Abstract
Stable isotope data are often used to assess diet, trophic level, trophic niche width and the extent of omnivory. Notwithstanding ongoing discussions about the value of these approaches, variations in isotopic signatures among individuals depend on inherent variability as well as differences in feeding habitats. Remarkably, the relative contributions of diet variation and inherent variability to differences in δ15N and δ13C among individuals have not been quantified for the same species at the same life history stages, and inherent variability has been ignored or assumed. We quantified inherent variability in δ13C and δ15N among individuals of a marine fish (the European sea bass, Dicentrarchus labrax) reared in a controlled environment on a diet of constant isotopic composition and compared it with variability in δ13C and δ15N among individuals from wild bass populations. The analysis showed that inherent variability among reared individuals on a controlled diet was equivalent to a large proportion of the observed variability among wild individuals and, therefore, that inherent variability should be measured to establish baseline variability in wild populations before any assumptions are made about the influence of diet. Given that inherent variability is known to be dependent on species, life history stage and the environment, our results show that it should be quantified on a case-by-case basis if diet studies are intended to provide absolute assessments of dietary habits.
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Acknowledgments
This work was funded by a NERC CASE studentship (NER/S/A/2003/11886) and CEFAS (DEFRA project M0731). We thank Stuart Hetherington at CEFAS for the daily care of the bass, Charlie Scrimgeour and all his team at SCRI and Gillian Taylor at Newcastle for the stable isotope analysis. All experiments comply with the current laws of the country in which the experiments were performed.
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Communicated by Roland Brandl.
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Barnes, C., Jennings, S., Polunin, N.V.C. et al. The importance of quantifying inherent variability when interpreting stable isotope field data. Oecologia 155, 227–235 (2008). https://doi.org/10.1007/s00442-007-0904-y
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DOI: https://doi.org/10.1007/s00442-007-0904-y