27.5: Trophic Efficiency
Trophic level transfer efficiency (TLTE) is a measure of the total energy transfer from one trophic level to the next. Due to extensive energy loss as metabolic heat, an average of only 10% of the original energy obtained is passed on to the next level. This pattern of energy loss severely limits the possible number of trophic levels in a food chain.
Trophic Level Transfer Efficiency
Following the second law of thermodynamics, large amounts of energy are lost from the ecosystem and from one trophic level to the next as it is transferred and transformed. In biological systems, this energy is lost as metabolic heat during respiration as one organism consumes the next. The measurement of energy transfer from one trophic level to the next is known as trophic level transfer efficiency (TLTE) and is a function of energy production of the present trophic level and that at the previous level. This measurement has broad implications concerning the total length of food chains.
The “10s Rule”
In general, only about 10% of energy is transferred from one trophic level to the next, and this number can vary from 5-20% depending on the ecosystem. This means that 90% of obtained energy is lost at each trophic level, greatly affecting the maximum number of possible levels in the ecosystem. For example, if an ecosystem received 600,000 Kcal of solar energy from the sun, primary producers would pass on only 60,000 Kcal to herbivores, which would pass only 6,000 Kcal to secondary consumers, 600 Kcal to tertiary consumers and 60 Kcal to quaternary consumers at the top of the food chain. An apex predator like a wolf—needing an average of 2000 Kcal per day—would need to consume a very high quantity of secondary or tertiary consumers to meet its calorie quota per day.