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

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.

Influence of fruit availability on macronutrient and energy intake by female chimpanzees

“…However, despite the increase in feeding time, there was no commensurate increase in food intake, presumably because the fibre‐rich foods that were eaten in greater amounts were eaten more slowly (Oftedal, ). The foraging strategy employed by female chimpanzees during fig‐months was thus typical of frugivorous primates during fruit‐scarce periods, involving changes both in diet composition and in time spent feeding (Clink et al, ; Conklin‐Brittain et al, ; Doran, ; Felton et al, ; Irwin et al, ; Tutin et al, ).…”

“…Despite this lower quality, figs are major fallback foods because they are abundant and available year‐round, allowing the proportion of figs in the diet to increase when drupes are scarce (Marshall & Wrangham, ; Wrangham et al, , ). Hence, it has been reported that Kanyawara chimpanzees, such as gibbons ( Hylobates albibarbis ), spider monkeys ( Ateles chamek ) and orangutans, prefer drupes when they are available (Clink, Dillis, Feilen, Beaudrot, & Marshall, ; Felton et al, ; Leighton, ; Wrangham et al, ). The previous studies of Kanyawara chimpanzees revealed that during drupe‐months, there were increased intake of nonstructural carbohydrates and reduced intake of fibre (Conklin‐Brittain, Wrangham, & Hunt, ; Wrangham, Conklin‐Brittain, & Hunt, ).…”

Chimpanzee feeding ecology and fallback food use in the montane forest of Nyungwe National Park, Rwanda

“…Primates display a wide array of dietary and behavioral adaptations to maintain adequate nutrient intake and balanced energy during periods of food scarcity (Clink, Dillis, Feilen, Beaudrot, & Marshall, ; Doran, ; Knott, ; Mitani & Watts, ; Remis, Dierenfeld, Mowry, & Carroll, ; Serckx et al, ). Chimpanzees ( Pan troglodytes ) primarily occupy tropical forests characterized by high rainfall (>1800 mm annually), but they are ecologically flexible and also use habitats such as savannah woodland and seasonally dry montane forests (Basabose, ; Gross‐Camp & Kaplin, ; Isabirye‐Basuta, ; Kano, ).…”

Mandibular shape variation in mainland and insular hylobatids

“…Although fallback food data is unknown for H. l. entelloides and H. l. carpenter , data on fallback foods is available for another Hylobates species. Hylobates albibarbis is known to eat foods that require increased postcanine masticatory loads, such as leaves and unripe fruit, during periods of fruit scarcity (Clink, Dillis, Feilen, Beaudrot, & Marshall, 2017; Vogel, Haag, Mitra‐Setia, van Schaik, & Dominy, 2009). Therefore, it is possible that relative to insular hylobatids, mainland taxa experience selective pressure for mastication of tougher and/or stiffer foods.…”