Nutritional Differences between Two Orangutan Habitats: Implications for Population Density

<div><p>Bottom-up regulatory factors have been proposed to exert a strong influence on mammalian population density. Studies relating habitat quality to population density have typically made comparisons among distant species or communities without considering variation in food quality among localities. We compared dietary nutritional quality of two Bornean orangutan populations with differing population densities in peatland habitats, Tuanan and Sabangau, separated by 63 km. We hypothesized that because Tuanan is alluvial, the plant species included in the orangutan diet would be of higher nutritional quality compared to Sabangau, resulting in higher daily caloric intake in Tuanan. We also predicted that forest productivity would be greater in Tuanan compared to Sabangau. In support of these hypotheses, the overall quality of the diet and the quality of matched dietary items were higher in Tuanan, resulting in higher daily caloric intake compared to Sabangau. These differences in dietary nutritional quality may provide insights into why orangutan population density is almost two times greater in Tuanan compared to Sabangau, in agreement with a potentially important influence of diet quality on primate population density.</p></div

Site variation in (a) Daily caloric intake, (b) Daily feeding time (min), and (c) Daily time spent feeding on fruit (min).

<p>All models include the variable age/sex class: FLM = flanged male; NUF = nulliparous independent female; UFM = unflanged adult male; AF = adult female; Age/Sex class comparisons are against AF. FAI = Percentage of fruiting trees.</p

Daily caloric intake (a), total feeding time (b), and fruit feeding time compared (c).

<p>Site differences in (a) Daily caloric intake (t-statistic = 12.26, p < 0.0001), (b) Total feeding time (t-statistic = -6.35, p < 0.0001), and (c) Fruit feeding time (t-statistic = -7.19, p < 0.0001) between the two sites. T = Tuanan, S = Sabangau. Generalized additive mixed models (GAMM) were used. A positive t-statistic indicates Tuanan is higher. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0138612#pone.0138612.t003" target="_blank">Table 3</a> for models and full statistical results.</p

Variation in macronutrient composition in the orangutan diets in Tuanan (T) and Sabangau (S).

<p>All comparisons are based on organic matter (OM) and Wilcoxon Signed Rank Test were used. A significant negative Z-statistic indicates Tuanan is greater. (a) Lipids (Z = -2.17, p = 0.03); (b) Total non-structural carbohydrates (TNC; Z = -5.43, p < 0.0001); (c) Neutral detergent fiber (NDF; Z = 5.63, p < 0.0001); (d) Crude protein (CP; Z = 0.64, p = 0.52); (e) Metabolizable energy (Kcal/100 g OM) (Z = -5.55, p < 0.0001); (f) Metabolizable energy/item (Kcal)(Z = -2.64, p = 0.008). See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0138612#pone.0138612.t001" target="_blank">Table 1</a> for complete statistical results.</p

Percentage of fruiting trees over the entire study period in Tuanan (red) and Sabangau (blue).

<p>Percentage of fruiting trees over the entire study period in Tuanan (red) and Sabangau (blue).</p