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

Abstract

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 delta N-15 in hyraceum often correlates with independent proxies for palaeo-aridity, the impacts of dietary and physiological controls on hyraceum delta N-15 remain to be resolved. We analyse delta C-13 and delta N-15 in plant foliage, hyrax faecal pellets and hyraceum from 21 sites across southern Africa. Faeces are generally depleted in C-13 (delta C-13 typically < -20 parts per thousand), suggesting significant browsing. Grazing is rarely dominant and probably occurs only when palatable grass is available. Variability in faecal and foliar delta N-15 is large, but foliar delta N-15 is positively correlated with faecal delta N-15. The diet-faeces delta N-15 offset is uncorrelated with climate (aridity), but is correlated with %N in faeces. Faecal delta N-15 is positively correlated with modem hyraceum delta N-15, and the relationships with aridity index for foliar and faecal (body tissue) delta N-15 are comparable. These observations implicate diet as a significant control on hyraceum delta N-15 and we observe no strong evidence for metabolic controls on hyraceum delta N-15. More data are required to refine these relationships, but these observations are consistent with current palaeoenvironmental interpretations of midden delta N-15 and delta C-13. (C) 2016 Elsevier Ltd. All rights reserved.