"When I was a student, back in the days when mammoths roamed the earth, ecologists tended to believe that the character of living systems was largely determined by abiotic factors. This means influences such as local climate, geology or the availability of nutrients. But it now seems that this belief arose from the study of depleted ecosystems. The rules they derived now appear to have described not the world in its natural state, but the world of our creation. We now know that living systems which retain their large carnivores and large herbivores often behave in radically different ways from those which have lost them."