Question

As you just learned, in real ecosystems, trophic efficiencies usually vary from about 5% to about 20%. as a result, net production diagrams for ecosystems have a pyramid shape. two key factors explain why trophic efficiencies are relatively low, and thus why net production diagrams are shaped like pyramids.

Answer 1

When energy passes from one trophic level to the next, I would guess that the two factors which decrease the total amount of energy from being passed up are: 
1. An organism does not assimilate all the energy of food consumed. Within a consumer, digestion and assimilation of energy is not 100% efficient: some of the energy is lost.
2. A large proportion of energy assimilated by a producer and consumer is lost through respiration, i.e., day-to-day maintenance of metabolic processes.