Question

why does evergy of herbivores never come back to the autotrophes

Answer 1

Organisms at each trophic level depend on those at the lower trophic level for their energy demands. The amount of energy decreases at successive trophic levels. According to the 10 per cent law - only 10 per cent of the energy is transferred to each trophic level from the lower trophic level. As producers (at lower level) are responsible to bring energy into the system. This energy passes on to the other trophic level and hence no longer available to the previous level.