Decades ago there was discussion (and action) regarding the concept of
"unoccupied niches" -- a natural system would have a variety of niches that
species could occupy and function in. If there was an unoccupied niche,
than a species could be deliberately brought in to fill that niche to
benefit an entire system. Some examples: ring-necked pheasants and
Hungarian partridge introduced to fill unoccupied niches created by
agricultural development. Chukar partridge brought in to occupy niches
created by spread of cheatgrass and extirpation of native gallinules. Wild
turkey brought in to occupy woodland niches presumably unoccupied or not
fully utilized by native grouse.
Granted, much of this was done under a rather naive understanding of
ecosystem dynamics. Some might consider wild turkey outside its historic
range an invasive species, and some such introductions may now seem unwise
in retrospect.
This also seems to tie to Kelly's comments about biodiversity -- a very
diverse ecosystem would have many more niches than a simpler ecosystem.
This could suggest that a diverse ecosystem might provide opportunities for
invasive species without penalizing native species. However, I think we can
find way too many examples of invasives displacing rather than supplementing
native species. For example, take a look at what I call the dirty dozen of
Oregon invasives that have taken over or are taking over native-occupied
niches:
European starling -- competing with and replacing native passerines
European rock dove ("pigeons") -- replacing native columbids
Herb robert -- replacing native ground covers in otherwise undisturbed
Columbia River Gorge forests
Knotweed (more than one species/subspecies) -- invading and simplifying
riparian corridors
English ivy -- taking over and simplifying urban and suburban woodland
ground cover
Armenian (Himalayan) blackberry -- extensive monocultures in riparian areas,
meadows and uplands
Cheatgrass brome -- replacing native bunchgrasses in a variety of semi-arid
grass and shrubland systems
Bullfrog -- replacing native amphibians
Reed canarygrass -- creating extensive riparian and wetland monocultures
(may be a native species)
Nutria -- replaced native beaver and muskrat in many habitats
Carp -- replaced native warmwater fishes and degraded their water habitats
Starthistle (more than one species) -- replacing native rangeland vegetation
The basic questions become: should we (or can we) control and eliminate the
worst invasives? Or are we condemned to an eternal effort to just limit and
contain them? Or should we, as some have suggested, just accept the
inevitable and learn to live with them and the resultant degraded
ecosystems?
Warren W. Aney
Senior Wildlife Ecologist
Tigard, Oregon
-----Original Message-----
From: Ecological Society of America: grants, jobs, news
[mailto:[EMAIL PROTECTED] Behalf Of James J. Roper
Sent: Tuesday, November 20, 2007 4:32 AM
To: [email protected]
Subject: Re: ECOLOG-L Digest - 15 Nov 2007 to 16 Nov 2007 (#2007-310)
Kelly,
I respectively disagree. Introduced species are bad, no ifs ands or
buts.... Some of them are naturalized and so there is probably absolutely
nothing we can do about them. The others often have potential for causing
catastrophe, and it is hubris to think that we can just USE them to suit OU=
R
purposes (of what, fixing something that we already messed up?) with no
repercussions.
Also, your argument below is circular. An ecosystem that is very diverse
has the exotics as part of the calculation of diversity, so less diverse
will have fewer species overall. Also, healthy does not equal diverse -
else deserts and alpine systems are all unhealthy. If you say that within
any biome, the most healthy are the most diverse, I bet you do not have the
data to support that stand.
Is leaching copper good? What does "filter" toxics mean? The take toxins
from the soil and do what with them? And, what do they do in areas that
have no toxins when they escape cultivation?
Complicated issues, and I think the best answer is never introduce, plant
natives, eliminate exotics.
Cheers,
Jim
On Nov 19, 2007 4:54 PM, Kelly Stettner <[EMAIL PROTECTED]> wrote=
:
> 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 atmosphe=
re,
> alter the soil chemistry and hence the soil zoology and biology (potentia=
lly
> for the better?), and some even filter toxic chemicals from the soil. Fo=
r
> example, Japanese knotweed (Fallopia japonica, Polygonum cuspidatum) appe=
ars
> 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 =3D Evil, no ifs, ands or buts=
.
> That is simply not a scientific approach, not is it realistic or pragmat=
ic.
> 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
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