The second law of thermodynamics states that during any transfer of energy, some energy is dispersed as unusable energy because of the tendency toward an increase in disorder (entropy).

Thus, we can expect that the cumulative available energy will decrease with each trophic level as we move from the first trophic

level upward. We know from our discussion of primary production in Chapters 5 and 20 that autotrophs and heterotrophs lose chemical energy through cellular respiration, lowering the amount of energy available to the organisms that consume them. In this section, we will examine more closely the factors influencing energy movement between trophic levels.