ecological pyramids- pyramid of number, biomass and energy

What are Ecological Pyramids?

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.

Pyramid of numbers – upright

  • In this pyramid, the number of individuals is decreased from a lower level to a higher trophic level.
  • This type of pyramid can be seen in the grassland ecosystem and pond ecosystem.
ecological pyramid of number grassland
ecological pyramid of number

Pyramid of numbers – inverted

In this pyramid, the number of individuals is increased from a lower level to a higher trophic level. E.g. Tree ecosystem.

Pyramid of Biomass

  • The 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.
Ecological Pyramid of biomass

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.
ecological pyramid of biomass upright

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.
inverted pyramid of biomass

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 the loss of energy at each transfer to another  . Hence the pyramid is always upward, with a large energy base at the bottom.
  • The 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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