B15.4 Competition in Animals

A free GCSE Combined Science: Trilogy lesson for AQA (8464) from OBA School: competing for food, mates and territory; how competition changes populations. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

• State the three main resources that animals compete for
• Tell the difference between interspecific and intraspecific competition
• Describe examples of competition for food, mates and territory
• Explain why specialist feeders are more at risk than generalists
• Explain how one species can outcompete another, using data

Key words

• Competition: When organisms need the same resource and there is not enough for all of them.
• Interspecific: Competition between individuals of different species.
• Intraspecific: Competition between individuals of the same species.
• Territory: An area an animal defends against others, usually to secure food, shelter or a place to breed.
• Specialist feeder: An animal that eats only one or a few types of food.
• Generalist feeder: An animal that eats many different types of food.

What animals compete for

Animals need food, mates and territory. These resources are limited, so animals compete for them. Animals of the same species (intraspecific competition) compete most strongly, because they need exactly the same things. Animals of different species (interspecific competition) compete when their needs overlap.

• food; Why it matters gives energy and materials for growth and reproduction; Example barn owls and kestrels both hunt field voles
• mates; Why it matters only animals that breed pass on their genes; Example male grouse display and fight on a lek in spring
• territory; Why it matters secures food, shelter and nesting space; Example badger groups mark the edges of their territory with dung pits

Key fact: Animals compete for food, mates and territory. Plants compete for light, space, water and mineral ions.

Food and feeding strategies

A generalist such as a badger eats many foods: earthworms, insects, fruit, bulbs and small mammals. If one food runs short it switches to another. A specialist such as the snail kite, a bird that eats almost only apple snails, faces less competition while that food is plentiful but is at great risk if it disappears.

Many animals reduce competition by feeding in different places or at different times. Barn owls hunt voles at night; kestrels hunt them by day.

Mates and territory

Males often compete for females. Some fight (stags, elephant seals); others display or call (peacocks spread their tails, male frogs croak). In a herd of red deer, the strongest stag mates with most of the females. Females usually choose the male with the best display, which is often the healthiest.

Holding a territory gives an animal a reliable food supply and a safe place to raise young. Animals mark territories with scent, song or display, so they do not waste energy fighting.

Worked example: territory size and breeding

A wood of 60 hectares has room for 60 ÷ 2.5 = 24 territories of 2.5 hectares each.
If 29 pairs of the bird arrive in spring, 29 − 24 = 5 pairs cannot hold a territory.
These 5 pairs are unlikely to breed, so competition limits the population.

Answer: 5 pairs without a territory

When one species outcompetes another

An introduced species may compete with a native species for the same food or nest sites. If it is better at getting the resource, breeds faster, or has no natural predators, it can outcompete the native species.

Worked example: percentage change

Native beetles fell from 150 to 45 in 5 years.
Percentage decrease = (150 − 45) ÷ 150 × 100 = 105 ÷ 150 × 100 = 70%.

Answer: 70% decrease

In the UK, grey squirrels from North America have replaced red squirrels in most of England and Wales. Greys are larger and store more fat, so more survive cold winters; they breed more successfully; and they carry squirrelpox, a virus that kills reds but rarely harms greys.

Exam tip: Percentage change = (new − original) ÷ original × 100. Always divide by the original value.

Common mistakes

• Saying animals compete for light or mineral ions – those are plant resources.
• Thinking competition happens only between different species. It is often strongest within one species.
• Dividing by the new value in a percentage-change calculation instead of the original value.
• Saying a specialist is always better off. It is only safe while its one food is plentiful.

Revision questions

Try these, then check your answers below each one.

Question 1. Which of these do animals not usually compete for? (Choose from: Light, Food, Mates, Territory.)

Answer: Light

Working: Animals compete for food, mates and territory. Light is a resource plants compete for.

Question 2. True or false? Competition only happens between animals of different species.

Answer: False

Working: False. Competition within a species (intraspecific) is often the strongest, because individuals need exactly the same resources.

Question 3. The bar charts show the diets of two animals, X and Y. Which animal is more at risk if its main food becomes scarce, and why? (Choose from: X, because it relies almost entirely on one food, Y, because it eats many different foods, Both equally, because they both eat food, Neither, because animals never run out of food.)

Answer: X, because it relies almost entirely on one food

Working: X is a specialist: 98% of its diet is eucalyptus leaves. Y is a generalist and can switch to other foods if one runs short.

Related lessons

• Previous lesson: B15.3 Distribution and Abundance
• Next lesson: B15.5 Competition in Plants
• In this chapter: B15.1 The Importance of Communities
• In this chapter: B15.2 Organisms in Their Environment
• In this chapter: B15.6 Adapt and Survive

Continue in the full course

This lesson is section B15.4 (AGCSC1504) of our free GCSE Combined Science course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Combined Science course.