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From Wikipedia, the free encyclopedia. Stream metabolism, also known as aquatic ecosystem metabolism in lakes, can be expressed as net ecosystem productivity (NEP), the difference between gross primary productivity (GPP) and ecosystem respiration (ER).
Producers funnel into the ecosystem the energy needed for its biological processes. The carbohydrates and other organic chemicals formed by the producers are consumed and utilized by the heterotrophs, or consumers. First, herbivores -- the primary consumers -- eat the plants. Predators -- the secondary, tertiary consumers -- eat the herbivores. But at each step, much energy is lost. Less than 10 percent of the energy stored in plants is converted to herbivore mass. The loss from herbivore to predator is similar. Thus, energy needs to be added to the ecosystem continuously. This is the producers' role. Shaping the Ecosystem The efficiency of the producers in adding energy to the ecosystem determines how robust that ecosystem will be.