Describe food chains and food webs, identify producers, consumers and predators and prey, and explain what happens when part of a food web changes

What this dot point is asking

This dot point wants you to describe food chains and food webs, name the different roles that living things play (producers, consumers, predators and prey), and explain what happens when part of a food web changes. The big idea is that living things are linked by what they eat. Energy from the Sun is captured by plants and then passed along from one living thing to the next when one is eaten by another. A food chain shows one path; a food web shows many linked paths.

The answer

What a food chain is

A food chain shows how energy and food pass from one living thing to another. It is written with arrows, like this:

grass goes to grasshopper goes to frog goes to snake

The arrows show the direction the food and energy pass, from the thing being eaten to the thing that eats it. So the arrow points from the grass to the grasshopper because the grasshopper eats the grass.

Producers and consumers

Living things in a food chain have roles:

• A producer is a green plant that makes its own food by photosynthesis. Producers are always at the start of a food chain, because they capture the Sun's energy. Grass is the producer in the chain above.
• A consumer is an animal that eats (consumes) other living things, because it cannot make its own food. The grasshopper, frog and snake are all consumers.

The first consumer eats the producer; the next consumer eats the first consumer, and so on. Energy passes along the chain each time.

Predators and prey

Among the consumers, we use two more words:

• A predator is an animal that hunts and eats other animals. The frog is a predator of the grasshopper; the snake is a predator of the frog.
• The prey is the animal that is hunted and eaten. The grasshopper is the prey of the frog; the frog is the prey of the snake.

So an animal can be both a predator (of what it eats) and prey (of what eats it), like the frog.

What a food web is

In real life, most animals eat more than one kind of food, and most plants and animals are eaten by more than one thing. A food web shows many food chains linked together. It gives a fuller picture than a single chain, showing how all the living things in one place depend on each other.

When a food web changes

Because the living things are linked, a change to one part affects the others. If a predator is removed, the animals it ate are no longer hunted, so their numbers increase. If a food source disappears, the animals that ate it may go hungry and their numbers fall. For example, if all the owls in a web were removed, the mice they ate would increase. This is why protecting one species can matter for many others.

Examples in context

Example 1. A pond food web. In a pond, tiny water plants are eaten by small water animals, which are eaten by small fish, which are eaten by bigger fish and birds. The water plants are the producers capturing the Sun's energy, and each animal is a consumer. The many links between them make a food web, not just a single chain.

Example 2. Removing a predator from farmland. If farmers remove all the foxes that hunt rabbits, the number of rabbits often rises sharply because they are no longer being eaten. The extra rabbits then eat far more crops and grass. This real effect shows why removing one predator can change a whole food web.

Try this

• Cue. In the food chain leaf goes to snail goes to bird, name the producer and one consumer. The producer is the leaf (a green plant); the consumers are the snail and the bird.

• Cue. State what the arrows in a food chain show. The arrows show the direction the food and energy pass, from the thing being eaten to the thing that eats it.

• Cue. In a food web, the hawks that eat rats are all removed. Predict what happens to the number of rats and explain why. The number of rats increases, because with the hawks gone fewer rats are eaten, so more survive and breed.