was that of low effective population size and high gene flow. The converse was found on the eastern side of Marion Island. Taken together, substantial differences in spatial genetic structure characterize H. fulvus populations across Marion Island, in keeping with the hypothesis that the complex history of the island, including the N26.5°E geological lineament, has influenced population genetic structure. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105, 131–145.
A global assessment of freshwater fish introductions in mediterranean-climate regions
04 June 2014
Stellenbosch University

Marr, S.M.;Olden, J.D.;Leprieur, F.;Arismendi, I.;Caleta, M.;Morgan, D.L.;Nocita, A.;Sanda, R.;Tarkan, A.S.;Berthou-Garcia, E.

Mediterranean-climate regions (medregions) are global hotspots of endemism facing mounting environmental threats associated with human-related activities, including the ecological impacts associated with non-native species introductions. We review freshwater fish introductions across med-regions to evaluate the influences of non-native fishes on the biogeography of taxonomic and functional diversity. Our synthesis revealed that 136 freshwater fish species (26 families, 13 orders) have been introduced into med-regions globally. These introductions, and local extirpations, have increased taxonomic and functional faunal similarity among regions by an average of 7.5% (4.6–11.4%; Jaccard) and 7.2% (1.4–14.0%; Bray–Curtis), respectively. Faunal homogenisation was highest in Chile and the western Med Basin, whereas sw Cape and the Aegean Sea drainages showed slight differentiation (decrease in faunal similarity) over time. At present, fish faunas of different med-regions have widespread species in common (e.g. Gambusia holbrooki, Cyprinus carpio, Oncorhynchus mykiss, Carassius auratus, and Micropterus salmoides) which are typically large-bodied, non-migratory, have higher physiological tolerance, and display fast population growth rates. Our findings suggest that intentional and accidental introductions of freshwater fish have dissolved dispersal barriers and significantly changed the present-day biogeography of med-regions across the globe. Conservation challenges in med-regions include understanding the ecosystem consequences of non-native species introductions at macro-ecological scales.
Synonymy of Spicatella Thibaud, 2002 with Delamarephorura Weiner & Najt, 1999, and description of two new species (Collembola: Tullbergiidae)
05 June 2014
Stellenbosch University

Janion, C.;Deharveng, L.;Weiner, W.M.

The monospecifi c genus Spicatella Thibaud, 2002 is synonymised with Delamarephorura Weiner & Najt, 1999. Delamarephorura is redefi ned and a key to its species is given. Delamarephorura capensis, new species, from South Africa and D. tami, new species, from Vietnam are described and illustrated. D. capensis, new species, is the only species of the genus with pseudocellar formula 11/111/11111; D. tami, new species, is the only species of the genus with chaetae M absent on tibiotarsi.
Deja vu? A second mytilid mussel, Semimytilus algosus, invades South Africa's west coast
11 June 2014
Stellenbosch University

de Greef, K.;Griffiths, C.L.;Zeeman, Z.

A second marine mussel is shown to have invaded South Africa’s west coast. Molecular techniques, based on intraspecific gene sequence divergences, prove its identity as Semimytilus algosus, a member of the family Mytilidae, native to Chile. The identity of an older introduced population found in Namibia is also confirmed. The present geographic range of S. algosus in South Africa extends some 500 km, from Groenriviersmond in the north to Bloubergstrand in the south. Together with Mytilus galloprovincialis, another previously established invasive mussel, S. algosus has become a dominant intertidal organism on wave-exposed rocky shores across this region. Both species are now much more abundant intertidally than either of the indigenous mussels Aulacomya ater and Choromytilus meridionalis, which have become largely confined to sublittoral and sand-inundated habitats respectively. The two invasive mussels display strong spatial segregation, with M. galloprovincialis dominating the midshore and S. algosus blanketing the lower shore. Through a combination of its small size and high abundance, S. algosus is likely to greatly increase food availability for a range of intertidal predators, many of which cannot consume mussels above a threshold size.
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.
Assessing the relative efficiency of termite sampling methods along a rainfall gradient in African savannas
13 June 2014
Stellenbosch University

Davies, A.B.;Eggleton, P.;Janse van Rensburg, B.;Parr, C.L.

