>
> >But someone else would argue that it cannot be natural if it is radically
> different from some prior pre-Columbian state.


This is where it gets tricky.  Say that an invasive weed is introduced, and
can't be eradicated.  We humans would be responsible for that change, and
some native species may be outcompeted by that weed (rat, pig, etc).

To me, it would behoove the humans then, to try to mitigate the impact upon
the native species.  This is the case when we then introduce a
carefully-selected biocontrol agent, introducing yet another exotic
species, but one that will help to bring the ecosystem back into some sort
of mature "balance" in which the weed can no longer invade unchecked by its
"normal" predators.


-- 
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

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