Ecological Pyramids

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Ecological pyramids are the diagrammatic representations of the feeding relationship and energy transfers in the ecosystem. They are of three types: Pyramid of Numbers, Pyramid of Biomass and Pyramid of Energy.

  1. Pyramid of Numbers: It represents the relationship between number of individuals of primary producers and consumers at different trophic levels. It can be upright or inverted.
    • In an upright pyramid of numbers, the number of individuals decrease from lower to higher trophic level. Example: In a grassland ecosystem.
    • In an inverted pyramid of number, the number of individuals increase from lower to higher trophic levels. Example: A large number of birds feeding on a single tree.

Issues: Among the three types of ecological pyramids, the pyramid of number is the least accurate because it does not take account the exact number of population and therefore cannot completely define the trophic structure in that ecosystem.

  1. Pyramid of Biomass: Biomass is the total mass (in g. dry weight) of living organisms in an area at a particular point of time. A pyramid of biomass is obtained when the rectangles used to construct the pyramid represent the masses of organisms at each trophic level.
  • Pyramid of biomass can be upright (e.g. in the grassland ecosystem) or inverted. Inverted pyramids can occur in aquatic ecosystems. This happens because in aquatic ecosystems producers are tiny phytoplankton. Thus, consumer biomass exceeds producer biomass.

  1. Pyramid of Energy: It represents the total amount of energy used at each trophic level per unit of area per unit of time. It thus shows how energy flows from one trophic level to another in an ecosystem. A pyramid of energy is always upright.
    • The pattern of the energy flow in PoE is based on the principles of thermodynamics (energy is neither be created nor destroyed; only transformed into another form.)
    • PoE shows that energy is transferred from lower trophic levels with more amount of energy (producers) to higher ones (consumers) and converted in the biomass.
      • Therefore, it can be concluded that organisms found at the highest trophic levels of shorter food chains bear a greater amount of energy than the ones found in longer ones.
    • Unlike the first two ecological pyramids, the pyramid of energy is always illustrated in an upright position, with the largest energy carriers at the base.
    • Significance of PoE: The idea of PoE is very crucial in the idea of biological magnification (tendency of toxic substances to increase in amount as we go up the trophic levels)

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