1Department of Anthropology, University of California at Davis, 2Graduate Group in Ecology, University of California at Davis, 3Animal Behavior Graduate Group, University of California at Davis, 4Ecological Evolution Group, Xishuangbanna Tropical Botanical Gardens, China, 5Chinese Academy of Sciences
Thursday 4:00-4:15, Galleria South
Understanding the factors that influence variation in orangutan population dispersion in space and time would both enhance our understanding of orangutan socioecology and contribute meaningfully to the conservation of this threatened taxon. We use data from a six year study of a population of Western Bornean Orangutans (Pongo pygmaeus wurmbii) at Gunung Palung National Park, West Kalimantan, Indonesia to test hypotheses about 1) the role of food resources (and different classes thereof) in determining orangutan dispersion across space and over time, and 2) how different age-sex classes respond to the availability of food and presence of conspecifics. We assessed orangutan population dispersion across seven distinct tropical rainforest types (spanning lowland peat swamp to montane forest) using direct observations of orangutans on fourteen survey transects. We also monitored the availability of orangutan plant foods monthly in ten randomly-placed phenology plots in each of the seven forest types. Orangutan population dispersion varied radically over the six year period, as did the absolute and relative availability of food in each forest type. The results of general linear models support the hypotheses that orangutan populations at Gunung Palung partially buffer themselves against resource scarcity by switching habitats, that population movements are best explained by the abundance of preferred foods, and that peat swamp forests serve as “fallback habitats”. Furthermore, patterns of dispersion differed among age-sex categories: as predicted by socio-ecological theory, movements of adult females across the landscape tracked variation in food availability far more closely than any other age-sex category.
This study was kindly supported by the University of California, Davis, the Hellman Foundation, and the Leakey Foundation.