TROPHIC LEVELS
- The levels of a food chain (food pyramid) are called Trophic levels.
- The various steps in a food chain at which the transfer of food (or energy) takes place are called trophic levels.
- In a food chain, each step representing an organism forms a trophic level.
- The plants are producers (or autotrophs) and constitute the first trophic level.
- They fix up the sun’s energy and make it available for consumers (or heterotrophs).
- Herbivores (which feed on plants) constitute the second trophic level.
- Carnivores (that feed on herbivores) constitute the third trophic level.
- Large carnivores or Top carnivores (which feed upon small carnivores), constitute the fourth trophic level
- When any organism dies, detritivores (like vultures, worms and crabs) eat them up.
- The rest are broken down by decomposers (mostly bacteria and fungi), and the exchange of energy continues.
- Decomposers start the cycle again.
ENERGY FLOW IS UNIDIRECTIONAL
- Ecosystem energy processes conform to the thermodynamic laws.
- Energy cannot be made or destroyed.
- Energy transformations are not perfect and energy is lost in each transformation in the form of heat.
- The flow of energy in the ecosystem is unidirectional.
- The energy enters the plants (from the sun) through photosynthesis during the making of food. This energy is then passed on from one organism to another in a food chain.
- Energy given out by the organisms as heat is lost to t used by the plants again.
- This makes the flow of energy in the ecosystem ‘unidirectional’.
- Thus the flow of energy in the ecosystem is said to be unidirectional because the energy lost as heat from the living organisms of a food chain cannot be reused by plants in photosynthesis.
- During the transfer of energy through successive trophic levels in an ecosystem, there is a loss of energy all along the path.
- No transfer of energy is 100 percent.
The energy available at each successive trophic level is 10 per cent of the previous level.
- Thus, there is a progressive decline gradual reduction) in the amount of energy available as we go from producer level to the higher trophic levels of organisms.
