Models of affiliative relationships among free-ranging rhesus monkeys (Macaca mulatta) .2. Testing predictions for three hypothesized organizing principles

Several organizing principles based on maternal kinship and/or dominance relationships, have been proposed to explain the structure of female-female macaque affiliative relationships. Social interactions among adult rhesus females of one free-ranging social group on Cayo Santiago, Puerto Rico were observed for four consecutive years to determine the extent to which patterns of affiliative interaction met several predictions of three such hypothesized organizing principles: kin-based attractiveness, attraction-to-high-rank and the similarity principle. We employed a multiple regression extension of the Mantel test (Smouse et al., 1986) to test the independent effects of kinship and rank distance on measures of affiliation and reciprocity. Close kin not only engaged in more affiliative behaviour than distant kin (see our companion paper, Kapsalis & Berman, this volume), they were more likely to support one another in agonistic encounters and to exchange grooming for alliance support and access to drinking water. We found evidence that low-ranking females were attracted to high-ranking females in some years of study, and that grooming by low-ranking females was exchanged with tolerance at a monopolizable resource by high-ranking grooming partners. However, we were unable to test conclusively for the effects of competitive exclusion. Little evidence was found to support the predictions of the similarity principle. We concluded that kin-based attractiveness was probably the primary organizing principle operating in the study group but that elements of attraction-to-high-rank may operate in concert to some extent.