But an ecosystem is not a system in the same sense that nature is a system. Nature consists of the physical laws that govern everything-- it sets the parameters for our existence, and we simply can't break them. An ecosystem, however, is no more significant than we are. The rules governing an ecoystem are conditions, not absolute parameters, and, while of course they're based on natural laws just as everything is, they themselves are not natural laws; they're general rules. And we can alter the cause/effect relationships that dictate these general rules. To apply my argument to your example, for instance: The humans would learn to breed the cows in captivity, increasing the cows' population to meet their own needs. Now, maybe, as the humans' agrictulture becomes more and more efficient, the human society will become unable to support its own weight and collapse, fulfilling your predictions and leaving the ecosystem to continue as it was. But there is also the chance that this won't occur. And that is because we always have the ability to exploit whatever can be altered, to stay one step ahead of our own destruction. Biology is not fate; it is a set of conditions that are often strongly adverse, but only appear to be written in stone because we're the only species we know of that has the capacity to resist them.
