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Summary: POPULATION ECOLOGY
Using d13
C stable isotopes to quantify individual-level
diet variation
Ma´rcio S. Arau´jo Æ Daniel I. Bolnick Æ
Glauco Machado Æ Ariovaldo A. Giaretta Æ
Se´rgio F. dos Reis
Received: 25 September 2006 / Accepted: 31 January 2007 / Published online: 14 March 2007
Ó Springer-Verlag 2007
Abstract Individual-level diet variation can be easily
quantified by gut-content analysis. However, because gut
contents are a `snapshot' of individuals' feeding habits,
such cross-sectional data can be subject to sampling error
and lead one to overestimate levels of diet variation. In
contrast, stable isotopes reflect an individual's long-term
diet, so isotope variation among individuals can be inter-
preted as diet variation. Nevertheless, population isotope
variances alone cannot be directly compared among pop-
ulations, because they depend on both the level of diet
variation and the variance of prey isotope ratios. We
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