Although termites are ecosystem engineers in tropical and sub-tropical environments, the study of termite ecology is often constrained by sampling difficulties and a lack of established sampling protocols, particularly for savannas. The efficiency and relevance of different methods along climatic gradients, even within a single biome, is largely unknown. Here, we compare the relative contribution of two commonly used sampling methods, cellulose baits and active searching transects, in quantifying savanna termite diversity along a rainfall gradient in South Africa; sampling was conducted during the wet season across four markedly different savanna types. We also assessed the usefulness of different forms of baiting techniques. The relative efficiency of sampling method varied with annual rainfall. In arid savannas, baiting was as effective as active searching transects at sampling termite diversity and we recommend the use of baiting rather due to it being less labor intensive. In savannas of moderately low to intermediate rainfall, baiting and transects sampled different termite species and so both are deemed necessary for an accurate assessment of termite diversity. In contrast, in wetter savannas transects gave a better assessment of diversity, with cellulose baits not contributing much to diversity assessment. The efficiency of baiting techniques differed across the rainfall gradient, with baits needing to be left in the field for a longer period in more arid savannas. We conclude that habitat type, even within a single biome, will determine the sampling method or methods necessary to quantify termite diversity accurately.
A unified classification on alien species based on the magnitude of their environmental impacts
29 July 2014
Stellenbosch University

Blackburn, T.M.;Essl, F.;Evans, T.;Hulme, P.E.;Jeschke, J.M.;Kuhn, I.;Kumschick, S.;Markova, Z.;Mrugala, A.;Nentwig, W.;Pergl, J.;Pysek, P.;Rabitsch, W.;Ricciardi, A.;Richardson, D.M.;Sendek, A.;Vila, M.;Wilson, J.R.U.;Winter, M.;Genovesi, P.;Bacher, S.

Species moved by human activities beyond the limits of their native geographic ranges into areas in which they do not naturally occur (termed aliens) can cause a broad range of significant changes to recipient ecosystems; however, their impacts vary greatly across species and the ecosystems into which they are introduced. There is therefore a critical need for a standardised method to evaluate, compare, and eventually predict the magnitudes of these different impacts. Here, we propose a straightforward system for classifying alien species according to themagnitude of their environmental impacts, based on the mechanisms of impact used to code species in the International Union for Conservation of Nature (IUCN) Global Invasive Species Database, which are presented here for the first time. The classification system uses five semi-quantitative scenarios describing impacts under each mechanism to assign species to different levels of impact— ranging from Minimal to Massive—with assignment corresponding to the highest level of deleterious impact associated with any of the mechanisms. The scheme also includes categories for species that are Not Evaluated, have No Alien Population, or are Data Deficient, and a method for assigning uncertainty to all the classifications.We show how this classification system is applicable at different levels of ecological complexity and different spatial and temporal scales, and embraces existing impact metrics. In fact, the scheme is analogous to the already widely adopted and accepted Red List approach to categorising extinction risk, and so could conceivably be readily integrated with existing practices and policies in many regions.
Advancing impact prediction and hypothesis testing in invasion ecology using a comparative functional response approach
30 July 2014
Stellenbosch University

Dick, J.T.A.;Alexander, M.E.;Jeschke, J.M.;Ricciardi, A.;MacIsaac, H.J.;Robinson, T.B.;Kumschick, S.;Weyl, O.L.F.;Dunn, A.M.;Hatcher, M.J.;Paterson, R.A.;Farnsworth, K.D.;Richardson, D.M.

Invasion ecology urgently requires predictive methodologies that can forecast the ecological impacts of existing, emerging and potential invasive species. We argue that many ecologically damaging invaders are characterised by their more efficient use of resources. Consequently, comparison of the classical ‘functional response’ (relationship between resource use and availability) between invasive and trophically analogous native species may allow prediction of invader ecological impact. We review the utility of species trait comparisons and the history and context of the use of functional responses in invasion ecology, then present our framework for the use of comparative functional responses. We show that functional response analyses, by describing the resource use of species over a range of resource availabilities, avoids many pitfalls of ‘snapshot’ assessments of resource use. Our framework demonstrates how comparisons of invader and native functional responses,within and between Type II and III functional responses, allow testing of the likely population-level outcomes of invasions for affected species. Furthermore, we describe how recent studies support the predictive capacity of this method; for example, the invasive ‘bloody red shrimp’ Hemimysis anomala shows higher Type II functional responses than native mysids and this corroborates, and could have predicted, actual invader impacts in the field. The comparative functional response method can also be used to examine differences in the impact of two or more invaders, two or more populations of the same invader, and the abiotic (e.g. temperature) and biotic (e.g. parasitism) context-dependencies of invader impacts. Our framework may also address the previous lack of rigour in testing major hypotheses in invasion ecology, such as the ‘enemy release’ and ‘biotic resistance’ hypotheses, as our approach explicitly considers demographic consequences for impacted resources, such as native and invasive prey species. We also identify potential challenges in the application of comparative functional responses in invasion ecology. These include incorporation of numerical responses, multiple predator effects and trait-mediated indirect interactions, replacement versus non-replacement study designs and the inclusion of functional responses in risk assessment frameworks. In future, the generation of sufficient case studies for a meta-analysis could test the overall hypothesis that comparative functional responses can indeed predict invasive species impacts.
Effects of temperature on heat-shock responses and survival of two species on marine invertebrates from sub-Antarctic Marion Island
30 July 2014
Stellenbosch University

