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Montoya, Joseph P.

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Author: Montoya, Joseph P. × End date: 2002 × Start date: 2002 × search.filters.applied.f.resourcesubtype: Article ×

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Use of stable isotopes to investigate individual differences in diets and mercury exposures among common terns Sterna hirundo in breeding and wintering grounds

2002-10-22 , Nisbet, Ian C. T. , Montoya, Joseph P. , Burger, Joanna , Hatch, Jeremy J.

We measured variations in stable isotope signatures (δ¹³C and δ¹⁵N) and concentrations of mercury (Hg) in breast feathers from pairs of common terns Sterna hirundo and their chicks at a breeding site in Buzzards Bay, northwestern Atlantic Ocean. By collecting 2 sets of feathers from the same adult birds, we compared values of δ¹³C, δ¹⁵N and Hg in feathers grown in the wintering area in the South Atlantic Ocean (‘southern’ feathers) and in the breeding area (‘regrown’ feathers). Regrown feathers had lower δ¹³C, higher δ¹⁵N and higher Hg than southern feathers. Values of δ¹³C , δ¹⁵N and Hg were much more variable in adults than chicks. Within families, δ¹³C and δ¹⁵N were correlated between parents and chicks; Hg was correlated between male and female parents. Among regrown feathers, Hg was positively correlated with δ¹³C and negatively correlated with δ¹⁵N. These findings suggest that high individual exposure of common terns to Hg results from consumption of inshore prey at low trophic levels in restricted parts of Buzzards Bay and that members of pairs have similar diets in the breeding season but not in winter. They demonstrate the power of stable isotope analyses in revealing individual differences in foraging habits, diet and contaminant exposure in generalist predators.

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Trophic relationships and the nitrogen isotopic composition of amino acids in plankton

2002 , McClelland, James W. , Montoya, Joseph P.

Stable nitrogen isotope ratios of whole organisms and tissues are routinely used in studies of trophic relationships and nitrogen flow through ecosystems, yet changes underlying increases in δ¹⁵ N from food source to consumer are not completely understood. In this study, the δ¹⁵ N of 16 amino acids in marine planktonic consumers and their food sources were examined using gas chromatography/combustion/isotope ratio mass spectrometry of their N-pivaloyl-i-propyl-amino acid ester derivatives. Moderate increases in bulk δ¹⁵ N with trophic position reflect an averaging of large increases in the δ¹⁵ N of some amino acids, and little or no change in others. Amino acids showing consistently large increases (e.g., glutamic acid changes by ~7‰ between food and consumer) provide greater scope for defining trophic position than the smaller isotopic changes in bulk material. In contrast, amino acids like phenylalanine show no change in δ¹⁵ N with trophic position and therefore preserve information about nitrogen sources at the base of the food web. The ability to acquire information about both trophic level and nitrogen sources at the base of the food web from single samples of consumer tissues offers a powerful new tool for elucidating pathways of N transfer through food webs.

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