Each successive level of nourishment as represented by links of the food chain is known as trophic level. Organisms whose food is obtained from plants by same number of steps belong to same trophic level. Thus, green plants (producer) occupy first trophic level; plant eaters (primary consumers) secondary level, and carnivores which eat herbivores, third level.
The trophic level equals the total assimilation at that level. This in turn equals the production of bio-mass plus respiration. Ecological pyramids represent the trophic structure and also the trophic function of an ecosystem. In ecological pyramids, first trophic level forms base and successive trophic levels the tiers, which make up the apex.
These pyramids may be of three types:
(i) Pyramid of Number: This emphasizes the importance of small organisms. (ii) Pyramid of Bio-mass: This emphasizes the importance of large organisms. (iii) Pyramid of Energy : This indicates the total energy at each trophic level of the food chain. It also shows the level of loss of energy and material at each trophic level. This is a more suitable index. The energy flow provides a suitable index for comparing any and all components of ecosystem.
The ecosystem is very complex and it is not very easy to study to understand the balance in the ecosystem, as the system will be strained due to various fluctuations and stratifications. However, the ecosystem maintains balance by meeting the strains by evolutionary changes resulting from natural selection. Changes are met by adjustments of the species present or by creating new ecological niches by new species. Thus, we can understand that nothing is unwanted or unwarranted in the ecosystem, as all spheres play their parts for sustaining life in the biosphere. Life is confined only in the biosphere and the natural environment of Man should be viewed in its totality and not in isolation.
Energy Flow Chart
The following figure depicts the Energy Flow and food chain discussed above, and also the trophic level of the ecosystem. The solid arrows indicate the flow of energy; the hollow arrows, material flow, and broken arrows both.