CNN.com - Scientists fret over 'alien invasion' - July 22, 2002

The Dreaded Chinese Snakehead Walking Fish of Maryland, of course, and not creatures from Outer Space. For one thing, this has a better plot than Independance Day.

I have a lot of fun with the DCSWF/M, of course. But there's a serious side here. Invasive species can drive out native ones, even cause ecosystem collapse. Zebra mussels have caused major problems in the Great Lakes, and now people are afraid of the invading Asian carp looking to join up there. Any species introduced into a new environment can wreak havoc if it gets established.

The greatest example, in recent times anyway, of that is certainly man, introduced to North America only a few dozen thousand years ago, and to Australia and New Zealand even more recently. Any number of species, including almost all large herbivores, were wiped out here, probably in large part by humans, and long before Europeans came along to make it more efficient.

What humans don't get (and this is a little more on topic, I suppose) our attendant species do. The most important here are dogs and cats (among pets), goats and pigs (among livestock) and rats (among pests). They go pretty much everywhere humans do, and in a lot of places they cause catastrophes. Feral pigs in particular have been a huge problem for native species in Australia, and flightless bird populations have been devastated or destroyed by rats and dogs.