Group size in wedge-capped capuchin monkeys Cebus olivaceus and the reproductive success of males and females

Summary The effect of variation in group size on age-specific survivorship and fecundity rates were examined in a population of wedge-capped capuchin monkeys Cebus olivaceus during a 10 year study. Life tables were constructed separately for four large (15 individuals) and four small groups (<15 individuals). Female reproductive success, and its relative contribution to population growth, was much higher in large groups, primarily through higher age-specific fecundity. Age-specific survivorship was similar in groups of different sizes. The reproductive success of the single breeding male in a group was much higher in large than small groups. Compared to small groups, breeding males in large groups had a longer breeding tenure, and access to greater numbers of reproductive females with a higher average fecundity. Differences in female reproductive success apparently resulted from variation in access to monopolizable fruit trees. Large groups predictably displaced small groups during intergroup encounters. Group rank depended on the number of males resident in groups. The large number of non-breeding males in large groups results from their longer average residency time. I explain the longer residency of males in large groups by the higher average reproductive success of breeding males in these groups.