There are various types of successions
1. Primary Succession:
In any of the basic environments (fresh water, marine, terrestrial), one type of succession is primary succession, which starts in a given area where the conditions of life are not favourable in the beginning. The first group of organisms establishing the known as the pioneers, primary community or primary colonisers, e.g., succession in sand on exposed rock surfaces etc.
In the primary succession-taking place on the exposed rock surface, usually, lichens their appearance first. Lichens followed by the mosses start the initial stage of succession, lichens and mosses change the physical environment so that the new species of autotrophs a in the area and establish themselves. Consequently, heterotrophs also arrive in the area. In way succession continues in the area, finally leading to the establishment of a stable community in the particular ecosystem.
2. Secondary Succession:
It starts from previously built-up substrata with already exists living matter. This type of succession starts in a given area where the conditions of life favourable because of the fact that the area was occupied earlier by well-developed community e.g., succession in an abandoned crop field. Such successions are comparatively more rapid
The development stages of ecological succession are called stages. Organisms (usually plants), which start the initial stage of succession, are called pioneers.
The pioneers established themselves in the given area, reproduce and survive in the area. Gradually, the physical environment this changed environment enables new species to arrive in the give area and establish themselves in the area. Depending on the types of autotrophs in heterotrophs (animals) also arrive in the area. In this way, the succession continues in the one community following the other.
The culminating stage in the succession is the establishment of a stable community in the area, and this is known as the climax community. Thus, the final stage of ecological succession is the formation of the climax community. The chain of stag from the pioneers to the climax community is called the sere.
In the abandoned crop-field, the weeds (autotrophs) are pioneers. The weeds modify physical environment so that more and more herbs invade the area in course of time. Later the shrubs enter the area and finally the trees and establish themselves forming the climax community
3. Autotrophic Succession: It is characterised by early and continued dominance o autotrophic organisms like green plants. It begins in a predominantly inorganic environment and the energy flow is maintained indefinitely.
4. Allogenic Succession: In some cases, however, the replacement of the existing community is caused largely by any another external condition and not by the existing organisms! Such a course is referred to as allogenic succession.
5. Autogenic Succession: After the succession has begun, in most of the cases, it is the community itself, which, as a result of its reactions with the environment, modifies its own1 environment and thus causing its own replacement by new communities.
6. Micro Succession: This involves the succession of microorganisms. It begins in a predominantly organic environment and there is a progressive decline in the energy content.
The succession of protozoa in the hay infusion is called micro-succession. The time taken for this succession is about 30 days. Dried hay is boiled in water and if the solution is kept for a few days, heterotrophic bacteria develop. If some pond water, containing various microscopic organisms, is added to this solution, the succession of protozoa can be observed in this culture. First small flagellates appear in the infusion and this is followed by ciliates. At this stage paramecia can be seen in plenty.
This may be followed by the appearance of amoeba and rotifiers. This represents the climax.
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