A measure of the total amount of energy or biomass transferred from one trophic level to the next. It is always less than 100% because most of the organisms use energy for life functions. Usually ten percent is passed on. Biomass decreases from one level to the next (not all of the organism is eaten, not everything is digested, energy is lost as heat). The lost in energy is why there are less carnivores than herbivores and less herbivores than plants.