Biotic interchange has structured Western Hemisphere mammal communities

Aim.— Many hypotheses posit that species-rich tropical communities are dominated by speciesspecies interactions, apparent as competitive exclusion or character displacement, whereas species-poor temperate communities are dominated by species-environment interactions. Recent studies demonstrate a strong influence of macroevolutionary and biogeographic factors. We simultaneously test for the effects of species interactions, climate, and biotic interchange on Western Hemisphere mammal communities using a phylogenetic and functional diversity approach. Location.— Western Hemisphere. Time period.— Modern Major taxa studied.— Mammalia Methods.— Using Western Hemisphere mammal distributional and body mass data, we calculate body mass dispersion, phylogenetic diversity (Net Relatedness Index), and assemblage-averaged rates of co-occurrence (Checkerboard scores) in 100 km by 100 km grid cells under an equal area projection. We model body mass dispersion as a function of phylogenetic diversity, cooccurrence rates, and species richness, as well as mean annual temperature and precipitation. We infer rates of dispersal among the temperate and tropical zones of the Western Hemisphere using phylogenetic methods. Results.— The dispersion of Northern Temperate mammal body masses is higher than null communities and shows correlated change with climate, consistent with resource competition and environmental filtering. Conversely, the dispersion of tropical and Southern Temperate mammal body masses are lower than and not differentiable from null expectations, respectively, suggesting a limited role of species-species and species-environment interactions at the grain of our analysis. Low tropical body mass dispersion and phylogenetic evenness are best explained by the high rates of faunal mixing. High rates of dispersal might also explain the similarity in community structure between the Southern temperate and tropical zones. Main Conclusions.— Mammal community assembly processes differ among the temperate and tropical zones of the Western Hemisphere and faunal mixture during dispersal events such as the Great American Biotic Interchange (Pliocene ~3 Ma) may have been important in structuring Western Hemisphere mammal communities. 9 (!) supplementary files attached below