GELIFES Seminars - Patricia Izar

Patricia Izar (University of São Paulo)

Ecological correlates of social variability in tufted capuchin monkeys, genus Sapajus

Socioecology models assume that primates adjust their social behavior to ecological conditions, and predict that food availability and distribution, predation risk and risk of infanticide by males affect patterns of social organization, social structure and mating system of primates. However, plasticity and variation of social behavior may be constrained by conservative adaptations and by phylogenetic inertia. The comparative study of closely related species can help to identify the relative contribution of ecological and of genetic determinants to primate social systems. We compared ecological features and social behavior of two species of the genus Sapajus, S. nigritus in Carlos Botelho State Park, an area of Atlantic Forest in São Paulo state, S. xanthosternos in Una Biological Reserve, an area of Atlantic Forest in the Bahia state, and S. libidinosus in Fazenda Boa Vista, a semi-arid habitat in Piauí state, Brazil. S. xanthosternos and S. libidinosus perceived higher predation risk than S. nigritus. In the three studied populations, capuchin monkeys fed on fruits in usurpable sources of variable size, small to intermediate in PECB, small to large in FBV, and intermediate to large in ReBio Una. As predicted by socioecology, females in FBV compete directly for usurpable foods, are philopatric, and establish a linear dominance hierarchy, with nepotistic coalitions. Females in PECB do not compete directly for food, can disperse, and do not establish hierarchical relationships. Females social relationships in ReBio Una are not sufficiently explained by features of food sources alone: they present greater tolerance than expected and compete significantly with males in food sources, suggesting an effect of predation risk. Grooming relations in the three populations are also not sufficiently explained by the models, indicating that the benefits of grooming can be multiple and not only the acquisition of allies in hierarchical disputes. Also according to socioecology, group size and cohesion varied according to the balance between food abundance and predation risk, with maximum group size and greater cohesion in ReBio Una and FBV, and lower values in PECB where predation risk was lower. The highest sex ratio found in ReBio Una also favors the hypothesis that males are more efficient in group protection against predators. The mating system varied more with variation in sex ratio of the groups than with variation in ecological features of the areas, favoring the hypothesis that mating systems result from male capacity of female monopolization and female strategies to avoid male coercive strategies.