BIOLOGY 171 Lecture Notes - Lecture 20: Mulch, Primary Production, Decomposer
Document Summary
Unit 4: ecosystems // section 3: energy flow. Ecosystems maintain themselves by cycling energy and nutrients obtained from external sources. At the first trophic level, primary producers (plants, algae, and some bacteria) use solar energy to produce organic plant material through photosynthesis. Herbivores animals that feed solely on plants make up the second trophic level. Predators that eat herbivores comprise the third trophic level; if larger predators are present, they represent still higher trophic levels. Organisms that feed at several trophic levels (for example, grizzly bears that eat berries and salmon) are classified at the highest of the trophic levels at which they feed. Decomposers, which include bacteria, fungi, molds, worms, and insects, break down wastes and dead organisms and return nutrients to the soil. On average about 10 percent of net energy production at one trophic level is passed on to the next level.
