It is not so much the eco-system, it is the need for a full food-chain of animals to keep populations in-check. We like deer but without wolves or large cats, the deer become a pest but we don't like wolves and large cats because we are all taught as children that they are scary and dangerous - although more children die from car accidents and stabbings than wild animals so whatever!
So natural predators for small rodents keep their numbers in check but that will be a long time because "won't somebody think of the children"..."and the farmers"
So natural predators for small rodents keep their numbers in check but that will be a long time because "won't somebody think of the children"..."and the farmers"