Ecological Succession

A process of directional change in vegetation on an ecological time scale. In this process, a series of communities replace one another due to large-scale natural or anthropogenic destructions.

Types of Ecological Succession

Primary Succession

  • When a terrestrial site is first colonised by the pioneer species. In primary succession on rocks, these are usually lichens which can secrete acids to dissolve rock, helping in weathering and soil formation.
  • These later pave the way to some very small plants like bryophytes, which can take hold in a small amount of soil.
  • They are, with time, succeeded by higher plants, and after several more stages, ultimately a stable climax forest community is formed.
  • In primary succession in water, the pioneers are the small phytoplankton, which is replaced with time by rooted-submerged plants, rooted-floating angiosperms followed by free-floating plants, then reed swamp, marsh-meadow, scrub and finally the trees. The climax again would be a forest. With time the water body is converted into land.
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Secondary Succession

  • Sequential development of biotic communities after disturbance/destruction.
  • In secondary succession, the species that invade depend on the condition of the soil, availability of water, environment and also seeds or other propagules present.
  • Since soil is already there, the rate of succession is much faster and hence, the climax is also reached more quickly.

Examples of succession

  • Terrestrial: Bare rocks – Lichens — Annual Plants — Perennial Plants and Grasses – Shrubs – Softwood Tress, Pines – Hardwood trees
  • Hydrosere: Phytoplankton – Submerged plant – Submerged free-floating plant – Reed swamp (Sedge) – Marsh meadow – Scrub – Forest

Seral Community (Sere)

Based on the nature of the habitat – whether it is water (or very wet areas) or it is on very dry areas – succession of plants is called hydrarch or xerarch, respectively. Hydrarch succession takes place in wet areas and the successional series progress from hydric to mesic conditions. As against this, xerarch succession takes place in dry areas and the series progress from xeric to mesic conditions. Hence, both hydrarch and xerarch successions lead to medium water conditions (mesic) – neither too dry (xeric) nor too wet (hydric).

Ecological Niche

  • It represents the range of conditions an organism can tolerate, the resources it utilizes and its functional role in the ecological system.
  • A habitat may contain many ecological niches and support a variety of species.
  • Each species has a distinct niche, and no two species are believed to occupy the same niche.

Edge effect and Ecotone

  • Edge effect is an ecological concept that describes how there is a greater diversity of life in the region where the edges of two adjacent ecosystems overlap, such as land/water, or forest/grassland.
  • Ecotone is a transition area between two biomes. It is where two communities meet and integrate. For ex –
    • Grassland (between forest and desert)
    • Estuary (between fresh water and salt water)
    • Riverbank or Marshland (between dry and wet)
    • Mangroves (b/w terrestrial & marine ecosystems)

Sentinel Species

  • They are organisms, often animals used to detect risks to humans by providing warning of danger. They serve as indicators of ecosystem health.
  • Ex. Canaries are birds that die early if an odourless Carbon Monoxide environment is present in a high concentration, this gives miners time to escape.
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