Aim One of the longest recognized patterns in macroecology, Bergmann’s rule, describes the tendency for homeothermic animals to have larger body sizes in cooler climates than their phylogenetic relatives in warmer climates. Here we provide an integrative process-based explanation for Bergmann’s rule at the global scale for the mammal order Carnivora.
Methods Our database comprises the body sizes of 209 species of extant terrestrial Carnivora, which were analysed using phylogenetic autocorrelation and phylogenetic eigenvector regression. The interspecific variation in body size was partitioned into phylogenetic (P) and specific (S) components, and mean P- and S-components across species were correlated with environmental variables and human occupation both globally and for regions glaciated or not during the last Ice Age.
Results Three-quarters of the variation in body size can be explained by phylogenetic relationships among species, and the geographical pattern of mean values of the P-component is the opposite of the pattern predicted by Bergmann’s rule. Partial regression revealed that at least 43% of global variation in the mean phylogenetic component is explained by current environmental factors. In contrast, the mean S-component of body size shows large positive deviations from ancestors across the Holarctic, and negative deviations in southern South America, the Sahara Desert, and tropical Asia. There is a moderately strong relationship between the human footprint and body size in glaciated regions, explaining 19% of the variance of the mean P-component. The relationship with the human footprint and the P-component is much weaker in the rest of the world, and there is no relationship between human footprint and S-component in any region.
Main conclusions Bergmannian clines are stronger at higher latitudes in the Northern Hemisphere because of the continuous alternation of glacial–interglacial cycles throughout the late Pliocene and Pleistocene, which generated increased species turnover, differential colonization and more intense adaptive processes soon after glaciated areas became exposed. Our analyses provide a unified explanation for an adaptive Bergmann’s rule within species and for an interspecific trend towards larger body sizes in assemblages resulting from historical changes in climate and contemporary human impacts.