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Question
__A____and ____B___ are the pioneer species in xerarch and hydrarch successions respectively.
__A____and ____B___ are the pioneer species in xerarch and hydrarch successions respectively.
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Solution
The correct option is A A - Lichens, B - phytoplankton
Ecological succession is a steady, gradual change in the composition and structure of biotic communities of an area. It is predictable, sequential and occurs in accordance with the changing physical environment i.e., the abiotic components such as duration of sunlight, water, soil, etc.
The ultimate purpose of ecological succession is to form an established climax community which is in near equilibrium with the environment. In an effort to reach this equilibrium, many transitional communities known as seral stages are formed. The entire sequence of communities that successively change in a given area is called sere.
The first species to invade the bare area during primary succession is called pioneer species.
Based on the nature of the habitat, succession of plants is of two types:
- Xerarch succession - It takes place in dry areas and progresses towards mesic conditions (medium water conditions). In case of xerarch succession, lichens are the pioneer species. Lichen is a symbiotic association between a fungus and algae and/or cyanobacteria where both the organisms involved benefit from each other. Lichens secrete acids which dissolve rock and hence, help in weathering and soil formation during succession. Soil formation is essential because it will help in the invasion of higher plants in the area. Lichens are followed by formation of mosses, small plants like herbs, shrubs and then bigger trees.
- Hydrarch succession - It takes place in wetter areas and progresses towards mesic conditions (medium water conditions). In hydrarch succession, phytoplankton are the pioneer species. The death of these organisms provides organic matter or humus to the bottom layer of soil. Phytoplankton is followed by free-floating angiosperms, rooted hydrophytes, sedges, grasses and finally the trees.
Ecological succession is a steady, gradual change in the composition and structure of biotic communities of an area. It is predictable, sequential and occurs in accordance with the changing physical environment i.e., the abiotic components such as duration of sunlight, water, soil, etc.
The ultimate purpose of ecological succession is to form an established climax community which is in near equilibrium with the environment. In an effort to reach this equilibrium, many transitional communities known as seral stages are formed. The entire sequence of communities that successively change in a given area is called sere.
The first species to invade the bare area during primary succession is called pioneer species.
Based on the nature of the habitat, succession of plants is of two types:
- Xerarch succession - It takes place in dry areas and progresses towards mesic conditions (medium water conditions). In case of xerarch succession, lichens are the pioneer species. Lichen is a symbiotic association between a fungus and algae and/or cyanobacteria where both the organisms involved benefit from each other. Lichens secrete acids which dissolve rock and hence, help in weathering and soil formation during succession. Soil formation is essential because it will help in the invasion of higher plants in the area. Lichens are followed by formation of mosses, small plants like herbs, shrubs and then bigger trees.
- Hydrarch succession - It takes place in wetter areas and progresses towards mesic conditions (medium water conditions). In hydrarch succession, phytoplankton are the pioneer species. The death of these organisms provides organic matter or humus to the bottom layer of soil. Phytoplankton is followed by free-floating angiosperms, rooted hydrophytes, sedges, grasses and finally the trees.
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