The Importance of Edge: Bornean Orangutan Resource Use in a Transitional Habitat (#682)
Species vary in their ability to utilize resources in ecotones, with studies showing that more behaviorally flexible species are more successful in these transitional habitats. The endangered Bornean orangutan (Pongo pygmaeus wurmbii) is a large arboreal and primarily frugivorous primate that exhibits both characteristics found in behaviorally flexible species and species particularly sensitive to disturbance. Because of this unique combination, it is unclear whether orangutans utilize ecotones at the same frequency as other areas in their home range. This study combines over 20,000 GPS points representing habitat use (individual activity, foraging, nesting) with extensive phenology data from the Tuanan Orangutan Research Project, Central Kalimantan, Indonesia to determine if orangutans preferably use ecotones, what factors influence their edge use, and explores the potential ramifications of an increased human-wildlife interface along edge. The Tuanan research area is peat swamp habitat encompassing over 1,000 hectares, with a density of 4.5 orangutans per square kilometer. To measure orangutan edge use, we created a scoring system that measures habitat use compared to a mean score of 1.00, representing equal use among randomly uniform resources across the home range. Within 200m of the defined edge, orangutans used edge resources 1.98 times more than expected (σ = 1.84, N = 6 individuals). For some individuals, edge was up to 5.53 times higher than expected use. Our study demonstrates the importance of this transitional edge habitat for orangutan ranging. However, edge habitat inherently faces the greatest threat from human exploitation due to the collection of forest products or its close spatial relationship to human development (roads, power lines, pipelines, etc.). Given that orangutans in TORP area extensively use these edge areas, the potential impact of a large-scale project, like the currently proposed provincial road, should be carefully planned and environmental assessments should be conducted prior to construction.