Drivers of compositional dissimilarity for native and alien birds: the relative roles of human activity and environmental suitability

20 April 2020

We assessed the relative importance of human activity and environmental suitability as drivers of compositional dissimilarity of alien birds for 65 of the most populous cities of the Iberian Peninsula. We examined how these drivers relate to Zeta diversity (zeta) for alien Passeriformes and Psittaciformes. We performed the analysis using multiple orders of zeta, which provides insight on the role played by rare and common species in determining levels of dissimilarity. We also ran the analyses using the community of native Passeriformes as a phylogenetically close contrasting control. Our results showed that the proportion of urban area, a variable related to colonization and propagule pressure, had a strong influence on Psittaciformes but not on alien Passeriformes. This latter group showed to be primarily influenced by environmental factors, similarly to what was found for native Passeriformes. On other hand, human connectivity, as measured by distance through roads and railways seemed to play a significant role in shaping the compositional dissimilarity of alien Passeriformes, but not Psittaciformes. Regardless of the group analysed, the relative importance of the explanatory variables was similar for both rare and common species. Our findings highlight differences between the factors driving compositional dissimilarity for distinct groups of birds. While the emerging biogeography of Psittaciformes is mainly a reflection of distinctiveness in urban areas, alien Passeriformes are more strongly affected by the natural environment and thus their biogeography may increasingly resemble the one of their native counterparts.