I am not disputing that there are thousands of invasive / non-native species everywhere, but if a species is displacing the native animals, and was put there by man then something needs to be done about it. Many many many places take AGGRESSIVE stances against non-native species. If you ever get a chance read the book "out of eden" which talks about the battle against invasive species, specifically snakes but it also touches on everything from birds to fish to flowers. A really big example is the everglades in Florida right now. The python got introduced, they can grow HUGE, the natural predator is the alligator there. Because of having BOTH predators and no one to take out the pythons since they are pretty evenly matched they are destroying the bird populations. This has nothing to do with man hunting down the natural predators. What predator in Australia do you suggest that man killed that would take care of these horses?
Another example is right off the coast of BC and while it may not be a huge problem yet it could be. Farmed Atlantic salmon are spreading lice to our native pacific salmon. They also have been escaping and have the potential to cause huge problems with our pacific salmon stocks.
http://www.env.gov.bc.ca/wld/aliensp/al ... uence.htmlrats DO get culled every day, its called Alberta. If a rat is found there is destroyed, period. Its an alien species, it does damage to their industries so they deal with it.