Anthropogenic impacts weaken Bergmann’s rule

Humans have modified species distributions in most of the world’s natural ecosystems. Analyses of species distributions tend to ignore these modifications, potentially masking the signatures of natural processes on them. We examine the strength of a classic pattern in ecology—the body mass-latitudinal relationship, aka Bergmann’s rule—for all mammal species worldwide using both contemporary and estimated natural distributions. We show that human modifications of mammal species distributions lead to substantially underestimating the strength of the Bergmann’s rule. We speculate that other broad-scale ecological patterns might be similarly affected.