ABSTRACT
A natural ecosytem is a self-regulating community of organisms in equilibrium with their physical environment. Species become adapted through processes of natural selection to the conditions – biological and non-biological – which exist in the ecosystem. These processes of natural selection have worked through evolution to give us a world which can support a rich variety of species. Precisely how many species are known has been estimated by E. O. Wilson to be 1·4 million, including all plants, animals and microorganisms. However, the accuracy of this figure is qualified by the fact that biologists agree that as an estimate it is probably less than a tenth of the number that actually live on Earth! In fact the true number probably lies somewhere between 10 million and 100 million species.
