I have to agree with Mark on this. I am sure there were much different
streams, lakes, and rivers before the glaciers, but they were here. Also
evident by pockets of fish long removed from their current main distribution
indicates that something happened along the way, most likely the glaciers.
The devils adovacte to my own view is : How do we know what really was here
before the glaciers? How do we know the habitats still are enough like they
were to support those fish (and other flora and fauna), let alone something
different?
Personally I think the glaciers were the greatest catastrophe to wildlife in
the upper midwest and plains in the past 50,000 years. Again, being my own
D.A. : Certain pockets especially around metro areas have been impacted more
by man made problems. To counter that, they were man made, man should clean
them up and turn them around. It can be done. And not to go down this road
but... Just because the glaciers were "natural" don't mean they were a good
thing. Glaciers are abstract because it happened well before history, and
little thought is probably given to what they had done. Imagine an
unstopable bulldozer coming through your neighborhood, flattening your
abode, and leaving it trapped under a mile of ice for several thousand
years. What would be left of your neighborhood after that? If you could
live that long, you could move back easily, but what about small things that
just don't have the mobility?
Now to go out on a limb. One reason I believe that these areas harbor exotic
species so well is there are niches that are void from the time of
glaciations. Often more than not these introductions have much smaller
impacts than intially thought. The rusty crawfish, a prime example of this.
In areas , locally anyways, that they have shown up they have caused little
of the predicted havoc. The exceptions locally are areas impacted by
pollution and habitat degragation. Where habitat remains "pure" rusties,
and carp for that matter, have came in and done little to resident species.
These places also , interestingly enough, have higher diversity to begin
with than the places I mention that are polluted or altered to the point
they are unsuitable for most plants and animals. That is where I root my
opinion from. " Places with already high diversity support exotics with
little impact to existing biomass, while places with low diversity caused by
habitat alterations ( be it pollution or physical changes) are showing signs
of higher impact from exotic species." Is there a connection there, or am I
just applying my own flawed thought process?
Ray
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