Autotrophic and Heterotrophic Succession
The succession where initially the green plants are much greater in quantity than the animals, is known as autotrophic succession. Such a succession takes place in a medium rich in inorganic substances. Since there are green plants, there is gradual increase in the organic matter content and energy flow in the ecosystem. On the other hand, in heterotrophic succession, the populations of heterotrophic organisms, like bacteria, actinomycetes, and fungi are present in greater quantity in the initial stages.
Such a succession begins in a medium rich in organic matter such as the rivers and streams which are polluted heavily with sewage, or in small pools receiving leaf litter in large quantities. As indicated earlier, it begins, prominently in organic environment, and there is a progressive decline in the energy content.