With regard to Kelly's first point, > Bill (and all): interestingly, it has been proven that ecosystems with a > large degree of biodiversity (read: "healthy ecosystems") have more > varieties of invasives present than those ecosystems that have less > biodiversity.
I think that the "healthy ecosystem" argument that was proposed is a weak one. Greater diversity means more niches (apologies to the strict Hutchinsonians!) and more opeinings for invaders. Also I suspect that a healthy human body may have more harmful microbes than a sick one, since the sick body will be prone to succumb. Anyway the biomathematicians claim that more complex ecosystems are actually less stable, although the argument is based on unrealistic models. As for the second point, I imagine that almost all organisms began their careers as invaders. Some are beneficial, some are not. Evolution involves not only stronger individuals within a species but also interspecies competition. We are here because mammals successfully invaded dinosaur territory. And while it is sad when we see species go extinct, this matter of some species losing out to others, whether invaders or natives, is a natural process. Bill Silvert PS -- Kelly and others, please use a meaningful subject line, not just the digest name. ----- Original Message ----- From: "Kelly Stettner" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Monday, November 19, 2007 6:54 PM Subject: Re: ECOLOG-L Digest - 15 Nov 2007 to 16 Nov 2007 (#2007-310) > Bill (and all): interestingly, it has been proven that ecosystems with a > large degree of biodiversity (read: "healthy ecosystems") have more > varieties of invasives present than those ecosystems that have less > biodiversity. I can dig up the studies, if anyone is interested. > > There is always the question of what good do invasive species > (particularly plants) do in an ecosystem? Yes, here I go again, playing > Devil's Advocate...but consider for a moment how some of these rampant, > densely-populated plant colonies effectively fix carbon from the > atmosphere, alter the soil chemistry and hence the soil zoology and > biology (potentially for the better?), and some even filter toxic > chemicals from the soil. For example, Japanese knotweed (Fallopia > japonica, Polygonum cuspidatum) appears to thrive in old mines, being > quite adept at leaching out copper from the soil. I think that a lot of > ecological thought can be turned on its ear by thinking outside one's > paradigm, looking at the bigger picture. But Bill is right in that so > very many people make abolishing invasives their life's work...their sole > raison d'etre. Invasive = Evil, no ifs, ands or buts. That is simply not > a scientific approach, not is it realistic or pragmatic. Other scenarios > and > paradigms must be recognized and considered in order for respectful and > honest discussion can take place. > > Working with knotweed in Vermont, > > Kelly Stettner, Director > Black River Action Team > Springfield, VT > www.blackriveractionteam.org > > > ---------------------------------------------------------------------- > > Date: Fri, 16 Nov 2007 10:18:47 -0000 > From: William Silvert > 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 > 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 > > --------------------------------- > Be a better sports nut! Let your teams follow you with Yahoo Mobile. Try > it now. >
