Interdepartmental Doctoral Program in Anthropological Sciences, Stony Brook University
Friday 5:00-5:15, Ballroom C
During resource bottlenecks, sympatric ecologically-similar species are expected to reduce feeding competition by diverging in their responses. Individuals should compensate by either increasing feeding and travel time or decreasing travel time. However, when foraging effort exceeds energy intake, dietary switching and increases in dietary breadth may prevent negative energy balance. I compared responses to seasonal changes in fruit availability between sympatric siamangs (Symphalangus syndactylus, 4 groups) and agile gibbons (Hylobates agilis, 2 groups) at Way Canguk, Sumatra. Although siamangs dominate gibbons, ecological overlap is high, with both species preferring ripe fruits. Data were collected from October 2008 through October 2009 on activity, diet (N=169 siamang and 115 gibbon all-day follows), and monthly fruit abundance across 100 10x50 m phenological plots. During periods of ripe fruit scarcity neither siamangs nor gibbons significantly altered feeding time or dietary breadth. However, both species increased consumption of fallback foods (ANOVAs: p<0.05). While siamangs increased fig consumption, slightly increased leaf consumption, and decreased travel time, gibbons decreased fig consumption and greatly increased feeding on young leaves (ANOVAs: p<0.05), but did not alter travel time. The dominant siamangs preferentially fed on large, productive fig patches, whereas gibbons used lower quality resources. Despite similar responses, siamangs and gibbons used divergent strategies during resource bottlenecks. Because hylobatid densities are predicted by fig availabilities, gibbon’s inability to access these resources during crunch times may contribute to their low density at Way Canguk. Gibbons may coexist as fugitive species by using resources less-preferred or overlooked by siamangs.
Supported by the American Society of Primatologists, the Leakey Foundation, a Mildred and Herbert Weisinger Dissertation Fellowship, and the National Science Foundation DDIG (BCS-0726089)