ECOLOGICAL SUCCESSION, TYPES CAUSES STAGES AND PROCESS

 As you develop and grow there are certain predictable changes that will occur, and they usually happen in a specific order. As a baby, you first learn to roll over, then crawl, then walk. You also learn new skills such as how to feed yourself and how to talk, but each skill you learn builds on those learned before it. Your body also changes as you grow taller, your muscles and bones develop, your hair grows longer, etc.

Meaning of ecological succession

• Ecological Succession: the series of changes in an ecosystem when one community is replaced by another community as a result of changes in biotic and abiotic factors

 • Can regenerate a damaged community

 • Can create a community in a previously uninhabited area

• Occurs in all types of ecosystems (forests, ponds, coral reefs, etc)

Ecological Succession Defined

1.     Ecological succession is the same idea. It is the observed changes in an ecological community over time. These changes are fairly predictable and orderly. Within an ecological community, the species composition will change over time as some species become more prominent while others may fade out of existence. As the community develops over time, vegetation grows taller, and the community becomes more established.

2.     Ecological Succession is a general process which refers to the gradual change in condition of environment and the replacement of older species with newer ones.

Characteristic of Ecological Succession:

1. It is a systematic process which involves change in species structure.

 2. The changes are directional and take place as a function of time.

3. The succession occurs due to the changes in physical environment and population of species.

4. The changes are predictable. The process of succession is self going, stake and biologically feasible.

5. The change also occur due to population explosion of the species,

Types of Ecological Succession:

1.   Primary Succession:

Primary Succession: the process of creating and developing an ecosystem in an area that was previously uninhabited

 Examples of uninhabited areas:

A.    Sides of volcanoes

B.    Sites of glacier recession

C.    Occurs in areas with no soil

• Is a very slow process

• The process of primary succession starts with the arrival of living things such as lichens and mosses that do not need soil to survive

• These first species are called pioneer species

• Pioneer species: the first organisms to live in a previously uninhabited area

1. Pioneer species move into an unoccupied area

• The pioneer species help create soil by breaking down the rock particles into smaller and smaller pieces

• As lichen and mosses die, they decompose and add small amounts of nutrients to the rock particles, creating soil

• During this early stage of succession there are not many habitats so not many organisms are found in the environment

    Once there is enough soil and nutrients, small plants such as flowers, ferns, and grasses grow

• These plants help to further break down the rocks and add nutrients to the soil when they die and decompose

The small plants create habitats for small animals like insects and small mammals

• Over time, as animals die and decompose, their bodies add nutrients to the soil allowing larger plant species to populate the area

• Larger animals follow the larger plants

• Eventually, a mature community is formed, this mature community is called a climax community

• A climax community is a community that is able to maintain itself for long periods of time with few changes in the species that populate it

DEF: 1. Primary succession is the colonization of new sites by communities of organisms. It often occurs after a devastating event has wiped out the organisms that lived in the area, or with the creation of a new habitat.

2.      It is the initial development of an ecosystem. When a community begins 2develop on a site that is previously unoccupied and then the progression from one biotic community to the next is termed as primary succession.

3.     It is characterised as initial stage of development of an ecosystem which begins with the creation of a community on such a location which was previously unoccupied by living organism. E.g., Formation of certain type of forests of dried lava.

2.  Secondary Succession:

the process of repairing a damaged ecosystem

• Occurs in areas where the soil was left intact

 Examples of events that damage ecosystems:

• Natural disasters

• Human activities

• Death of organisms

• Is typically a much faster process than primary succession because there is already soil

• Secondary succession is a never ending process

• Any disturbance in an ecosystem results in secondary succession starting over

• If an ecosystem is frequently disturbed it will not be able to support large trees and animals so it will consist of the animals typical of the early stages of succession

DEFF: 1. It is characterised as a stage of re establishment of an ecosystem which existed earlier but was destroyed due to some natural calamities like fire, flood, etc. Such re establishment occurs due to the presence of seeds and organic matte’ of biological community in soil. E.g., Vegetation grows once again which was destroyed due to flood.

2.     Secondary succession occurs when an area that has previously had an ecological community is so disturbed or changed that the original community was destroyed, and a new community moves in. This is more common than primary succession and is often the result of natural disasters such as fires, floods, and winds, as well as human interference such as logging and clear-cutting.

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.

 

 

Causes of Ecological Succession:

Following are the causes of ecological succession:

1. Initial Causes:

Causes those are responsible for the destruction existing habitat. Such occurrences happen due to the following factors:

(a) Climatic Factor:

Such as wind, deposits, erosion, fire etc.

(b) Biotic Factor: Such as various activity of organisms.

2. Continuing Causes:

Causes those are responsible for changes in population shifting features of an area. Such factors are:

(a) Migration for safety against outside aggregation.

(b) Migration due to industrialization and urbanization.

(c) As a reactionary step against local problems.

(d) Feeling of competition

3. Stabilising Cause:

Causes which bring stability to the communities. Such factors are:

(a) Fertility of land

(b) Climatic condition of the area

(c) Abundance of availability of minerals etc.

The process of succession takes place in systematic sequential order having following steps:

       Nudation: It is the development of a bare area without any life form.

      Invasion: It is achieved through dispersal or migration when a species establishes itself over a bare area. When the growth and reproduction starts these pioneer species increase in number and form groups or aggregates.

    Competition and co-action: There is competition both inter-specific i.e., between organisms of different species and intra specific i.e., within organisms of same species for nutrients, space etc. co-action is the influence they have on each other.

     Reaction: Due to competition and co-action there is modification of the environment which has a strong influence on the physical environment and is referred to as reaction

      Stabilization: The formation of the climax ecosystem which is in equilibrium with the environment is referred to as stabilization.

Factors of ecological succession:

Topographic factor: volcanic eruption, landslides

Climatic factor: drought, forest fire

Biotic factor: overgrazing, industrial activities

Causes of succession:

A number of causes induce together the process of succession.

Some important causes may be outlined as below:

(i) Climatic Causes:

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:

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:

(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.

Stages

When succession first begins, pioneer species are the first to colonize the new area. Pioneer species are usually fast-growing, opportunistic, and able to disperse easily. These are called r-selected species. These are things like bacteria, moss, insects, and smaller plants.

 (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 condition, 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.