This is because energy is lost at each trophic level leaving the last/tertiary consumer with the lowest amount of energy. Energy is lost by respiration, assimilation and excretion. It is important for animals to respire so they also lose most of their energy gained. energy is consumed as 10 percent and lost as 90 percent along the food chain. Only decomposers can use most of the rest of energy as they are the last in trophic level.
