Dietary diversity, feeding selectivity, and responses to fruit scarcity of two sympatric Bornean primates (Hylobates albibarbis and Presbytis rubicunda rubida).

Brenda A Wilson,Dena J. Clink,Katie L. Feilen,Christopher Dillis,Andrew J. Marshall,Lydia Beaudrot

doi:10.1371/journal.pone.0173369

Abstract

Effectively characterizing primate diets is fundamental to understanding primate behavior, ecology and morphology. Examining temporal variation in a species’ diet, as well as comparing the responses of different species to variation in resource availability, can enhance understanding of the evolution of morphology and socioecology. In this study, we use feeding data collected over five years to describe the diets of two sympatric Southeast Asian primate species of similar body size: white-bearded gibbons (Hylobates albibarbis) and red leaf monkeys (Presbytis rubicunda rubida), in Gunung Palung National Park, West Kalimantan, Indonesia. Long-term data sets are especially important for characterizing primate diets in Southeast Asia, where the forests exhibit supra-annual mast fruiting events. We found that gibbons were mainly frugivorous, with fruit and figs comprising 70% of their 145 independent feeding observations, whereas leaf monkeys ate a substantial amount of seeds (26%), fruits and figs (26.5%) and leaves (30%, n = 219 independent feeding observations). Leaf monkeys consumed a higher number of plant genera, and this was due mostly to the non-frugivorous portion of their diet. To investigate resource selection by these primates we utilized two different approaches: the Manly Selectivity Ratio, which did not take into account temporal variation of resource availability, and a model selection framework which did incorporate temporal variation. Both species selected figs (Ficus) more than predicted based on their availability under the Manly Selectivity Ratio. Model selection allowed us to determine how these primates alter the proportion of leaves, flowers, seeds, figs and fruit in their diets in response to variation in fruit availability. When fruits were scarce, both gibbons and leaf monkeys incorporated more leaves and figs into their diets, indicating that these two food classes are fallback foods for these primates. We discuss how different measures of resource selection can provide seemingly contradictory results, and emphasize the importance of long term studies that combine independent feeding observations with rigorous assessment of temporal variation in resource availability when modelling feeding selectivity.

Highlights

A thorough investigation of primate diets, and how primates alter their diets in response to variation in food availability, is fundamental for understanding primate behavior, ecology and morphology [1,2,3,4,5,6,7,8,9]
We examine the feeding ecology of sympatric populations of gibbons and leaf monkeys to: 1) characterize and compare gibbon and leaf monkey diets, identify the genera consumed and their importance, the relative contribution of different plant parts to overall diets, and overall dietary richness, diversity and overlap; 2) analyze feeding selectivity for each primate species; and 3) assess how these primates respond to temporal variation in fruit availability
41% of feeding observations were recorded on census routes (NGIBBONS = 102 observations or 46% of total gibbon observations, NLEAF MONKEYS = 120 observations or 38% of total leaf monkey observations), and the remainder were made during focal follows

Summary

Introduction

A thorough investigation of primate diets, and how primates alter their diets in response to variation in food availability, is fundamental for understanding primate behavior, ecology and morphology [1,2,3,4,5,6,7,8,9]. Periods of resource scarcity may have important impacts on primate fitness because during these times feeding competition can be intense and food quality poor [10]. While such periods can have disproportionate impacts on primate feeding adaptations and sociality, they occur infrequently in some environments [9,11,12,13]. Mast fruiting events are periods of super-abundance of resources, and are characteristically followed by periods of extreme food scarcity [14,19] These phenological cycles are linked to EL Niño Southern Oscillation events [18,21] and occur at irregular intervals that are unpredictable from the perspective of vertebrate frugivores. Studying the responses of frugivores to these fluctuations in food availability—especially the responses of multiple taxa that differ in their dietary adaptations, life histories, and feeding strategies [23,24]–can shed light on the evolution of primate feeding adaptations

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Discussion

Conclusion