Definition
A trophic level is a nutritive status that an organism occupies in a food web. A food web is a graphical representation of what eats what in an ecological community. It is an interconnection of several food chains. A food chain can be defined as a linear network of the transfer of matter and energy from one organism to another.
History
August Thienemann gave the terminologies producers, consumers and reducers in 1926. Building upon his concept, Raymond Lindeman gave the idea of trophic levels in 1942.
The Levels
- Primary producer
The plants and algae that make up their own food are referred to as producers. They do not feed on other organisms but extract their nutrients from the soil or manufacture their own food by photosynthesis. They occupy the first trophic level in an ecological pyramid and are hence referred to as primary producers.
- Primary consumer
Primary consumers are the ones that occupy the second trophic level in an ecological pyramid. Herbivores that feed on producers are called primary consumers. For example – cow, goat and horse.
- Secondary consumer
The third trophic level is occupied by organisms that feed on the primary consumers. Such organisms include carnivores and predators. They are organisms that kill and prey on other smaller organisms to feed their hunger. Such examples include – lions and polar bears.
- Tertiary consumer
The tertiary consumers are the apex predators that occupy the fourth and last trophic level. These organisms are called detritivores or decomposers. The decomposers are organisms that feed on waste and dead materials and release them back to the environment in the form of nutrients and energy.
Energy Levels in a Food Chain
Energy is transferred from one trophic level to another in discreet packages. The amount of energy reduces as it gets transferred from one trophic level to another. Generally, only 10% of the energy is transferred. The rest of the energy is lost in the form of heat at each trophic level, and hence one food chain does not contain more than 4-5 trophic levels. The length of an ecosystem depends on various factors, such as the reduction of energy at each level, the size of the ecosystem, and the proposition that long food chains are usually unstable. The food chain holds an important place in ecotoxicological studies as it helps in tracing pathways of biomagnification and environmental contaminants.
Example of a Food Chain
There are two types of food chain found in our ecosystem –
- Detritus food chain
This food chain is unique as it begins with the dead and organic matter. It starts with the microorganisms feeding on the dead material, which are now called decomposers. The decomposers are then eaten by smaller carnivores like maggots. These maggots become a meal for bigger carnivores such as frogs and snakes. The primary consumers that feed on the dead material include bacteria, fungi and protozoans.
- Grazing food chain
A grazing food chain starts with primary producers such as plants or algae, passes on to herbivores, carnivores and finally to the decomposers. A classic example of such a food chain is Plant → Grasshopper → Frog → Snake → Hawk.
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