Question

What is ecological succession? What is its impact?

Answer 1

Ecological succession is defined as an orderly process of changes in the community structure and function with time. These changes are mediated through modifications in the physical environment and ultimately culminating in a stabilized ecosystem.

Two different types of succession have been distinguished:

• Primary succession occurs in essentially lifeless areas, regions in which the soil is incapable of sustaining life as a result of factors like lava flows, newly formed sand dunes, or rocks left from a retreating glacier.
• Secondary succession occurs in areas where a community that previously existed has been removed; it is typified by smaller-scale disturbances that do not eliminate all life and nutrients from the environment such as fires, floods, and winds, as well as human interference such as logging and clear-cutting.
• 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:
  o Topographic: The existing community may disappear due to soil erosion (by gravity, water or wind), land slide, volcanic activity etc.
  o Climatic: The existing community may be destroyed due to storm, fire, frost, drought.
  o 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.
• 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:
  o Migration (Dispersal): The seeds, spores or other propagules of the species are brought to the bare area by the agents like air, water etc.
  o 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.
  o Aggregation: After ecesis, the individuals of species, the pioneer community increase their number by reproduction and thus, are aggregated in a particular area.
• 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.
• 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. 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.
  Stablisation: At last a final 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.