[Biology Class Notes] on Ecological Succession Pdf

The most widely accepted definition of ecological succession is as follows “ecological succession is a sequence of changes that occur in an ecological system over time.” In simpler terms, it can be defined as the sequence of colonization of species in an ecosystem from a barren or an unfertile region of land. The first species to inhabit an area are mosses and lichens. These make the region suitable for the growth of advanced species like grasses, shrubs, and trees. Ecological succession is a very necessary type of growth and development of a progressing ecosystem as a whole. It also ensures new areas are colonized, and deteriorated ecosystems are recolonized so that the organisms can easily adapt to the constant changes in the environment and continue to survive well.

The definition of ecological succession as mentioned above is discussed widely in the article, the stages of succession are also mentioned in the article. The types and examples are also discussed in the article.

What is Ecological Succession?

The gradual and progressive growth of a species in any given area with respect to its changing surroundings is called an ecological succession. It is an anticipated change that beholds the biotic components being an inevitable part of them in the environment. Ecological succession aims at reaching the equilibrium in the ecological system. This is achieved by a community called the climax community. To attain this point of equilibrium constant change (increase or decrease) in the number of species is observed. The area in which the order of communities undergoes a specific change is called sere. Each changing community is therefore called a seral community. All communities around us have undergone ecological succession ever since their existence was identified. Evolution thus is a simultaneously occurring process along with ecological succession.  Also, the initiation of life on earth can be considered to be a result of this succession process.

Any area where life started from scratch by succession is termed to have been gone under a process called primary succession. If on the other hand, if life begins at a place that has lost all its existing life forms then the process is called secondary succession. Primary succession is a gradual and low process because in this case, life starts from nothing. Secondary succession is a faster process because life has already been supported in these conditions earlier. The first species that come into existence during primary succession is known as pioneer species.

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Types of Ecological Succession

As mentioned above primary and secondary succession are the two main types of ecological succession. The following stages of ecological succession are discussed below:

Primary Succession

Primary succession is the succession that begins in lifeless areas such as the regions devoid of soil or barren lands where the soil is unable to sustain life. When the planet was first formed there was no soil on earth. The earth was only made up of rocks. These rocks were broken down by microorganisms and eroded to form soil. This is a process called erosion. The soil then becomes the foundation of plant life. These plants help in the persistence of different animals and progress from primary succession to the climax community. When the primary ecosystem is destroyed, secondary succession takes place.

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Secondary Succession

Secondary succession occurs when the primary ecosystem gets wiped out. For e.g., a climax community gets destroyed by fire. It gets recolonized after the devastation. This is known as secondary ecological succession. Small plants emerge first, followed by larger plants. The tall trees block the sunlight and change the structure of the organisms below the canopy. Finally, the climax community comes into action.

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What is Cyclic Succession?

The change in the structure of an ecological system on a cyclic basis is called cyclic succession. There are some plants that stay dormant for most of the year but emerge all at once. This can cause structural variations in the ecosystem.

What is Seral Community?

“A seral community is a transitional stage of ecological succession progressing in the direction of the climax community.” A sere, or seral community, is described as the progression of an ecological community’s growth phases from the pioneers to the climax. A climax community in the ecological community wherein the  populations are stable and coexist in harmony with one another and their surroundings is defined as the last stage of succession, and it remains basically intact until it is destroyed by a natural disaster or human intervention. Seral community is substituted by the succeeding community. It consists of simple food webs and food chains. It exhibits a very low degree of diversity. The individuals are less in number and the nutrients are also less.

Types of Seres

There are seven different types of seres, these are mentioned below in the table below along with their meaning.

 

Examples of Ecological Succession

Following are the important examples of ecological succession:

Acadia National Park

This national park faced a dreading wildfire. Restoration of the forest was left on to Mother Nature. In the initial years, only small plants grew on the charred soil. After several years, the forest showed diversity in tree species. However, the trees before the fire were mostly evergreen, while the trees that grew after the fire turned out to be deciduous in nature.

Ecological Succession of Coral Reefs

Small cor
al growths colonize the rocks. These polyps grow and divide to form coral colonies. The shape of the coral reefs attracts small fish and crustaceans that are food for the larger fish. Thus, a fully functional coral reef is formed.

Causes of Ecological Succession

Some important causes may be defined as below:

• Climatic Causes: these can be rainfall, temperature variations, humidity, gas composition, etc.

• Biotic Causes: the organisms in a community compete to thrive for existence. Some of them are lost in the process while some new ones are incorporated.

• External Causes: soil conditions are affected by the process of migration, invasion, and competition amongst various species. 

Characteristics of Ecological Succession

Ecological succession has subsequent characteristics:

• It results from the disparity in the physical atmosphere of the community.

• It is a systematic procedure of community development.

• It involves variations in species structure and it increases the diversity of species.

• Nutrient variation regulates the settlement of new communities.

• Succession operates in a stabilized ecosystem.

Mechanism of Ecological Succession

The entire process of primary succession is accomplished through a series of progressive steps followed one after another. The different sequential steps may be outlined as below:

Nudation:

It is a process of formation of a bare area without any form of life for the arrival of new species. The causes of nudation may be:

Topographic: E

The existing community may fade away due to soil erosion, landslide, volcanic activity, etc.

• Climatic: The existing community may be demolished due to storm, fire, frost, drought.

• Biotic: The community may also be destroyed by anthropogenic activities like the destruction of the forest, the destruction of grassland, etc. 

Invasion:

The successful establishment of a species in a vacant area is called invasion. This process of establishment is completed in three successive steps:

• Migration (dispersal): The seeds, spores of the species are carried to the unadorned area by the agents like air, water, etc.

• Establishment: The process of the 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.

• Aggregation: After ecesis, the individuals of species increase their number by reproduction and thus, are aggregated in a particular area.

Competition and Coaction:

As the species aggregate within a restricted space, there happens competition for space and nutrition. Secondly, the life process of one individual is affected by the surrounding species in various ways which are known as coaction. 

Reaction:

The species present in an environment constantly interact with it by causing its modification. The mechanism of the modification of the environment through the influence of living organisms on it is known as a reaction. Hence, the existing community may be replaced by another community. 

Stabilization:

At last, a final or terminal community is established which can maintain equilibrium. This community is known as the climax community.

In conclusion of the article, we have developed an understanding of ecological succession along with the types and examples of it.