Trophic levels and Energy Variation with Trophic levels

Trophic Levels

A trophic level is a group of organisms within an ecosystem that occupy the same level in a food chain. There are 5 main trophic levels within a food chain, each of which varies in its dietary relationship with the primary energy source. The primary energy source in any community is the Sun.

The solar radiation from the Sun supplies the input of energy which is used by primary producers, likewise known as autotrophs. Primary producers are normally plants and algae, which perform photosynthesis in order to produce their own food source. Primary producers comprise the first trophic level.

The second trophic level includes herbivores, these organisms gain energy by eating primary producers and are called primary consumers.

Trophic level three consists of predators and omnivores which eat herbivores; these are the secondary consumers.

Trophic level four includes carnivores and omnivores which eat secondary consumers and are referred to as tertiary consumers.

Trophic level five consists of apex predators; these animals have no natural predators and are therefore at the top of the food chain.

Decomposers or detritivores are organisms that take in dead plant and animal material, transforming it into energy and nutrients that plants can use for effective growth. Although they do not fill an independent trophic level, decomposers and detritivores, such as fungi, bacteria, earthworms, and flies, recycle waste products from all other trophic levels and are a fundamental part of a functioning ecosystem.


Energy Flow

Energy flow is the circulation of energy through living things within an ecosystem. The chemical energy of food is the main source of energy needed by all living organisms. This energy is transferred to various trophic levels along the food chain. This energy circulation is based on two different laws of thermodynamics:

  • The first law of thermodynamics, that states that energy can neither be created nor be destroyed, it can just alter or change from one kind to another.
  • Second law of thermodynamics, that states that as energy is transferred increasingly more of it is squandered.
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The energy flow in the ecosystem is one of the significant aspects that support the survival of such a multitude of organisms. For almost all organisms in the world, the main source of energy is solar energy. It is amusing to find that we get less than 50 percent of the sun’s efficient radiation on earth.

When we state effective radiation, we indicate the radiation, which can be utilized by plants to carry out photosynthesis. Most of the sun’s radiation that falls on the earth is generally reflected back into space by the earth’s environment. This efficient radiation is described as Photosynthetically Active Radiation (PAR).

Overall, we get about 40 to 50 percent of the energy having Photosynthetically Active Radiation and just around 2-10 percent of it is used by plants for the procedure of photosynthesis. Thus, this percent of PAR supports the whole world as plants are the producers in the ecosystem and all the other organisms are either directly or indirectly depending on them for their survival.

The energy flow takes place via the food chain and food web. Throughout the procedure of energy flow in the ecosystem, plants being the manufacturers take in sunlight with the help of the chloroplasts, and a part of it is transformed into chemical energy in the process of photosynthesis.


The herbivores at the second trophic level, use the plants as food which provides energy. A large part of this energy is used up for the metabolic functions of these animals such as breathing, digesting food, supporting the growth of tissues, controlling blood circulation and body temperature level.

The carnivores at the next trophic level, feed upon the herbivores and derive energy for their nourishment and development. If big predators are present, they represent still greater trophic levels and they eat predators to get energy. Therefore, the different plants and animal species are connected to one another through the food chain.

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Decomposers that include bacteria, fungi, molds, worms, and insects break down wastes and dead organisms, and return the nutrients to the soil, which is then taken up by the producers. Energy is not recycled during decomposition, but it is released.

As energy is transferred from one trophic level to the next, from producer to primary consumer, in between 80 to 90% of last as the original energy is heat and released as a byproduct of respiration. However, a constant flux of energy from the sun prevents the ecosystem from diminishing. A pyramid of energy can be built showing energy transfer in a community of organisms.


In a forest ecosystem, the bear (an omnivore) may feed directly on fruits (which being producers inhabit first trophic level) or it may prey upon rabbit (which being an herbivore occupy Second trophic level) or it may hunt a fox (which occupies Third trophic level) or it might prowl near the edge of a stream and consume a fish (which is a tertiary consumer, inhabits Forth trophic level).

The bear, therefore, inhabits the 2nd trophic level in the very first instance, the third trophic level in the second circumstances, and so on.


The organism having a specific position in food chain within the ecosystem is called trophic level. The energy source starts from the Sun. Plants at the first trophic level use the energy of the sun for preparing their own food.

Organisms like herbivores at second trophic level utilize plants for their food and metabolic activities. Similarly, the organisms of next trophic level utilize previous ones for their food.

Only 1 % of energy is trapped from the sun by the ecosystem that then trickles down to other trophic levels. In the end, there are decomposers and during decomposition, energy is released back into ecosystem.

The reason for the great diversity of life forms on Earth is due to multitude food chains forming food webs and flow of energy in ecosystem insures the survival of biodiversity.