Effect of resource competition on the long-term allocation of grooming by female baboons: evaluating Seyfarth's model

Seyfarth (1977, Journal of Theoretical Biology, 65, 671-698) proposed an influential model that explained the long-term patterning of grooming relationships between female primates in terms of an interaction between the idealized grooming objectives of females and competition for valuable grooming partners. A critical test of the model requires a demonstration not only that competition for partners exists, but also that females do have an underlying target for the amount of grooming that they would like to receive relative to the amount they need to give. As it is not possible to stipulate a priori what this target is, or to detect it directly, we assessed its applicability by making a set of predictions, within the framework of Seyfarth's model, as to how observed grooming patterns should change with changes in the intensity of resource competition. We tested the se predictions with data from a troop of baboons, Papio hamadryas ursinus, for which the within-bout structure of grooming has already been shown to be sensitive to changes in resource competition (Barrett et al. 2002, Animal Behaviour, 63, 1047-1053). We found no evidence of competition for grooming partners and our results do not support the predictions of the modified model with respect to the existence of underlying grooming objectives. The findings that the grooming of female baboons is more diverse and that the mean rank distance separating partners increases when resource competition is greater, together with the absence of rank effects on long-term patterns, are, however, supportive of the recent biological market approach to social interactions. (C) 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.