No abstract

The reproductive performance of 760 free-ranging female rhesus monkeys (Macaca mulatta), 168 of whom were 20 years of age and older at the time observations were begun, was assessed. The monkeys were resident on Raccoon Key or Key Lois, two islands located in the Florida Keys, USA. During 1992 and 1993, live birth rates generally declined with age among the Raccoon and Lois females aged eight years and older. This age-related deterioration of female fertility was the result of proportionately more younger females bearing live young during successive birth seasons, and proportionately more older females experiencing an inability to bear live offspring even after a barren year. It is suggested that (1) older females may be more strongly inhibited by the suckling stimulus than are their younger peers, and (2) the risk of a permanent loss of fecundity increases with each additional year of life or parturition. The live birth rates of females aged 16-24 years were greater on Raccoon Key than they were on Key Lois, because the Raccoon females within this age range were more successful at bearing live offspring during successive birth seasons; the reason for this difference could not be determined. Inter-population differences in both the body condition of the females and the severity of female-female competition for access to males were not considered to be plausible explanations. It is possible that the difference in female fertility between the islands is the result of the greater age of the adult males on Key Lois, or the phytochemicals eaten by the females on Raccoon Key.

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.