Nutritional Differences between Two Orangutan Habitats: Implications for Population Density

Abstract

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.

Cyclical nursing patterns in wild orangutans

“…( 22 , 51 )]. Top: The percentage of fruiting trees derives from 1868 marked trees in monthly monitored phenology plots, 98% of which are species consumed by orangutans.…”

Nutritional composition of the diet of the western gorilla (Gorilla gorilla): Interspecific variation in diet quality

“…Following the approach utilized by Vogel et al () to increase the total proportion of diet represented, we substituted data on (a) ingestion rates (g/min) and (b) macronutrient content from congeneric species (where available) or the average value per food part (for leaves, herbs, flowers) or part subcategory (for fruits: subdivided by size and form). Food items with substituted ingestion rates ( n = 30 food items) together accounted for <10% of average monthly feeding time (Table ).…”

“…Nonetheless, when field sites are separated by wide geographic distances and/or diverge in their altitude, climate, plant composition, and resource characteristics, then the macronutrient composition of primate diets may differ. For example, in a comparison of two Bornean orangutans ( Pongo pygmaeus ) populations living in hydrologically distinct peat‐swamp forests (separated by only 63 km), the nutritional content of their diets differed markedly as a result of differences in food quality between sites (Vogel et al, ). Black‐and‐white colobus monkeys ( Colobus angolensis ) in a degraded forest also differed in their dietary composition and macronutrient intake from those in primary forest, a finding attributed to differences in food quality and availability (Dunham & Rodriguez‐Saona, ).…”

Biological Anthropology in 2015: Open Access, Biocultural Interactions, and Social Change

“…High‐quality food can shorten interbirth intervals; low‐quality food will reduce reproductive success and keep populations low. A recent study comparing food quality in two orangutan habitats that were superficially similar underscored the fact that relatively small differences in habitat can make a significant difference in energy intake (Vogel ). As orangutans are relocated to make room for palm oil plantations, sufficient attention must be given to the quality and availability of food to avoid prolonged energy deficits in the populations.…”