alt Hacker NewsHe was wrong. Animals don't "instinctively" reach a natural equilibrium when they're introduced to a new environment. They eat all the available food, die off en masse, and repeat, until the food sources which were vulnerable have all gone extinct and the only things left are able to survive.
See mouse and grasshopper plagues, feral cats, etc.
Sometimes yes, sometimes an equilibrium is finally reached. The fact that we see more equilibrium than extinction is purely "survivor's bias".