, Volume 147, Issue 2, pp 195–203 | Cite as

Estimating the timing of diet shifts using stable isotopes

  • Donald L. PhillipsEmail author
  • Peter M. Eldridge


Stable isotope analysis has become an important tool in studies of trophic food webs and animal feeding patterns. When animals undergo rapid dietary shifts due to migration, metamorphosis, or other reasons, the isotopic composition of their tissues begins changing to reflect that of their diet. This can occur both as a result of growth and metabolic turnover of existing tissue. Tissues vary in their rate of isotopic change, with high turnover tissues such as liver changing rapidly, while relatively low turnover tissues such as bone change more slowly. A model is outlined that uses the varying isotopic changes in multiple tissues as a chemical clock to estimate the time elapsed since a diet shift, and the magnitude of the isotopic shift in the tissues at the new equilibrium. This model was tested using published results from controlled feeding experiments on a bird and a mammal. For the model to be effective, the tissues utilized must be sufficiently different in their turnover rates. The model did a reasonable job of estimating elapsed time and equilibrial isotopic changes, except when the time since the diet shift was less than a small fraction of the half-life of the slowest turnover tissue or greater than 5–10 half-lives of the slowest turnover tissue. Sensitivity analyses independently corroborated that model estimates became unstable at extremely short and long sample times due to the effect of random measurement error. Subject to some limitations, the model may be useful for studying the movement and behavior of animals changing isotopic environments, such as anadromous fish, migratory birds, animals undergoing metamorphosis, or animals changing diets because of shifts in food abundance or competitive interactions.


Diet shift Isotopic turnover Tissues Model 



The information in this document has been funded by the U.S. Environmental Protection Agency. It has been subjected to the Agency’s peer and administrative review, and approved for publication as an EPA document. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. We thank Keith Bosley, Claudio Gratton, Diane O’Brien, Bob Ozretich, David Post, and two anonymous reviewers for constructive reviews.


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Copyright information

© Springer-Verlag 2005

Authors and Affiliations

  1. 1.National Health and Environmental Effects Research LaboratoryU.S. Environmental Protection AgencyCorvallisUSA

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