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

This study examined high temperature survival and heat shock protein 70 (Hsp70) responses to temperature variation for two marine invertebrate species on sub-Antarctic Marion Island. The isopod Exosphaeroma gigas Leach and the amphipod Hyale hirtipalma Dana had the same tolerance to high temperature. The mean upper temperature which was lethal for 50% of the population (upper lethal temperature, ULT50) was 26.48C for both species. However, the isopod E. gigas showed significant plasticity of ULT50, with a positive response to acclimation. In addition, the isopod had a heat shock response of Hsp70 at all acclimations, and the amount of Hsp70 protein increased significantly from basal levels upon an acute warm exposure after a cold acclimation. By contrast, the amphipod H. hirtipalma showed limited plasticity of ULT50 and no evidence for a heat shock response (failure of three different Hsp70 antibodies to bind to the extracted 70kDa proteins). Overall, these results reflect different flexibility of thermal tolerance of intertidal invertebrate species on Marion Island, with possible variation in the underlying cellular mechanisms, suggesting that warming associated with climate change may result in changes in species assemblage structure in sub-polar environments.
Killer whale ecotypes: is there a global model?
31 July 2014
Stellenbosch University

de Bruyn, P.J.N.;Tosh, C.A.;Terauds, A.

Killer whales, Orcinus orca, are top predators occupying key ecological roles in a variety of ecosystems and are one of the most widely distributed mammals on the planet. In consequence, there has been significant interest in understanding their basic biology and ecology. Long-term studies of Northern Hemisphere killer whales, particularly in the eastern North Pacific (ENP), have identified three ecologically distinct communities or ecotypes in that region. The success of these prominent ENP studies has led to similar efforts at clarifying the role of killer whale ecology in other regions, including Antarctica. In the Southern Hemisphere, killer whales present a range of behavioural, social and morphological characteristics to biologists, who often interpret this as evidence to categorize individuals or groups, and draw general ecological conclusions about these super-predators. Morphologically distinct forms (Type A, B, C, and D) occur in the Southern Ocean and studies of these different forms are often presented in conjunction with evidence for specialised ecology and behaviours. Here we review current knowledge of killer whale ecology and ecotyping globally and present a synthesis of existing knowledge. In particular, we highlight the complexity of killer whale ecology in the Southern Hemisphere and examine this in the context of comparatively well-studied Northern Hemisphere populations. We suggest that assigning erroneous or prefatory ecotypic status in the Southern Hemisphere could be detrimental to subsequent killer whale studies, because unsubstantiated characteristics may be assumed as a result of such classification. On this basis, we also recommend that ecotypic status classification for Southern Ocean killer whale morphotypes be reserved until more evidence-based ecological and taxonomic data are obtained.
Population trends and breeding success of albatrosses and giant petrels at Gough Island in the face of at-sea and on-land threats
31 July 2014
Stellenbosch University

Cuthbert, R.J.;Cooper, J.;Ryan, P.G.

Several factors threaten populations of albatrosses and giant petrels, including the impact of fisheries bycatch and, at some colonies, predation from introduced mammals. We undertook population monitoring on Gough Island of three albatross species (Tristan albatross Diomedea dabbenena L., sooty albatross Phoebetria fusca Hilsenberg, Atlantic yellow-nosed albatross Thalassarche chlororhynchos Gmelin) and southern giant petrels Macronectes giganteus (Gmelin). Over the study period, numbers of the Critically Endangered Tristan albatross decreased at 3.0% a year. Breeding success for this species was low (23%), and in eight count areas was correlated (r250.808) with rates of population decline, demonstrating chick predation by house mice Mus musculus L. is driving site-specific trends and an overall decline. Numbers of southern giant petrels were stable, contrasting with large increases in this small population since 1979. Significant population declines were not detected for either the Atlantic yellow-nosed or sooty albatross, however, caution should be applied to these results due to the small proportion of the population monitored (sooty albatross) and significant interannual variation in numbers. These trends confirm the Critically Endangered status of the Tristan albatross but further information, including a more accurate estimate of sooty albatross population size, is required before determining island wide and global population trends of the remaining species.
Alien reef-building polychaete drives long-term changes in invertebrate biomass and diversity in a small, urban estuary
31 July 2014
Stellenbosch University

McQuaid, K.A.;Griffiths, C.L.

