Trophic Levels

The accumulating biomass of primary producers is a source of fixed energy that can be utilized by heterotrophic organisms by directly feeding on the autotrophic biomass. The primary consumers of autotrophic biomass are also known as herbivores and include the tiny crustacean zooplankton that filter microscopic algal cells out of the surface waters of lakes, ponds, and oceans, as well as much larger, mammalian herbivores, such as mice, deer, cows, and elephants. Herbivores utilize the fixed energy and nutrients in their food of autotrophic biomass to drive their own metabolic processes and to achieve their own growth.