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Component, group and demographic Allee effects in a cooperatively breeding bird species, the Arabian babbler (Turdoides squamiceps)

Abstract

In population dynamics, inverse density dependence can be manifested by individual fitness traits (component Allee effects), and population-level traits (demographic Allee effects). Cooperatively breeding species are an excellent model for investigating the relative importance of Allee effects, because there is a disproportionately larger benefit to an individual of being part of a large group. As a consequence, larger groups have greater performance than small groups, known as the group Allee effect. Although small populations of cooperative breeders may be prone to all levels of Allee effects, empirical evidence for the existence of a demographic Allee effects is scarce. To determine the extent to which Allee effects are present in a cooperatively breeding species, we used a comprehensive 35-year life history database for cooperatively breeding Arabian babblers (Turdoides squamiceps). Firstly, we confirmed the existence of a component Allee effect by showing that breeding individuals in large groups receive greater benefits than those in small groups; second, we confirmed the existence of group Allee effect by showing that larger groups survive longer. And thirdly, we identified a demographic Allee effect by showing that per capita population growth rate is positively affected by population density. Finally, we found that emigration and immigration rates, although dependent on group size, do not buffer against component and group-level Allee effects becoming a demographic Allee effect. Our finding of the existence of all three levels of Allee effects in a cooperative breeder may have important implications for future research and conservation decisions.

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Acknowledgments

We are extremely grateful to Profs. Amotz and Avishag Zahavi for allowing us to work at the research station, access the long-term database, and for useful discussion and advice. We Thank Prof. Arnon Lotem and Dr. Peter Santema for providing helpful comments on the manuscript; Tali Ouzen, Yitzchak Ben Mocha, Zachary Teitel, Meike Zemihn, Andrew Fullmer and Dr. Peter Santema for their help in the field, and all past researchers and student who collected data at the field station throughout the years. We thank Dr. Bruno Buzatto from the University of Western Australia for his statistical help and we thank Dr. Simon Griffith from Macquarie University for his support. We are grateful to Prof. Hannu J. Ylonen, Prof. Hannu Pöysä and two anonymous reviewers who provided useful comments and advice that greatly improved the manuscript. Finally, we thank our colleagues from Tel Aviv University, Macquarie University, the Dead Sea and Arava Science Center, and the University of Western Australia for their friendship, support and advice.

Author contribution statement

OK designed the analysis and analysed the data with the supervision of ARR. OK & ARR wrote the manuscript.

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Correspondence to Oded Keynan.

Ethics declarations

All applicable institutional and/or national guidelines for the care and use of animals were followed. All birds were captured and ringed under a ringing license from the Israeli Nature and Parks Authority; the research was approved by the Israeli Nature and Parks Authority (License Nos. 2011/38268, 2012/38711) and by the Australian Research Authority (ARA, License No. 2011/038).

Conflict of interest

None.

Funding

We would like to acknowledge the following funding sources that have supported our research: Macquarie University Research Excellence Scholarship Scheme (MQRES); the Australian Research Council (ARC) Future Fellowship Scheme; the Israeli Ministry of Science, Technology and Space; the Smaller Winnicow Fellowship Fund; Yair Goron Foundation; and The Hoopoe foundation.

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Communicated by Hannu Pöysä.

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Keynan, O., Ridley, A.R. Component, group and demographic Allee effects in a cooperatively breeding bird species, the Arabian babbler (Turdoides squamiceps) . Oecologia 182, 153–161 (2016). https://doi.org/10.1007/s00442-016-3656-8

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  • DOI: https://doi.org/10.1007/s00442-016-3656-8

Keywords

  • Allee effect
  • Arabian babblers
  • Cooperation
  • Density dependence
  • Group size population dynamics