Class 12 Biology Ecosystem Ecological pyramid

Ecological pyramid

Ecological pyramid is the graphical representation of various trophic levels of food chain designed to show their number, biomass and energy.

The base of a pyramid is broad and it narrows down at the apex.

The base of each pyramid represents the producers or the first trophic level while the apex represents tertiary or top level consumer.

The three ecological pyramids that are usually studied are

  • pyramid of number
  • pyramid of biomass
  • pyramid of energy.

A given species may occupy more than one trophic level in the same ecosystem at the same time. For example, a sparrow is a primary consumer when it eats seeds, fruits, peas, and a secondary consumer when it eats insects and worms.

Producers are more in number and biomass than the herbivores, and herbivores are more in number and biomass than the carnivores so all the pyramids, of number, of energy and biomass are upright.

The pyramid of biomass in sea is also generally inverted because the biomass of fishes far exceeds that of phytoplankton.

Pyramid of energy is always upright because when energy flows from a particular trophic level to the next trophic level, some energy is always lost as heat at each step.

Limitations of ecological pyramids

  • It does not take into account the same species belonging to two or more trophic levels.
  • It assumes a simple food chain, something that almost never exists in nature
  • It does not accommodate a food web.
  • Saprophytes are not given any place in ecological pyramids.

Fig. ecological pyramids  

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