Ecological Pyramids- of Numer, 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.

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.

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 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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