Unnatural? Not sure I understand the use of the term here. They were here for several hundred thousand years so there were only natural forces at work. There must have been some kind of balance if they thrived for that long. At the very least food availability would have limited their numbers in some way. It isn't dissimilar to the situation with bears.
Just guessing, but I would think there would have been a lot of cougars eating a lot of calves. That would also have some restraining impact on the population.
> 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.
I think you're missing the fact that Native Americans were here in number for thousands of year before Europeans. The herds were a result of North America before the Columbian exchange. Not a result of a pristine wilderness with only "natural forces at work"
Just guessing, but I would think there would have been a lot of cougars eating a lot of calves. That would also have some restraining impact on the population.