Two of the greatest threats to native biodiversity are the construction of artificial structures in natural environments and the introduction of invasive species. As the development and urbanisation of estuaries continues at an increasing rate worldwide, these environments are being simultaneously affected by these threats. This study quantifies the spread of an invasive reef-building polychaete, Ficopomatus enigmaticus, in a small, highly manipulated urban estuary in South Africa and investigates its role as an ecosystem engineer. Anthropogenic changes to the Zandvlei Estuary, including construction of a rubble weir and canalisation near the estuary mouth, construction of an extensive marina development and hardening of the banks with concrete, have facilitated the expansion of F. enigmaticus. The standing stock of F. enigmaticus increased from 13.69 t, as measured in 1986, to 50.03 t in 2012, due both to increase in the total area colonised and standing stock per m2. Since F. enigmaticus reefs support a greater biomass of infauna than adjacent sandy areas, total invertebrate biomass in the estuary is estimated to have increased from less than 0.30 t in 1942, to over 56.80 t in 2012, due mainly to hardening of banks in parts of the main estuary with concrete and construction of a marina system. A positive correlation between reef mass and infaunal biomass, density and diversity was also found.
Predicting the ecological impacts of a new freshwater invader: functional responses and prey selectivity of the ‘killer shrimp’, Dikerogammarus villosus, compared to the native Gammarus pulex
31 July 2014
Stellenbosch University

Dodd, J.A.;Dick, J.T.A.;Alexander, M.E.;MacNeil, C.;Dunn, A.M.;Aldridge, D.C.

1. The ability to predict the likely ecological impacts of invasive species in fresh waters is a pressing research requirement. Whilst comparisons of species traits and considerations of invasion history have some efficacy in this respect, we require robust methods that can compare the effects of native and invasive species. Here, we utilise comparative functional responses and prey selectivity experiments to understand and predict the ecological impact of an invader as compared to a native. 2. We compared the predatory functional responses of an emerging invasive species in Europe, the ‘killer shrimp’, Dikerogammarus villosus, and an analogous native species, Gammarus pulex, towards three representative prey species: Asellus aquaticus, Daphnia magna and Chironomus sp. Furthermore, as ecological impact may be greater for invasive species with more indiscriminate feeding habits, we compared the selectivity for the three prey types between the invasive and native species. 3. In both the presence and absence of experimental habitats, large D. villosus, and those matched for body size with G. pulex, generally showed higher (Type II) functional responses than G. pulex, with the invasive species exhibiting higher maximum feeding rates. Further, D. villosus exhibited significantly more indiscriminate prey selection compared with G. pulex, a trait that became more evident as the invader increased in size. Differences in functional responses and prey selectivity were prey species specific, with higher to lower predicted impacts in the order A. aquaticus, D. magna and Chironomus sp. This is in accord with the impact of this invasive species on macroinvertebrates in the field. 4. We thus provide understanding of the known ecological impact of D. villosus and discuss the utility of the phenomenological use of comparative functional responses and resource use as a tool through which the potential ecological impacts of invasive species may be identified.
Niche differentiation among invasive crayfish and their impacts on ecosystem structure and functioning
18 August 2014
Stellenbosch University

Jackson, M.C.;Jones, T.;Milligan, M.;Sheath, D.;Taylor., J.;Ellis, A.;England, J.;Grey, J.

