Doctoral Dissertation Research: Effects of a Dispersal Barrier on Cultural Similarity in Wild Orangutans (Pongo pygmaeus wurmbii)

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This project will contribute broadly to our growing knowledge of great ape behavioral ecology and genetics, while furthering the study of human origins through an investigation of cultural behavior on two sides of a dispersal barrier. The identification of arbitrary signal variation and rudimentary symbol use in orangutans suggests that previous studies may only have scratched the surface of existing cultural variation in this lineage, a phenomenon that is inherently interesting to humans and therefore capable of generating significant interest in orangutan conservation. Because animals cannot cross dispersal boundaries, cultural variants should reflect the history of diffusion from the locations(s) of innovation until blocked by a dispersal barrier. This project will test the ability of a cultural interpretation to account for patterns of behavioral variation exhibited by wild Bornean orangutans (Pongo pygmaeus wurmbii) ranging on either side of a 150m-wide river in Central Kalimantan, which currently serves as an effective barrier for orangutan dispersal in the study region, but offers opportunities for gene flow at its more narrow headwaters. The synchronized study of orangutans on opposite sides of a river barrier offers an exceptional opportunity to empirically evaluate the assumptions of a cultural interpretation for behavioral variation (based on opportunities for social learning), while holding both ecological variation and genetic relatedness constant. This project will assess the impact of social learning on the presence of skills required for orangutan survival and local adaptation, which are critical to the success of reintroduction efforts currently underway. It will also give us a greater understanding of the ecological and social contexts that favor cultural solutions for orangutans in particular situations but not in others, which will give us insight into the likely extent of culture in the last common ancestor of the great apes. More broadly, this project will aid conservation initiatives by documenting the extent to which geographic variation in wild orangutan behavior is maintained by social transmission and, therefore, the extent to which reintroduced or translocated animals have difficulty achieving full adaptation to local conditions. This research will provide numerous opportunities for promoting student training and participation in research. Preliminary data were collected with the help of a Duke University undergraduate student as well as several local Indonesian assistants and university students. The proposed research will continue to provide training for Indonesian students and assistants and will promote international collaboration with Indonesian, European, and American counterparts. The orangutan is presently confined to highly fragmented populations in small forest patches on the islands of Borneo and Sumatra. Despite its formally protected status, the orangutan has become a critically endangered species, the extinction of which is anticipated within the next two decades due to the continuing threat of timber exploitation and human encroachment throughout its range. It is critical that this research be carried out soon, because there is a danger that as habitat devastation continues, individual orangutan populations with unique local traditions will vanish, resulting in lost opportunities to document the full extent of cultural behavior in wild orangutans.