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Isotopic segregation between sympatric seabird species increases with nutritional stress

TitleIsotopic segregation between sympatric seabird species increases with nutritional stress
Publication TypeJournal Article
Year of Publication2012
AuthorsBarger, CP, Kitaysky, AS
JournalBiology Letters

Dietary segregation is essential for the coexistenceof closely related species of animals. However,little is known about how changes in availability offood resources might affect trophic interactions ofwild animals breeding in sympatry. Here, we examinedhow interannual variations in relative foodavailability (as reflected in blood levels of stresshormone corticosterone, CORT) affect food partitioning(assessed via a comparison of stableisotope d15N and d13C ratios of blood) between thecommon murre (Uria aalge) and thick-billedmurre (Uria lomvia), breeding on a single colonyin the Bering Sea. During a 6-year study, CORTvaried among years but not between species,whereas stable isotope ratios varied among yearsand between species. Isotopic distance betweenspecies increased with increasing CORT. Theseresults indicate that, when food was not limiting,both species relied on similar food resources. Asforaging conditions deteriorated, murres divergedin their diets.We conclude that the degree of dietarysegregation between Uria spp. varies with changesin the availability of food and is greatest duringfood shortages.

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