Stable isotope analyses of rock hyrax faecal pellets, hyraceum and associated vegetation in southern Africa: implications for dietary ecology and palaeoenvironmental reconstructions

Rock hyrax middens are important palaeoenvironmental archives in southern Africa. Carbon and nitrogen isotope measurements on middens (hyraceum) are key components of climate reconstructions, but their interpretations require refinement. Although δ15N in hyraceum often correlates with independent proxies for palaeo-aridity, the impacts of dietary and physiological controls on hyraceum δ15N remain to be resolved. We analyse δ13C and δ15N in plant foliage, hyrax faecal pellets and hyraceum from 21 sites across southern Africa. Faeces are generally depleted in 13C (δ13C typically < −20‰), suggesting significant browsing. Grazing is rarely dominant and probably occurs only when palatable grass is available. Variability in faecal and foliar δ15N is large, but foliar δ15N is positively correlated with faecal δ15N. The diet-faeces δ15N offset is uncorrelated with climate (aridity), but is correlated with %N in faeces. Faecal δ15N is positively correlated with modern hyraceum δ15N, and the relationships with aridity index for foliar and faecal (body tissue) δ15N are comparable. These observations implicate diet as a significant control on hyraceum δ15N and we observe no strong evidence for metabolic controls on hyraceum δ15N. More data are required to refine these relationships, but these observations are consistent with current palaeoenvironmental interpretations of midden δ15N and δ13C.