Sun is the source of energy for almost all the activities on the earth. Less than 50 percent of the incident solar radiation, that we receive on earth, 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 percent 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 requires energy. Plants and trees are autotrophic and capable of converting solar energy into a usable form of energy for their sustenance, but animals are not capable of converting solar energy into a usable form 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 the 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 in an organism does not remain in it forever, it is either passed to the next trophic level (for example from the 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
Autotrophs
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, and Higher Plants are the primary producers in an aquatic ecosystem.
Primary Consumer
They are also known as herbivores and they feed on the primary producer. In terrestrial ecosystems Insects, Birds, and Mammals are some common herbivores while in the aquatic systems, Mollusca is more common than herbivores.
Secondary Consumer
Secondary Consumers are the organisms that eat Primary Consumers and they can either be carnivores (meat eater) or Omnivores (eat both plant and animal matter), unlike Primary consumers which are only, herbivores (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 consumers and are considered 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 the 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 the 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 the form of heat and as tiny as 10% of the total energy at any trophic level is moved to the ne xt 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 are 1000 kilocalories of energy present at the Grassland trophic level, only around 100 kilocalories of energy will be transferred to the next level i.e. Primary consumer and very little around 1 kilocalorie will reach the tertiary consumer level.
