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.

By contrast with a multitude of laboratory studies on the social organization of fish, relatively little is known about the size, composition and dynamics of free-ranging fish shoals. We give an overview of the available information on fish shoals and assess to what degree the predictions made from laboratory studies are consistent with field data. The section on shoal choice behaviour in the laboratory is structured so that the evidence for different shoaling preferences is discussed in the context of their mechanisms and functions. Predictions based on experiments in captivity regarding preferences for conspecifics, individuals of similar body length and unparasitized fish were highly consistent with field observations on free-ranging shoals whereas preferences for familiar conspecifics and kin remain to be conclusively demonstrated in the field. In general, there is a shortage of studies in which shoaling preferences have been investigated both in the laboratory and the field, and field studies have so far been largely descriptive revealing little about the underlying mechanisms of observed patterns. Given the great importance of fish shoals both in fundamental and applied research, an advancement of our knowledge of their social organization should significantly contribute to a better understanding of a whole range of topics including reciprocal altruism, group-living and self-organization.