Primate Distribution Dynamics and the Effects of Contemporary Climate Change Along an Elevational Gradient in Indonesian Borneo

Abstract

Climate is a major driver of global change and can force both gradual and abrupt environmental transitions that profoundly influence traits of organisms, the quality of their habitats, and the persistence of populations. In an age when humans are drastically altering global patterns of temperature and precipitation, field studies of extant species are crucial to generate predictions about the future of modern populations, as well as grasp the ecological foundations underlying differential evolved species’ responses to climatic change. To that end, interest in how climate change affects modern species and ecosystems is surging, and studies of diverse taxa have shown that most species respond by either shifting their ranges or altering their behaviors. However, investigations of primates and their evolved response mechanisms remain rare and challenging, in part due to their slow life histories and fragmented habitats that may impede their potential to disperse.

This dissertation addresses these gaps by summarizing the state of knowledge of nonhuman primates and the effects of contemporary climate change, followed by two studies that consider whether climate change may drive nonhuman primates to shift their distributions along a continuous elevational gradient at the Cabang Panti Research Station in Gunung Palung National Park, Indonesian Borneo. At Cabang Panti, decades of data have been collected on weather, food availability, and the abundance of five diurnal primate species: Western Bornean orangutans (Pongo pygmaeus wurmbii), White-bearded gibbons (Hylobates albibarbis), Red leaf monkeys (Presbytis rubicunda), Long-tailed macaques (Macaca fascicularis), and Pig-tailed macaques (Macaca nemestrina).

For all primates except pig-tailed macaques, abundance of individuals declined over 35 years and withdrew from certain lowland forests disproportionately relative to upland forests. Upward distribution leans (i.e. relative abundance increases towards the uphill range limit, and relative decreases at the downhill range limit) were also evident for orangutans and gibbons as relative counts increased in upland forests. Maximum temperature was not strongly related to counts for any species. Minimum temperature, precipitation, and food availability were not strong predictors of overall trends in primate abundance but were reliably associated with counts at certain elevations. Weather conditions themselves at Gunung Palung were not consistent with broader regional patterns. Over the last 15 years, Cabang Panti has gotten cooler and wetter while Borneo generally trends hotter and drier. Collectively, these results provide key insights into the diversity of ecological parameters that can influence primate behavior in a heterogeneous landscape, and thus the importance of accounting for both species’ abiotic and biotic environments in projections of future change. These findings also reinforce the significance of elevation gradients in an evolutionary context as potential climate refugia for primates and other tropical vertebrates.