Stable Isotope Ecology 

A conceptual model for interpreting variability in isotope niche breadths of fossil populations (Daryl Codron, James Brink)

The trophic niche breadths of animal populations are determined by variability within and between individuals. This variability has ecological causes like exploitation competition, predation, and resource hetrogeneity, and has consequences for the evolution of faunal communities. Stable isotope distributions are expected to reflect the distributions of trophic states within populations. We are investigating relationships between isotopic variability with changes in density, and with changes in community composition, across habitats within extant ungulate assemblages to determine how biotic interactions influence population niche breadths. Such relationships are predicted based on derivatives of the ideal-free distribution model of habitat selection, hence we are testing the hypothesis that the distribution of trophic states within populations converges on an evolutionarily stable strategy. Emerging concepts will then be applied to stable isotope studies of extinct ungulate assemblages recovered from the central interior of South Africa, with our aim being to reconstruct the community interactions responsible for isotopic distributions in the fossil record.

Factors influencing stable isotope abundances and distributions in African savanna and grassland ecosystems (Daryl Codron)

Stable isotope analysis of savanna ungulates is an important technique for answering questions related to the hypothesis for evolutionary diversification along the browser-grazer axis in this group. The technique is equally applicable to extant and fossil faunas, and so provides some of our best empirical evidence for the evolution of dietary niches within lineages. Uncertainties about i) variation in isotopic changes between consumers and their diets (fractionation effects); ii) rates of isotope turnover within consumer tissues; and iii) relationships between changes in consumer and resource isotope compositions across environmental gradients, are considered the major limitations for using stable isotopes in ecological/palaeoecological studies. This project combines evidence from field and experimental studies to resolve these key issues with respect to ungulates. In particular, the research aims to uncover the extent to which these limitations impact on our ability to use stable isotopes as a dietary/palaeodietary tool, and to develop novel analytical approaches to overcome constraints inherent to the technique.