Data from: A global assessment of Bergmann’s rule in mammals and birds

Bergmann’s rule states that endotherms have a large body size in high
latitudes and cold climates. However, previous empirical studies have
reported mixed evidence on the relationships between body size and
latitude, raising the question of why some clades of endotherms follow
Bergmann’s rule whereas others do not. Here, we synthesized the
interspecific relationships between body size and latitude among 16,187
endothermic species (5,422 mammals and 10,765 birds) using Bayesian
phylogenetic generalized linear mixed models to examine the strength and
magnitude of Bergmann’s rule. We further assessed the effect of biological
and ecological factors (i.e., body mass categories, dietary guild, winter
activity, habitat openness, and climate zone) on the variations in the
body mass–latitude relationships by adding an interaction term in the
models. Our results revealed a generally weak but significant adherence to
Bergmann’s rule among all endotherms at the global scale. Despite
taxonomic variation in the strength of Bergmann’s rule, the body mass of
species within most animal orders showed an increasing trend toward high
latitudes. Generally, large-bodied, temperate species, non-hibernating
mammals, and migratory and open-habitat birds tend to conform to
Bergmann’s rule more than their relatives do. Our results suggest that
whether Bergmann’s rule applies to a particular taxon is mediated by not
only geographical and biological features but also potential alternate
strategies that species might have for thermoregulation. Future studies
could explore the potential of integrating comprehensive trait data into
phylogenetic comparative analysis to re-assess the classic ecogeographical
rules on a global scale.