Energy and biomass decline at higher trophic levels due to energy loss associated with metabolic processes and the inefficiency of energy transfer.

In any ecosystem, energy flows from one trophic level to the next, beginning with producers, such as plants, and progressing through various levels of consumers, including herbivores and carnivores. However, not all the energy absorbed by an organism is transferred to the subsequent level. A substantial portion of this energy is utilized by the organism for metabolic activities, including growth, reproduction, and the maintenance of bodily functions. This energy is ultimately lost as heat and is not available for transfer to the next trophic level.

Furthermore, the transfer of energy between trophic levels is inherently inefficient. On average, only about $10\%$ of the energy consumed by an organism is passed on to the next trophic level, a concept commonly referred to as the “10% rule.” The remaining energy is lost during digestion or excreted as waste products. Consequently, as one ascends the food chain, the amount of available energy diminishes significantly.

Biomass, defined as the total mass of organisms within a specific area or volume, also experiences a decline at higher trophic levels. This reduction is closely linked to the aforementioned energy losses at each level. Since energy is essential for growth and reproduction, reduced energy availability translates to lower biomass. This explains why there are typically fewer organisms at higher trophic levels, as well as why these organisms tend to be larger; they must consume more in order to acquire sufficient energy for survival.

In conclusion, both energy and biomass decrease at higher trophic levels due to energy losses occurring during metabolic processes and the inefficiency of energy transfer. This principle is fundamental to ecology and is essential for understanding the structure and function of ecosystems.