EFFECTS OF GROUP DEMOGRAPHY ON DOMINANCE RELATIONSHIPS AMONG FEMALE PRIMATES .1. MOTHER-DAUGHTER AND SISTER-SISTER RELATIONS

In this paper we present a simulation model of the acquisition and maintenance of rank among female primates that includes the effects of demographic factors on the direction of dominance between mothers and daughters and between sisters. Our approach is based on realistic assumptions about the processes and behavioral propensities underlying rank relations. It takes into account the fact that the acquisition and maintenance of rank depend on asymmetries in the availability of allies, as well as on asymmetries in intrinsic fighting ability. Life-history parameters, which affect the age, size, and kinship structure among females, are therefore expected to have an important influence on the patterning of dominance relationships among females. We show that in expanding populations (population A), in which females achieve sexual maturity early, interbirth intervals are short, and the mortality rate is relatively low, younger sisters will usually be able to outrank older sisters by sexual maturity, and old mothers will often be able to remain dominant over full-grown daughters. However, in declining populations (population B), in which females are older at sexual maturity, interbirth intervals are relatively long, and the mortality rate is relatively high, younger sisters will be less likely to outrank older sisters by sexual maturity, and old mothers will be less able to remain dominant over full-grown daughters. At least two implications follow: observed differences in dominance pattern among females are not necessarily due to adaptive differences in underlying female propensities or strategies, and how successful a female is in pursuing fitness-biasing strategies can be significantly affected by population status. We suggest that demographic variation may be a significant, and comparatively neglected, source of intragroup, interpopulation, and interspecies variation in dominance pattern among female primates.