Abstract
A central paradigm in invasion biology is that more releases of higher numbers of individuals increase the likelihood that an exotic population successfully establishes and persists. Recently, however, it has been suggested that, in cases where the data are sourced from historical records of purposefully released species, the direction of causality is reversed, and that initial success leads to higher numbers being released. Here, we explore the implications of this alternative hypothesis, and derive six a priori predictions from it. We test these predictions using data on Acclimatization Society introductions of passerine bird species to New Zealand, which have previously been used to support both hypotheses for the direction of causality. All our predictions are falsified. This study reaffirms that the conventional paradigm in invasion biology is indeed the correct one for New Zealand passerine bird introductions, for which numbers released determine establishment success. Our predictions are not restricted to this fauna, however, and we keenly anticipate their application to other suitable datasets.
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Acknowledgments
We thank Stuart Pimm for discussions that led to many of the ideas in this manuscript, Jason Sadowski for collating the data presented in Fig. 1, and two anonymous referees for comments on an earlier version of this work. TMB was supported by funding from the King Saud University Distinguished Scientist Fellowship Programme. P.C. is an ARC Future Fellow (FT0991420).
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Blackburn, T.M., Prowse, T.A.A., Lockwood, J.L. et al. Propagule pressure as a driver of establishment success in deliberately introduced exotic species: fact or artefact?. Biol Invasions 15, 1459–1469 (2013). https://doi.org/10.1007/s10530-013-0451-x
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DOI: https://doi.org/10.1007/s10530-013-0451-x