Concept of Trophic Level in an Ecosystem

A trophic level (from the Greek trophē, meaning food or feeding) describes an organism's position in a food chain, and the total number of trophic levels in a chain equals the number of feeding steps it contains. Green plants — the producers — sit at the base as the first trophic level (T1). Herbivores that eat these producers are the primary consumers, occupying the second trophic level (T2) — the example used is a rabbit feeding on plants. Carnivores that eat herbivores are secondary consumers (also called primary carnivores), occupying the third trophic level (T3) — a snake preying on the rabbit. Carnivores that in turn eat other carnivores are tertiary consumers (also called secondary carnivores), occupying the fourth trophic level (T4) — an eagle preying on the snake. Omnivores, such as a crow that eats both plant and animal matter, do not sit neatly at one level — they can occupy more than one trophic level depending on what they happen to be eating at the time. This level-by-level structure is what makes a food …