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PLoS One. 2015 Jan 30;10(1):e0116182. doi: 10.1371/journal.pone.0116182. eCollection 2015.

Stable isotope turnover and half-life in animal tissues: a literature synthesis.

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Center for Limnology, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
Department of Statistics, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
Center for Limnology, University of Wisconsin-Madison, Madison, Wisconsin, United States of America; School of Life Sciences, Arizona State University, Tempe, Arizona, United States of America.
Department of Natural Resource Sciences, McGill University, Ste. Anne de Bellevue, Quebec, Canada.
Lake Ontario Biological Station, USGS, Oswego, New York, United States of America.


Stable isotopes of carbon, nitrogen, and sulfur are used as ecological tracers for a variety of applications, such as studies of animal migrations, energy sources, and food web pathways. Yet uncertainty relating to the time period integrated by isotopic measurement of animal tissues can confound the interpretation of isotopic data. There have been a large number of experimental isotopic diet shift studies aimed at quantifying animal tissue isotopic turnover rate λ (%·day(-1), often expressed as isotopic half-life, ln(2)/λ, days). Yet no studies have evaluated or summarized the many individual half-life estimates in an effort to both seek broad-scale patterns and characterize the degree of variability. Here, we collect previously published half-life estimates, examine how half-life is related to body size, and test for tissue- and taxa-varying allometric relationships. Half-life generally increases with animal body mass, and is longer in muscle and blood compared to plasma and internal organs. Half-life was longest in ecotherms, followed by mammals, and finally birds. For ectotherms, different taxa-tissue combinations had similar allometric slopes that generally matched predictions of metabolic theory. Half-life for ectotherms can be approximated as: ln (half-life) = 0.22*ln (body mass) + group-specific intercept; n = 261, p<0.0001, r2 = 0.63. For endothermic groups, relationships with body mass were weak and model slopes and intercepts were heterogeneous. While isotopic half-life can be approximated using simple allometric relationships for some taxa and tissue types, there is also a high degree of unexplained variation in our models. Our study highlights several strong and general patterns, though accurate prediction of isotopic half-life from readily available variables such as animal body mass remains elusive.

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