What Is the Source of Energy for Most Ecosystems?

For many ecosystems, the sun provides the primary source of energy. The sun provides light and fuel necessary for the growth of many living organisms, ranging from tiny microbes and bacteria to plants and animals. Some species, primarily photosynthetic plants, use sunlight for creating energy of their own, which in turn helps them grow and reproduce.

In sunlight-dependent ecosystems, the sun delivers energy to all organisms, which use that energy in different ways. Base-level organisms, called producers, absorb sunlight directly. They grow and reproduce using photosynthesis, which involves the absorption of sunlight and conversion of that light into sugar and energy.

Producers live in terrestrial and aquatic environments. Most take the form of photosynthetic producers, such as algae and plants. Others exist in the form of bacteria, and reside in oceans. These producers, also called autotrophs, serve as food for organisms slightly higher on the food chain, called primary consumers. These animals obtain energy from consuming plants, seaweed and fungi. They classify as vegetarians, and eat a variety of leafy green matter.

Secondary and tertiary consumers rank higher on the food chain. These species include larger animals that consume primary producers. Some classify as omnivores too, eating plants along with other animals. Food and nutrients pass through ecosystems, eventually decomposing in a long recycling process. Energy from the sun, however, does not recycle, and requires a constant injection into ecosystems to sustain life.