Our Environment of Class 10
An ecological pyramid is a graphical representation of an ecological parameter like number of individuals or amount of biomass or amount of energy present in various trophic levels of a food chain with producers forming the base and top carnivores from the tip. Ecological pyramids could be upright, inversed or spindle shaped. There are three important parameters of each trophic level in a food chain i.e. number of individuals, amount of biomass and amount of energy.
Pyramid of Number: In this type of pyramid the number of individual organisms in various trophic levels is shown These pyramids may be upright or inverted. The number of organisms of any trophic level depends upon the availability of organisms which are used as food on lower level so that availability of food is the main factor. These producers are of two types:
(i) Phytoplanktons: They are the inactive floating plants, because they do not have locomotory organs e.g. Diatoms.
(ii) Phytonektons: These plants swim actively in water, because in them locomotary organs are present. Usually flagella are present in these plants. e.g. Chlamydomonas and dinoflagellates. The number of phytoplanktons and phytonektons are higher per unit area of water because they are unicellular.
- In a tree ecosystem the pyramid of number is inverted. This is called as parasitic ecosystem because birds depend upon tree and parasites depend upon birds. Therefore with the increase in the number of trophic levels, the number of the organisms increases sequentially.
- Pyramid of number shows biotic potential of an ecosystem.
- The number of members of any particular species in a favourable condition is called as their biotic potential.
- When the number of the members of any species increases then it is called as population explosion.
Pyramid of Biomass:
The biomass of each trophic level is shown by this pyramid. Mostly these pyramids are also upright (erect). e.g. Tree ecosystem.
- Pyramid of biomass in aquatic ecosystem is inverted, because in this producers are micro organisms and their biomass is lesser than other trophic levels.
- Pyramids of biomass show the standing crop of ecosystem. It means total amount of living matter at a particular time in an ecosystem is called as standing crop.
- Total amount of nonliving matter in an ecosystem is called as standing state.
Pyramid of Energy :
It always remains erect, because flow of energy is not cyclic. i.e. during the flow of energy at each trophic level goes on decreasing.
- According to the 10% law of Linderman the 90% part of obtained energy of each organism is utilized in their various metabolic activities and only 10% energy is transferred to the next trophic level. So that 90% energy is lost at each trophic level therefore, top consumers like lion etc., are weakest ecologically.
- Pyramids of energy show the productivity of any ecosystem.
- Plant community: All types of plants present at a particular place to form a community, is called as plant community. The distribution of any species at a place depends upon social nature of that species which indicates cooperation between them.
- Synecology: The ecological study of any plant community is called as "synecology".
- Phytosociology: The study of structure of plant community is known as "phytosociology".
- Phytogeography: The study of distribution of the plants on the earth is called as "phytogeography". Some characteristics of plant community are as follows :
(i) Species diversity: There are many varieties of organisms found in a community. The total number of species of plants called as population. The ecological study of population is called as Autoecology. The maximum species diversity is found in tropical forest. The plants are called as flora and animals are termed as fauna. The lowest species diversity is found in Tundra biome or Arctic desert.
(ii) Dominant species: The highest number of plants of a species present in a community is called as dominant species and whole plant community is known as the name of that species. Such as Prosop is community on Aravali hills and Pinus community on Himalaya.
- B.O.D :It shows the deficiency of oxygen in the water. Daphnia is the indicator of B.O.D.