Stable carbon isotope ecology of small mammals from the Sterkfontein Valley: Implications for habitat reconstruction
Abstract Carbon isotope analyses of tooth enamel have been widely employed by paleoecologists to understand past habitats. Most such studies use large- to medium-bodied mammals and exclude small taxa. However, analysis of fossil small mammals holds promise for resolving questions about past environments because these animals are often present in the fossil record (especially in South African cave sites), are diverse in dietary and habitat preference, yet have limited lifespans and home range sizes. Thus, the carbon isotope compositions of small mammal communities and/or species might reflect the composition of vegetation in local environments at fine scales. In this study, we assessed the degree to which carbon isotope compositions of small mammal tooth enamel record spatial changes in habitat in a southern African savanna environment. Modern small mammal specimens were collected from the pellet accumulations of three barn owl ( Tyto alba africanus ) roosts located within microhabitats varying from open grassland to mixed woodland. We examined rodent carbon isotope compositions within taxa, between taxa, and between tooth types in an effort to characterize variation within this group. We also compared rodent community δ 13 C enamel composition between microhabitat types to evaluate how well small mammal isotope data reflect vegetation composition local to the roosts. Our analyses suggest that the relationship between small mammal community carbon isotopic means and vegetation composition is complex, but that with appropriate taxonomic control and consideration of relative abundance, small mammals have potential as a proxy for reconstructing past habitats. To complement this modern study, we performed isotopic analysis of the enamel of small mammals from three hominin-bearing sites in the Cradle of Humankind World Heritage Site, South Africa. Our results suggest a greater contribution of C4 resources to the diets of small mammals and likely more C4 grass in the past than occurs today.