成人快手

Key points

  • Predator-prey cycles show the natural rise and fall of numbers of predators and prey over time.
  • All organisms in a food web depend upon each other and changes to one can affect the others.
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Predators and prey

Can you answer these questions based on the video?

1. What adaptation does the fox have?

2. What is the graph of predators and prey called?

Animals that are hunted and eaten are prey, and these are consumed by predators. The final consumer at the top of the is called a top (or apex) predator and is not eaten by anything else.

Over time the numbers of predators and prey in an ecosystem rises and falls in a . As the number of prey increases, so does the number of predators shortly afterwards. This is because there is more food. This reduces the number of prey because they are hunted. Which reduces the number of predators because there is less food. This increases the number of prey and the cycle repeats.

a graph showing that overtime the prey population and the predator population increases and decreases in waves.
Figure caption,
The predator-prey cycle almost always has more prey than predators
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Adaptations of predators and prey

a rabbit's skull
Image caption,
A rabbit skull showing eyes facing to the side and sharp teeth at the front for cutting grass and flat teeth at the back for grinding it up

Prey have to avoid being hunted, such as good hearing or eyes on the sides of their heads for a wide field of vision. This means it鈥檚 easier for them to see predators coming. Prey often have very good camouflage to avoid being seen.

a rabbit's skull
Image caption,
A rabbit skull showing eyes facing to the side and sharp teeth at the front for cutting grass and flat teeth at the back for grinding it up
a fox skull
Image caption,
A fox skull showing eyes facing to the front and sharp teeth for killing prey and cutting meat

Predators have adaptations to hunt effectively like sharp claws and teeth, with eyes at the front of their heads to judge distances well. Some predators, for example cheetahs, can run very fast for short distances. Wolves can run great distances over longer periods of time, until their prey run out of energy.

a fox skull
Image caption,
A fox skull showing eyes facing to the front and sharp teeth for killing prey and cutting meat
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Interdependence

All organisms in a food web depend upon each other. This is interdependence. If one organism increases or decreases its numbers dramatically, this has consequences for others.

Use the food web to answer the following questions:

1. What happens if the grass dies?

2. What happens if the population of slugs decreased?

3. What happens if the population of insects decreased?

a food web showing what eats what and the transfer of energy between organisms

Food webs are able to flex and quickly bounce back to small changes in numbers. However big changes are more difficult for food webs to stabilise. These large changes are often due to human activity, such as , constructing roads and buildings, and the use of chemical .

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Food security

All the food we eat relies on plants. This includes meat because animals such as pigs, sheep and cattle eat plants. Grasses such as wheat, barley and rice use the wind for . Plants that produce fruit rely on insects and other animals for their pollination.

If the population of pollinating insects goes down, it reduces the amount of these plants for us to eat, and also the number of seeds for new plants to grow. Food security means having a reliable source of nutritious food.

a bee on a flower
Image caption,
If the bee population reduces the amount of food available for humans is affected
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Test your knowledge

Quiz

Test questions

Describe the stages in a predator-prey cycle.

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Play the Atomic Labs game! game

Try out practical experiments in this KS3 science game.

Play the Atomic Labs game!
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More on Ecosystems and habitats

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