Sexual dimorphism and trophic constraints: Prey selection in the European polecat (Mustela putorius)

Abstract

Although widespread among mammals, sexual dimorphism raises several evolutionary and ecological issues. Despite strong sexual dimorphism (reaching the ratio 1.81), a study of diet and prey selection in polecats (Mustela putorius) revealed only minor differences in their feeding habits. There was a greater frequency of large-sized prey (mainly lagomorphs) in the summer diet of females than in that of males. The frequency of anurans (Rana dalmatina and Bufo bufo) in the diet did not differ significantly between the two sexes. Male prey predominated in the diet of both sexes. Although prey availability, as indicated by the trapping of small rodents and anurans, showed a predominance of males in populations, Ivlev's index for selectivity demonstrated selective predation on male prey exceeding availability both by male and female polecats. This selective predation by polecats may affect both population structure and population exchanges. My results suggest that sexual dimorphism of polecats was not linked to a different prey choice but results from independent intrasexual selective pressures, thus refuting the predictions of the trophic niche differentiation hypothesis. The wide size dimorphism reflects selection both for mating access in males and for food in females, illustrating the complementary influence of sexual selection and environmental constraints on sex divergence in growth.