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My comments are interspersed:
2008/9/10 Stephen Shaw <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.)
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.
> 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
_________________________________
RF Lauff
Way in the boonies of
Antigonish County, NS.
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<div dir="ltr">My comments are interspersed:<br><br>
<div class="gmail_quote">2008/9/10 Stephen Shaw <span dir="ltr"><srshaw@dal.ca></span><br>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid"> 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.</blockquote>
</blockquote></blockquote>
<div> </div>
<div>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.</div>
<div> </div>
<div> </div>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">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.</blockquote>
<div> </div>
<div>Ok...name any unutilized, or underutilized niche. (I don't think anyone can.)</div>
<div> </div>
<div>Now, add a foreign species of your choice.</div>
<div> </div>
<div>Now, tell me that there are no repurussions on the native fauna. I don't think anyone can.</div>
<div> </div>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid"><span id=""></span>I argued instead the biological party line that the invaders usually displace native species and take over a niche,</blockquote>
<div> </div>
<div>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.</div>
<div> </div>
<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>("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 mus