> They were here for several hundred thousand years so there were only natural forces at work.
Only if you include Native Americans in the "natural" forces. They were responsible for the disappearance of the local megafauna.
> At the very least food availability would have limited their numbers in some way.
Or maybe periodic population collapses due to disease.
> It isn't dissimilar to the situation with bears.
Grizzly bears have one of the slowest reproduction rates, though. They simply won't have cubs if there isn't enough food. In Africa, it's a similar story with elephants, nothing can hunt them consistently, but they reproduce so slowly that they can't really overpopulate the area.
Only if you include Native Americans in the "natural" forces. They were responsible for the disappearance of the local megafauna.
> At the very least food availability would have limited their numbers in some way.
Or maybe periodic population collapses due to disease.
> It isn't dissimilar to the situation with bears.
Grizzly bears have one of the slowest reproduction rates, though. They simply won't have cubs if there isn't enough food. In Africa, it's a similar story with elephants, nothing can hunt them consistently, but they reproduce so slowly that they can't really overpopulate the area.