The amount of life which can be supported is basically the Surface Area of the Earth X The Amount of Sunlight that Gets Through the Atmosphere. And then the end result of evolution is that all spare energy that is available, thanks to the Sun, will be eaten. If there’s some niche that is avoiding consumption, that’s an easy niche to invade, and consequently it will disappear and, again, 100% of energy will be consumed by life.
On the other hand, if the total energy available is less than the needs of life, then some number of lives will be lost.
But in no case does food go uneaten.
So while it may be true that a large number of life forms may have been collected into one location, since man has no control over the Sun, we are still limited to the available energy that the Sun has naturally produced. We aren’t producing bonus energy and thereby bonus vegetaion to feed our slaughter animals. We’re just aggregating our vegetation to a single location to feed a localized population, where naturally that vegetation would have stayed in its original location and been eaten by a distributed and varied population of animals.