| Abstract: |
This study tested multiple hypotheses about the correlation between diet, ecology, and bone chemistry using stable isotope ratios in five species of nonhuman primates that inhabit Kibale National Park, Uganda. A faunal collection of animals that died naturally was sampled for chemical testing. Also sampled were plants and soils that characterize the diverse primate microhabitats. Previous research has shown that tissues of animals that browse in the forest have lower carbon isotope ratios than grassland grazers because the different types of forage vegetation (C<sub>3</sub> vs. C<sub>4</sub> plants, respectively) have different photosynthetic pathways that alter the total amount of heavy isotope. For this reason, African forest primates were previously thought to eat only C<sub>3</sub> plants. This study found that plant foods commonly eaten by Kibale primates are C<sub>4</sub> plants, such as elephant grass, found in forest clearings, and crop foods, like maize and sugar cane. This reliance on C<sub>4</sub> resources, however, is not discernible from the bone chemical data. Plant samples collected from narrow 5-meter intervals in Kibale did not support published observations that leaves from higher levels in the canopy are less depleted in the heavy isotope of carbon than lower levels. This “canopy effect” is believed to be caused by the atmospheric recycling of carbon dioxide near the forest floor. When Kibale plant data were reorganized, however, into only two major height divisions (low versus middle), the trend was evident. Contrary to previous studies of hair from prosimians, carbon isotopes in bone collagen and bone apatite are not correlated with reported vertical niches of the Kibale primates. This suggests that habitat overlap between these species is greater than reported from field observations. Despite the lack of significant ranking between carbon isotope ratios of arboreal primates, data comparisons with the forest ungulates show significant differences between adaptation to arboreal versus terrestrial diets. Nitrogen isotope ratios in bone have been shown to be positively correlated with the relative amount of animal flesh in the diet, but this was not apparent among Kibale primates. Because oxygen molecules in bone carbonate are obtained from drinking water, oxygen isotope ratios were expected to be similar among forest primates that have access to the same local watershed. Surprisingly, the distribution of oxygen isotope values are species-specific and are related to the amount of leaves in the diet. (Abstract shortened by UMI.)
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