Do Javan gibbons (Hylobates moloch) use fruiting synchrony as a foraging strategy?

Abstract

Tropical rainforests are characterized by a high diversity of plant species. Each plant species presents with differential phenological patterns in fruit production. In some species, all individual trees produce fruit simultaneously within clustered periods; whereas in others, each individual tree fruits at irregular time intervals. By observing this pattern, some primate species use the presence of fruits in one tree as a cue to find fruit in other trees of the same synchronously fruiting tree species. Here, we investigated whether the highly frugivorous Javan gibbons (Hylobates moloch) in Gunung Halimun‐Salak National Park in Indonesia have knowledge of synchronous characteristics of fruiting trees and whether they can further distinguish fruit species with different synchrony levels, that is, tree species with highly synchronous fruiting patterns versus tree species with less synchronous fruiting patterns. Across 12 months we collected biweekly phenological data on 250 trees from 10 fruit species and observed Javan gibbons' visits to those species. We found that a fruit discovery in the beginning of fruiting seasons triggered gibbons to visit trees of the same fruit species. However, gibbons' visit rates did not differ between highly synchronous and asynchronous species. Our results suggest that Javan gibbons have knowledge of synchronous characteristics of fruiting trees in general, but they do not differentiate highly synchronous versus asynchronous fruit species. We speculate that Javan gibbons, who live in relatively small ranges with very low tree density of preferred fruit species, are likely able to track and remember fruiting states of individual trees without needing to distinguish fruit species with different synchrony levels. Moreover, gibbons may make little benefit of distinguishing highly synchronous versus asynchronous fruit species, probably due to gibbons' heavy use of asynchronous figs. Our study provides an insight into how gibbon's foraging strategies may have been shaped in response to their ecological environment.

Floristic Composition and Structure of Vegetation in Gunung Salak Geothermal Power Plant, West Java, Indonesia

“…Ficus fistulosa and F. padana are also foraging sources for the javan gibbon (Hylobates moloch), which has a home range around geothermal areas. Generally, the javan gibbon consumes the leaves and fruits of F. fistulosa and F. padana (Jang et al, 2021;Zulfa et al, 2021). Schima wallichii has a good process of regeneration (Shrestha & Devkota, 2019).…”

Food plant diversity determines home range area and formation of a new family group of the world’s rarest primate

“…However, until now, it remains unknown whether food plant diversity can directly determine the Hainan gibbon home range area. Primates can use spatial memory of food tree locations (Garber, 1989;Jang et al, 2021). Since group E originates from group C, if food plant diversity can indeed determine the home range area of Hainan gibbon, both groups C and E will select a home range with high food plant diversity.…”

“…Quantifying food diversity and nutrients is also a prerequisite for exploring the interaction mechanism between animals and habitats (Clink et al, 2017;Deng and Zhou, 2018). Primates will select a home range with high food tree diversity and high calorie likely as an adaptation for fluctuating food environments (Hladik and Simmen, 1996;Jang et al, 2021). Importantly, this "high-calorie bias" in primates' spatial memory seems to yield consequences for individual eating behavior in foodabundant settings (Arce et al, 2010;de Vries et al, 2022).…”

Intra-group competition and social dynamics regarding dispersal and maturation in wild Javan gibbon (Hylobates moloch)

“…Wild Hylobates moloch population in the Citalahab forest, Gunung Halimun-Salak National Park, West Java, Indonesia (S 6° 44′ 19″, E 106° 31′ 45″) has been followed since 2007, as a part of a long-term project called “Javan Gibbon Research & Conservation Project” 39 – 43 . We have habituated and observed two groups (A and B) since 2007 and one group (S) since 2012.…”