The absolute and relative importance of different causes behind the latitudinal gradient in species richness remain contested. Advances in the completeness and quality of phylogenetic, environmental, and species distribution information, and increased appreciation of the scale-dependence of different processes have led to significant progress. Specifically, empirical and conceptual progress is enabling a more explicitly multi-causal, hierarchical, and macroevolutionary perspective.
I will present recent work on terrestrial vertebrates that attempts to take an integrative approach to compare multiple predictors of regional variation in species richness and gage the relative importance of energy availability vs. species functional similarity on broad-scale species coexistence. I will also draw on recent phylogenetic and macroevolutionary findings from the NSF “VertLife” project addressing the global diversification and species richness of terrestrial vertebrates in geographic space. The Bayesian phylogenetic placement of all extant amphibians, mammals, reptiles, and birds allows us to conduct general tests of key hypotheses about the variation in diversification rates and environmental niche evolution along environmental gradients and the the groups' major biogeographic regions and large-scale evolutionary arenas.