Incidentally, this concept of modifying one's ecosystem comes up in Richard Dawkins' book The Extended Phenotype, which is a follow up to The Selfish Gene. One of the illustrative examples is beavers turning fast moving streams into convenient slow moving fisheries by building dams. The ecosystem the beavers built is "natural" in the sense that beavers are animals and it's in their nature to chew through trees. But presumably, at least some other animals were pushed to extinction when their habitat was modified by the beavers.