Producers are the first trophic level in an ecosystem. They determine how many trophic levels a rainforest ecosystem can support because they are the primary source of energy for all living organisms. Generally only about 10 percent of the energy at one level is available to the next level. The other amount of energy is used for metabolic processes or given off to the environment as heat. This loss of energy explains why there are rarely more than four trophic levels in a food chain or web because there's not enough energy left to support any additional levels.
