This research project investigates the question whether food availability and intraspecific competition are significant sources of stress in adult female Cercopithecus mitis. Furthermore, we characterize individual differences in stress responses, and evaluate behavioral strategies that the animals use to cope with physiological and psychological stressors.

According to the predictive framework of primate socio-ecology, female social relationships in primate societies are associated with the relative strength of within and between group feeding competition (competitive regime), which in turn is determined by the abundance and distribution of resources. Fluctuations in food availability and energy demand can lead to nutritional stress, and direct competition creates social stress and reinforces dominance hierarchies. However, little is known about physiological stress responses in relation to competitive regimes, and about their impacts on individual fitness. Reproductive success may not be the best measure of fitness effects, as even chronic stress may not have short-term effects on reproduction, but rather long term effects on immunity and lifespan. Measuring physiological stress levels non-invasively can provide a feasible alternative for assessing the relationship between competitive regimes and fitness costs to female non-human primates.

Several field studies have measured stress levels through analysis of glucocorticoid metabolites (GC) in feces and urine of non-human primates. All of them have investigated social status as a predictor of stress levels, relating to the common idea that social hierarchies result in unequal allocation of resources within groups, especially where hierarchies are strongly enforced through agonistic interactions. However, individual differences in GC levels may depend more on behavioral strategies than on dominance status per se. Furthermore, physiological stress levels are not associated with aggression in all species with well differentiated social hierarchies, and social status may be related to GC levels only where it carries significant energetic costs. Resource characteristics and the resulting competitive regime could complement a predictive framework of physiological stress responses in wild non-human primates and other mammals, because they influence both energetic costs and the frequency and distribution of aggression among social groups.

Results from this research will be important for predicting the susceptibility of guenon populations to environmental change, particularly human induced changes. It will help to evaluate the impacts of provisioning on primate behavior and physiology, which can have implications in area of animal welfare. Furthermore, this study may help us understand some of the proximate causes behind the success of modern hominids, because there is evidence that increasing seasonality was associated with metabolic stress in early hominids. However, the drastic environmental changes of the late Cenozoic did not seem to affect the distribution and spread of modern hominids and cercopithecid lineages as much as other forest living primates. In fact, environmental instability may have played an important role for the emergence of behavioral versatility and ecological diversity in hominids, providing an advantage over less adaptable taxa.