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<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">UPDATE: a recent New York Times article, 9 September 2008 in the science section<br>(&quot;Friendly Invaders&quot; by Carl Zimmer) reports on a recent publication in the journal PNAS that in fact argues in favour of Dave&#39;s view. &nbsp;In a number of examples, diversity has increased historically without the ousting of native species, supporting the idea (surprising to me) that there mus
Hi Steve, Randy & All, Sept 11, 2008
Thanks for pointing out the article in PNAS, Steve.
Before going on, to comment on some of Randy's points, I wish to
make some comments from a personal perspective. This is an interesting
topic and I think a fairly important one. With all topics, and
especially with one as fundamental as this, one should if possible avoid
becoming emotional.
In addition, a discussion becomes hopelessly confused if someone
misrepresents a statement or attempts to prove some statement to be
incorrect without having read the statement. My remark about
'underutilized resource' was limited to plants. Plants do not nest in
trees or butt heads with Rhioniceri.
I tend to believe what I see with my own eyes and tend to question
the 'findings' of modern so-called biologists because in many cases they
are activists dressed up in a lab coat and with a heavy thumb on the
balance. Or perhaps neutral but feel coerced to toe the party line.
Randy Lauff wrote:
> My comments are interspersed:
>
> 2008/9/10 Stephen Shaw < srshaw@dal.ca <mailto:srshaw@dal.ca> >
>
> I think we should judge plants and animals by behavior
> and properties not by point of origin. In general, when a
> plant is invasive it is because there is some
> underutilized resource that happens to meet their (its)
> requirements.
>
>
>
> I disagree with David's "underutilized resource" suggestion. Assume
> you have one moose and one poplar tree upon which the moose is
> foraging. Now add one rhinoceros. That one poplar tree was not
> underutilized (in fact, from the perspective of the poplar tree, it
> was being overutilized). The rhinoceros butts the moose away. That's
> competition for a limited resource, not exploitation of an
> underutilized one.
>
>
>
>
>
> I objected to this off-the-cuff idea of Dave Webster's, given in
> the last sentence above: that invasive (plant) species exploit
> niches that are un- or under-utilized by native species, so they
> don't really compete with the natives.
>
>
>
> Ok...name any unutilized, or underutilized niche. (I don't think
> anyone can.)
>
>
>
Actually, I did that several weeks ago. Humans tend to generate bare
(i.e. underutilized) ground. This anthropogenic steppe (to use the 25
cent term) is quickly invaded by weedy species that follow humans and
agriculture, not be crowding out native plants but by making use of bare
or partially bare ground (and thank heavens for that).
Specific examples of frequently underutilized ground include
'Roadsides and waste ground around towns' (Roland & Smith); the typical
habitat of Japanese Knotweed.
> Now, add a foreign species of your choice.
>
>
>
> Now, tell me that there are no repurussions on the native fauna. I
> don't think anyone can.
>
>
>
Nth order repercussions are no doubt difficult to figure but examine
the habitat of typical introduced weedy species. Or better yet, consider
a specific example. Chenopodium album (Lamb's Quarters) can do a good
job of crowding out Carrots, Beets or even Turnips, if you don't take
sides and control it, but when did Lamb's Quarters ever compete with a
native plant ?
Apple trees are often present on abandoned farms and in clearings.
They feed Squirrels, Mice (and Mouse-like critters), Rabbits (AKA Hare),
Ruffed Grouse, Porcupine, Deer, many insects and insect-eating birds.
When the forest canopy closes apple trees die and the formerly positive
effects of apple on the fauna will become negative. Until someone makes
a clearing and throws and apple core away.
Yt, DW
> I argued instead the biological party line that the invaders
> usually displace native species and take over a niche,
>
>
>
> Very rarely, perhaps never, would any two species have identical
> niches, so I don't think the "take over a niche" arguement is valid.
> An invading species (whether foreign or by natural range expansion),
> may nest in the same type of tree as a native species, may eat many of
> the same insects as an already-established species, may drink dew
> drops like a native species. But in all liklihood, an invader will
> have a niche that overlaps those of many natives, sometimes
> marginally, sometimes by a lot.
>
>
>
> UPDATE: a recent New York Times article, 9 September 2008 in the
> science section
> ("Friendly Invaders" by Carl Zimmer) reports on a recent
> publication in the journal PNAS that in fact argues in favour of
> Dave's view. In a number of examples, diversity has increased
> historically without the ousting of native species, supporting the
> idea (surprising to me) that there must be many underutilized
> niches that the invaders can slot into.
>
>
> Of course diversity has increased...another species has been added
> (assuming no native ones go extinct). And many people fall into the
> trap of thinking that a HIGHER diversity is good...in reality, what we
> are targetting is the native diversity.
>
> And just so we're clear on "diversity" - when a biologist uses that
> term, it does not mean "number of species", which is "richness".
> Diversity refers to the richness and the abundances of each species.
>
>
>
> "Not all the people consulted bought the idea [behind the PNAS
> article]..." I read one email on a different list that I'm on that
> suggested the article was widely criticized.
>
>
> Randy
> _______________