Determinants of individual foraging specialization in large marine vertebrates, the Antarctic and subantarctic fur seals

Abstract

Summary1. 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. 2. 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. 3. 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. 4. 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. 5. 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.

Individual variation in seasonal movements and foraging strategies of a land-locked, ice-breeding pinniped

“…between Galapagos fur seals Arctocephalus galapagoensis and sea lions Zalophus wollebaeki (Villegas-Amtmann et al 2013), grey seals and harbour seals (Svensson 2012) and, within species, between juveniles and adults (Crawford et al 2012, Breed et al 2013) and mature males and females (Andersen et al 2013). However, it is less commonly reported among adults of the same sex within species (Kernaléguen et al 2015), as here. In the Caspian Sea the partitioning may be facilitated by the varied habitats creating a range of exploitable niches, and an absence of other competing large predators.…”

Foraging strategies of a generalist marine predator inhabiting a dynamic environment

“…This variability may arise as a result of intrinsic factors such as individual differences in physiology, morphology, or behavior (Killen et al 2011;Patrick and Weimerskirch 2014;Hoskins et al 2015), or from external factors such as prey and habitat availability (Svanbäck and Bolnick 2005;Kernaléguen et al 2015;Newsome et al 2015;Rosenblatt et al 2015). Population-level descriptions largely overlook this individual variability, which may result in incomplete descriptions of foraging behavior and obscure the responses of individuals and populations to environmental variability.…”

Drivers of intrapopulation variation in resource use in a generalist predator, the macaroni penguin

“…Intrinsic drivers of opportunity include biological constraints that affect an individual's ability to exploit specific prey resources, e.g. sex, experience and foraging range (González-Solís et al 2000, Weimerskirch et al 2014, Kernaléguen et al 2015. In contrast, extrinsic drivers of opportunity reflect conditions that directly affect local prey biomass or availability, e.g.…”