Bergmann’s rule in global terrestrial vertebrates

To date, whether Bergmann’s rule, initially developed for individual species or closely related taxa, can be applied to broader taxa remains elusive. Using global distribution data for birds, mammals, reptiles, and amphibians, both species- and assemblage-based, we examined the role of species richness and related climate variables in shaping body size patterns across the globe and the Northern Hemisphere only and whether the temperature–body size relationship had a phylogenetic signal. The results show that when species in all four classes were combined, body size increased with latitude but declined with temperature, consistent with Bergmann’s rule. Each group showed somewhat unique patterns but was mostly consistent with Bergmann’s rule. The body size–temperature relationships were not constrained by phylogenetic relatedness. Warmer places had both large and many small-bodied species, whereas cold places had proportionally more large species. The temperature-dependent variations in body size have important implications for macroecology under climate change.