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Open Access Research

Do social groups prevent Allee effect related extinctions?: The case of wild dogs

Elena Angulo12*, Greg S A Rasmussen3, David W Macdonald3 and Franck Courchamp1

Author Affiliations

1 Ecologie, Systématique & Evolution, UMR CNRS 8079, University Paris Sud, Orsay Cedex, 91405, France

2 Estación Biológica de Doñana, CSIC, Avda. Americo Vespucio s/n, Sevilla, 41092, Spain

3 Wildlife Conservation Research Unit, Zoology Department, University of Oxford, The Recanati-Kaplan Centre, Tubney House, Tubney, Oxfordshire, OX13 5QL, UK

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Frontiers in Zoology 2013, 10:11  doi:10.1186/1742-9994-10-11

Published: 15 March 2013

Abstract

Background

Allee effects may arise as the number of individuals decreases, thereby reducing opportunities for cooperation and constraining individual fitness, which can lead to population decrease and extinction. Obligate cooperative breeders rely on a minimum group size to subsist and are thus expected to be particularly susceptible to Allee effects. Although Allee effects in some components of the fitness of cooperative breeders have been detected, empirical confirmation of population extinction due to Allee effects is lacking yet. Because previous studies of cooperation have focused on Allee effects affecting individual fitness (component Allee effect) and population dynamics (demographic Allee effect), we argue that a new conceptual level of Allee effect, the group Allee effect, is needed to understand the special case of cooperative breeders.

Results

We hypothesize that whilst individuals are vulnerable to Allee effects, the group could act as a buffer against population extinction if: (i) individual fitness and group fate depend on group size but not on population size and (ii) group size is independent of population size (that is, at any population size, populations comprise both large and small groups). We found that both conditions apply for the African wild dog, Lycaon pictus, and data on this species in Zimbabwe support our hypothesis.

Conclusions

The importance of groups in obligate cooperative breeders needs to be accounted for within the Allee effect framework, through a group Allee effect, because the group mediates the relationship between individual fitness and population performance. Whilst sociality is associated with a high probability of Allee effects, we suggest that cooperative individuals organized in relatively autonomous groups within populations might be behaving in ways that diminish extinction risks caused by Allee effects. This study opens new avenues to a better understanding of the role of the evolution of group-living on the probability of extinction faced by social species.

Keywords:
Group augmentation; Group size; Lycaon pictus; Obligate cooperative breeding; Positive density dependence