Orangutan Energetics and the Influence of Fruit Availability in the Nonmasting Peat-swamp Forest of Sabangau,Indonesian Borneo |
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Authors: | Mark E Harrison Helen C Morrogh-Bernard David J Chivers |
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Institution: | (1) Wildlife Research Group, The Anatomy School, University of Cambridge, Downing Street, Cambridge, CB2 3DY, UK;(2) Orangutan Tropical Peatland Project, Centre for the International Cooperation in Management of Tropical Peatlands, University of Palangka Raya, Palangka Raya, Central Kalimantan, Indonesia |
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Abstract: | Data on energy intake and the effects of fluctuations in fruit availability on energy intake for African apes, and orangutans
in mast-fruiting habitats, indicate that orangutans may face greater energetic challenges than do their African counterparts.
Comparable data on orangutans in nonmasting forests, which experience lower fluctuations in fruit availability, have been
lacking, however, complicating interpretations. We conducted a 46-mo study of orangutan energetics in the nonmasting Sabangau
peat-swamp forest, Indonesian Borneo. Sabangau orangutans experienced periods of negative energy balance apparently even longer
than in mast-fruiting habitats, as indicated by comparisons of observed energy intake with theoretical requirements and analysis
of urinary ketones. Daily energy intake was positively related to fruit availability in flanged males, but not in adult females
or unflanged males. This may represent different foraging strategies between age-sex classes and suggests that fruit availability
is not always an accurate indicator of ape energy intake/balance. Urinary ketone levels were not generally related to fruit
availability, daily energy intake, day range, or party size. This is probably due to low energy intake, and consequently high
ketone production, throughout much of the study period. Comparisons with published results on African apes support the hypothesis
that orangutans are unique among hominoids in regularly experiencing prolonged periods of negative energy balance. This has
important effects on orangutan behavior and socioecology, and has likely been a key factor driving the evolutionary divergence
of orangutans and African apes. |
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