Christ, enough of the anti-beaver comments. Beavers co-evolved with species and their environment for a long time and (were) part of the eco system before we nearly eradicated them like we did many other species. From the article you linked:
> Even though the beaver destroys life, its actions give way to new life and help conserve the overall environment. The positive effects of the beaver on its environment far outweigh the negative effects.
That depends how much alternative space there is in the ecosystem. Just because the species could evolve together in an entire wilderness doesn’t mean they can co-exist in every square kilometer.
Just to play devil's advocate: the first algae were extremely damaging to the environment by releasing toxic oxygen. Of course, that took millions of years to take effect.
So beavers could in principle also be damaging, but taking a long time to kill. (And, of course, nowadays a lot of organisms have come to depend on the once-toxic emissions of algae. Beavers might have a similar effect on the ecosystem.)
Killing off nearly all the wolves, mountain lions, lynx, bears, coyotes, foxes, etc, is probably a good chunk of the problem when talking about small mammal populations.