Contest and scramble competition: patterns of female aggression and ranging behavior among primates

The fact that most female primates (and many other mammals)live in groups is paradoxical, given that the presence of otherspresumably increases competition for foods and may, for some,reduce reproductive success. Competition for food resourcesis generally inferred from any of the following observations:(1) female dominance hierarchies within groups; (2) female aggressionbetween groups; (3) increasing home-range size with increasinggroup size; (4) longer day-range length with increasing groupsize; and (5) lower reproductive rates in larger groups. Bothfemale aggression (interference competition) and adjustmentsof ranging behavior to group size (exploitative competition)have been linked in the past to patterns of food distributionand abundance. Using data largely from the literature, thispaper examines the covariance of female aggression and rangingbehavior among 20 species of primates in an attempt to betterexplain the variation in female relationships within and betweengroups of primates. Results show that groups of females areaggressive toward other groups and that home-range size increaseswith increasing group size in most species. In addition, inthose species with strong dominance hierarchies within groups,day-range length increases as a function of group size. However,in those species that do not have strong dominance hierarchieswithin groups, dayrange length does not increase as a functionof group size. The implications of these results are presentedin a model that suggests that intergroup competition is determinedby food abundance, whereas intragroup competition is determinedby food distribution. This model differs from earlier modelsin its explanation of the ecological conditions that influencefemale relationships within and between groups of primates.[Behav Ecol 1991;2:143–155]