Experimental island invasion of house mice
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The ability of invasive species to recurrently establish populations from small numbers of founders, while threatened species struggle at the same low population sizes, is a paradox in conservation biology. Little is known about the mechanisms contributing to the post-arrival success of low density invasive populations as most invasive species research focuses on established, high density populations. Experimental studies are powerful, but generally limited to laboratory or invertebrate experiments. Here, we experimentally demonstrate that vertebrate mammal invasion from a very small (n = 2) number of founders follows relatively simple deterministic predictions. An intentional island invasion of introduced house mice (Mus musculus Linnaeus) from one founding pair closely tracked the density dependent logistic growth curve and reached the seasonal carrying capacity of a previously extant population in only 5 months. Carrying capacity reflected both density dependent and independent processes. In contrast to the previously incumbent population, the invading population retained a marked genetic signal of its recent founder event, but the populations were otherwise demographically indistinguishable. Stochastic events such as individual variability, supplemental immigration and ecological release, but not Allee effects, played important roles during colonisation, but following establishment dynamics rapidly became deterministic, with little demographic impact of reduced genetic diversity. The small population paradigm appears to have little influence on the population dynamics of highly successful invasive species.
KeywordsBottleneck Carrying capacity Founder Incursion Logistic Mus musculus
We wish to thank the New Zealand Department of Conservation for funding and Thelma Wilson in particular for logistical support. Additional funding was provided by the University of Auckland. Genetic sequencing was performed by Ecogene Ltd. Figure 1 was constructed with the assistance of Vivian Ward and Craig Fredrickson. We thank Tad Fukami and Andrea Byrom for reading and providing feedback on an early version of the manuscript. The content of this manuscript was greatly improved by the helpful suggestions of two anonymous reviewers.
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