Non-equilibrium processes prevail in shaping species richness and functional diversity of terrestrial vertebrates in a global hotspot

Background/Question/Methods

: Species diversity at large spatial scales is usually driven by a combination of equilibrium and non-equilibrium processes. Although the relative importance of these two processes explaining geographical variation in species richness have received considerable attention in the last decades, studies integrating alternative facets of biodiversity, such as functional diversity, and evaluating the congruence among multiple taxa yet remain to be investigated. Functional diversity can better discriminate the relative importance of such processes, because it describes more accurately niche space of a community. Here, we evaluated which variables representing equilibrium (altitude, climate, and primary productivity) and non-equilibrium (diversification rate and evolutionary time) processes best explain species richness and functional diversity of tetrapods in the Brazilian Atlantic Forest. We used functional traits (habitat, circadian activity, body mass/body size and range size), phylogenetic and spatial data of 1,487 vertebrate species (421 anurans, 261 squamates, 638 birds, and 167 mammals). We used a spatially-explicit Structural Equation Model to test how species richness and functional dispersion are influenced by variables representing equilibrium and non-equilibrium mechanisms. Additionally, we tested for a congruence in the spatial pattern of functional dispersion among clades using spatial correlation.

Results/Conclusions

: We found that non-equilibrium predictors were more important in explaining the functional dispersion and species richness of ectotherms and endotherms. Assemblage age significantly influenced the functional dispersion of the four clades as well as the species richness of frogs, birds, and mammals. Assemblage age was also correlated with diversification rate in ectotherms, but not endotherms. Diversification rates had the highest slopes for the species richness of frogs, squamates, and mammals. Conversely, at least one climate predictor was related to evolutionary variables and species richness in the four clades. Climate was related to diversification rates in ectotherms. In frogs and birds, the elevation was significantly associated with assemblege age. Climate was also associated with species richness in birds, squamates, and mammals. Elevation was also related to diversification rate in squamates and mammals. These results suggest that non-equilibrium processes were relatively more important in explaining the species richness and functional diversity in all groups. Equilibrium mechanisms, such as climate and elevation were strongly related to the response variables via assemblage age and diversification rates. Our results are in line with the idea that continental communities are temporary set of species in ever-changing environments.