For a long time it was thought that we were only having these invasive species coming into disturbed habitats, places which have been disrupted by human activity. We commissioned a study for people to look at national parks around the world. What they found was that, even in places put aside to preserve the natural systems, they are being invaded and the actual rate of invasion is related to the number of visitors through that park. This is the log, number of visitors per week. These are national parks around the world in temperate forest regions and these are the numbers of new species into that system. We're not talking small numbers even in the parks.

Charles Elton wrote a book quite a number of years ago, a beautiful little book, Ecology Invasion of Plants and Animals, and he makes a statement which has been widely quoted. He said we are seeing "one of the great historical convolutions of the world's flora and fauna. In fact, Gordon Orians has termed this era that we're now in the "Homogocene Age".

Darwin's view on invasives

Darwin examined this phenomenon and pointed out one very important thing about invasive species: once invasives come into an area, quite often they come in without their predators and without their pathogens. They quite often have explosive growth and really come to dominate the new system. And I'll talk about that.

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