Evidence for an Allee effect in a declining fur seal population

This is a Preprint and has not been peer reviewed. The published version of this Preprint is available: https://doi.org/10.1098/rspb.2020.2882. This is version 1 of this Preprint.

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Authors

Rebecca Nagel, Claire Stainfield, Cameron Fox-Clarke, Camille Toscani, Jaume Forcada, Joe Hoffman

Abstract

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 amongst 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 also 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.

DOI

https://doi.org/10.32942/osf.io/acu5h

Subjects

Ecology and Evolutionary Biology, Life Sciences, Marine Biology, Population Biology

Keywords

Allee effect, Antarctic fur seal (Arctocephalus gazella), body condition, Density dependence, offspring mortality, pinniped

Dates

Published: 2020-11-27 13:50

License

CC-By Attribution-ShareAlike 4.0 International

Additional Metadata

Data and Code Availability Statement:
Raw data and R scripts for data analysis will be uploaded to Dyrad and is now freely available upon request (e-mail Rebecca Nagel rebecca.nagel@uni-bielefeld.de).