ECOLOGICAL SUCCESSION

ECOLOGICAL SUCCESSION:

  • The gradual and fairly predictable change in the species composition of a given area is called ecological succession.
  • Composition and structure of the community constantly change in response to changing environmental condition.
  • This change is orderly and sequential, parallel with the changes in the physical environment.
  • All the changes lead finally to a community that is in near equilibrium with the environment and that is called climax community.
  • During succession some species colonize and area and their populations become more numerous, whereas populations of other species decline and even disappear.
  • The entire sequences of communities that successively change in a given area are called sere.
  • The individual transitional communities are termed as seral stages.
  • In the successive seral stages there is a change in the diversity of species of organisms, increase in number of species and total biomass.
  • Primary succession: succession that starts where no living organisms are there- these could be areas where no living organism ever existed may be a bare rock or new water body.
  • Secondary succession:  succession that starts in areas that somehow, lost all the living organisms that existed there.
  • Primary succession occurs in newly cooled lava, bare rock, newly created pond or reservoir.
  • Secondary succession begins in areas where natural biotic communities have been destroyed such as in abandoned farm lands, Burned or cut forest, land that have been flooded.
  • Since some soil or sediment is present, secondary succession is faster than primary succession.

Succession in plants:

  • Based on the nature of habitat – whether it is water or it is on very dry areas- succession of plants is called hydrarch or xerarch.
  • Hydrarch succession takes place in water areas and the successional series progress from hydric to mesiccondition.
  • Xerarch succession takes place in dry areas and the series progress from xeric to mesic conditions.
  • Both hydrarch and xerarch successions lead to medium water conditions (mesic) – neither too dry (xeric) nor too wet (hydric)

Xerarch succession: Succession in bare rock:

  • The species that invades bare area are called pioneer species.
  • In primary succession on bare rock the pioneer species is the lichen.
  • Lichen secretes acid to dissolve rock, helping in weathering and soil formation.
  • The little soil, leads to growth of bryophytes (mosses).
  • The mosses speed up the process of soil accumulation by trapping wind-blown particles.
  • Lichen moss carpet provides suitable substratum for the germination of seeds of herbaceous plants.
  • Gradually more soil is accumulated and herbaceous species make way for the invasion of shrubs followed by trees.
  • The climax community is generally dominated by trees.

 Hydrarch (succession in aquatic environment)

  • In primary succession in water, the pioneer species are phytoplankton and Zooplanktons.
  • Sub merged plant stage. (rooted hydrophytes)
  • Sub merged and free-floating plant stage.
  • Reed-swamp stage.
  • Marsh-meadow stage.
  • Shrub stage
  • Trees
  • The climax again would be the forest
  • All the succession whether taking place in water or on land, proceeds to a similar climax community – the mesic.

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