Orangutan Energetics and the Influence of Fruit Availability in the Nonmasting Peat-swamp Forest of Sabangau, Indonesian Borneo

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 mastfruiting 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.

Linking feeding ecology and population abundance: a review of food resource limitation on primates

“…Deficiency in macronutrients can also be shown by urinalysis that quantify ketone and c-peptide concentrations as indices of energy balance (Harris et al 2009;Harrison et al 2010;MacIntosh et al 2012) and urea and d…”

Functional Anatomy and Adaptation of Male Gorillas (Gorilla gorilla gorilla) With Comparison to Male Orangutans (Pongo pygmaeus)

“…The capacity to accumulate fat is part of the orangutan adaptation to help maintain a positive energy balance in the face of a highly seasonal environment. High caloric intake accompanied by increased fat stores, however, is punctuated by periods of low food quality, lower caloric diet, and fat loss (Knott, 1998;Harrison et al, 2010). Fat depots provide additional energy stores to sustain males in the quest for food and mates, and in fighting with other males during reproductive times (Knott, 1998).…”

A Noninvasive Method for Estimating Nitrogen Balance in Free-Ranging Primates

“…The forests of Southeast Asia, where orangutans occur, are characterized by unpredictable periods of fruit abundance, known as mastings, that are commonly followed by long periods of fruit scarcity (Cannon et al 2007a, b;Curran and Leighton 2000;Knott 1998;Leighton and Wirawan 1986;van Schaik et al 1993;Wich and van Schaik 2000). Orangutans prefer to feed on ripe, and in some cases unripe, fruit when it is available, but they often increase the percentage of inner-bark/cambium, leaves, flowers, and other vegetative plant parts in their diets when fruit is scarce (Bastian et al 2010;Harrison et al 2010;Knott 1998;Morrogh-Bernard et al 2009;Vogel et al 2008;2009;Wich et al 2006).…”

“…Using such collection and storage methods, these authors tested ketone levels in the field using fresh urine (Knott 1998) and they examined C-peptide levels as a proxy for energy balance (Emery Thompson and Knott 2008) in wild orangutans. Results suggest that when fruit is scarce orangutans: 1) consume significantly fewer total kilocalories per day (Emery Thompson and Knott 2008;Harrison et al 2010;Knott 1998); 2) are in a negative energy balance, i.e., energy intake < energy loss, as evidenced by low C-peptide levels (Emery Thompson and Knott 2008); and 3) metabolize excess body fat, as evidenced by the presence of ketones in their urine (Harrison et al 2010;Knott 1998). Such findings suggest that orangutans could also be susceptible to a negative protein balance; however, nothing is known about protein cycling in these populations or how it might be related to periodic energy deficits.…”