The energy available from primary producers in an ecosystem is limited due to several factors, which contribute to the inefficiency of energy transfer through the food chain. Primary producers, such as plants and phytoplankton, convert sunlight into energy through photosynthesis. However, only a fraction of this energy is passed on to the next trophic levels.
One major reason for this inefficiency is that not all sunlight that hits a plant is converted into chemical energy. For instance, some light is reflected, while some wavelengths are not absorbed by plants. Moreover, only a portion of the energy captured by photosynthesis is used for growth and reproduction; much of it is used for the plant’s own metabolic processes.
Additionally, when primary producers are consumed by primary consumers (herbivores), again, a significant amount of energy is lost as heat and through waste products. Estimates suggest that only about 10% of the energy from one trophic level is available to the next, known as the 10% Rule. This means that by the time energy reaches higher trophic levels, like an orange roughy fish, only a small fraction of the energy from primary producers remains available.
This multi-level loss of energy through trophic levels contributes to why orange roughy fish, as a fourth-level consumer, may require almost ten times the amount of food available from primary producers in an ecosystem. This inefficiency clearly illustrates the energy limits imposed by ecological hierarchies.