Evol Ecol Res 7: 37-51 (2005)     Full PDF if your library subscribes.

Adaptation and propagule pressure determine invasion dynamics: insights from a spatially explicit model for sexually reproducing species

J.M.J. Travis,1* M. Hammershøj2 and C. Stephenson3

1NERC Centre for Ecology and Hydrology, Banchory, Aberdeenshire, UK,  2Department of Wildlife Ecology and Biodiversity, National Environmental Research Institute, Rønde and Department of Population Ecology, Zoological Institute, University of Copenhagen, Copenhagen, Denmark and  3Centre for Conservation Science, The Observatory, University of St Andrews, Fife, UK

Address all correspondence to J.M.J. Travis, NERC Centre for Ecology and Hydrology, Hill of Brathens, Banchory, Aberdeenshire AB31 4BW, UK.
e-mail: jmjt@ceh.ac.uk


Propagule pressure is often considered to be one of the key factors determining the probability that a species becomes invasive. However, there has been relatively little work, either empirical or theoretical, that has tested this assertion. Here, we develop a patch occupancy model for diploid organisms that reproduce sexually, and use it to investigate the dynamics of an introduced species. The model produces some interesting insights: If the introduced individuals are already well-adapted to the wild conditions, then the number of escapees is always larger when there are more introductions. However, when the introduced individuals are relatively poorly adapted to the natural conditions, this is often not the case. Under these conditions, the most rapid invasion occurs for an intermediate number of introductions. When the number of introductions is high, adaptation to local conditions is dramatically slowed and in some cases a well-adapted population never establishes. Thus, high propagule pressure does not necessarily lead to greater invasability. We believe that the model framework described in this paper can be a powerful tool for biologists interested in the genetics and evolution of invasive species, and spatially structured populations in general.

Keywords: genetics, introduced species, invasion, lattice model, patch occupancy, simulation.

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