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Marine Ecology Progress Series

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MEPS 403:291-301 (2010)  -  DOI:

Resource partitioning by species but not sex in sympatric boobies in the central Pacific Ocean

Hillary S. Young1,*, Scott A. Shaffer2,5, Douglas J. McCauley1, Dave G. Foley3,4, Rodolfo Dirzo1, Barbara A. Block1

1Department of Biology, Stanford University, 371 Serra Mall, Stanford, California 94305, USA
2Ecology & Evolutionary Biology, University of California Santa Cruz, Santa Cruz 95060, USA
3Joint Institute for Marine and Atmospheric Research, University of Hawaii, Honolulu, Hawaii 96822, USA
4NOAA/NMFS/SWFSC/Environmental Research Division, 1352 Lighthouse Avenue, Pacific Grove, California 93950-2097, USA
5Present address: Department of Biological Sciences, San José State University, San José, California 95192, USA

ABSTRACT: Sympatric species with similar ecological requirements and differences in body size would be expected to partition resources to facilitate coexistence. For sexually dimorphic species, we may expect resource partitioning by gender as well as by species identity. However, it is difficult to document species and sexual resource partitioning in marine ecosystems, given the intractability of these systems and the vagility of many marine animals. Here, we examined differences in the foraging behavior and prey selection of 2 congeneric and coexisting seabird species—masked boobies Sula dactylatra and red-footed boobies Sula sula—on Palmyra Atoll in the equatorial Pacific Ocean. These seabirds exhibit substantial size dimorphism between species and also have reverse sexual dimorphism within species. Pronounced interspecific differences in foraging patterns were observed with high-resolution GPS tracking devices, where smaller red-footed boobies conducted longer foraging trips (in both time and distance). Red-footed boobies also had more frequent landings on the sea surface, slower mean and maximum travel speeds, and more westerly trip azimuths. Stable isotope and diet analyses produced data that complemented returns from electronic tagging. Stable isotope ratios of carbon indicated that masked boobies foraged on prey with a less pelagic δ13C signature compared to red-footed boobies. In contrast, no gender differences were identified in any foraging parameters. The mechanisms for maintenance of these pronounced differences in niche partitioning across species were not explicitly examined, yet the data suggest physiological variation across species may be a more plausible mechanism than competitive interactions.

KEY WORDS: Resource partitioning · Reverse sexual dimorphism · Foraging ecology · GPS tracking · Sula sula · S. dactylatra

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Cite this article as: Young HS, Shaffer SA, McCauley DJ, Foley DG, Dirzo R, Block BA (2010) Resource partitioning by species but not sex in sympatric boobies in the central Pacific Ocean. Mar Ecol Prog Ser 403:291-301.

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