Ecology Feeding Competition and Social Relationships of Phayre's Leaf Monkeys

Nonhuman primates are the most social among all organisms and exhibit the broadest range of variation in social organization. Consequently, research on the behavior and ecology of nonhuman primates has been most influential in addressing questions as to why organisms including humans live in groups in the first place, why they live in groups of particular sizes, and what factors influence the social relationships among group members. Leaf-eating monkeys are particularly interesting, because the relationship between their ecology and social organization is not consistent with current theory. Feeding on supposedly large abundant resources, they should live in large groups and exhibit weak dominance relationships. Quite often, however, they live in small groups with strong dominance hierarchies. The study is following up new explanatory ideas to resolve this controversy examining (i) whether indirect feeding competition or infanticide or both constrain group size of Phayre's leaf monkeys (Trachypithecus phayrei) and (ii) whether resource distribution, feeding competition, and female reproductive success conform to the predicted female social relationships and dispersal patterns. Research is conducted at Phu Khieo Wildlife Sanctuary, Northeastern Thailand harboring eight sympatric primates including two leaf monkeys (T. cristatus, T. phayrei) and four macaques (Macaca arctoides, M. assamensis, M. mulatta, M. nemestrina). The study area (156,000 ha) is undisturbed including two major habitat types (hill evergreen and dry evergreen forest). In the long range this setting will allow comparisons within primate genera and species of similar body size across habitats as well as across species and genera of similar body size within the same habitat. The study is based on a collaboration with researchers from two Thai Universities (Kasetsart and Mahidol University, Bangkok) and officials from governmental agencies (Royal Forest Department, Bangkok). Per year it will involve a minimum of two local staff, two recent graduates and one post-doctoral researcher and provide the opportunity for thesis research. The study will foster cooperation within Thailand and with the United States, support conservation efforts in the sanctuary, and provide training and career opportunities for students.