Have human impacts exceeded climate in shaping mammalian distributions?

Xin Chen, Luis José Aguirre, Xiao Feng

Human impacts are increasingly recognized as drivers of biogeographic patterns, yet it remains unclear whether they surpass climate in shaping species distributions. Here we aim to investigate the relative importance of anthropogenic vs. climatic factors in determining mammalian distributions. We modeled the relationship between the geographic distributions of 219 mammal species and 12 representative anthropogenic and climatic factors, and quantified variable importance with ecological niche models and explainable artificial intelligence at range-wide and local scales. We also constructed the response curve of human impact index (HII) for each species, and investigated the association between the response curves and species' biological traits. We found that anthropogenic factors were ranked as top contributors for nearly half of the species examined, and the average effect of HII has exceeded that of average and seasonal climatic conditions across spatial scales. While dominating effects of HII were widespread across the continent, the other factors often showed spatial clusters at different subsections of species’ ranges. Species’ response to human impacts displayed diverse patterns, and the positive responses were associated with traits of reduced conflicts with humans, faster reproduction, and greater mobility. The extent of human impacts is comparable to, and in some cases exceeds, that of climate in shaping contemporary mammalian biogeography patterns. The heterogeneous responses of mammal species to human impacts highlight the need to broadly consider anthropogenic factors, in addition to climate, in studying biodiversity in the Anthropocene.