Efficacité trophique

Trophic level transfer efficiency (TLTE) measures the energy transferred from one trophic level to the next in an ecosystem. Following the second law of thermodynamics, only about 10% of energy is passed forward while 90% is lost as metabolic heat during respiration. This efficiency severely limits the number of trophic levels a food chain can support.

Energy is lost as metabolic heat when organisms consume and process food. In biological systems, respiration converts most acquired energy into heat rather than biomass. The remaining 10% becomes available to the next trophic level, though this percentage can vary from 5-20% depending on ecosystem conditions.

If an ecosystem receives 600,000 kilocalories of solar energy, primary producers pass only 60,000 to herbivores, which pass 6,000 to secondary consumers, then 600 to tertiary consumers, and 60 to quaternary consumers. With each level retaining just 10%, energy becomes insufficient to support additional trophic levels, capping food chain length.

The 90% of energy lost at each trophic level is released as metabolic heat during cellular respiration as organisms break down food for energy and maintenance. This heat energy dissipates into the environment and cannot be recaptured by the next trophic level, making it unavailable for further biological use.

An apex predator like a wolf requires approximately 2,000 kilocalories per day. Due to the 10 percent rule, a wolf must consume a very high quantity of secondary or tertiary consumers to accumulate enough energy to meet its daily caloric requirements from the limited energy available at upper trophic levels.

In a temperate forest, primary producers make about 6,000 kilocalories per square meter per year available to primary consumers. However, primary consumers assimilate only 10% of that energy. This cascading loss means upper trophic levels receive progressively less energy, directly determining how many organisms can exist at each level.

The second law of thermodynamics states that energy transforms from organized to disorganized forms, with entropy increasing. As energy flows through trophic levels, large amounts convert to heat during metabolic processes. This irreversible energy loss as heat is why ecosystems cannot recycle energy and must rely on continuous solar input.