title: Determinants of individual foraging specialization in large marine vertebrates, the Antarctic and subantarctic fur seals.
abstract: The degree of individual specialization in resource use differs widely among wild populations where individuals range from fully generalized to highly specialized. This interindividual variation has profound implications in many ecological and evolutionary processes. A recent review proposed four main ecological causes of individual specialization: interspecific and intraspecific competition, ecological opportunity and predation. Using the isotopic signature of subsampled whiskers, we investigated to what degree three of these factors (interspecific and intraspecific competition and ecological opportunity) affect the population niche width and the level of individual foraging specialization in two fur seal species, the Antarctic and subantarctic fur seals (Arctocephalus gazella and Arctocephalus tropicalis), over several years. Population niche width was greater when the two seal species bred in allopatry (low interspecific competition) than in sympatry or when seals bred in high-density stabilized colonies (high intraspecific competition). In agreement with the niche variation hypothesis (NVH), higher population niche width was associated with higher interindividual niche variation. However, in contrast to the NVH, all Antarctic females increased their niche width during the interbreeding period when they had potential access to a wider diversity of foraging grounds and associated prey (high ecological opportunities), suggesting they all dispersed to a similar productive area. The degree of individual specialization varied among populations and within the annual cycle. Highest levels of interindividual variation were found in a context of lower interspecific or higher intraspecific competition. Contrasted results were found concerning the effect of ecological opportunity. Depending on seal species, females exhibited either a greater or lower degree of individual specialization during the interbreeding period, reflecting species-specific biological constraints during that period. These results suggest a significant impact of ecological interactions on the population niche width and degree of individual specialization. Such variation at the individual level may be an important factor in the species plasticity with significant consequences on how it may respond to environmental variability.
authors: School of Life and Environmental Sciences, Deakin University, 221 Burwood Highway, 3125 Burwood, Vic., Australia.|Centre d'Etudes Biologiques de Chizé, UMR 7372 du CNRS-Université de La Rochelle, BP 14, 79360, Villiers-en-Bois, France.
authors: Laëtitia
authors: L
authors: Kernaléguen
authors: School of Life and Environmental Sciences, Deakin University, 221 Burwood Highway, 3125 Burwood, Vic., Australia.
authors: John P Y
authors: JP
authors: Arnould
authors: Centre d'Etudes Biologiques de Chizé, UMR 7372 du CNRS-Université de La Rochelle, BP 14, 79360, Villiers-en-Bois, France.
authors: Christophe
authors: C
authors: Guinet
authors: Centre d'Etudes Biologiques de Chizé, UMR 7372 du CNRS-Université de La Rochelle, BP 14, 79360, Villiers-en-Bois, France.
authors: Yves
authors: Y
authors: Cherel
mesh_terms: D000818:Animals; D000864:Antarctic Regions; D002247:Carbon Isotopes; D003163:Competitive Behavior; D005247:Feeding Behavior; D005260:Female; D046069:Fur Seals / Q000502:physiology*; D019156:Indian Ocean; D009587:Nitrogen Isotopes; D011235:Predatory Behavior; D013045:Species Specificity; D061350:Sympatry; D014738:Vibrissae / Q000737:chemistry
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes
keywords: competition; diet; foraging ecology; niche variation hypothesis; niche width; otariid; pinniped; stable isotopes; vibrissae; whisker