The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)

Variation in the nutritional quality of the diets of two populations of Bornean orangutans (Pongo pygmaeus wurmbii): implications for population density


1Department of Anthropology, Rutgers, The State University of New Jersey, 2Department of Anthropology, The George Washington University, 3Wildlife Research Group, The Anatomy School, Cambridge University, 4Orangutan Tropical Peatland Project, Centre for the International Cooperation in Sustainable Management of Tropical Peatlands, University of Palangkaraya, 5Anthropological Institute and Museum, University of Zurich

Thursday 4:30-4:45, Galleria South Add to calendar

Understanding the factors that contribute to variation in primate population density is of primary concern for conservation efforts. Recent studies of dietary and nutritional ecology in wild primates have demonstrated that great intra-specific variation can exist between nearby populations. We compared the nutritional quality of the diets of two Bornean orangutan populations, in the Tuanan and Sabangau peat-swamp forests, separated by 52 km. We hypothesized that the nutritional quality of food resources at Tuanan would be higher, as Tuanan is more alluvial, whereas Sabangau is entirely ombrogenous. We collected samples of food items consumed by orangutans at both sites, and analyzed them in the same laboratory using standardized nutritional chemical analysis. To calculate energy intake rates for each site, we analyzed over 10,000 hours of focal data collected between 2003-2009. Both total energy and metabolizable energy of dietary items are significantly greater at Tuanan compared to Sabangau (n= 215, 183; p=0.02 and p<0.0001 respectively). Dietary items at Tuanan are significantly higher in lipids and total non-structural carbohydrates (TNC), but lower in neutral-detergent fiber (NDF). To examine this relationship more thoroughly, we compared those species that are consumed at both sites using non-parametric matched tests. Metabolizable energy, crude protein, TNC, and energy intake rate values were all higher at Tuanan, while NDF values were higher at Sabangau. These differences in dietary nutritional quality may provide insights into why orangutan population density is two times greater at Tuanan compared to Sabangau, and attest to the importance of distinguishing peat-swamp forest types.

Funding was received from the Conservation, Food and Health Foundation, George Washington University Selective Excellence Fund, Packard Foundation (2007-31754), Leakey Foundation, National Geographic Society, National Science Foundation (BCS-0643122, -721288, and -9414388), Orangutan Conservancy, US Fish and Wildlife Service, and Wenner-Gren Foundation.

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