Canine carnassials: character displacement in the wolves, jackals and foxes of Israel

Abstract

Previous research implies that competitive character displacement in felids and mustelids of Israel is expressed by canine size. Anatomy and observed killing behaviour of canids suggest that canines in this group are less adapted for the stylized role they play in felids and mustelids. Thus we hypothesized that character displacement, if it exists in canids, should not be manifested more clearly by canine size than by other traits. Five sympatric and at least partially syntopic canids occupy Israel, while in North Africa the largest (wolf) and smallest (Blanford's fox) are absent. Sexual size dimorphism in Israeli canids is generally less than in felids and mustelids (in which we analysed each sex as a separate ‘morphospecies’), so we used mixed-sex samples to represent each species. The three largest species (wolf, golden jackal and red fox) are also represented by Middle Palaeolithic samples in Israel, and all three had larger carnassial lengths then. Carnassial lengths, canine diameters and skull lengths are all remarkable evenly spaced among the five recent species in Israel. In Egypt, no trait manifests significant equality. Despite regional fluctuations in size, the carnassial length ratios of the three smaller species (foxes) are strikingly constant (1.18–1.21) throughout the region, while the ratios for the three larger species (wolf, jackal and red fox), sympatric only in Israel, are larger (1.33–1.34). Finally, mean carnassial length of jackals is constant across North Africa, while skull length and canine diameter both increase from Algeria through Egypt. All three traits are larger in Egypt than in Israel. We tentatively ascribe the equal ratios in Israel to competitive character displacement, though this hypothesis is speculative because of numerous lacunae in knowledge of diet, killing behaviour, available resources and extent of food limitation. Furthermore, humans have greatly affected range, density and ecology of wolves and jackals in the last century. Larger sizes in the Palaeolithic may well be manifestations of Bergmann's rule. The constancy of carnassial length in North African jackals, notwithstanding a longitudinal cline in CBLs of these populations, and the constant ratio between jackal and red fox carnassial length are both consistent with a hypothesis of character release in the absence of the wolf.