Variability and sexual size dimorphism in carnivores: Testing the niche variation hypothesis

The niche variation hypothesis predicts greater morphological variability in populations occupying wide ecological niches than in those occupying narrow ones. Island populations of carnivores are often assumed to have wider niches than mainland populations, because the number of competing species on islands is usually smaller. We compared coefficients of variation and degrees of sexual size dimorphism in skulls and canines of pairs of related insular and mainland populations belonging to 39 carnivore species. Mainland populations were more variable than insular ones. Averaging population values for the different species, we found no significant differences in the variability of insular and mainland taxa. There was no consistent difference in the degree of sexual size dimorphism between insular and mainland carnivores for either skull length or canine diameter. We hypothesize that gene flow is the main source of the greater variability in mainland populations. The niche variation hypothesis is not supported.