Human-driven body size reduction in worldwide terrestrial mammal communities
Since Bergman's observation that homoeothermic animals increase in size with latitude, body size
distribution has been a central focus of macroecological research. More than 160 years later, the socalled
Bergman's rule and its causes are still under debate, with a number of different hypotheses
proposed. Meanwhile, human activities have led to hundreds of species extinctions, and have
narrowed the distribution of many of the remaining species.
We assess the extent to which human impact has shaped the current distribution of body size in
mammalian community. We used a comprehensive set of ecological, climatic and anthropogenic
variables to predict the body size values observed in 1-degree grid cells covering terrestrial land.
We then explored how model's predictions are affected by the inclusion of human impact variables,
and identified areas where predicted body size is lower than expected due to human impact.
Our model suggests that human impact has led to a general reduction in body size of terrestrial
mammal communities. Mean and maximum body size predicted in grid cells would be much higher
removing the effect of human impact variables, especially in the Afrotropical and Oriental regions.
Our study supports previous findings on the pervasive effects of human impact on nature, and
confirms the human-induced distortion of global macroecological patterns. While in the short-term
human impact is causing species decline and extinction, in the longer term it is causing a broader
structural re-shaping of animal communities with yet unpredicted ecological implications.