Population regulation in group-living birds: predictive models of the Seychelles warbler

Authors

  • Jo Ridley,

    Corresponding author
    1. Centre for Ecology, Evolution and Conservation, School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ, UK; and
      J. Ridley, Centre for Ecology, Evolution and Conservation, School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ, UK. Tel. + 44 1603 592056; Fax: + 44 1603 592250; E-mail: j.ridley@uea.ac.uk
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  • Jan Komdeur,

    1. Zoological Laboratory, Animal Ecology, University of Groningen, PO Box 14, 975 AA Haren, The Netherlands
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  • William J. Sutherland

    1. Centre for Ecology, Evolution and Conservation, School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ, UK; and
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J. Ridley, Centre for Ecology, Evolution and Conservation, School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ, UK. Tel. + 44 1603 592056; Fax: + 44 1603 592250; E-mail: j.ridley@uea.ac.uk

Summary

  • 1A major challenge for population ecology is to predict population responses to novel conditions, such as habitat loss. This frequently involves understanding dispersal decisions, in terms of their consequences for fitness. However, this approach requires detailed data, and is thus often inappropriate for urgent problems on poorly known species. This may be resolved by developing a predictive framework based on well-studied species, for applying to those that are less well understood.
  • 2Population size, group sizes and habitat occupancy of the Seychelles warbler (Acrocephalus sechellensis) can be predicted by determining the evolutionary stable dispersal strategy. For densities near to demographic equilibrium, regulation results from the combined effects of non-breeding and use of sink habitats.
  • 3In the Seychelles warbler, resident male non-breeders compete for breeding vacancies on neighbouring territories. The resulting kin competition is a key process for predicting the observed balance between regulation by non-breeding and regulation by sink use. Family groups, in which offspring delay dispersal, hoping to fill a vacancy on a local territory, are common among group-living species. This suggests that kin competition may frequently play a central role in the population regulation of socially complex species.
  • 4Although all the model variants considered are complex, predictions are shown to be insensitive to a range of simplifications, illustrating that, despite significant evolutionary import at the individual level, some behaviour can be unimportant when considering population level questions. Identifying which behavioural strategies have significant demographic consequences is key to the further development of population models based on fitness maximizing behaviour.

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