Nutrient Cycling

Food webs transfer nutrients through different parts of the ecosystem. Many organisms are unable to acquire their nutrients from inorganic sources with the notable exception of primary producers.

Energy Input

Primary producers bring energy into the food web from sunlight or other sources. This energy is then distributed to other organisms in the food web. Each organism uses this energy for life processes resulting in loss of energy available to the ecosystem.

Trophic Levels

Organisms can be classified according to the role they play in a food web. These categories include producers, grazers, predators and decomposers.

Producers

Producers create organic molecules from inorganic nutrients. They also capture energy that is incorporated into these organic molecules.

Grazers and Predators

Grazers and predators rely directly or indirectly on the food and nutrients made available by producers. Grazers feed directly on producers while predators feed on grazers and/or other predators.

Food Web Mobility

Some organisms occupy different potions of the food web at different times during their life. For example, insects may be prey for certain species during their larval stage and prey for other predators during their adult stage.

Source:

North Carolina Agricultural and Technical State University: Food Chains and Food Webs

Marietta College: Ecosystems

Department of Oceanography, Texas A&M University: Marine Food Webs