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Marine Ecology Progress Series

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MEPS 606:201-214 (2018)  -  DOI:

Multi-isotopic assessments of spatio-temporal diet variability: the case of two sympatric gulls in the western Mediterranean

Virginia Morera-Pujol1,*, Raül Ramos1, Néstor Pérez-Méndez2, Marta Cerdà-Cuéllar3, Jacob González-Solís1

1Institut de Recerca de la Biodiversitat (IRBio) and Departament de Biologia Evolutiva, Ecologia i Ciències Ambientals, Universitat de Barcelona, 08028-Barcelona, Spain
2Instituto de Investigaciones en Recursos Naturales, Agroecología y Desarrollo Rural (IRNAD), Sede Andina, Universidad Nacional de Río Negro, 8400-San Carlos de Bariloche, Río Negro, Argentina
3Centre de Recerca en Sanitat Animal (CReSA), IRTA, Campus Universitat Autònoma de Barcelona, 08193-Bellaterra, Barcelona, Spain
*Corresponding author:

ABSTRACT: In predator populations, changes in foraging behaviour in response to spatio-temporal variability of prey are expected. Prey depletion might cause trophic niche widening in generalist species, but not in specialists, which are expected to increase their foraging effort without diet shifts. In sympatric species feeding on similar resources, reduced food availability can increase interspecific competition and cause trophic niche segregation. To understand these processes, we studied the spatio-temporal variability in diet and niche width in 2 sympatric gull species, the yellow-legged gull Larus michahellis and Audouin’s gull Ichthyaetus audouinii, which have experienced exponential growth in recent decades due to an increase in anthropogenic food subsidies. We sampled feathers from chicks of both species in several colonies along the western Mediterranean from 2009 to 2011 and performed stable isotope analysis of carbon, nitrogen and sulphur on these feathers. Bayesian modelling shows that both species displayed opportunistic behaviour if different types of resources were available, but could also narrow their trophic niche if 1 resource was abundant. We also provide evidence of trophic segregation between the 2 gull species, suggesting the occurrence of interspecific competition for food. Our meta-population approach provides a comprehensive view of the trophic ecology and the competitive interactions of these gull species. We emphasize the usefulness of 3-dimensional isotope analyses to correctly assess spatio-temporal variability in trophic behaviour of predator species, revealing differences that would remain hidden in single population studies or when using only the isotopic ratios of 2 elements.

KEY WORDS: Foraging ecology · Bayesian modelling · Niche segregation · Stable isotopes · Diet variability

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Cite this article as: Morera-Pujol V, Ramos R, Pérez-Méndez N, Cerdà-Cuéllar M, González-Solís J (2018) Multi-isotopic assessments of spatio-temporal diet variability: the case of two sympatric gulls in the western Mediterranean. Mar Ecol Prog Ser 606:201-214.

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