How much energy is available for the next available level as moving upward through the biomass pyramid?

In an ecological pyramid (also known as a biomass pyramid), the energy that is available to the next trophic level as you move upward is significantly less than the level below it. The rule of thumb for the energy transfer between trophic levels is often referred to as the "10% rule." According to this rule, only about 10% of the energy at one trophic level is transferred to the next higher level. This means that if there are 1000 units of energy available at one level, only about 100 units of energy will be available to organisms at the next level.

The energy loss occurs because not all parts of the organisms are consumed or digested by the creatures at the next level. Moreover, a large percentage of energy is expended by the organisms as they conduct their life processes, such as for movement, growth, and reproduction. This lost energy is mainly given off as heat. As a result, with each step up the trophic levels of the biomass pyramid, there is a substantial decrease in energy availability.