Evidence for an Allee effect in a declining fur seal population

Nagel, R.; Stainfield, C.; Fox-Clarke, C.; Toscani, C.; Forcada, J. ORCID:; Hoffman, J.I.. 2021 Evidence for an Allee effect in a declining fur seal population. Proceedings of the Royal Society B: Biological Sciences, 288 (1947). 20202882.

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Allee effects play an important role in the dynamics of many populations and can increase the risk of local extinction. However, some authors have questioned the weight of evidence for Allee effects in wild populations. We therefore exploited a natural experiment provided by two adjacent breeding colonies of contrasting density to investigate the potential for Allee effects in an Antarctic fur seal (Arctocephalus gazella) population that is declining in response to climate change-induced reductions in food availability. Biometric time-series data were collected from 25 pups per colony during two consecutive breeding seasons, the first of which was among the worst on record in terms of breeding female numbers, pup birth weights and foraging trip durations. In previous decades when population densities were higher, pup mortality was consistently negatively density dependent, with rates of trauma and starvation scaling positively with density. However, we found the opposite, with higher pup mortality at low density and the majority of deaths attributable to predation. In parallel, body condition was depressed at low density, particularly in the poor-quality season. Our findings shed light on Allee effects in wild populations and highlight a potential emerging role of predators in the ongoing decline of a pinniped species.

Item Type: Publication - Article
Digital Object Identifier (DOI):
ISSN: 14712954
Additional Keywords: Allee effect, Antarctic fur seal (Arctocephalus gazella), body condition, density dependence, offspring mortality, pinniped
Date made live: 09 Apr 2021 08:48 +0 (UTC)

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