Small mammal insectivore stable carbon isotope compositions as habitat proxies in a South African savanna ecosystem

Abstract

Carbon isotope analysis of fossil micromammalian insectivores holds promise for resolving questions about past environments because these animals have restricted home ranges and are generalist feeders. Thus, their diets likely integrate ecological information about local habitats. In this study, we assessed the degree to which carbon isotope compositions of three sympatric shrew species record spatial changes in habitat in a mosaic southern African savanna environment. Sampling sites were located within 2km of one another, and microhabitat conditions ranged from very open (<5% canopy cover) to wooded (~60% canopy cover). We compared shrew hair δ13C values between microhabitat types, and across taxa, in order to test whether these data follow predictable patterns based on local vegetation.Shrew carbon isotope compositions varied with habitat in a predictable manner within our study area. While taxonomy also influenced δ13C values, this was largely due to differences in habitat preferences of individual taxa and the resultant variation in their relative abundance within each environment. Isotopic differences between habitat types were preserved within taxa where taxa occurred in multiple habitats. To complement this modern study, we performed isotopic analysis of the enamel of insect-eating fossil micromammals from the hominin sites Gladysvale and Sterkfontein in the Cradle of Humankind, South Africa. This subset of fossil micromammals consumed primarily C4-derived carbon.