Relative roles of ecological and energetic constraints, diversification rates and region history on global species richness gradients

Regions worldwide differ markedly in species richness. Here, for birds and mammals worldwide, we directly compare four sets of hypotheses regarding geographical richness gradients: (1) evolutionary, emphasising heterogeneity in diversification rates, (2) historical, related to differences in region ages and sizes, (3) energetic, associated with variation in productive or ambient energy and (4) ecological, reflecting differences in ecological...