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Alimentary niche partitioning in the Galapagos sea lion, Zalophus wollebaeki

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Abstract

Sea lions are generally considered opportunistic feeders. However, studies from different areas suggest their diet consists mostly of four to five types of prey. Previous studies in Galapagos sea lions have identified at least three feeding strategies for this species, suggesting diversification of their diet. Diet diversification is favored in organisms with relatively high trophic position and subject to high intra-specific and low inter-specific competition. Zalophus wollebaeki meet these criteria as the only pinniped on San Cristobal Island, where three sea lion rookeries are located within 11 km: a distance considerably shorter than their 41 km foraging range. To measure the degree of diet diversification, we used scats and stable isotope analyses. A total of 270 scat samples from lactating females and 142 fur samples from sea lion pups were collected during the breeding season 2006. The scat analysis identified distinct diets among rookeries, with minimal trophic overlap (Cλ = 0.19), a trophic level TL = 4.5 (secondary–tertiary carnivore), and trophic breadth of a specialist predator (B i  = 0.37). The mean δ15N and δ13C values were 13.07 ± 0.52 and −16.34 ± 0.37, respectively. No significant difference was found in the δ15N values from the sea lion rookeries, but differences were found inter- and intra-population in δ13C values for pups from different groups (ANOVA P < 0.05). Our results indicate that diet diversification is present in the Galapagos sea lion and may play important role to the survival of the species in a habitat where pinniped populations are limited.

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Acknowledgments

We thank the Consejo Nacional de Ciencia y Tecnologia (CONACyT), Servicio de Relaciones Exteriores de Mexico (SRE), and CICIMAR of the Instituto Politecnico Nacional for their support in the form of scholarships and laboratory services. We also thank the Parque Nacional Galapagos (PNG) for providing permits for sampling on the islands and for their help in planning the field work. Thanks to Adrian Hurtado, Rodrigo Páez, and Johana Aguilar for their help during the sampling phase. This research was made possible through the financial support provided by CONACYT grant SEP-2004-C01-46806. Thanks to the anonymous reviewers that helped to improve the manuscript.

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  1. Laboratorio de Ecología de Pinnípedos “Burney J. Le Boeuf”. Centro Interdisciplinario de Ciencias Marinas, Instituto Politécnico Nacional, Ave. Instituto Politécnico Nacional s/n. Colonia Playa Palo de Santa Rita, 23096, La Paz, B.C.S., México

    Diego Páez-Rosas & David Aurioles-Gamboa

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  1. Diego Páez-Rosas
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Correspondence to Diego Páez-Rosas.

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Communicated by S. Garthe.

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Páez-Rosas, D., Aurioles-Gamboa, D. Alimentary niche partitioning in the Galapagos sea lion, Zalophus wollebaeki . Mar Biol 157, 2769–2781 (2010). https://doi.org/10.1007/s00227-010-1535-0

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