I'll pick up on two of Wayne's points. One is that "some aliens that do little harm" -- this is true, and some aliens are introduced deliberately. Mustangs are alien to N. America, and are widely appreciated. Many ornamental plants are deliberately introduced. My mother was a member of the Florida Native Plants Society, and felt that they were fighting a losing battle against the imports. An interesting downside is that often introduced plants in dry areas require lots of water and this creates problems.
As for the comment that healthy ecosystems resist invasion, this depends on whether they have had a chance to immunise themselves by past experience. Because mammals were unknown in Australia, their introduction was impossible to resist. The same is often true when snakes or mosquitos arrive in regions where nothing similar has every been present. Often the best defence against an invading species is a predator that can control it, but if such predators are not already present, it may take a few million years for them to evolve. Sometimes man has tried to counter one alien invasion by introducing another alien species to control it -- which brings into action the Law of Unintended Consequences. It's a tricky game to play. Bill Silvert ----- Original Message ----- From: "Wayne Tyson" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Friday, November 16, 2007 1:08 AM Subject: ECOSYSTEM Health Alien invasions persistence decline limits control Re: semi-silly question from John Nielsen > There are some aliens that do little harm; some even provide > benefits. This statement is anathema, heresy, fighting words, to > many, many very caring people. But so many of those caring people > have their egos inextricably wrapped up in this very laudable > mission--it is often their reason for living, often it is a filler of > a hole in a person's life. One can't argue with that. > > Here's the heart of my "rant." Healthy ecosystems tend to resist > invasion. (However, the introduction of an alien species can, in > some cases, but not all, truly invade healthy ecosystems.
