Question

The pioneer species in xerarch and hydrarch succession are respectively
(a) Lichens and sedges
(b) Lichens and rooted hydrophytes
(c ) Phytoplanktons and lichens
(d) Lichens and phytoplankton
(e) Sedges and phytoplanktons

Answer 1

Hint: Any succession has its beginning and end points interspersed with sub-stages in between. The pioneer species marks the beginning of a succession. Xerarch succession takes place in drier areas while hydrarch succession takes place in wet areas.

Complete answer:
Succession is a universal process of unidirectional series of changes in community composition on an ecological time scale. It finally leads to the establishment of a stable community known as a climax community. They are the first ones to colonize any unoccupied or barren land and thus initiate primary succession. The pioneer communities in hydrarch succession are phytoplanktons. The pioneer communities in xerarch succession are lichens.
The ecological succession can be further classified into hydrarch and xerarch succession based on their habitat.
The hydrarch succession may take place in freshwater ecosystems such as ponds, lakes, etc, or in saline water ecosystems such as mangroves, estuaries. Initially, the pond water is poor in nutrients and thus is capable of supporting only microscopic life forms like phytoplanktons. These pioneer species multiply and become the food of dependent animals. With their death, decomposers bring about their decomposition, release the minerals, and enrich the aquatic habitat. This stage is further carried by many transitional stages such as rooted hydrophytes and sedges. It ultimately terminates into a forest, its climax community.
While in search succession, the pioneer communities are established in the drier area such as rocks or sandy areas like sand dunes. Rocks may be produced when a volcano erupts or by glaciers. They are eroded by rain, water, and wind. Cracks and crevices appear in the rocks which are further filled by soil particles. The spores of algae and fungi carried by wind form lichens and occupy these crevices. These pioneer species accumulate dust particles and retain water. They also secrete acidic secretion. All this helps in further solubilization of the rocks into fine particles. Their decomposition enriches the new soil with humus and thus paves way for the future plants and animals.
So, the correct answer is ‘Phytoplanktons and lichens.’

Note: Some important keywords to remember are:
- Phytoplanktons: They are microscopic photosynthetic organisms that are passively drifted by the water currents. These include dinoflagellates, diatoms, and algae.
- Lichens: They are the symbiotic association of fungi and algae. They have a thalloid body and are pollution indicators.
- Primary succession: Succession in areas such as a new volcanic island or a bare rock exposed, where no community existed before, is known as primary succession.