Why is each level of energy pyramid smaller than the level directly below it?
Each level of an energy pyramid is smaller than the level directly below it because of the concept called energy transfer and the inefficiency of energy transfer across trophic levels.
Energy is transferred from one trophic level to another as organisms are consumed by other organisms. As energy passes from one level to the next, there is a loss of energy through various processes such as respiration, heat loss, and waste production. This loss of energy limits the amount of energy available for organisms at higher trophic levels.
The energy transfer between trophic levels is also inefficient due to the laws of thermodynamics. According to the second law of thermodynamics, energy is lost as heat during energy transformations. This means that only a fraction of the energy from one trophic level is available to support the next trophic level.
As a result, each trophic level receives less energy than the one below it, leading to a decrease in biomass and population size of organisms at higher trophic levels. This phenomenon is known as the 10% rule, which states that only approximately 10% of the energy from one trophic level is transferred to the next.
Overall, the progressive decrease in energy availability from one trophic level to another is the main reason why each level of an energy pyramid is smaller than the level directly below it.