1. Many aquatic ecosystems sustain multiple invasive species and interactions among them have important implications for ecosystem structure and functioning. Here, we examine interactions among two pairs of invasive crayfish species because of their close proximity and thus chance of sympatric populations in the near future within the Thames catchment, U.K. (signal, Pacifastacus leniusculus and virile crayfish, Orconectes virilis within a river system; red swamp, Procambarus clarkii and Turkish crayfish, Astacus leptodactylus found within a suite of ponds). We address two questions: do sympatric invasive crayfish occupy a smaller niche than their allopatric counterparts due to potential resource competition? and do interactions among invasive species amplify or mitigate one another’s impacts on the ecosystem? 2. Two fully factorial mesocosm experiments (one for each crayfish pair) were used to investigate crayfish diet and their impact on benthic invertebrate community structure, benthic algal standing stock and leaf litter decomposition rates in allopatric and sympatric populations, compared with a crayfish-free control. We used stable isotope analysis to examine crayfish diet in the mesocosms and in allopatric populations of each species in the Thames catchment. 3. Isotopic niche width did not vary significantly between allopatric and sympatric populations of crayfish in the mesocosm experiments, and isotopic niche partitioning in all the wild populations suggests the invaders can coexist. 4. All four species altered benthic invertebrate community structure but with differing functional effects, often mediated via trophic cascades. Red swamp crayfish predation upon snails evidently promoted benthic algal standing stock via reduction in grazing pressure. However, a trophic cascade whereby the crayfish consumed native invertebrate shredders, causing a reduction in net leaf litter decomposition, was decoupled by red swamp and signal crayfish since they consumed leaf litter directly and thus moderated the cascade to a trickle when in sympatry with Turkish or virile crayfish, respectively. 5. Benthic invertebrate predator abundance was significantly reduced by sympatric red swamp and Turkish crayfish but not independently when in allopatry, indicating an amplified effect overall when in sympatry. 6. Our results suggest that the combined effect of multiple invasions on the ecosystem can reflect either an additive effect of their independent impacts or an amplified effect, which is greater than the sum of their independent impacts. A lack of general pattern in their effects makes any potential management strategy more complex.
Patterns and drivers of marine bioinvasions in eight Western Cape harbours, South Africa
19 August 2014
Stellenbosch University

Peters, K.;Griffiths, C.L.;Robinson, T.B.

In South Africa, fouling is the dominant vector of marine invasions, being responsible for 48% of the 86 alien introductions that are known. This study aimed to document alien species in fouling assemblages in eight Western Cape harbours and to assess patterns and potential drivers of these invasions. In each harbour, 10 visual (1 m × 1 m) and 10 scrape (15 cm × 15 cm) subtidal samples were randomly collected at depths between 1 and 5 m. In total, 22 marine alien species were detected and, although no statistical differences were evident in the number of alien species recorded per harbour, the number of alien species per m2 differed significantly among harbours, with Hout Bay Harbour having the highest. The brachiopod Discinisca tenuis, documented for the first time outside of aquaculture facilities, was found to have spread from Saldanha Bay to St Helena Bay. A previously unknown alien amphipod, Ericthonius difformis, was detected in Simon’s Town Harbour. CART (classification and regression tree) analyses revealed that relatively small harbours with yachts supported more alien fouling species than other harbours. This finding could be useful for managers wishing to prioritise Western Cape harbours for monitoring.
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.
Spatial assortment of mixed propagules explains the acceleration of range expansion
11 February 2015
Stellenbosch University

Ramanantoanina, A.;Ouhinou, A.;Hui, C.

Range expansion of spreading organisms has been found to follow three types: (i) linear expansion with a constant rate of spread; (ii) bi-phase expansion with a faster linear expansion following a slower linear expansion; and (iii) accelerating expansion with a continuously increasing rate of spread. To date, no overarching formula exists that can be applied to all three types of range expansion. We investigated how propagule pressure, i.e., the initial number of individuals and their composition in terms of dispersal ability, affects the spread of a population. A system of integrodifference equations was then used to model the spatiotemporal dynamics of the population. We studied the dynamics of dispersal ability as well as the instantaneous and asymptotic rate of spread. We found that individuals with different dispersal abilities were spatially sorted with the stronger dispersers situated at the expanding range front, causing the velocity of expansion to accelerate. The instantaneous rate of spread was found to be fully determined by the growth and dispersal abilities of the population at the advancing edge of the invasion. We derived a formula for the asymptotic rate of spread under different scenarios of propagule pressure. The results suggest that data collected from the core of the invasion may underestimate the spreading rate of the population. Aside from better managing of invasive species, the derived formula could conceivably also be applied to conservation management of relocated, endangered or extra-limital species.
Horizon scanning for invasive alien species with the potential to threaten biodiversity in Great Britain
24 March 2015
Stellenbosch University

Roy, H.E.;Peyton, J.;Aldridge, D.C.;Bantock, T.;Blackburn, T.M.;Britton, R.;Clark, P.;Cook, E.;Dehnen-Schmutz, K.;Dines, T.;Dobson, M.;Edwards, F.;Harrower, C.;Harvey, M.C.;Minchin, D.;Noble, D.G.;Parrott, D.;Pocock, M.J.O.;Preston, C.D.;Roy, S.;Salisbury, A.;Schönrogge, K.;Sewell, J.;Shaw, R.;Stebbing, P.;Stewart, A.J.A.;Walker, K.J.

