What are trophic levels?
Trophic levels number the positions in a food chain from producer (level 1) up to apex predator (level 4 or 5).
(Biology only — 4.7.4.1) Every organism in an ecosystem fits into a trophic level — its feeding position in a food chain. The word comes from the Greek trophe, meaning 'nourishment'.
Level 1 — Producers. Plants and algae that make their own food by photosynthesis. They convert light energy into glucose, which is stored in their tissues. Examples in the UK: grass, oak trees, phytoplankton in ponds and seas.
Level 2 — Primary consumers (herbivores). Animals that eat producers. Examples: rabbits, sheep, caterpillars, aphids, zooplankton.
Level 3 — Secondary consumers (carnivores). Animals that eat primary consumers. Examples: foxes (eating rabbits), ladybirds (eating aphids), small fish (eating zooplankton).
Level 4 — Tertiary consumers / apex predators. Carnivores that eat other carnivores. Often the top of the food chain with no natural predators. Examples: golden eagles (eating foxes), pike (eating smaller fish), sparrowhawks.
Some ecosystems have a level 5 (e.g. orcas eating sharks eating tuna).
Decomposers. Bacteria and fungi that break down dead organisms (and animal waste) at every level. They aren't usually given a 'level' number, but they're vital — they release nutrients back into the soil so producers can use them again.
Level 1 producer → Level 2 primary → Level 3 secondary → Level 4 tertiary.
Producers make food; consumers eat others.
Decomposers recycle dead material at every level.
Food chain arrows go from food → eater (= direction of energy flow).