The number of trophic levels in an ecosystem are limited and are not more than 3-4. Because the amount of energy flow decreases with successive trophic level, as only 10% of energy is transferred from one trophic level to the next trophic level. So, rest of the energy is lost in the form of respiration and other vital activities to maintain life. If more trophic levels are present, the residual energy will be limited and will decrease to such an extent that it cannot further support any trophic level. So, the food chain is generally limited to 3-4 trophic levels only.