A food chain’s length is restricted to just 3 or 4 steps due to energy loss. Moreover, the energy added to the biomass of each trophic level is significantly lower than the one preceding it. This occurs as a result of material wastage from subsequently trophic levels and for the maintenance of various life processes. Consequently, the shorter the food chain, the more energy that is available to the final consumer. Less energy is transferred at each level of the food chain, so the biomass gets smaller. A shorter food chain is also considerably more efficient as less energy is lost.
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Further Reading: Food Web