Joe makes some interesting points. I've inserted some comments [[thus--WT]].
WT At 10:04 AM 11/16/2007, Joe Tyburczy wrote: >Another point I'd like to pick up on is that a distinction should be >made between introduced species (those outside of their native range) >and invaders (introduced species that aggressively expand their range >and cause problems). [[This point needs no introduction, but should be introduced and reintroduced and introduced ad infinitum, because many don't get it and even more don't refine it and organize it and dig into the details rather than rely upon the generalities alone (including myself). A further distinction might be those which are merely ruderal (dependent upon disturbance and which fade to insignificance or disappear within healthy ecosystems and those which invade, persist, and expand their populations within healthy ecosystems. Others may wish to refine or redefine this point further. --WT]] > While I agree that it may be counterproductive to >be hyper-vigilant and crusade against every introduced species, I think >that increasing awareness of the problems posed by invaders is >valuable. [[I hope I did not imply such an extreme characterization. I intended only to starkly point out that the term "Weed Nazi" has not arisen for no reason, and to suggest with the gentlest subtlety that ecologists might help in drawing distinctions for those very well-meaning folks so that they could better distinguish between "every introduced species" and the value of that very "increasing awareness." Once aware of the distinctions, the "Weed Nazi" appellation would then fade away in such a healthy intellectual ecosystem, and the allocation of scarce resources could then be focused on the worst cases in which sufficient resources are available to be permanently effective. --WT]] > Furthermore, because a fraction of species introductions >inevitably become invasive, minimizing introductions is a way of >averting future invasions. [[Ah, yes--would that this would be so in the real world! --WT]] > One very important example of this is the >ongoing introduction of species to San Francisco Bay in ballast water -- >at a rate of 1 every 14 weeks! (Cohen & Carlton 1998, Science) I think >that directing the public's attention to the importance of concerns like >this is the only way that we'll convince our leaders to muster the >political will to address these problems. [[Given agreement on the "nasty quotient" of a particular species, the effectiveness of countermeasures, and the adequacy of the available resources to be applied to the task with a reasonable certainty of effectiveness, one would be ill-advised to argue. Unless someone has a suggestion as to how one or more of these requirements for feasibility might be left out and still achieve effectiveness, all that is likely to be left is the option of thrashing about and hoping for the best. Science, I suggest, just might be able to assist the well-intentioned multitudes in providing more reason for hope. --WT]] >Additionally, the hypothesis that healthy, intact ecosystems are >necessarily resistant to invasion, is at best context dependent. [[What might it be at worst? Does this mean that healthy, intact ecosystems do not resist invasion? Please provide example contexts (I do not disagree on this point, but I don't want to presume to interpret your meaning. --WT]] > While >in general, anthropogenic disturbance often facilitates invasion [[Might it be worthwhile to consider at greater length whether or not the anthropogenic disturbance merely refers to the site of the disturbance and not "healthy ecosystems," and whether or not the anthropogenic disturbance (human>cow>grazing, trampling, wallowing, etc.>dispersal>population increase>invasion of healthy ecosystem) facilitated the actual INVASION of the ecosystem as a result of, ecotype selection or the mere fecundity of the invading organism? --WT]] >, there >is variation in the aggressiveness of invaders -- and there is also >variation in the susceptibility of different ecosystems and habitat >types. [[Are these not intimately connected? Do invaders possess some special weapon for invasion, or do they merely sneak across the border and find salubrious circumstances? --WT]] > I strongly disagree with the implication that without other >human impacts, invasions would not be a problem. [[May I meekly suggest that I inferred no such implication? Kindly attach the offending text. --WT]] >-Joe Tyburczy > >P.S. In keeping with my marine theme, the invader I love to hate is >Caulerpa taxifolia, the introduced green alga that has few natural >enemies and has invaded marine environments across the globe, including >large areas of the Mediterranean. [[Quite! We--or at least I--need to know much more about the biology of colonizing species. --WT]] >William Silvert wrote: > > 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: <ECOLOG-L@LISTSERV.UMD.EDU> > > 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. > >-- >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >Joe A. Tyburczy >Oregon State University >Department of Zoology >3029 Cordley Hall >Corvallis, OR 97331-2914 >541-737-5359 >[EMAIL PROTECTED] >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
