Autogenic and Allogenic Succession
In many cases the living beings of an ecosystem, modify their environment considerably by their growth, death and decay. The changed conditions lead to the establishment of new kinds of species in that area. The whole process goes on and on, that is, there is replacement of one kind of community with another. Such a succession process is called autogenic succession. To sum up, autogenic succession results because of the changes brought about in the habitat by the members of the community themselves.
In some cases, the changes brought about in the habitat are caused by external agencies and not by the existing vegetation itself. This is called as allogenic succession. Such a succession may occur in a highly disturbed or eroded area or in ponds where nutrients and pollutants enter from outside and modify the environment and in turn the communities.