Comparative Isotope Ecology of African Great Apes

The isotope ecology of great apes is a useful reference for palaeodietary reconstructions in fossil hominins. As extant apes live in C3 dominated habitats, variation in isotope signatures is assumed to be low compared to hominoids also exploiting C4-plant resources. However, isotopic differences between sites and between and within individuals were poorly understood due to the lack of vegetation baseline data. In this comparative study we included all species of free-ranging African great apes (Pan troglodytes, Pan paniscus, Gorilla gorilla gorilla and Gorilla beringeri beringei). We explore differences in isotope baselines across different habitats and how isotopic signatures in apes can be related to feeding niches (faunivory and folivory). Secondly, we illustrate how stable isotopic variation within African ape populations compares to other primates, including hominins from the fossil record, and discuss possible implications for dietary flexibility. Using 815 carbon and nitrogen isotope data from 155 sectioned hair samples and an additional collection of 189 fruit samples we compare six different great ape sites. We investigate the relationship between vegetation baselines and climatic variables, and subsequently correct great ape isotope data to a standardized plant baseline from the respective sites. We gained temporal isotopic profiles of individual animals by sectioning hair along its growth trajectory. Isotopic signatures of great apes differed between sites, mainly as vegetation isotope baselines were correlated with site-specific climatic conditions. We show that controlling for plant isotopic characteristics at a given site is essential for data interpretation. When controlling for plant baseline effects, we found distinct isotopic profiles for each great ape population. Based on evidence from habituated groups and sympatric great ape species these differences could be related to faunivory and folivory. Dietary flexibility in extant apes varies between species and populations, but temporal isotopic variation was overall lower than in species shifting from C3 to C4-resources, including fossil hominins and extant primates.