Competition and the exchange of grooming among female samango monkeys (Cercopithecus mitis erythrarchus)

Current socioecological models argue that multi-female primate groups engaging in cooperative, between-group resource competition (BGC), should have egalitarian social relations that promote cohesion among group members, while those that experience strong within-group competition (WGC) should exhibit nepotistic and despotic social behaviour (van Schaik, 1989; Sterck et al., 1997). Here we investigate the idea that very slight WGC can have strong effects on social relationships, even in 'egalitarian' populations, and that individual responses to ecological conditions may vary among group members. We estimated the intensity of both BGC and WGC and used the Biological Markets model to examine their effects on female dominance and grooming distributions for a group of samango monkeys (Cercopithecus mitis erythrarchus) in a high-density, territorial population. We found high levels of territorial activity consistent with female resource defence, low levels of within-group aggression and only slight effects of contest competition on diet. Individual grooming bouts were reciprocal, with no effects of rank, demonstrating that grooming was not exchanged for feeding tolerance. However, in contrast to other C. mitis populations, female samangos maintained a consistent, linear dominance hierarchy that was reflected in the overall patterns of association and grooming, with high-ranking females receiving more grooming, and lower-ranking females were less likely to take part in territorial activity. Our results support the prediction of the current socioecological model that WGC effects on female relationships will always be greater than the cohesive effects of BGC (Wrangham, 1980; Cheney, 1992), and show that a simple 'egalitarian' description of C. mitis female relationships is insufficient.