This means that nutrient cycling, water cycling, and food chains must not be disturbed. The species that live in the protected area must be allowed to expand into areas in which they would naturally occur. These are the normal areas of species distribution. It isn't enough to have just one area that is protected. You need to have an area large enough that you get variations in the ecosystems.
Natural selection works on the variability.
Natural environmental change is going to require that species adapt. Without some variability, you may be preserving species in an environment that won't be able to adapt. By having more variability, you increase the chance that a species can survive environmental changes. These requirements tell us that most of our preserves are too small. Maintenance You can get a sense of this problem when you look at the maintenance of species in an area.