Doctoral Dissertation Improvement: Predicting Intergroup Relationships in Primates (Two Case Studies)

Interactions between groups are an important aspect of social life because they can affect an individual's access to critical resources and thus its reproductive success. Primates, more than most other vertebrates, exhibit many kinds of group-level interactions yet the factors that give rise to this diversity are not well understood. For example, groups may interact aggressively or peacefully; males and/or females may participate; and an individual may defend access to food, mates, infants, and/or other resources. This study will field-test a predictive framework designed to explain the different group-level interaction patterns seen in social primates. This framework consists of two pre-existing hypotheses (one slightly modified) concerning food defense by females and males, and one novel hypothesis concerning male defense of fertile female mates. Each hypothesis proposes a set of ecological and social conditions under which a resource is economically defendable; that is, when the costs of defense are outweighed by the benefits associated with access to the resource in question. To test these hypotheses, the group-level interactions of grey-cheeked mangabeys and redtail monkeys will be examined in Kibale National Park, Uganda. The nature of group-level interactions in these two species has yet to be studied in populations that are near the environmental carrying capacity, where groups compete over limited resources. These two species are ideal for testing the hypotheses because they share certain key characteristics (and thus some predictions are the same for the two species) while differing in other key characteristics (leading to contrasting predictions). The study consists of behavioral observations of three groups of each species and playback experiments, in which calls from neighboring groups are played to the study groups to mimic the presence of competing neighbors. Behavioral responses of males and females during both naturally-occurring and simulated group encounters will be documented. The research will also monitor spatial and temporal variation in food availability to determine whether differences in food defense patterns stem from differences in food availability.

Like competition between individuals, competition between social groups is a pervasive and important aspect of animal life, yet the factors that determine who competes, and under what conditions, are poorly understood. This research will clarify how social and ecological factors shape behavioral strategies during group-level conflicts. Although the immediate research is focused on non-human primates, the findings may have relevance for other group-living vertebrates.