Estimating the timing of diet shifts using stable isotopes |
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Authors: | Donald L Phillips Peter M Eldridge |
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Institution: | (1) National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, 200 SW 35th St., Corvallis, OR 97333, USA |
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Abstract: | 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. |
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Keywords: | Diet shift Isotopic turnover Tissues Model |
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