16.4 Competition in Animals

A free GCSE Biology lesson for AQA (8461) 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
• 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.
• Territory: An area an animal defends against others, usually to secure food, shelter or a place to breed.
• Mate: A partner of the same species for sexual reproduction.
• 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.
• Introduced species: A species brought (often by humans) into an area where it did not live before.

What animals compete for

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

• food; Why it matters gives energy and materials for growth and reproduction; Example gulls and crows squabble over scraps on a beach
• mates; Why it matters only animals that breed pass on their genes; Example male red deer roar and clash antlers in autumn
• territory; Why it matters secures food, shelter and nesting space; Example a robin sings to warn other robins away from its garden

Key fact: AQA: 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 fox eats many foods: rabbits, mice, birds, insects, fruit and scraps. If one food runs short it switches to another. A specialist such as a koala, which eats almost only eucalyptus leaves, 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. Owls and kestrels both hunt voles, but owls hunt mainly at night and kestrels by day.

Mates and territory

Males often compete for females. Some fight (stags, elephant seals), others display (peacocks spread their tails, many birds sing). 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 45 hectares has room for about 18 territories of 2.5 hectares each (45 ÷ 2.5 = 18).
If 24 pairs of a bird species arrive in spring, 24 − 18 = 6 pairs cannot hold a territory.
These 6 pairs are unlikely to breed, so competition limits the population.

Answer: 6 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, or breeds faster, or has no natural predators, it can outcompete the native species.

Worked example: percentage change

Native beetles fell from 120 to 30 in 5 years.
Percentage decrease = (120 − 30) ÷ 120 × 100 = 90 ÷ 120 × 100 = 75%.

Answer: 75% decrease

In the UK, grey squirrels from North America have replaced red squirrels in most of England and Wales. Greys are larger, can digest acorns that reds cannot, and carry squirrelpox, a virus that kills reds but rarely harms greys. So both competition and a new pathogen are involved.

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 is often strongest between members of the same species, because they need exactly the same resources.

Question 3. Koalas eat almost only eucalyptus leaves. Foxes eat many different foods. Which statement is correct? (Choose from: Koalas are more at risk if their food becomes scarce, Foxes are more at risk if one food becomes scarce, Both are equally at risk, Neither is affected by food supply.)

Answer: Koalas are more at risk if their food becomes scarce

Working: The koala is a specialist feeder, so it cannot switch to another food. The fox is a generalist and can eat something else.

Related lessons

• Previous lesson: 16.3 Distribution and Abundance
• Next lesson: 16.5 Competition in Plants
• In this chapter: 16.1 The Importance of Communities
• In this chapter: 16.2 Organisms in Their Environment
• In this chapter: 16.6 Adapt and Survive

Continue in the full course

This lesson is section 16.4 (AGCBH1604) of our free GCSE Biology 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 Biology course.