That "mammals were unknown in Australia" would be quite surprising to Australians.
Marsupials and monotremes are mammals--albeit not placental ones. And Australia has a robust population of native rodents and bats (and marine mammals if we want to go that far).=20 And the arrival of the dingo in Australia approximately 5000 years ago from Asia begs the question: when does an invader become native? Jennifer Hobden -----Original Message----- From: Ecological Society of America: grants, jobs, news [mailto:[EMAIL PROTECTED] On Behalf Of William Silvert Sent: Friday, November 16, 2007 2:19 AM To: [email protected] Subject: Re: ECOSYSTEM Health Alien invasions persistence decline limits control Re: semi-silly question from John Nielsen I'll pick up on two of Wayne's points. One is that "some aliens that do=20 little harm" -- this is true, and some aliens are introduced deliberately.=20 Mustangs are alien to N. America, and are widely appreciated. Many=20 ornamental plants are deliberately introduced. My mother was a member of the=20 Florida Native Plants Society, and felt that they were fighting a losing battle against the imports. An interesting downside is that often introduced=20 plants in dry areas require lots of water and this creates problems. As for the comment that healthy ecosystems resist invasion, this depends on=20 whether they have had a chance to immunise themselves by past experience.=20 Because mammals were unknown in Australia, their introduction was impossible=20 to resist. The same is often true when snakes or mosquitos arrive in regions=20 where nothing similar has every been present. Often the best defence against=20 an invading species is a predator that can control it, but if such predators=20 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=20 alien species to control it -- which brings into action the Law of=20 Unintended Consequences. It's a tricky game to play. Bill Silvert ----- Original Message -----=20 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=20 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.=20
