Final answer:
The general rule for energy transfer in ecosystems is the 10% rule, where each trophic level receives about 10 percent of the energy from the level below it.
Step-by-step explanation:
The general rule that can be applied to estimate the amount of energy transferred from one trophic level to another in an energy pyramid is the 10% rule. This states that, on average, only about 10 percent of the energy at one level is available to the next level. The remaining 90 percent is used for metabolism, repair, growth, and is lost as heat due to the inefficiency of energy transfer as described by the second law of thermodynamics.
For example, if the primary producers in an ecosystem produce 1,000,000 kilocalories of energy, then only about 100,000 kilocalories are available to the primary consumers. This pattern continues at each trophic level, resulting in diminished available energy and often limiting the number of trophic levels to four. This is due to the ecological efficiency and the trophic level transfer efficiency (TLTE) reflecting how much energy is passed to the successive level.