Living in permanent social groups with a wide variation in social organization, social structure, and mating systems is characteristic for many nonhuman primates. Correspondingly, many studies have been addressing questions as to why primates live in groups, what determines group size, and what factors influence the social relationships and mating strategies of the individuals. Leaf-eating monkeys are particularly interesting in this regard, because the relationship between ecology, social organization, and social structure is not well understood. Recent research suggests that folivore group size might be limited via scramble competition for food, however, its strength and the importance of dietary fiber as a constraining factor remains to be disclosed. Furthermore, despotic female social relationships found in some (folivorous) species, in which females leave their natal group, are in disagreement with current models. Finally, in many primate species male social relationships are strongly antagonistic and guided by mate competition. The occurrence of male policing and strong male bonds are, however, poorly understood.
This study aims to address these controversies by observing Phayre's leaf monkeys (Trachypithecus phayrei) to evaluate hypotheses on (i) constraints of group size in a folivorous primate, (ii) the ecology of female social relationships in a female dispersal species with despotic dominance relationships, and (iii) the behavior of males in terms of male policing and male affiliation. Research will be conducted at Phu Khieo Wildlife Sanctuary, Northeastern Thailand. Koenig and colleagues will collect extensive data on resource characteristics, female social relationships, male affiliative and agonistic behavior, estimates of energy intake and activity for individuals in several groups. Koenig will investigate the energetic consequences of increasing group size as well as the underlying mechanisms in terms of day range, feeding time, and fiber content. The PI will analyze the interrelations of energetic consequences of feeding competition with female social behavior. The PI will examine the influence of male interventions on female conflicts and relationships. Finally, Koenig will examine male care and male affiliation in order to address questions related to paternity, mating effort, and the formation/ maintenance of coalitions.
This long-term project has had and will have broader impacts in several regards. It is based on collaboration with sanctuary authorities and two Thai Universities providing training and research opportunities for sanctuary personnel and Thai graduate students. In addition, the project is providing training, career, and research opportunities for post-doctoral fellows and graduate students. The study, furthermore, involves recent university graduates who use the experience gained in the project to later go on to graduate school. The PI and the Co-PI have established a training program on primate ecology and conservation geared towards Thai forest research officers, lecturers, and graduate students. Finally, the project provides data on forest composition, phenology, and animal abundance to the local conservation project to be used in an overall database of the sanctuary, part of the only major forest area left in the northeast of Thailand.
