Comparison of faecal nitrogen concentration between sexes of white-tailed deer in a tropical dry forest in southern Mexico

Abstract

Sexual segregation in the white-tailed deer is very common in temperate habitats. Two main hypotheses have been used to explain this pattern: one based on the differential risk of predation between the sexes and the other, sexual dimorphism. We evaluated whether sexual segregation is occurring in a tropical population of white-tailed deer by examining diet quality as measured by the concentration of faecal nitrogen (FN), expressed as a percentage of crude protein in the diet. A fuzzy clustering method of classification was used to separate the faecal groups of adult males and females over two different reproductive seasons. Using permanent transects during the reproductive and non-reproductive seasons, we collected 113 faecal groups in a large area of tropical dry forest. Sixty-three faecal groups belonged to females, and 50 belonged to males according to the fuzzy classification. There were significant differences in the percentage of faecal crude protein between sexes [analysis of variance (ANOVA) F = 7.011; df = 1; P = 0.009], with higher concentrations in the pellets identified as those of females. However, there was no difference in the concentration of FN between the reproductive and non-reproductive seasons (ANOVA F = 1.997; df = 1; P = 0.1604). The results show that in wild populations of white-tailed deer in the tropics there is sexual segregation: the observed differences in FN concentration best fit the prediction of the sexual dimorphism hypothesis, given that the females appear to consistently feed on better quality forage. As such, the explanation of sexual segregation of deer in a tropical dry forest must take into account that the forces behind segregation are not only reproductive strategies, but also the morphological and physiological differences imposed by sexual dimorphism in this species.