Core area quality is associated with variance in reproductive success among female chimpanzees at Kibale National Park

Female East African chimpanzees, Pan troglodytes schweinfurthii, tend to range apart from each other in dispersed core areas, and they have dominance interactions with each other so rarely that it is difficult for observers to assess a dominance hierarchy. Nevertheless female chimpanzees can have high variance in fitness. Here, we test the hypothesis that female chimpanzee fitness variance is associated with variation in the foraging quality of their ranges. We studied range usage of 21 wild adult female chimpanzees within the Kanyawara community, Kibale National Park, Uganda. Core areas of individuals remained stable over a 9-year period and varied in their density of preferred foods. Females in neighbourhoods containing more preferred foods had elevated ovarian hormone production, shorter birth intervals and higher infant survivorship. Our results thus suggest that superior access to food may have enabled some community females to reproduce more successfully than others. Although dominance interactions are less frequent among females than among males of this species, we propose that the intensity of selection on intrasexual competition may be similar between the sexes. We discuss potential applications to other fission-fusion species.