4.7 - Trophic Levels

Trophic levels and producers

• A trophic level is the position (feeding level) an organism occupies in a food chain.
• The levels are numbered from level 1 upwards, so a food chain reads as a sequence of trophic levels from the producer at the bottom to the top predator.
• Each step up the chain is the next number.

Level 1 - Producers

• Level 1 is always a producer.
• Producers are plants and algae. They're called producers because they make their own food by photosynthesis, using light energy from the Sun.
• This makes them the base of the whole chain:
  • They capture the energy that everything else depends on.
  • They produce the biomass (the mass of living material) that is passed along the chain to organisms above them.
• All the energy in a food chain originally enters through the producers.

The consumer levels

The levels above the producer are the consumers - animals that get their energy by eating other organisms.

• A fourth consumer can also be called a quaternary consumer.
• The pattern then keeps repeating up the chain.
• A carnivore at the very top of a chain, with no predators of its own, is an apex predator.

Organisms that don't fit the ladder

• Omnivores, such as bears, eat both producers and other animals, so they don't sit cleanly at one level. They feed at more than one trophic level: level 2 when they eat producers and level 3 when they eat primary consumers.
• Food chains rarely have more than four or five levels, because energy is lost at each transfer (only about a tenth passes on each time), so there's too little left to support organisms much higher up.