title: Isotopic segregation between sympatric seabird species increases with nutritional stress.
abstract: Dietary segregation is essential for the coexistence of closely related species of animals. However, little is known about how changes in availability of food resources might affect trophic interactions of wild animals breeding in sympatry. Here, we examined how interannual variations in relative food availability (as reflected in blood levels of stress hormone corticosterone, CORT) affect food partitioning (assessed via a comparison of stable isotope δ(15)N and δ(13)C ratios of blood) between the common murre (Uria aalge) and thick-billed murre (Uria lomvia), breeding on a single colony in the Bering Sea. During a 6-year study, CORT varied among years but not between species, whereas stable isotope ratios varied among years and between species. Isotopic distance between species increased with increasing CORT. These results indicate that, when food was not limiting, both species relied on similar food resources. As foraging conditions deteriorated, murres diverged in their diets. We conclude that the degree of dietary segregation between Uria spp. varies with changes in the availability of food and is greatest during food shortages.
authors.affiliation: Department of Biology and Wildlife, Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK 99775, USA. cpbarger@alaska.edu
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Barger
authors.forename: Alexander S
authors.initials: AS
authors.lastname: Kitaysky
mesh_terms: D000818:Animals; D002244:Carbon / Q000097:blood*; D002247:Carbon Isotopes / Q000097:blood; D046091:Charadriiformes / Q000502:physiology*; D003163:Competitive Behavior; D003345:Corticosterone / Q000097:blood*; D005518:Food Preferences; D009584:Nitrogen / Q000097:blood*; D009587:Nitrogen Isotopes / Q000097:blood; D012621:Seasons; D013045:Species Specificity; D013312:Stress, Physiological; D061350:Sympatry
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D002244:Carbon; D009584:Nitrogen; D003345:Corticosterone