The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)

Of fugitives and refuges: coexistence despite intense interspecific competition in hylobatids


Interdepartmental Doctoral Program in Anthropological Sciences, Stony Brook University

Thursday 8:15-8:30, Galleria South Add to calendar

Competition between ecologically-similar species can be particularly intense; however, coexistence may be possible through interspecific dominance relationships. Because dominant groups cannot occupy all food patches at one time, resources may be divided spatio-temporally. It has been hypothesized that subordinate species may 1) function as “fugitives” by avoiding encounters and more rapidly utilizing renewed patches, or 2) rely on competition refuges (i.e., lower-quality, less-defended resources). Either strategy may promote coexistence, but will increase travel costs and decrease energy intake for the subordinate species. I investigated these mechanisms in sympatric siamangs (Symphalangus syndactylus, 4 groups) and agile gibbons (Hylobates agilis, 2 groups). Siamangs dominated agile gibbons in encounters that were frequent, aggressive, and energetically costly. Data were collected from September 2008 to October 2009 on ranging and feeding patch use (N=1,900 feeding bouts, 1,492 patches) at Way Canguk, Sumatra. The location, size and yield (i.e. % of crown covered by food items) of all patches, as well as patch residencies and feeding bout durations were recorded. Contra to the predictions for fugitives, agile gibbons neither started to feed earlier in the morning (Chi-square: P>0.05) nor traveled further between feeding patches (ANOVA: P>0.05) than siamangs. In support of the competition refuge hypothesis, agile gibbons used patches with significantly less available food and had shorter patch residencies and feeding bout durations than siamangs. Patches used by agile gibbons, however, were significantly larger than those used by siamangs (ANOVAs: Ps<0.05). In conclusion, agile gibbons are not fugitives, but rely, instead, on competition refuges for survival.

Supported by the American Society of Primatologists, the Leakey Foundation, and the National Science Foundation DDIG (BCS-0726089).

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