Final answer:
As we move down an ecological pyramid, the number of organisms and biomass increase because of the higher energy availability at lower levels.
Step-by-step explanation:
As we examine an ecological pyramid, we notice a pattern related to the number of organisms and the biomass at each trophic level. The amount of energy available to organisms at each level sets a limit to how many organisms can survive there. Starting with the producers, who typically have the highest amount of energy at their disposal, the number of organisms and the biomass decrease as we move up the trophic levels to primary consumers, secondary consumers, and so on.
Let's consider a pyramid where producers have 1,000,000 kilocalories of energy. Following the rule of thumb in ecological efficiency, only about 10% of the energy is transferred to the next level—primary consumers. Therefore, primary consumers would have approximately 100,000 kilocalories of energy available to them.
Energy pyramids are always upright because energy, unlike biomass or numbers, cannot increase as it moves up the trophic levels. It can only decrease due to the laws of thermodynamics, particularly the law of energy conservation and the second law of thermodynamics, which states that energy efficiency decreases with each transfer.