Resource partitioning among air-breathing marine predators: are body size and mouth diameter the major determinants?

SAPORITI, FABIANA; BEARHOP, STUART; VALES, DAMIÁN GUSTAVO; SILVA, LAURA ALEJANDRA; ZENTENO, LISETTE; TAVARES, MAURICIO; CRESPO, ENRIQUE ALBERTO; CARDONA, LUIS

MARINE ECOLOGY-PUBBLICAZIONI DELLA STAZIONE ZOOLOGICA DI NAPOLI I

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2016 vol. 37 p. 97 - 969

0173-9565

Although the body size of consumers may be a determinant factor in structuring food webs, recent evidence indicates that body size may fail to fully explain differences in resource use patterns of predators of the same order of magnitude. Here we compare the trophic niche of three sympatric and sexually dimorphic air-breathing marine predators (the South American sea lion Otaria flavescens, the South American fur seal Arctocephalus australis and the Magellanic penguin Spheniscus magellanicus) in three areas of the south-western Atlantic Ocean (Río de la Plata and adjoining areas, northern Patagonia and southern Patagonia) to assess the importance the body size and mouth diameter in determining resource partitioning. Body weight and palate/bill breadth were used to characterize the morphology of each sex and species, whereas the trophic niche was assessed through the use of stable isotope ratios of carbon and nitrogen. The quantitative method SIBER (Stable Isotope Bayesian Ellipses in R) was used to compute the area of the Bayesian ellipses and the overlap of the isotopic niches. Results showed that morphological similarity was significantly correlated with isotopic distance between groups within the δ13C?δ15N bi-plot space in Río de la Plata area, but not in northern and southern Patagonia. Furthermore, resource partitioning between groups changed regionally and some morphologically distinct groups exhibited a large trophic overlap in certain areas, such as the case of male penguins and male sea lions in southern Patagonia. Conversely, female sea lions always overlapped with the much larger males of the same species, but never overlapped with the morphologically similar male fur seals. These results indicate that body size and mouth diameter are just two of the factors involved in resource partitioning within the guild of air-breathing predators considered here and that under certain environmental conditions other factors are more important than morphology.