| Summary: | ABSTRACT: Individual specialization can be an advantageous strategy that increases predation success and diminishes intra-population competition. However, trophic specialization can be a handicap in changing environments if the individuals are unable to use different prey or feeding grounds in response to change. Southern elephant seals Mirounga leonina allow us to explore this trade-off as they migrate, returning to haul out on land, for 2 extended periods, to breed and to moult. They fast during both periods, but the energetic cost is higher during the breeding season, leading to a poorer body condition after the breeding fast than after the moulting fast. We analysed the carbon (δ13C) and nitrogen (δ15N) isotopic composition of skin and fur samples from Falkland Islands elephant seals. The isotopic values provided information about the foraging strategy of the seals during the pre-breeding season and pre-moulting season, respectively. We assessed individual specialization as the variation between periods of an individual with respect to the variability of the whole population. The high specialization and the correlation between periods suggest that each animal feeds in a similar region and on similar prey during both feeding migrations. The comparison with data from other populations and particulate organic matter suggests that the Falkland Islands elephant seals fed both on the Patagonian Continental Shelf and in the Southern Ocean. The high specialization among individuals within this species could potentially limit the individual capacity of adaptation in the face of changing conditions or leave those abilities to the few generalist individual.
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