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

GATTO, A.; YORIO, P.

Conferencia; 3rd World Seabird Conference; 2021

Following the competitive exclusion principle, twoclosely-related species living in sympatry can only coexist if ecological nichepartitioning occurs. Throughout their distribution range, Imperial Cormorant (Leucocarboatriceps) and Rock Shag (L. magellanicus) often breed inmixed-species colonies in Patagonia, Argentina. Isotopic niche assessment ofboth species was performed during two breeding seasons (2010/11 and 2011/12) inthree different colonies were they breed syntopically. The three colonies, IslaGran Robredo (45°07'54''S, 66°03'40''W), Isla Leones (45°03'28''S,65°35'08''W), and Isla Viana (45°11'27''S, 63°23'50''W), are located within the'Patagonia Austral Marine Park'. Whole blood samples were obtained simultaneouslyfrom breeding adults of both species during the early chick stage and used forstable isotope analysis. Isotopic niche was described by means of centroidanalysis and Bayesian ellipse-based metrics. The isotopic niche overlap betweenspecies was in general small or insignificant, suggesting niche partitioning,and the isotopic niche width in the different colonies and seasons wassignificantly smaller in the Imperial Cormorant than in the Rock Shag. However,the isotopic niche of the Imperial Cormorant in Isla Viana during the secondstudy season was totally included in the isotopic niche of the Rock Shag,suggesting an important niche overlap. Results showed evidence that nichepartitioning processes in these cormorants is context dependent. However,further studies are needed including independent measures of prey availabilityand niche evaluation at additional colonies where these species breed alone andwith other cormorant species, considering that the metacommunity  framework predicts that the combination ofspecies in metapopulation contexts could be sometimes achieved through pairs ofspecies with similar resource utilization.