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Over-Invasion of Invasive Species

With invasive species colonising more and more locations it is only a matter of time before two similar species come in to contact with one another. Looking at the existing literature it seems there are already many cases of this, such as in similar species of foxes, wasps, ants, crayfish and plants. Our work looking at the competitive interactions among very similar invasive species is published this month in the journal Ecology, and I presented it at the Island Biology conference in Hawai’i. We termed this phenomenon over-invasion, as typically a more dominating invasive species replaces an existing one, such as the case with rats from Europe colonising Pacific Islands and supplanting the established Polynesian rat.

Figure 1 from Russell et al. (2014)
Rat over-invasion model (Figure 1 from Russell et al. (2014) Copyright Ecological Society of America)

Using population growth models we demonstrate some other outcomes such as a propagule pressure effect (the species which has more individuals arriving succeeds) or incumbent advantage effect (the species whihch is already established succeeds). Colleagues from the University of Auckland have also independently considered the importance of competition outcomes in phylogeographic models, just published in Systematic Biology. I hope all these studies will encourage other scientists to consider how such competitive structuring forces may affect invasive species in novel ecosystems they study, and what the most appropriate form of conservation management should be.