Stable isotope ratios of a tropical marine predator: confounding effects of nutritional status during growth |
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Authors: | Larisa Lee Cruz Rona A R McGill Simon J Goodman Keith C Hamer |
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Institution: | (1) Institute of Integrative and Comparative Biology, University of Leeds, Manton Building, Leeds, LS2 9PS, UK;(2) NERC Life Science Mass Spectrometry Facility, Scottish Universities Environmental Research Centre, East Kilbride, UK |
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Abstract: | Stable isotope analysis of carbon and nitrogen is frequently used to study the diets and foraging ecology of marine predators.
However, isotopic values may also be affected by an individual’s nutritional status and associated physiological processes.
Here, we use C and N stable isotopes in blood and feathers of blue-footed booby chicks at the Galápagos Islands to examine
how isotopic values are related to body condition and growth rate, and to assess the consistency in the isotope ratios of
individuals during growth. Size dimorphism in blue-footed boobies provided an additional opportunity to examine how isotope
ratios differ between sexes in relation to body size and growth rate. There was no significant difference between sexes but
both C and N stable isotopes were significantly negatively related to the body condition of chicks. These data were consistent
with individual variation in physiological processes affecting fractionation, although we cannot rule out the possibility
that they were also influenced to some extent by population-level variation in the stable isotope ratios of prey fed to chicks,
for instance related to prey size, depth or lipid content. Our results highlight the need for methods that take proper account
of confounding physiological factors in isotopic studies of foraging ecology and diet. |
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