Trophic Levels

The food chain shows the feeding relationships in a specific ecosystem. It is a simplified version of a food web, as it shows just one chain of interactions in a web. Therefore, it ignores other interactions.

Below is an example of a food chain:

Illustration of a simple food chain representing the flow of energy from the sun to various trophic levels: the sun fuels the grass labelled as 'Primary Producer', which is consumed by the grasshopper labelled as 'Primary Consumer'. The bird, labelled as 'Secondary Consumer', preys on the grasshopper, and finally, the snake, labelled as 'Tertiary Consumer', preys on the bird, showcasing the interconnected relationships and energy transfer between different species in an ecosystem.

Grass → Grasshopper → Bird → Snake

The basic stages in a food chain or web are called trophic levels, which are represented by numbers. The arrows in a food chain show the direction of biomass, which transfers from one trophic level to another.

Stages of a Food Chain

Level 1: Producer

Food chains start with a producer, which is a photosynthetic organism (e.g. green plant or algae). Photosynthetic organisms use the Sun’s energy to perform photosynthesis.

Photosynthesis produces glucose, which is a biological molecule. This provides the biomass for the whole food chain.

  • In the example, the producer is grass

Level 2: Primary consumer

At the second trophic level is the primary consumer, which is an herbivore or omnivore that eats the producers. Keep in mind that there might be many different primary consumers. However, you only need to include one in a food chain.

  • In the example, the primary consumer is a grasshopper.

Level 3: Secondary consumer

At the third trophic level is the secondary consumer, which is a carnivore or omnivore that eats the primary consumer.

  • In the example, the secondary consumer is the bird

Level 4: Tertiary consumer

The third consumer is called the tertiary consumer.

  • In the example, the tertiary consumer is the snake

The final level, when present, is often a carnivore known as an apex predator. Organisms at the top of the food chain do not have any predators.

Some ecosystems may have more than three consumers, for example:

LevelWhat it feeds on
Primary ConsumersFeed directly on producers (like plants)
Secondary ConsumersFeed on primary consumers
Tertiary ConsumersFeed on secondary consumers
Quaternary ConsumersFeed on tertiary consumers

  • The fourth consumer level is the tertiary consumer,

Decomposers

Decomposers are organisms that break down dead or decaying organic matter, returning nutrients to the environment. They do this by secreting enzymes.

Decomposers aren’t necessarily part of the linear food chain, but instead play a vital role in the ecosystem. In the food chain above, when the snakes die, their bodies are decomposed by decomposers, such as bacteria and fungi. They break down the organic matter and release the nutrients back into the soil. These nutrients can then be used by the grass and other plants to grow, starting the cycle over again.

By breaking down organic matter and releasing nutrients back into the environment, decomposers help to sustain the ecosystem and support the growth and survival of other organisms. Without decomposers, dead or decaying plant and animal matter will accumulate in the soil and eventually deplete it of nutrients, which will have negative impacts on the entire ecosystem.

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