Invasive alien species (IAS) are considered one of the greatest threats to biodiversity, particularly through their interactions with other drivers of change. Horizon scanning, the systematic examination of future potential threats and opportunities, leading to prioritization of IAS threats is seen as an essential component of IAS management. Our aim was to consider IAS that were likely to impact on native biodiversity but were not yet established in the wild in Great Britain. To achieve this, we developed an approach which coupled consensus methods (which have previously been used for collaboratively identifying priorities in other contexts) with rapid risk assessment. The process involved two distinct phases: 1. Preliminary consultation with experts within five groups (plants, terrestrial invertebrates, freshwater invertebrates, vertebrates and marine species) to derive ranked lists of potential IAS. 2. Consensus-building across expert groups to compile and rank the entire list of potential IAS. Five hundred and ninety-one species not native to Great Britain were considered. Ninety-three of these species were agreed to constitute at least a medium risk (based on score and consensus) with respect to them arriving, establishing and posing a threat to native biodiversity. The quagga mussel, Dreissena rostriformis bugensis, received maximum scores for risk of arrival, establishment and impact; following discussions the unanimous consensus was to rank it in the top position. A further 29 species were considered to constitute a high risk and were grouped according to their ranked risk. The remaining 63 species were considered as medium risk, and included in an unranked long list. The information collated through this novel extension of the consensus method for horizon scanning provides evidence for underpinning and prioritizing management both for the species and, perhaps more importantly, their pathways of arrival. Although our study focused on Great Britain, we suggest that the methods adopted are applicable globally.
Reflections on the history of aquatic science in South Africa with particular reference to the period after 1994
24 March 2015
Stellenbosch University

Roux, D.J.;Breen, C.M.;Carruthers, J.

In this article we reflect on how freshwater research has evolved in South Africa from its beginnings in the early 20th century and how it has altered over time to align with the post-1994 socio-political environment. We situate aquatic science within a research question to explore why aquatic science has developed in the manner it has done, providing some of the broader environment of political change, access to funding, the relevance of particular research themes at different times, and the research agenda of some prominent individual scientists. We do not, therefore, intend merely to itemise what has been achieved over the years. Our intention is to develop an historical context that may help frame research in ways that bridge the cultural divides that persist between the humanities and the sciences. Moreover, although water is crucial to life and livelihoods in a country of scarce water resources, the fields of aquatic study are not generally familiar to the South African public and do not have the high profile they merit. In order to chart important current developments in freshwater research, this article highlights significant aspects of this scientific arena during the earlier part of the 20th century that are pertinent to explaining how and why the current situation, by way of research fields, policy and legislation came into being. The history has been necessitated by, and driven by, regional socio-economic and geopolitical factors as well as developments in the relevant scientific disciplines. After examining how this state of affairs came to be, an overview of the present state of the field is provided.
Repeat photography as a tool for detecting and monitoring historical changes in South African coastal habitats
25 March 2015
Stellenbosch University

Reimers, B.;Griffiths, C.L.;Hoffman, M.T.

Repeat photography was used to illustrate long-term changes occurring in coastal habitats in the Western Cape, South Africa. Historic images were sourced from books and theses, the public and subject specialists, and repeat photographs were then taken from the same perspectives. Visible changes could be categorised into four types: (1) changes in species’ ranges; (2) biological invasions; (3) sea level changes; and (4) direct engineering impacts. In terms of range changes, the images depict a progressive easterly spread of the cold-water kelp Ecklonia maxima and parallel easterly contraction of the warmer-water mussel Perna perna, both evidence for declining water temperatures along the South-West Coast. Since c. 1980 most shores have also become conspicuously invaded by the alien Mediterranean mussel Mytilus galloprovincialis, while those on the West Coast have also been visibly invaded by the more-recently introduced Pacific barnacle Balanus glandula. No changes in vertical zonation due to changing sea levels could be detected, despite suitable images being available. Construction along the shore has radically altered the appearance of the shoreline in urban areas. Repeat photography thus proved a useful tool for both detecting and dramatically illustrating historic changes over the past century. These changes have altered substantially both the appearance and ecological attributes of many rocky shores in this region.

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