Striking variation in the geographical distribution of biodiversity is among the most prominent ecological patterns. Environmental conditions such as climate are known to strongly affect biodiversity, but historical contingencies such as biogeographic history may also impact how communities are structured. However, comparisons of the relative influence of climate and biogeography remain scant, limiting our ability to predict whether and how communities in similar environments might converge. We wanted to directly compare how biogeographic history and climate affect the structure of mammal and bird communities. We used global, publicly-available datasets to calculate phylobetadiversity (reflecting biogeographic history) and contemporary climate for 2-degree global grid cells. We then used linear models and multiple regression on distance matrices to determine the relative contributions of phylobetadiversity and climate in predicting the species richness, functional richness, phylogenetic diversity, and functional composition of mammal and bird assemblages across the world.
Results/Conclusions
Globally, the influence of climate on mammal and bird communities was much higher than that of biogeography. For both mammals and birds, climate alone explained much more variance than biogeography alone for species richness (43.7% vs. 4.9% mammals; 66.2% vs. 3.7% birds), phylogenetic diversity (48.0% vs. 5.8%; 70.3% vs. 3.5%), and the distribution of ecological functional traits (31.6% vs. 0.9%; 34.8% vs. 1.0%). Unlike birds, mammal functional richness was relatively strongly related to biogeography (21.2% of variance) though the effects of climate were still more than twice as strong (43.6%). However, differences in residuals showed that biogeography improved model fit for mammal species richness, functional richness, and functional composition in isolated regions, especially Australia. Australian mammal assemblages had lower species richness, had lower functional richness, and lay completely outside the functional composition space of other regions. Biogeographic history did not matter for birds, likely because of their extraordinary dispersal abilities. Biogeography also did not matter for other continental mammal communities, which are far less geographically and historically isolated than Australia. Overall, though, Australian mammals appear to be a rare exception to the overall rule of climatic determinism, which has led to convergent and largely predictable ecological communities around the world.
