Doctoral Dissertation Improvement: Contest competition and its relation to behavior and stress physiology in wild Cercopithecus mitis

Environmental conditions are known to affect several key aspects of animal social systems including group size and composition, and the frequency of aggression, affiliation and cooperation. In non-human primates, there is evidence that the abundance and distribution of food are especially important variables, exerting their effect through the competition they bring about, both within and between groups. Socioecological theory suggests that when scarce resources can be monopolized by individuals and groups, there will be high levels of aggressive (direct) competition between the competing parties; however, resources from which others cannot be effectively excluded should result in scramble (indirect) competition, with competing parties racing to consume the food first, with little or no aggression. Only aggressive competition leads to increased social conflict and (according to theory) to the formation of strong social hierarchies. Under such circumstances, individuals with high status should benefit in terms of lifetime reproductive success, or fitness. However, the low reproductive rate and long lifespan of human and non-human primates has so far made it difficult to measure reproductive success, and thus to examine the link between food resources and fitness. In the study species, for example, previous research revealed linear dominance hierarchies among females, indicating within-group aggressive competition; surprisingly, however, reproductive rates were not related to social status. A possible reason for this finding is that reproductive rates alone may not accurately assess fitness consequences of social and ecological conditions in these slowly reproducing animals. Physiological stress may provide a new alternative measure of fitness in mammalian societies. Deviations from the normal stress response pattern, particularly chronically elevated levels, are known to have many pathological consequences, including long-term effects on immunity and lifespan. This research will investigate how variation in competition for food influences stress physiology and behavioral adjustments, using blue monkeys in two populations in Kenya as a model system. Cords and Foerster will characterize aggressive competition in three wild social groups that differ in the level of food supplementation they receive from humans. Over an 18-month period, they will monitor glucocorticoid (stress) hormone metabolites non-invasively, using fecal extracts from individually known females at an unprecedented sampling frequency. They will simultaneously sample social and foraging behavior. Unlike previous studies, this intensive sampling regime allows the investigators to assess what determines both within- and between-subject variation in glucocorticoid levels in response to both short- and long-term social and environmental stressors. Cords and Foerster will control for other factors known to influence stress levels, such as reproductive status, food availability, energy expenditure, and the occurrence of coping behavior. In terms of broader impacts, this research completes the doctoral training of Foerster. In addition, both local Kenyan and international field assistants will receive training in field methods of primate behavioral ecology. A Kenyan graduate student will conduct a parasitological study on fecal samples in collaboration with the Institute of Primate Research, Nairobi. Results from this research will help to assess long-term effects of food supplementation on the health of this and other species of wild non-human primates, and thus has implications for the conservation and management of wild animal populations.