Why is the length of a food chain in an ecosystem limited to 3-4 tropic levels?

Explanation

In a food chain the energy flows from producers through herbivores to carnivores and the amount of energy flow decreases with succesive trophic levels. Producers captures only a small fraction of small energy and the bulk of unutilized energy is dissipated mostly as heat. Similarly, herbivores gain approximately 10 percent of the gross productivity of producers. The energy assimilated by the herbivores is used in respiration and a fraction of unassimilated energy in transferred to decomposers and carnivores (about 10 percent) Similarly, the energy available at carnivore trophic level is again partitioned , leaving a very small fraction to next trophic level. The respiration cost also increases sharply along successive higher trophic levels and so, there is tremendous loss of energy at each successive higher trophic levels . Thus in this energy flow process, the residual energy is decreased to such an extent that no further trophic level can be supported. Therefore, the length of food chain in an ecosystem is generally limited to 3-4 trophic levels.