Communities do not remain the same but alter over a period of time. This is majorly due to a process known as ecological succession. We see this process all around us as abandoned farmland alters to weed fields, brush land and subsequently to a forest.
One community succeeds another in various stages as conditions change that is favorable to another suite of wildlife species.
The first stage in succession is known as the pioneer stage, which is made up of bare habitat conditions, like an exposed rock. This stage stays until conditions alter to the extent that soil gathers up and plants are capable of thriving there.
These changes go on and on till formation of a climax community, which is in equilibrium with soil and climatic conditions. Species of a climax community do not generate conditions unfavorable to themselves or additionally favorable to other species.