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Difference between Ecological Pyramid and Food Web

Difference between Ecological Pyramid and Food Web

FOOD WEB

  • A network of food chains is called food web.
  • Typically, the same food resource is a part of more than one food chain, especially when that resource is at the lower trophic level.

ECOLOGICAL PYRAMID

  • An ecological pyramid consists of a number of horizontal bars depicting specific trophic levels which are arranged sequentially from primary producers to top carnivores.
  • The ecological pyramid is used to depict the amount of energy, biomass and number of organisms at each trophic level.

Upright Pyramid

  • Usually, the pyramid of energy depicting biomass and the number of organisms is upright.
  • In the given pyramid, the number of individuals decreases as we move to higher trophic levels in the food chain.
  • Similarly, the amount of biomass and energy available at higher trophic levels significantly reduce as most of the energy is consumed by the organisms to carry out their day-to-day activities and only some energy is passed to the next trophic level.

Inverted Pyramid

  • In rare circumstances, a pyramid of number may be inverted. For instance, a tree provides food to many birds and a bird is a food for many parasites.
  • Similarly, a pyramid of biomass can also be inverted.
  • It can be inverted in aquatic ecosystems, since the primary producers (phytoplanktons) make up less biomass than the primary consumers (zooplanktons).
  • Zooplanktons have high biomass, because their rate of reproduction is very high.
  • Pyramid of biomass in aquatic ecosystems is also inverted because the biomass of fishes far exceeds than that of the phytoplankton.
  • However, a pyramid of energy is never inverted even in rare circumstances because when energy is transferred from a particular trophic level to the next trophic level, some energy is always lost at each step.                      Difference between Ecological Pyramid and Food Web

Limitations of Ecological Pyramids

  1. It never takes into account, the same species belonging to two or more trophic levels.
  2. It assumes a simple food chain, something that almost never exists in nature. It does not accommodate a food web.
  3. Saprophytes are not given any place in ecological pyramids, even though they play an important role in the ecosystem.

Bioaccumulation

  • Bioaccumulation refers to increase in the concentration of harmful substances in our body with the passage of time.
  • These substances do not degrade and their rate of discharge from the body is less than their rate of absorption from the environment.
  • Due to our interaction with the environment, we consume certain fat and water-soluble substances.
  • These water-soluble substances are discharged regularly by our body through urine.
  • Fat-soluble substances do not get dissolved in water and may remain concentrated in our body.

Bioconcentration

  • Bioconcentration refers to the accumulation of harmful substances in our body from the intake of polluted water.
  • Thus, when bioaccumulation occurs from the consumption of polluted water, it is called bioconcentration.

Biomagnification

  • Biomagnification (also called, ‘biological magnification’) refers to the tendency of toxic substances to progressively increase in concentration as these substances move up to higher levels of food chain.                              Difference between Ecological Pyramid and Food Web
  • Human beings are at the highest risk due to biomagnification, because they are at the top of the food chain.
  • Mercury contamination is a good example of the bioaccumulation process.
  • Typically, mercury (or a chemical version called ‘methylmercury’) is taken up by the bacteria and phytoplankton.
  • Small fishes eat the bacteria and phytoplankton. Mercury accumulates in bodies of small fishes.
  • The small fishes are in turn eaten by larger fishes, which can become food for humans and animals. The result can be progressive increase in the concentrations of mercury in humans and animals.                                      Difference between Ecological Pyramid and Food Web

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