Abstract
We tested the reliability of herbivore faecal δ 13C and δ 15N values for reconstructing diet through review of an extensive database derived from a 3-year study of ungulates in South Africa's Kruger National Park. Faeces are a useful material for stable isotope studies of diet because they record dietary turnover at very short time scales, and because sampling is non-invasive. However, the validity of faecal isotope proxies may be questioned because they represent only undigested food remains. Results from Kruger Park confirm that free-ranging browsers have faecal δ 13C consistent with C 3 feeding, grazer faeces are C 4, and mixed-feeder faeces intermediate. Although the respective ranges do not overlap, there is significant variation in faecal δ 13C of browsers and grazers (∼2.0–4.0‰) across space and through time. We demonstrate that most (∼70%) of this variation can be ascribed to corresponding patterns of variation in the δ 13C of C 3 and C 4 plants, respectively, re-enforcing the fidelity of faecal isotope proxies for diet but highlighting a need for mixing models that control for variations in plant δ 13C in order to achieve accurate diet reconstructions. Predictions for the effects of climate (rainfall) and ecophysiology on 15N-abundance variations in mammals do not persist in faeces. Rather, faecal δ 15N tracks changes in plant δ 15N, with further fractionation occurring primarily due to variations in dietary protein (reflected by %N). Controlling for these effects, we show that a dual-isotope multiple source mixing model (Isosource) can extend diet reconstructions for African savanna herbivores beyond simplified C 3/C 4 distinctions, although further understanding of variations in mammal δ 15N are needed for greater confidence in this approach.
Published Version
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