“Producers” and “consumers” are terms used to describe the different roles played by species within ecosystems. Producers are those who “fix” energy—that is, they take energy from one source and convert it into a form (their biomass) that makes it accessible to others within the system (the consumers). Consumer levels are numbered according to their reliance on producers as a main source of energy. So primary consumers are those that rely heavily on producers, while secondary and tertiary (and even quaternary) consumers exploit other consumers as their preferred energy sources.