In this paper we argue that even spacing of the logarithmic diameter of canine teeth in mustelids and felids as shown by DAYAN et al. (1989a, 1990) may be more likely to result from behaviourally mediated competition for space than exploitative competition for prey resources. Felids and mustelids have several characteristics in common: a high degree of carnivory, the use of canines in threat displays, solitary living including intrasexual territories and sexual dimorphism. We model the ecological and evolutionary divergence of a character that is associated with territory defence such as canine size. We show that an assumption of size-dependent territorial aggressiveness can lead both to character divergence and to sexual dimorphism.