Biotic succession

 Succession :

An orderly and progressive replacement of one community by another until a relatively stable community (climax community) is established in an area is called biotic succession.

A. Causes of succession:

It involves a series of complex processes, so it controlled by a number of causes- 

a. Initiating causes:

It includes all these biotic and abiotic causes which helps in production of barren area e.g. fire, wind, grazing, cutting, cultivation, draught etc.

b. Continuing causes:

Causes of successive waves of population e.g. Migration, competition, aggregation, reation etc.

c. Stabilizing causes:

These helps in stabilise the community in an  area. Climatic factors has major influences on stabilisation.

B. Basic types of succession:

There are two main types of succession-

a. Primary succession:

- It is a process of colonization on the substratum initially free of life. 

- The substratum serves for primary succession may be river delta's, sand dune, base rock etc. and the succession ends with the formation of clmax community.

- The first group of plants establishes there are known as pioneer.

- It takes longer period of time that may be 1000yrs.

b. Secondary succession:

- This type of succession starts from previously built up substratum with organic matters but no life.

- As organic matters of original community already exists, succession is comparatively more rapid.

- Time takes by this type of succession is about 50- 100yrs for grassland.

C. General process of succession:

The whole process of primary autotrophic succession is actually completed through a number of initial steps like - 

1. Nudation:

- It is the process of formation of barren area without  anylife.

- Nudation may be caused by climatic ( hails, fire etc.) or topographical (soil erosion, land slides etc. )

2. Invasion:

- It is the process through which organism enters into a barren area.

- it involves three sequential steps- 

a. Migration:

 It takes place by arrivals of spores, seeds etc. in a barren area through the agencies like air, water etc.

b. Ecosis ( Establishment):

 It involves the successful establishment of organisms with prevailing conditions of that area.

c. Aggregation:

It involves the increase in number of organisms through the process of reproduction.

3. Competition and co action:

It deals with the intraspecific and interspecific competition among the members for limited food and space e.g. positive and negative inta as well as interspecific competition.

4. Reaction: 

- It involves the modification of the environment through the influence of migrated organism.

- The modified area become lesserfavorable for existing community thus they sooner or later replaced by other community called seral community.

5. Stabilization ( climax):

This  phase deals with the attainment of more or less stable community which is itself in equilibrium with the climate of the area. This final community is called climax community.