Ecological Mechanisms Underlying Differences in Agonistic behavior Among Females in Two Cercopithecine Primate Species

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This research project will elucidate the ecological mechanisms that are ultimately responsible for differences between vervet monkeys (Cercopithecus aethiops) and patas monkeys (Erythrocebus patas) in female agonistic relationships within groups. Despite their sympatry and phylogenetically close relationship, vervets and patas differ in their expression of female competitive relationships: female vervets have stable, linear dominance hierarchies whereas female patas have less stable, non-linear dominance hierarchies. Although theoretical and empirical evidence suggests that these behavioral differences can be explained ultimately by differences in some quality of food resources, the critical characteristic of food that is responsible for variation in female competitive behavior in primates still eludes us. Spatial distribution of foods has long been the leading contender as the critical characteristic. Recent research on this population of vervets and patas suggests, however, that the critical characteristic is actually feeding site depletion time, which is determined by food size and handling time. Although the foods of patas are more widely spaced than the foods of vervets, they also have shorter depletion times. More revealing is that when vervets forage in two adjacent habitats, they eat foods that do not differ in their spatial distribution but that do differ in their depletion times, and agonistic interactions occur more frequently in the habitat with foods having the longer depletion times. Foods that are depleted slowly may be easier to usurp than foods that are depleted quickly. This project will clarify the roles of feeding site depletion time and interfood distance in determining the differences between vervets and patas in female agonistic relationships. Feeding site depletion time and interfood distance will be systematically manipulated in a series of field experiments to determine the temporal and spatial threshold levels of usurpability for vervets and patas. The thresholds of usurpability obtained in the experiments will then be compared to interfood distances and depletion times of wild foods to assess whether the thresholds can predict agonistic behavior over foods under natural conditions.