Energy Flow In An Ecosystem

Sun is the source of energy for almost all the activities on the earth. Of the incident solar radiation, that we receive on earth, less than 50 per cent of it is photosynthetically active radiation (PAR is the light in the 400-700 Nano-meter wavelength range which is available for photosynthesis) and Plants capture only 2-10 per cent of the PAR; this small amount of energy sustains the entire living world.

Energy is vital for the sustenance of life on earth as all the metabolic activity in plants and animals require energy. Plants and trees are autotrophic and so capable of converting the solar energy into a usable form of energy for their sustenance, but animals are not capable to convert solar energy into usable form and so animals depend on plants and other animals for their energy need. Thus the sustenance of life on earth is dependent on the flow of energy from autotrophs to consumers, and so the study of this energy flow in an ecosystem is vital to understand whether an ecosystem is sustainable or not.

Flow of Energy

  • The energy flow in the ecosystem is unidirectional i.e. energy flows from producer to the top consumer.
  • Either directly or indirectly all the organisms are dependent on the producer for their food.
  • Trophic level interaction gives the idea of energy flow within an ecosystem.
  • The energy trapped into an organism does not remain in it forever, it is either passed to the next trophic level (for example from Producer to the consumer) or when the organism dies, the death of the organism leads to the start of the detritus food chain/ web.

Trophic Levels

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  • They are also known as the producer since they can produce their own food through the process of photosynthesis. Plants fall under this category.
  • Phytoplankton, Algae, Higher Plants are the primary producer in an aquatic ecosystem.

Primary Consumer

  • They are also known as Herbivore and they feed on the primary producer.
  • In terrestrial ecosystem Insects, Birds, Mammals are some common herbivores while in aquatic system Molluscs are more common as Herbivore.

Secondary Consumer

  • Secondary Consumers are the organisms that eat Primary Consumers and they can either be Carnivore (meat eater) or Omnivores (eat both plant and animal matter), unlike Primary consumers which are only, Herbivore (eat plant only).

Tertiary Consumer

  • They feed largely on Primary and Secondary consumers and are generally carnivores. Frog and Snake fall under this category.

Quaternary Consumer

  • They feed on tertiary consumer and are considered as Top Carnivores. Hawk is considered among this category which feeds upon the snake i.e. tertiary consumer.

Energy Flow Via Trophic Level Interaction

  • The energy flows from the lower trophic level (producer) to higher trophic level (herbivore, carnivore etc.) and it does not flow in the opposite direction i.e. from Carnivore to Producer etc.
  • The trophic level interaction leads to the formation of Food Web, Food Chain and Ecological Pyramid.

Energy Flow and No. Of Trophic Levels

At each trophic level there is a loss of energy in form of heat and as tiny as 10% of the total energy at any trophic level is moved to the next level. Due to this reason there exist limited no. of trophic levels generally, 4 or 5 and seldom 6 since the energy left to support the organism is very less.

Example- Suppose there is 1000 kilocalorie of energy present at the Grassland trophic level, only around 100-kilocalorie energy will be transferred to the next level i.e. Primary consumer and very little around 1 kilocalorie will reach till the tertiary consumer level.

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