Niche Divergence Among Sex and Age Classes in Black-and-White Snub-nosed Monkeys (Rhinopithecus bieti)

A wide range of dimorphic species exhibit intraspecific differences in feeding ecology and habitat use; however, studies comparing resource partitioning between males and females and between age groups occur mainly at the community and species level. We here classified the main habitat of black-and-white snub-nosed monkeys ( Rhinopithecus bieti ) –fir tree crown– into six microhabitats; examined the lichen-load of the microhabitats; and investigated the microhabitat use of age–sex groups within one-male units (OMUs: an adult male, several females, and juveniles) of R. bieti using instantaneous scanning sampling methods to test whether there is resource niche partitioning in social units of this sexually dimorphic primate in a reserve in Yunnan, China. Our results showed that adult females and juveniles often foraged in the outer layer of the fir tree crown, whereas adult males often foraged in the inner layer, closer to the trunk where food abundance was highest. Adult females and juveniles, however, both shifted microhabitat-use patterns to the inner layer of the fir tree crown when the adult male was absent from the tree. We suggested that the preference for and benefit of the central layer of fir tree crown lies in food availability, but that adult male competitively excluded group members. Microhabitat segregation may serve to maximize the fitness of the group members by reducing intragroup competition, while also increasing interindividual distance, thereby reducing the possible effects of scramble competition.