Doctoral Dissertation Improvement: Diet, Ranging Patterns and Social Behavior of Lar Gibbons at Huai Kha Khaeng, Thailand: Exploring the Limits of Flexibility

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Under the guidance of Dr. Thad Bartlett, Lydia Overbaugh will explore the degree of behavioral flexibility in the endangered white-handed gibbon in the Huai Kha Khaeng Wildlife Sanctuary (HKK), Thailand. White-handed gibbons living at HKK inhabit an environment that is unique in many ways. First, the forest is considerably drier than other white-handed gibbon study sites, receiving less than half the amount of rainfall than elsewhere, making this forest the ecological extreme of the range of white-handed gibbons. Second, the forest is part of the largest continuous protected area in Southeast Asia, which has led to the reduction in anthropogenic stresses while maintaining a largely intact large mammal community (including elephant, tiger, 8 diurnal primates, two leopards and two canids). Finally, gibbons at HKK inhabit a mosaic landscape, including seasonally dry evergreen, hill evergreen, mixed deciduous and deciduous dipterocarp forest types. This presents a unique opportunity to examine how white-handed gibbons respond to ecological differences at the extreme of their range and in a diversity of habitats. To determine how habitat quality impacts gibbon behavior and ecology, the feeding and ranging behavior of 6 gibbon social groups will be studied over a period of 12 months to test the following predicitions: first, that gibbons in evergreen forest will (i) have smaller home ranges and travel less per day, (ii) spend less time foraging, and (iii) have a higher quality diet; and second, that these differences are a result of differences in home range quality as indicated by the density of fruiting trees.Current hypotheses in human evolution favor an increase in the behavioral and dietary flexibility of Homo as an explanation for the success of our lineage. By examining the degree of flexibility present in a more distantly related ape species, we can better evaluate the assertion that flexibility is a uniquely human innovation. As many gibbon researchers have described gibbons as being dependent upon evergreen forest, this study will demonstrate the ways in which white-handed gibbons cope with ecologically marginal habitats. Furthermore, gibbons are primarily monogamous, but significant rates of polyandry and polygyny have been recorded for some populations and these occurrences have been linked to ecological differences such as seasonal and geographic resource availability. This project will therefore increase our understanding of the role of habitat quality in the maintenance of social monogamy in white-handed gibbons.The proposed project will assist in graduate student training and increase the participation of women in scientific research while promoting a minority-serving institution. Additionally, the establishment of a new field site will provide opportunities for training Thai field assistants and instructing US undergraduate students. The most tangible impact of the proposed research is its applicability to primate conservation. By better understanding the degree of behavioral flexibility under distinct ecological conditions and at this species' ecological extreme, this project will inform conservation policies for white-handed gibbons. This knowledge can also provisionally be used for conservation purposes in the absence of comprehensive knowledge of other more critically endangered gibbon species.