Online CBSE Biology Class 12 Ecological Succession
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Ecological Succession(ecological means related to ecology i.e study of the surrounding and succession means series of things following one after another) so ecological succession literally means series of changes that are occurring in the surrounding of a given place. Over the period of time, the change occurs in the conditions of the environment/ surroundings which lead to the disappearance of old species and appearance of the new ones.
Ecological Succession can be defined as a gradual process which leads to the sequential change in the species structure due to the change in the conditions of the environment at a particular place over a certain period of time. The time scale can be decades or millions of years. During ecological succession, the old species are replaced by new ones.This process continues and the successive communities develop one after another over the same area until a relatively stable community is established. This relatively stable community is known as the climax community which has a tolerance for the changing environment. This community will persist indefinitely, facing a major disturbance and this end point of succession is known as the climax.
Ecological succession is of two types-
- Primary succession– It takes place, when an area/ habitat that has never previously supported an ecological community/ biological community,is occupied by the colonies of plants and animals. The ecological community starts living in the new form of habitat which was not present earlier. For example; this could happen on the newly exposed rock surface due to landslides, theappearance of forest on the dried lava etc.
The primary succession begins with the appearance of species like lichen, mosses, and fungi which can grow on rocks or other newly exposed rocks. These are small organisms that can survive the harsh conditions, fix nitrogen. As these organisms die and decompose, their organic matter forms the thin layer of soil, thus altering the physical environment of the habitat. This gives way to the appearance of the more complex organisms. Once the grasses or weeds begin to grow, the soil formation is accelerated and more animal species arise. The presence of moisture in the environment helps in theappearance of shrubs and small trees, which is followed by the growth of larger trees and big animals. With the appearance of several species in the given habitat, there begins a typical interaction between the organisms.
- Secondary succession: This type of ecological succession occurs when a new biological community replaces the old one. Some natural disasters like floods, famine, fires, or some human interference like cutting down of forests etc.; destroys the habitat of the existing species/community of living organisms. Hence the species that were present are destroyed. Though it appears that the region is dead, the soil remains fertile as it contains enough organic matter to sustain the reappearance of the living organisms. Hence the new biological communities occur due to the presence of seeds or other organic matter of the living organisms in the soil. For example; vegetation is produced once again after floods in a given area. Grasses are the first to appear, which is followed by the emergence of shrubs and small trees.
Characteristics of ecological succession;
- It results from the modification of the physical environment of the community.
- It is a well-defined and orderly process of the community development.
- It brings about changes in the structure of species and hence increases thediversity of species.
- Nutrient variation determines the settlement of new community.
- The process of succession is self-going, stable and biologically feasible.
Causes of Ecological Succession
There are three major causes that are responsible for ecological succession-
- Initiating Causes: They are the factors that lead to the destruction of the existing habitat and population over there, thus initiating the process of ecological succession. There are two main factors; climatic factors like wind, fire, natural calamities, etc. and biotic factors which include activities of various organisms.
- Continuing causes: The continuing causes of succession are also known asecesis.The processessuch as aggregation, competition, migration etc.occur continuously in a particular habitat. These processes cause changes in soil structure of that area like a change of soil nutrients, accumulation of organic matter, soil pH etc.
- Stabilizing causes: These include the factors that result in stabilizing the community. Some factors are fertility of the land, the climate of an area, an abundance of nutrientsetc.
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