An ecosystem includes both biotic and abiotic materials and functions as a structural interacting whole. The functioning of an ecosystem is achieved by the flow of energy from one trophic level to another in succession. Energy is the ability to work which is the essence of life. Such energy is derived from the sun.
In an ecosystem the green plants trap radiant energy by the process of photosynthesis and making it available as food to other organisms.
It is in this way that all living organisms are sustained by the transference of energy from one level of organism e.g. plants, to plant-eating animals and from the latter to flesh-eating animals, and from there to decomposing organisms e.g. bacteria and fungi etc.
Such a pathway is called a Food Chain, e.g. plants to grasshopper, grasshopper to frog, frog to snake, and snake to an eagle, such is the food chain. Each of the feeding level in the food chain is called a trophic level.
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From what has been discussed above, it is the autotrophs who are the primary producers since green plants being the primary producers form the very base of the food chain, so this base is called the trophic level 1.
There are organisms that do not produce their food, but depend on the primary producer belonging to trophic level one (green plants), are called herbivores and primary consumers. Such organisms belong to the trophic level 2.
Then, there are carnivores or secondary consumers that depend on herbivores (sheep, goats, and cows etc who are grazers) for their food requirement and are placed in the trophic level 3.
In the trophic level 3 energy is transferred from trophic level 2. As stated earlier, human beings are called Omnivores, so they derive their food from trophic level 2 and trophic level 3.
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This simple chain of eating and being eaten away is known as food chain. In other words, the transfer of food from the plants through herbivores to cornivores is called the food chain. Each organism in the food chain feeds, and derives energy from the preceding level, as shown in the following simple linear food chain in terrestrial ecosystem:
In nature, however, there are two types of Food chain: (1) Grazing Food Chain, and (2) Detritus Food Chain.
1. Grazing Food Chain:
It starts from a green plant base and goes through grazing herbivores to carnivores.
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2. Detritus Food Chain:
The detritus food chain begins from dead organic matter into micro-organisms and then to organisms feeding on detritus and their predators. Such type of food chain operates in the decomposing matter in a temperate forest.
]Such ecosystems are less dependent on direct solar energy. These depend on the influx of organic matter produced in another system.