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Energy Transfer Between Trophic Levels

The Sun is the source of energy for ecosystems.

However, as little as 1% of this light energy may be captured by green plants and so made available to organisms in the food chain.

These organisms in turn pass only a small fraction of the energy that they receive to each successive stage in the chain.

Energy Losses in Food Chains
Plants

  • Over 90% of the Sun’s energy is reflected back into space by clouds and dust or absorbed by the atmosphere
  • Not all wavelengths of light can be absorbed and used for photosynthesis
  • Light may not fall on a chlorophyll molecule
  • A factor, such as low carbon dioxide levels, may limit the rate of photosynthesis

Consumers

  • Some parts of the organism is not eaten
  • Some parts of the organism is eaten but cannot be digested and therefore lost in faeces
  • Some of the energy is lost in excretory materials
  • Some energy loses occur as heat from respiration and directly from the body to the environment

These losses are high in mammals because of their high body temperature Much energy is needed to maintain their body temperature when heat is constantly being lost to the environment

It is the relative inefficiency of energy transfer between trophic levels that explains why:

  • Most food chains have only four or five trophic levels because insufficient energy is available to support a large enough breeding population at trophic levels higher than these
  • The total mass of organisms in a particular place is less at higher trophic levels
  • The total amount of energy stored is less at each level as one moves up a food chain

Calculating the Efficiency of Energy Transfers