Populations will stop growing when “resources become scarce” — which resources and what level of scarcity is adjustable. Another way to put it is that “populations often won’t grow bigger than their environments can comfortably support”. Populations that undergo boom-bust cycles aren’t tuned like this, but the vast majority are — ecosystems are stable.

Naturally evolved ecosystems have a lot of plenty, much of the time — go take a walk in the woods. The squirrels are only eating a tiny fraction of the avaliable acorns; when the humans who lived here (and probably didn’t change a lot) for ten thousand years, there was plenty for them, too.

The competitive view of ecosystem and evolutionary dynamics is part and parcel of the capitalist world view.