What Are Trophic Levels in a Food Chain?

Trophic levels are the positions organisms occupy in a food chain. They show how far an organism is from the producer at the start of the chain. This is part of AQA GCSE Biology separate science; I’m assuming that is the course you are studying.

How are the levels numbered?

• Level $1$: producers. Plants and algae make their own food by photosynthesis.
• Level $2$: primary consumers. These eat producers and are usually herbivores.
• Level $3$: secondary consumers. These eat primary consumers.
• Level $4$: tertiary consumers. These eat secondary consumers.

A consumer gets food by eating other organisms. An apex predator is a carnivore with no predators of its own. It may be at the top of a food chain, but it is not automatically at level $4$: its level depends on the chain shown.

Worked example

Consider this food chain:

$$grass⟶rabbit⟶fox$$

Grass is the producer at level $1$. The rabbit eats grass, so it is the primary consumer at level $2$. The fox eats the rabbit, so it is the secondary consumer at level $3$. Each arrow points towards the organism doing the eating; it shows the direction in which food is passed along the chain.

To find a trophic level in any unfamiliar chain, begin at the organism making its own food. Count along the arrows one step at a time. An animal’s label depends on what it eats in the particular chain, not just its species.

Decomposers, such as microorganisms, break down dead plant and animal matter. They are important in the ecosystem, but do not simply add them as the next numbered level after the last consumer.

Common exam mistake: calling the producer level $2$ because the Sun provides energy for photosynthesis. The Sun is not an organism in the food chain. Start counting with the producer at level $1$, then follow who eats whom.