Test: Ecological Succession (NCERT) - NEET MCQ

Bacteria are important decomposers of ecosystem. Because of their small size, they are also called as micro consumers. Green plants (producers) are also called transducers because they convert light energy into chemical energy.
Primary succession (=Prisere) is the biotic succession that occurs on a previously bare area. Lithosere (or Xerosere) refers | to the sequence of successional stages that occur on bare rock.

Primary succession starts from the primitive substratum, where previously there was not any sort of living matter. The first groups of plants establishing there are known as the pioneers, primary community or primary colonisers. Newly formed river delta, newly exposed sea floor, igneous rocks, sand dunes, new cooled lava sediments are some examples of primary bare area. Primary succession takes a long time for completion, several hundred to several thousand years.

In lithosere (xerosere or xerarch), the pioneer community is usually constituted by crustose lichens (e.g., Graphis, Rhizocarpon). Foliose lichens (e.g., Dermatocarpon, Parmelia) kill the crustose lichens by shading them, cause deeper depressions and accumulate more soil particles and organic matter. Foliose lichens make the conditions favourable for the growth of hardy mosses (e.g., Tortula, Grimmia).

Series of biotic communities that develop in a newly formed pond or lake is called hydrosere. Various seral stages of hydrosere are:
Planktons (Phytoplanktons and zooplanktons) → rooted submerged hydrophytes → floating hydrophytes → reed swamps → sedges or marsh-meadow stage → woodland stage → climax forest.

The various serai stages of lithosere (succession on bare rock) are as follows:
Lichens (Pioneer community) → Mosses → Annual grasses→ Perennial grasses → Shrubs → Trees (Climax community).

Pioneer community is the first community to inhabit an area while the last stable community of an ecological succession is climax community. Climax community has the maximum diversity and niche specialisation.

In the given figure, A represents submerged stage (e.g., Hydrilla, Potamogeton, Vallisneria, etc.), B represents floating leaved anchored plant stage (e.g., Nymphaea, Nelumbo, Pistia, etc.), C represents reed-swamp stage (e.g., Phragmites, Typha, Scirpus, Sagittaria, etc.), D represents marsh-meadow stage (e.g., Carex, Cyperus, Juncus, etc.), E represents woodland stage (e.g., Salix, Populus, Alnus, etc.) and F represents the climax community of forest (e.g., Acer, Quercus, Ulmus, etc.).

If an ecosystem is easily dameged, that means it is not very stable. But since, it recovers fast when the damaging effect stops, it certainly has high resilience.

High species diversity is the most important factor in bringing stability to a climax ecosystem.

Second stage of hydrosere is represented by submerged plants. The bottom lined by soft mud having organic matter is favourable for growth of submerged plants like Hydrilla, Potamogeton, Vallisneria abd Najas. They are rooted in the mud and form dense growth.