How Social Behaviour Links Environment and Body Size in Mammalian Carnivores

Many hypotheses for larger body size with increasing latitude invoke environmental explanations, such as de- creasing temperature. We propose a novel explanation that links environmental selection pressures and body size with spacing behaviour. We test for causal pathways between (1) environment (snow, latitude, primary productivity, seasonal- ity, and temperature) and (2) spacing behaviour (home range size and population density) and (3) body size and sexual size dimorphism using structural equation modelling of independent contrasts derived from 101 mammalian terrestrial carnivore species. Although strong intercorrelations existed among all five environmental variables, primary productivity and seasonality best related to body size and size dimorphism. Using information-theoretic approach to select optimal model fit established that body size was not influenced directly by environment but rather through the intermediary vari- ables, home range or density. For example, species living in highly seasonal environments were associated with larger home ranges and low density that in turn selected for larger body mass and greater sexual size dimorphism. Thus, spacing behaviour provides an important evolutionary link explaining interspecific body size variation.