Proboscis monkey (Nasalis larvatus) social organization and ecology

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" Proboscis monkey (Nasalis larvatus) social organization and ecology "
C. P. Yeager

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	1112458
Doc. No	:	TLpq303683122
Main Entry	:	C. P. Yeager
Title & Author	:	Proboscis monkey (Nasalis larvatus) social organization and ecology\ C. P. Yeager
College	:	University of California, Davis
Date	:	1989
student score	:	1989
Degree	:	Ph.D.
Page No	:	148
Abstract	:	Proboscis monkeys' (Nasalis larvatus) social organization and ecology were studied in Kalimantan Tengah, Indonesia in 1984/1985. Data were collected on ten one-male groups and two all-male groups using scan sampling, event sampling and evening census surveys. Proboscis monkeys were found to follow the typical Asian colobine pattern of one-male social groups, with extra-group males forming all-male groups. One-male groups appear to be "female bonded". Specific groups associated at their sleeping sites at the river's edge, similar to the fission-fusion pattern described for hamadryas and gelada baboons. Analyses indicated that the groups formed two separate bands, apparently a secondary level of organization. This is the first evidence for such a two-tiered system of organization in an arboreal colobine species. Proboscis monkeys closely resemble gelada baboons in their organizational pattern. Home ranges of both groups and bands of proboscis monkeys overlapped extensively; temporal avoidance between bands may have been mediated by early morning displays. Intergroup displacement at sleeping and feeding sites was occasionally observed. A potential function of group associations may be to avoid displacement. Proboscis monkeys were folivore/frugivores, specializing in seed predation. The most preferred food sources were tree species among the most frequent and most dominant based on data from vegetational plots. They were, however, selective feeders; use of tree species as food sources was not based simply on relative density. During times of low food abundance and/or availability they switched dietary strategies and increased dietary diversity. The estimated home range and group density were similar to those reported for other colobines. The average biomass per kilometer2 was estimated to be 499.51 kg. Given their high biomass and predilection for seed predation on dominant species, proboscis monkeys may help to maintain and increase vegetational diversity. Their major predator appears to be false gavial (Tomistoma schlegii). One animal was preyed upon by a false gavial during this study. Behavioral responses to predation threat were varied, including crossing the river at narrower points. A potential function of group associations at the river's edge may be to allow groups to synchronize their movement to other groups during river crossings. Associations between groups may thus play a role in both predation avoidance and/or displacement avoidance at feeding or sleeping sites.
Subject	:	Biological sciences
	:	Monkey
	:	Psychobiology
	:	Psychology
	:	Zoology