Ecosystem "health" is not just weak, but it is undefinable. Either it is circular (what is healthy is "natural") or it is multifarious...that is, defined differently in each case in which it used. If it is the former, then diversity is NOT a measure of ecosystem health, since there are so man= y variously diverse and natural ecosystems out there. If it is the latter, then by being anything, it is nothing.
We all know what we think we mean by the terms, but we just are unable to "measure" it beyond merely stating that healthy ecosystems are less perturbed by man. The less perturbed, the healthier. Yet, defining that using ambiguous indices such as diversity, richness and so, does not clarif= y nor help. Cheers, Jim On 11/21/07, Wayne Tyson <[EMAIL PROTECTED]> wrote: > > Ecosystem "health" is a broad term, but are broad terms necessarily > invalid or lacking in utility? If it is "weak," let us explore the > reason why it is so. And, let us find another that is stronger. Is > it (whatever term is best) necessarily--or at all--equivalent to > "greater diversity?" Are there ecosystems with lower diversity that > are "healthy" in terms of their persistence, resistance to invasion, > and resilience? Is diversity a measure of ecosystem health, or is it > more of a measure of its interest to humans? Is it a simple matter > of counting the number of niches and species? Is ecosystem (as a > well-considered division) composition (species, populations, biomass, > distributions, etc.) a reflection of the habitat that supports (or > permits) it? > > I quite agree that more diverse ecosystems might well (as a matter of > common sense) have a greater number of invasive species (I wonder how > it acquired such diversity), but I simply don't know that it means > they are more susceptible to invasions from, shall we say, "distant" > ecosystems? Where does one draw the line between an "invader" and a > shift in species composition due to, shall we say, climate change? > > WT > > PS: Is the history of the development of life on earth one of > invasion? If not, what? Is "beneficial" an invalid term? (I > confess to having used it.) How might "value-free" and "value-laden" > apply to this discussion? > > > At 01:48 AM 11/20/2007, William Silvert wrote: > >With regard to Kelly's first point, > > > > > Bill (and all): interestingly, it has been proven that ecosystems wit= h > 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 wea= k > >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 wit= h > 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 s= o > > > very many people make abolishing invasives their life's work...their > sole > > > raison d'etre. Invasive =3D Evil, no ifs, ands or buts. That is sim= ply > 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. > > > > --=20 James J. Roper, Ph.D. Ecologia e Din=E2micas Populacionais de Vertebrados Terrestres Caixa Postal 19034 81531-990 Curitiba, Paran=E1, Brasil E-mail: [EMAIL PROTECTED] Telefone: 55 41 33857249 Mobile: 55 41 99870543 http://www.bio.ufpr.br/ecologia/ Ecologia e Conserva=E7=E3o na UFPR http://jjroper.googlespages.com Personal Pages
