The Ecology and behaviour of the proboscis monkey (nasalis larvatus) in the lower Kinabatangan, Sabah
Loading...
Date
1993
Authors
Boonratana, Ramesh
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Nasalis larvatus is a large, sexually dimorphic,
monotypic arboreal colobine, endemic to the island.of
Borneo, where it is largely restricted to riverine, peat
swamp and mangrove forests of the coastal lowlands. The
aims of the study were to assess the ecology and behaviour
of N. larvatus in relation to the botany and phytochemistry
of the habitat flora. This involved two years field work in
the mangrove and riverine forests in the Lower Kinabatangan
area.
The basic social unit of N. larvatus is a
relatively stable harem, comprising a single adult male,
several adult females and their offspring. The social
structure of N. larvatus in the Lower Kinabatangan is
flexible, and comprised relatively stable harem, all-male
and predominantly male non-breed~ng groups. Different
groups frequently selected riverside sleeping sites that
were close to one another. Some groups associated more than
others, implying a secondary level of social organisation,
the band. Intra-group agonistic and social interactions
were rare, implying that intra-group competition was low.
This, in turn suggested that food was abundant and
available.
All colobines, including N. larvatus, possess
specialised digestive physiology and sacculated stomachs with
anaerobic, cellulolytic bacteria in their fore-stomachs. This
adaptation allows them to break down cell wall constituents and
defensive chemicals found in plant foods. N. larvatus· is a
folivore-frugivore, with a strong preference for seeds. They are
highly selective feeders, avoiding items with high levels of
digestion inhibitors.
Nasalis larvatus groups in the Lower Kinabatangan
were wide-ranging, returning to sleep by the Kinabatangan
River or its tributaries every evening. N. larvatus are not
territorial, and the ranges of different groups completely
overlapped each other. The horne range size of the focal
harem group, SUI, at Sukau was observed to be 221 ha. SUl
increased its day range lengths as high quality foods become
scarcer, and the group selected particular quadrats on days
when its members ate high quality foods. This suggested
that food resources were unevenly distributed and highly
clumped.
Differences in horne range size, group size,
population density of N. larvatus between sites, and the
fact that groups were non-territorial, with completely
overlapping ranges and low level of intra-group
interactions, strongly implied that these variables were
influenced by ecological pressures, particularly by the
distribution, size and abundance of food resources.
Description
Keywords
Proboscis monkey , (Nasalis larvatus) , Lower Kinabatangan, Sabah