Ecology is the branch of science that studies the distribution and abundance of living organisms, and the interactions between organisms and their environment. Any ecological group is always in a dynamic equilibrium. If you change one part, some other part will change in response to that change. Changes may come from man, climate, pollution or any other change. In this case conservationists have been so successful at protecting endangered birds in a Spanish nature reserve that the birds are now killing the reserve’s ancient cork oak forest. This may mean some bird colonies will have to be moved to protect the trees, some of which date back to the seventeenth century. Move is one method. In other cases (for example New Jersey) bears and deers are periodically hunted and killed because the alternative is that they will starve because of a lack of natural predation and food supply as a result of burgeoning populations. In order for ecology to work, it must be balanced.