Food chains

A food chain is a sequence that shows the feeding relationships of organisms in an ecosystem, so it shows what eats what. In a food chain, one organism consumes another, and the energy from the consumed organism is transferred to the predator. So, a food chain also shows the transfer of energy, from one organism to another.

  • One species eats the organism that is below it in the chain and is eaten by the organism above it

However, a food chain is just a small part of a larger network of feeding relationships, called a food web. Let’s first look at a basic food chain:

Grass → Grasshopper → Bird → Snake

We have grass which gets eaten by a grasshopper, which gets eaten by a bird, which gets eaten by a snake.

Producers and Consumers

The organism at the beginning of the food chain is called the producer. These organisms produce their own food, through photosynthesis. Green plants are the most common producers, but some bacteria and algae can also act as producers. Every other organism in the food chain is called a consumer.

  • The first consumer in the food chain is called the primary consumer, and they feed on the producers. Primary consumers can be herbivores, which only eat plants, or omnivores, which eat both plants and animals.
  • After the primary consumer is the secondary consumer, which feeds on the primary consumer.
  • The tertiary consumer is the next step in the food chain, and it feeds on the secondary consumer

Secondary and tertiary consumers are often carnivores, which only eat other animals. However, they can also be omnivores.

In a food chain, the arrows show the direction of energy transfer from one organism to the next. This is why the arrows point from the producer (green plants) to the snake (tertiary consumer). In the earlier example, we can see that the energy is transferred from the green plants to the grasshopper, then from the grasshopper to the bird and finally, from the bird to the snake.

The loss of energy

At each step of the food chain, energy is lost in different ways.

  • Organisms use energy for movement
  • Some parts of the organism cannot be eaten
  • Energy is lost through waste (e.g. urine and faeces)
  • Organisms use energy to keep warm

So, the lost energy cannot be passed along the food chain. There are typically only four to five organisms in a food chain, as the energy at the top of the food chain is limited.

Predators and prey

A predator is an animal that naturally hunts and eats other animals. The prey is the animal that is being hunted and eaten by the predator.

For example:

Fish → White-tailed eagle

  • The white-tailed eagle is the predator, as it is hunting the fish to eat
  • The fish is the prey because it is being hunted and eaten by the white-tailed eagle

This relationship is important for maintaining balance in the ecosystem, as predators help to regulate the populations of their prey.