AS-HOPE report

Number:AS-22-004

Effects of environmental factors on social evolution in proboscis monkey

Report:Matsuda Ikki

Date:2011/02/10 - 2011/03/27

I focus on environmental factors and clarify what "environmental conditions" are important in formation of multi-level society in proboscis monkeys. Environmental condition in this study means the vegetation patterns: mangrove and riverine forest. In this study, I will clarify the ecology and social structure of proboscis monkeys inhabiting mangrove forest, and then evaluate the effects of environmental condition on their social structure in mangrove forest by comparing ecology and social structure of proboscis monkeys inhabiting riverine forest in my former study. In this trip, I collected the behavioral data of proboscis monkeys in the mangrove forests along the Kinabatangan River in Sabah, Malaysia. In addition to the behavioral observations, I conducted the vegetation survey. The diversity of flora and fauna in mangrove forest was lower than those in riverine forest. Therefore, it is expected that food availability in mangrove forest is lower than that in riverine forest. Indeed, the dietary diversity of the monkeys living in the mangrove forests was much lower than that in the riverin forest. Furthermore, the distribution patterns of the sleeping sites along the river appeared to be different between the habitat types; the distance among one-male groups of proboscis monkeys in the riverine forest was shorter than that in the mangrove forest. Further studies are needed to clarify the detailed effects of the vegetation types on the social system in proboscis monkeys.

Nipah forest along the Kinabatangan River



Infant proboscis monkey in the mangrove forest

Nipah forest along the Kinabatangan River


Infant proboscis monkey in the mangrove forest

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