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Ecosystems — BIOLOGY STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceBIOLOGYEcosystems4 Marks
Question
  1. Comment on the pattern in which all communities undergo a change in composition and structure with changing environmental conditions.
  2. Explain 'climax community' and 'sere'.
  3. Differentiate between primary and secondary Succession, with examples.
✓

Answer

  1.  
  • The change is orderly and sequential; it is also parallel with the changes in the physical environmental The gradual and fairly predicatable change in the species composition of a region, is called ecological succession.
  • During succession, some species colonisc an area and their populations become more numerous, whereas populations of some other species decline or even disappear.
  • In the successive stages, there is a change in the diversity of species of organisms, increase in the number of species and organisms and an increase in the biomass.
  1.  
  • Climax community refers to the community that gets established finally in succession and is in equilibrium with the environment.
  • Sere refers to the entire sequence of communities that successively change in a given area. 
  1.  Differences:
S.No.
Primary Succession
Secondary Succession
(i)
The ecological succession that takes place in a region, where no life existed before, is called primary succession.
The ecological succession that occurs in a region where natural biotic communities existed before, but got wiped out completely, is called secondary succession.
(ii)
It is a slow process, as suitable substratum/ soil has to be formed e.g. sucession on a bare rock or a newly formewd pond.
It is comparatively faster as the soil or sediment is already present. e.g. succession on a fire.devaStated forest or land that has been floaded.

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