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Ecological succession An orderly and progressive replacement of one community by another till a stable community formed is called ecological succession. The entire sequence of communities that successively change in a given area is called a sere.
Types of successional communities: 1. Pioneer communities: It is the first community that develops over a bare area. It has a very little diversity and takes long time to convert the bare area suitable for the second or seral communities. 2. Seral or Transitional Communities: These are communities that develop on an area during biotic succession between pioneer and climax communities. 3. Climax communities: It is a stable self perpetuating biotic community with more complex food webs.
Pioneer communities Climax communities . It is the first community to colonise an area. It is the final community over an area. Individuals or small sized. Individuals are of both small and large sized. Life span of individuals is generally short. Life span of individuals is generally very long. It builds up the soil. Members show high rate of growth. The soil is already built up. Members show slow rate of growth.
TYPES OF SUCCESSION 1) Primary Succession 2) Secondary Succession PRIMARY SUCCESSION Ecological succession that takes place in a place where no life existed before is called primary succession. It is comparatively slow as suitable soil has to be formed which is a very slow process. Depending on the climate, it takes a natural processes several hundred to several thousand years to produce fertile soil on bare rock.
TYPES OF SUCESSION BASED ON THE PLACE WHERE IT IS ESTABLISHED In water body-Hydrarch On Barren rock-Xerarch
Secondary Succession Ecological succession that takes place in a region where life existed in the past, but not destroyed completely such as in abandoned farm lands, burned or cut forests, lands that have been flooded is called secondary succession. It is comparatively faster, as some soils sediments are already present. In secondary condition the type of pioneer species depend on the following: 1. Condition of the soil 2. Availability of water 3. Environmental condition 4. Seeds/other propagules present.
Primary succession Secondary succession . It occurs in an area where no It occurs in an area where community had existed before. Lichens are the first organisms to appear. Grasses, shrubs and weeds are the first organisms to appear. It may take a very long time. (1000 yrs or more) It takes shorter time(50 to 200 yrs) It has a number of seral communities. Number of seral communities very low.
Two general facts about succession are: Primary succession is very slow process that may take thousands of years for the establishment climax community. All successions hydrarch or xerarch lead to establishment of similar mesic communities.
Succession of plants: Based on the nature of habitat succession of plants can be grouped in to two categories: 1. Hydrarch succession 2. Xerarch succession Hydrarch succession takes place in water bodies or wet areas and the succession progress from hydric to mesic condition. Xerarch succession takes place in dry xeric condition (bare rocks) and progress from xeric to mesic conditions.
Ecological succession usually focuses on vegetation only. Why? As vegetation of an area determine the consumers –animals and other communities so it is focusing on vegetation.
Hydrarch succession stages : 1. Plankton stage: It is the pioneer community that develop over the surface of newly formed water body. The first to develop are phyto plankton and is almost immediately followed by its consumer called zooplankton.
Hydrarch succession stages : 2. Submerged plant stage : It develops where water is clear and 3 to 6 meters in depth. eg -Hydrilla, vallisneria. These plants collects silt and form more humus.
Hydrarch succession stages : 3. Floating leafed anchored stage : It develops where water depth is 1 to 3 meters. The plants are rooted in the mud present at the bottom. The leaves reach the surface of water with the help of flexible stems eg. Waterlily, lotus.
Hydrarch succession stages : 4. Free floating plant stage: Enrichment of water with minerals and organic matter invites fast growing free floating plants. eg lemna, wolffia, pistia. The floating plant generate lot of organic matter which settles down at the bottom and the bottom rises.
Hydrarch succession stages : 5. Reed swamp stage: It develops on shallow banks where the depth of water is 0. 3 to 1 meter. The plants are amphibious with the lower part inside water and the wild upper part is aerial eg. Typha
Hydrarch succession stages : 6. Marsh meadow stage: This stage develop on newly built shore.
Hydrarch succession stages : 7. Woodland stage: It consists of shrubs and small trees which can tolerate bright sunlight and water logged conditions.
Hydrarch succession stages : 8. Climax forest: Slowly the wood land is replaced by forest which depends upon the climax of the area. eg: Deciduous forest, coniferous forest etc.
Xerarch succession stages: 1. Crustose lichen stage: On a bare rock, where there is no water, no soil, less minerals , the first formed organisms are Crustose lichens. During rain or heavy dew the lichen propagules settle over the rock surface and get attached to several points of rock by their rhizoids.
Xerarch succession stages: 2. Foliose lichen stage: These lichens fixed to substratum at a single point. They generate more organic matter.
Xerarch succession stages: 3. Moss stage: They grow in large groups driving away foliose lichen. Growth of mosses disintegrates the rock surface and builds up soil.
Xerarch succession stages: 4. Annual grass stage: The grasses the shade the mosses their roots penetrate e deeper and causes weathering of rock which builds up more soil.
Xerarch succession stages: 5. Perennial grass stage: They shade others their roots penetrates deeper several animals reach the area at this stage.
Xerarch succession stages: 6. Shrub stage: They help in creating a soil profile. Bio geo chemical cycle begin operating.
Xerarch succession stages: 7. Climax forest: Depending upon the climate of the area the forest is formed.
Xerarch succession :
Changes in community: Characteristics, climax, the sequence of species and the communities appearing during primary or secondary succession is not fixed. It shows variations with habitats and other environmental conditions.
Review Questions 1. What is meant by ecological succession ? 2. What are seral communities? 3. How the succession of plants can be classified based on the nature of habitat of succession? 4. Differentiate between a)Primary succession and Secondary succession. b) Pioneer communities and Climax communities. 5. What is the ecological succession of bare rock technically called? 6. How is the ecological succession in a water body technically called?