Food chains and predator-prey graphs

In a nutshell

Food chains show which organisms eat what. They start with producers and then contain consumers. Predator and prey populations are linked: changes in one population directly affect the other population.

Food chains

Food chains are a way of showing what is eaten by what. They always start with a producer.

Example

Here is an example of a food chain.

Biology; Ecology; KS4 Year 10; Food chains and predator-prey graphs

Producers

Producers make their own food using energy from the Sun. Some glucose is used to make the plant's biomass. This is the mass of living material. Biomass is passed along a food chain when an organism eats another organism.

Example

Green plants and algae make glucose by photosynthesis.

Consumers

Consumers are organisms that eat other organisms.

Biology; Ecology; KS4 Year 10; Food chains and predator-prey graphs

1.	Producer.
2.	Primary consumers eat producers.
3.	Secondary consumers eat primary consumers.
4.	Tertiary consumers eat secondary consumers.

Predator and prey populations

Predator and prey populations go in cycles. Consumers that hunt and kill other animals are called predators. The animals that predators eat are called prey. In a stable community, the population size of a species is limited by the amount of food it has. This means the population size of predators is directly affected by the population size of prey.

Biology; Ecology; KS4 Year 10; Food chains and predator-prey graphs — A: Time, B: Population. 1; Rabbits, 2: Foxes

i.	Foxes are predators, rabbits are prey.
ii.	If the number of rabbits increases, the number of foxes will also increase as they have more food.
iii.	As the number of foxes increases, the number of rabbits will decrease as more rabbits are eaten by the foxes.

Note: It takes a while for one population to respond to changes in the other as it takes time for foxes to reproduce.