The Ecological Pyramids are the pyramidal representation of trophic levels.
The ecological pyramids are of three categories:
1. Pyramid of numbers,
2. Pyramid of biomass, and
3. Pyramid of energy or productivity.
Pyramid of Numbers
- Depending upon the size, the pyramid of numbers may not always be upright, and may even be completely inverted.
- In this pyramid, the number of individuals is decreased from lower level to higher trophic level.
- This type of pyramid can be seen in the grassland ecosystem and pond ecosystem.
Pyramid of numbers – inverted
- In this pyramid, the number of individuals is increased from lower level to higher trophic level. E.g. Tree ecosystem.
Pyramid of Biomass
- Pyramid of biomass is usually determined by collecting all organisms occupying each trophic level separately and measuring their dry weight.
- This overcomes the size difference problem because all kinds of organisms at a trophic level are weighed.
- Each trophic level has a certain mass of living material at a particular time called the standing crop.
Pyramid of Biomass – upright
- For most ecosystems on land, the pyramid of biomass has a large base of primary producers with a smaller trophic level perched on top.
Pyramid of Biomass – Inverted
- In contrast, in many aquatic ecosystems, the pyramid of biomass may assume an inverted form. (In contrast, a pyramid of numbers for the aquatic ecosystem is upright)
- This is because the producers are tiny phytoplankton that grows and reproduces rapidly.
Pyramid of Energy
- To compare the functional roles of the trophic levels in an ecosystem, an energy pyramid is most suitable.
- An energy pyramid represents the amount of energy at each trophic level and loss of energy at each transfer to another . Hence the pyramid is always upward, with a large energy base at the bottom.
- Energy pyramid concept helps to explain the phenomenon of biological magnification.
Limitations of Ecological Pyramids
- It assumes a simple food chain, something that seldom exists in nature; it does not accommodate a food web.
- Moreover, saprophytes (plant, fungus, or microorganism that lives on decaying matter) are not given any place in ecological pyramids even though they play a vital role in the ecosystem.
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