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

PLoS One. 2017 Mar 9;12(3):e0173369. doi: 10.1371/journal.pone.0173369. eCollection 2017.

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.

MeSH terms

  • Animals
  • Cercopithecidae / physiology*
  • Diet*
  • Feeding Behavior*
  • Food Supply
  • Fruit*
  • Hylobates / physiology*
  • Sympatry / physiology*

Grants and funding

This work was supported by: UC Davis Hellman Fellowship, 2009-2010, $25,500; UC Davis Small Grant in Aid of Research, Effects of spatial and temporal variation in plant productivity on the population ecology of Bornean rainforest primates, 2013, $2,000; UC Davis Small Grant in Aid of Research, Effects of spatial and temporal variation in plant productivity on the population ecology of Bornean rainforest primates, 2012, $2,000; Seneca Park Zoo, Grant for orangutan- gibbon field research and habitat conservation, 2012, $750; Mohamed bin Zayed Species Conservation Fund, Promoting gibbon conservation in Gunung Palung National Park, West Kalimantan through training and participatory monitoring activities with Indonesian university students and citizen scientists, 2012, $10,000 (URL: http://www.speciesconservation.org/); Victoria University, Wellington, New Zealand, The importance of mast seeding for vertebrate community structure and dynamics, 2012, with Heiko U. Wittmer, $40,000 NZD; Victoria University, Wellington, New Zealand, The importance of mast seeding for community dynamics, 2011, with Heiko U. Wittmer, $4,000 NZD; UC Davis Small Grant in Aid of Research, Effects of spatial and temporal variation in plant productivity on the population ecology of Bornean rainforest primates, 2011, $2,000; Orangutan Conservancy Grant, Emergency funding for Gunung Palung, 2011, $9,000; Leakey Foundation Research Grant, Emergency funding for Gunung Palung, 2011, $6,000 (URL: https://leakeyfoundation.org/grants/research-grants/); UC Davis Small Grant in Aid of Research, Effects of spatial and temporal variation in plant productivity on the population ecology of Bornean rainforest primates, 2010, $1,800; UC Davis New Research Initiatives, From individuals to landscapes: testing fundamental hypotheses about the reproduction of Bornean rainforest plants across a complex tropical landscape, 2009, $12,000; Leakey Foundation Research Grant, Causes and consequences of habitat quality variation for Bornean primates, 2009, $15,000 (URL: https://leakeyfoundation.org/grants/research-grants/); UC Davis Principal Investigator Bridge Program, Continued research on the population ecology of Bornean rainforest primates, 2008, $12,000; UC Davis Small Grant in Aid of Research, Continued research on the population ecology of Bornean rainforest primates, 2008, $2,000; Orangutan Conservancy, Infrastructure completion of the Cabang Panti Research Station and reestablishment of research at Gunung Palung (with C. Knott), 2007, $10,000; UC Davis Small Grant in Aid of Research, Effects of spatial and temporal variation in plant productivity on the population ecology of Bornean rainforest primates, 2007, $2,000. Disney’s Animals, Science and Environment provided support in the form of salaries for author KLF, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific role of this author is articulated in the ‘author contributions’ section.