II.

Trophic Levels

The food web can be viewed not only as a network of chains but also as a series of trophic (nutritional) levels. Green plants, the primary producers of food in most terrestrial food webs, belong to the first trophic level. Herbivores, consumers of green plants, belong to the second trophic level. Carnivores, predators feeding upon the herbivores, belong to the third. Omnivores, consumers of both plants and animals, belong to the second and third. Secondary carnivores, which are predators that feed on predators, belong to the fourth trophic level. As the trophic levels rise, the predators become fewer, larger, fiercer, and more agile. At the second and higher levels, decomposers of the available materials function as herbivores or carnivores depending on whether their food is plant or animal material.