What happens to energy as it flows through different trophic levels?

As energy flows through different trophic levels in an ecosystem, it indeed decreases at each step primarily due to energy loss as heat. This phenomenon is a result of the second law of thermodynamics, which states that energy transformations are not 100% efficient. For example, when an organism consumes another organism for energy, much of the energy is lost in metabolic processes such as respiration, movement, and heat production.

Only a fraction of the energy is stored and available to the next trophic level, typically about 10% of the energy is transferred from one level to the next in what is known as the "10% Rule." This means that as energy moves from producers to primary consumers and then to secondary consumers and beyond, there is a significant loss at each level, primarily as heat. This concept is critical in understanding energy flow in ecosystems and explains why there are generally fewer organisms, and thus less energy available, at higher trophic levels compared to lower ones.