Evaluating the coexistence of Imperial Cormorant and Rock Shag through isotopic niches at different colonies in central Patagonia, Argentina

YORIO, PABLO; GATTO, ALEJANDRO

Congreso; 3rd World Seabird Conference; 2021

World Seabird Union

Followingthe competitive exclusion principle, two closely-related species living insympatry can only coexist if ecological niche partitioning occurs. Throughouttheir distribution range, Imperial Cormorant (Leucocarbo atriceps) and Rock Shag (L. magellanicus) often breed in mixed-species colonies inPatagonia, Argentina. Isotopic niche assessment of both species was performed duringtwo breeding seasons (2010/11 and 2011/12) in three differentcolonies were they breed syntopically. The three colonies, Isla Gran Robredo(45°07?54??S, 66°03?40??W), Isla Leones (45°03?28??S, 65°35?08??W), and IslaViana (45°11?27??S, 63°23?50??W), are located within the ?Patagonia AustralMarine Park?. Whole blood samples were obtained simultaneously from breedingadults of both species during the early chick stage and used for stable isotopeanalysis. Isotopic niche was described by means of centroid analysis andBayesian ellipse-based metrics. The isotopic niche overlap between species wasin general small or insignificant, suggesting niche partitioning, and the isotopicniche width in the different colonies and seasons was significantly smaller in theImperial Cormorant than in the Rock Shag. However, the isotopic niche of theImperial Cormorant in Isla Viana during the second study season was totallyincluded in the isotopic niche of the Rock Shag, suggesting an important nicheoverlap. Results showed evidence that niche partitioning processes in thesecormorants is context dependent. However, further studies are needed including independentmeasures of prey availability and niche evaluation at additional colonies wherethese species breed alone and with other cormorant species, considering thatthe metacommunity framework predicts that the combination of species in metapopulationcontexts could be sometimes achieved through pairs of species with similarresource utilization.