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Why Invasions Succeed and Fail

The second class of Invasive Species Ecology was minorly intimidating--the prof broke out some graphs with formulae indicating how the lag effect affects population growth and geographic distribution of invasives. I didn't sweat, but am worried as to how much math will be on the test. Numbers--my Achilles heel. Well, not numbers themselves, but doing things with those numbers sometimes swamps my cerebral canoe.

Anyway we discussed why most contemporary invasions occur--accidental or deliberate importation by us and why most fail.

Most invasive species fail to establish themselves because of the "Rule of tens." For every 1,000 species imported, by natural or human means, only 100 may escape into the wild. Of those 100 species, perhaps 10 may establish a resident population. Of those 10, probably only one will reach sustainable levels that cross over into the pest category. So much works against exotics coming in and being successful in a new, foreign ecosystem. The ones that do succeed--zebra mussels, lampreys, European rabbits, cane toads, purple loosestrife--succeed spectacularly.

Thus endeth the lesson.


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