>
> These are interesting points that can be clarified by dynamic
>ecological models (like those described so accessibly in Roughgarden's new
>*Primer of Ecological Theory*). For example, sometimes an occupant in a
>niche is essential to the survival of others. For example, every century
>or so Lake Superior freezes over hard enough for mooses to migrate to Isle
>Royale. If they migrate there without wolves, they soon so overpopulate
>the Isle that available moose resources are used up. Extinction by
>starvation is very likely under those circumstances. If the wolves follow,
>however, stable populations of both survive.
I have been to Isle Royale as have many others of course. The moose
population is permanent. It is not dependent on the lake freezing and the
moose coming over, although this is what happened at least once for them to
be there at all. There is also a pack of wolves that walked over the
frozen lake from Minnesota at some point. Their population is not stable
and the last time I was there (four years ago) their numbers had declined
to the point that genetic diversity was a problem and it was not
anticipated that there numbers would recover. Because their existence
there is natural, the National Park Service is reluctance to bring more
wolves there. The problem is that the moose can thrive in close proximity
to each other. Wolves need lots of space. The two populations certainly
interact. When the moose population goes up, so does the wolf population,
but then the wolves eat too many moose and their numbers decline to the
point where the wolves then run out of food. The problem is that the moose
can continue to thrive through these changes, but the wolves can't.
I know this does not endanger your thesis, but I find the ecology of Isle
Royale quite interesting and I couldn't resist throwing in my two cents worth.