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The confounding effects of source isotopic heterogeneity on consumer–diet and tissue–tissue stable isotope relationships

  • Physiological ecology - Original research
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Abstract

Stable isotope analysis of consumer tissues document patterns of resource use because data are linearly related to isotope compositions of their source(s) (i.e., food, water, etc.). Deviations in parameters estimated for these relationships can arise from variations in consumer tissue–diet spacing (Δ TS ) and the level of isotopic heterogeneity in the source(s). We present a set of simple hypotheses that distinguish between the effects of Δ TS and source isotope heterogeneity. The latter may arise via mixed diets, during tissue turnover, or by isotopic routing of dietary components. We apply these concepts to stable carbon and nitrogen isotope relationships between gut contents and body tissues of large mammal herbivores from mixed C3/C4 South African savannas and test predictions based on the compound- and/or time-specific data archived within each material. Predicted effects of source isotope heterogeneity are readily detected in carbon isotope relationships between materials representing different time periods or comprising bulk versus protein-only diet components. Differences in Δ TS of carbon isotopes across mammal herbivore species with very different feeding niches (and diet isotope compositions) are likely to be small or non-existent in these habitats. Variations in Δ TS estimated for nitrogen isotopes are much greater, leading to inconsistencies that cannot be explained by diet or trophic level effects alone. The effects of source heterogeneity on isotopic relationships generate numerical artefacts that have been misinterpreted as variations in Δ TS . We caution against generalized application of hypotheses based on assumptions of source isotopic homogeneity, even for single diets commonly used in laboratory studies. More careful consideration of how heterogeneity affects consumer–diet relationships is needed for many field and laboratory systems.

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Acknowledgments

We thank J. Brink, S. Vrahmis, F. Malie, E. Codron, T. Boleme, I. Thapo, P. Mdala, A. Thibeletsa, B. Nduma, A. Dichakane, and S. Dlamini for assisting with the fieldwork. Scott McWilliams, Karl Auerswald, and two anonymous reviewers are thanked for comments on an earlier version. The study was approved by the animal ethics committee of the University of KwaZulu-Natal, and by the Free State Department of Tourism, Environmental and Economic Affairs. Funding was provided by the European Union (Marie-Curie PIIF-GA-2009-236670), the Swiss National Fund (IZ32Z0-125787), the National Research Foundation of South Africa, the University of KwaZulu-Natal, the National Museum, and the Palaeontological Scientific Trust of South Africa.

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  1. Daryl Codron

    Present address: Florisbad Quaternary Research Department, National Museum, P.O. Box 266, Bloemfontein, Republic of South Africa

Authors and Affiliations

  1. Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Winterthurerstr. 260, 8057, Zurich, Switzerland

    Daryl Codron & Marcus Clauss

  2. School of Biological and Conservation Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville, 3209, Republic of South Africa

    Daryl Codron & Jacqui Codron

  3. Department of Anthropology, University of Colorado at Boulder, Boulder, CO80309, USA

    Daryl Codron & Matt Sponheimer

  4. Department of Archaeology, University of Cape Town, Private Bag, Rondebosch, 7701, Republic of South Africa

    Ian Newton & John L. Lanham

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  1. Daryl Codron
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Correspondence to Daryl Codron.

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Communicated by Scott McWilliams.

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Codron, D., Sponheimer, M., Codron, J. et al. The confounding effects of source isotopic heterogeneity on consumer–diet and tissue–tissue stable isotope relationships. Oecologia 169, 939–953 (2012). https://doi.org/10.1007/s00442-012-2274-3

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