Factors influencing riverine utilization patterns in two sympatric macaques

Yosuke Otani,Joseph Tangah,Ikki Matsuda,Goro Hanya,Augustine Tuuga,Henry Bernard,Anna Wong

doi:10.1038/s41598-020-72606-2

Abstract

Many species of terrestrial animals, including primates, live in varied association with the aquatic (e.g., riverine or coastal) environment. However, the benefits that each species receive from the aquatic environment are thought to vary depending on their social and ecological characteristics, and thus, elucidating those benefits to each species is important for understanding the principles of wild animal behaviour. In the present study, to gain a more complete picture of aquatic environment use, including social and ecological factors in primates, factors affecting riverine habitat utilization of two macaque species (Macaca nemestrina and M. fascicularis) were identified and qualitative comparisons were made with sympatric proboscis monkeys (Nasalis larvatus), which have different social and ecological characteristics. Temporal variation in sighting frequency of macaques at the riverbanks was positively related to the fruit availability of a dominant riparian plant species and negatively related to the river water level which affects the extent of predation pressure. Riverine utilization of macaques was greatly influenced by distribution and abundance of food (especially fruit) resources, possibly in association with predation pressure. Additionally, qualitative ecological comparisons with sympatric proboscis monkeys suggest that the drivers of riverine utilization depend on the feeding niches of the species, and different anti-predator strategies resulting from their differing social structures.

Highlights

Type for research contributing to a fundamental understanding of primate behavioural ecology, including how the aquatic environment affects primate distribution and ranging behaviours
We evaluated the effects of the availability of C. trifolia fruits, rainfall and river width on the sighting frequency of the two macaque species counted during the boat-based surveys, using a hierarchical Bayesian continuoustime structural equation model (CtSEM)
Cayratia trifolia was entangled in only four of 1645 marked trees (0.24%), and was located in well-lit forest gaps caused by fallen trees

Summary

Introduction

Type for research contributing to a fundamental understanding of primate behavioural ecology, including how the aquatic environment affects primate distribution and ranging behaviours. At this site, it has been reported that sympatric primates, including the two study macaque species, proboscis monkeys and other species, prefer to utilize riveredge trees for night-time sleeping, the frequency of riverine usage is different among these sympatric primates[32]. To gain a more complete picture of the riverine utilization patterns in the two species of sympatric macaques, we sought to (1) evaluate temporal variation in their riverine usage and asses the factors affecting riverine usage, including physical environment, i.e., river width and water level, and (2) describe their diets in river-edge areas, with a comparison of food availability. The effects of feeding niches and social structure on ranging behaviour are discussed by qualitatively comparing the characteristics of riverine utilization of the two species of macaques with those of proboscis monkeys reported in previous studies[17,21,23]

Methods

Results

Conclusion