Why are group-living badgers (Meles meles) sexually dimorphic?

One of the hypotheses proposed to account for why badgers Meles meles are highly social in the U.K., the resource dispersion hypothesis, is that patchy resources are unpredictably dispersed in the environment and therefore must be shared, but that these patches are rich enough, when available, to support several badgers at any one time. Previous empiricists in our study site at Wytham Woods calculated that single patches could be rich enough to support 30 badgers in a night. The sustained increase in population density in Wytham Woods suggests that food was not limiting and territories were below capacity, and therefore that feeding competition was relatively low. Low feeding competition would predict an absence of dimorphism in trophic apparatus between the sexes. Contrary to this, significant sexual dimorphism was found, after removing effects resulting from body size allometry, in canine cross-section length, width (both P < 0.0001) and skull breadth (P < 0.001). The differences in canine dimensions were still significant when allometry of both body length and skull breadth are accounted for statistically (P < 0.0001). It is therefore suggested that feeding competition may not necessarily be low, which would have implications for understanding the costs of social behaviour. Alternative explanations involving sexual selection and phylogenetic inertia are discussed.