Spatial benefits afforded by high rank in white-faced capuchins

Abstract

Group living is a source of both costs and benefits for animals. Benefits may include decreased predation risk, and an increased ability to find food and defend clumped resources; the most prominent cost is probably increased competition for food within the group. Presumably, animals will always try to minimize the cost they receive relative to the corresponding benefit. Since costs and benefits will vary between spatial positions within the group, animals should prefer those spatial positions with the lowest costs relative to benefits. For groups whose members are organized by a social dominance hierarchy, access to preferred spatial positions may be a benefit of high rank. We examined the relationship between dominance rank and spatial patterns in two groups of white-faced capuchins,Cebus capucinus. We expected the animals to be faced with two cost–benefit gradients: predation risk increasing from centre to edge, and depletion costs increasing from front to back. Depletion was a significant factor in the dry season but not in the wet season; therefore, presumably only the predation risk gradient was present in the wet season. Dominant animals were more central than their subordinate counterparts during both seasons, and within the centre, they preferred the most forward position during the dry season but not during the wet season. The absence of variation in agonism across spatial positions suggests that active exclusion of subordinates by dominant animals cannot explain the spatial patterns observed. Instead, we conclude that subordinates avoid dominant animals as a strategy to reduce contest competition.