Read this article to learn about the ecological succession: meaning, causes, characteristics, types and general process!
Meaning:
The term ecological succession refers to the changes in the biotic communities over a period of time at a particular place. The changes are due to climatic or physiographic conditions. When there happens a change in environment due to biological activities the modified form of environment may not be suitable for the existing community.
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Such a process induces the formation of a new and developed community in place of old ones one after another over the same area. The process continues and successive communities develop one after another over the same area until a relatively stable community is established.
This relatively stable community is known as climax community which has potentiality to tolerate the changing environment. Thus, the sequential changes of communities with the modification of environment over a period of time in the same area is known as ecological succession.
Causes of succession:
A number of causes induce together the process of succession.
Some important causes may be outlined as below:
(i) Climatic Causes:
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The climatic causes include temperature, rainfall, light intensity, gaseous composition, wind etc.
(ii) Biotic Causes:
In a community, there is competition amongst different members for their existence. In such a process, some of the members are not found suitable and thus are gradually replaced by new ones.
(iii) Ecesis Causes:
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The soil condition is also changing by the process of invasion, migration, competition and reaction of the Population.
(iv) Stabilising Causes:
Succession is taking place in order to attain the climax stage.
Characteristics:
Ecological succession has the following characteristics:
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(1) It results from modification of the physical environment of the community.
(2) It is an orderly process of community development.
(3) It involves changes in species structure and it increases diversity of species.
(4) Nutrient variation determines the settlement of new community.
(5) Succession cumulates in a stabilized ecosystem.
Types of succession:
Some basic types of successions may be outlined as below:
(1) Primary sucession:
This type of succession being in a sterile area or barren land or in an inorganic environment. When a bare or nude area is colonized by organisms for the first time and subsequently the communities are changed in a successive form, the process in known as primary succession.
(2) Secondary succession:
The community development on area previously occupied by another well developed living community amidst the interruption due to adverse conditions like natural calamities, biotic intervention etc. is designated as secondary succession. The natural calamities include forest fire, disease, flood, grazing etc.
(3) Autotrophic succession:
When the population of autotrophs (plants) dominate the population of heterotrophs, the succession caused is known as autotrophic succession.
(4) Heterotrophic succession:
It is characterised by early dominance of heterotrophs like bacteria, fungi and some animals in an organic environment. Since the environment is dominated by heterotrophs the succession is called heterotrophic succession.
(5) Autogenic succession:
Due to the continuous interaction of community with environment, there happens a modification of the later. Such a modification of environment causes the replacement of an old community by a new one, which is known as autogenic succession.
(6) Allogeneic succession:
When the replacement of a community is caused by any other external condition and not by the existing organisms, the course of succession is known as allogeneic succession.
(7) Habitat Succession:
Successions are also named differently basing upon the type of habitat from which the phasic replacement starts.
(a) Hydrosere:
The succession starting from aquatic habitat is known as “Hydrach” and the series of changes occurring in the vegetation of hydrarch are called ‘Hydrosere’.
(b) Mesarch:
The succession starting from a habitat where adequate moisture condition are present.
(c) Halosere:
The succession occurring at saline water or soil is known as holosere.
(d) Xerosere:
Succession taking place in xeric havitat like sand or rocks where moisute is present at minimal amount is known as xerosere. Xeroseres can further be subdivided into:
(i) Psammosere:
Where the succession starts on sandy habitat.
(ii) Lithosere:
Where the succession starts on the surface of rocks.
(e) Oxylosere:
The succession starting on acidic soils in known as oxylosere.
General process of succession:
The entire process of primary autotrophic succession is completed through a series of sequential steps followed by one after another.
The different sequential steps may be outlined as below:
(1) Nudation:
It is a process of developing a bare area without any form of life for the arrival of new species. The causes of nudation may be:
(a) Topographic:
The existing community may disappear due to soil erosion (by gravity, water or wind), land slide, volcanic activity etc.
(b) Climatic:
The existing community may be destroyed due to storm, fire, frost, drought.
(c) Biotic:
The community may also be destroyed by anthropogenic activities like destruction of forest, destruction of grass land etc. Besides, diseases induced by bacteria and virus can also destroy the population.
(2) Invasion:
The successful establishment of a species in a bare area is called as invasion. This process of establishment is completed in three successive steps:
(a) Migration (dispersal):
The seeds, spores or other progagules of the species are brought to the bare area by the agents like air, water etc.
(b) Ecesis (Establishment):
The process of successful establishment (germination and growth) of the species in the new area as a result of adjustment with the prevailing conditions is known as ecesis.
(c) Aggregation:
After ecesis, the individuals of species increase their number by reproduction and thus, are aggregated in a particular area.
(3) Competition and Coaction:
As the species aggregate at a limited space, there happens competition (inter as well as intra specific) mainly for space and nutrition. Secondly the life process of one individual is affected by the surrounding species in various ways which is known as coaction. The species which are found unable to compete with others in the existing environment get discarded.
(4) Reaction:
The species present in an environment constantly interact with it there by causing its modification. The mechanism of the modification of the environment through the influence of living organisms on it, is known as reaction.
Reaction induces changes in soil composition, water content and light organisms on it and is known as reaction. Reaction induces changes in soil composition, water content, light conditon, temperature etc. Due to drastic modifications of the environment/ it may not be suitable for the existing community.
Hence, the existing community may be replaced by another community. The whole sequence of communities that substitute one another in the given area is known as sere and the various communities constituting the sere are known as seral communities or seral stages.
(5) Stablisation (Climax):
At last a final or terminal community is established. Which is stabilized for a longer period of time and which can maintain an equilibrium with the environment of that area. This community is known as climax community and the stage is as climax stage.