Each step along a feeding pathway is known as a trophic (feeding) level. It is also explained as the temporary stopping point in the movement of energy from one organism to the other in a food chain. These feeding pathways (trophic levels) follow a particular sequence:
1. It must start from a primary producer (green plant).
2. The green plant must be eaten by a primary consumer (herbivore).
3. The herbivore must be eaten by a secondary consumer, which is in turn eaten by another consumer (tertiary).
4. When the final consumer dies, some decomposers now break down its complex tissues into simple inorganic substances, which return to the non-living environment.
These features are unique in all ecosystems except that some may terminate at the secondary consumer level or may go onto the tertiary or even proceed to the decomposer stage.
In a food relationship (food chain), trophic levels are denoted by (T) as shown in the below image
T1 Grass – primary producer
T2 Grasshopper – primary consumer
T3 Lizard – secondary consumer
T4 Hawk – tertiary consume~
T5 Bacteria and Fungi – decomposers
Chain showing trophic levels
T1 always consists of autotrophs (green plants).
T2 is usually made up of organisms which depend directly on green plants for food.
T3 and T4 includes organisms such as carnivores (predators) like cats, dogs, lions, eagles and sharks; parasites such as lice and flukes, and cavengers like vultures and hyenas (animals that prey on dead animals).
T5 represents the decomposer (micro and macro-decomposers).
When an organism at the top (that which has escaped being eaten) dies, it is decomposed by organisms of this level, which convert the dead organism to simple substances, e.g, nitrogen, carbon, etc., and the life cycle starts all over because these simple substances are reabsorbed by green plants to stay alive.