intraspecific and interspecific competition
Laura Armstrong & Joe Wolfensohn
Teachers
Recall Questions
This topic requires prior knowledge of competition from GCSE Biology. You can test your knowledge on this below.
What do animals compete for in their habitats?
Food, mates, territory.
Why do plants compete with each other?
Light, water, space, and mineral ions.
What is the consequence of too much competition in a population?
Population size decreases due to limited resources.
Topic Explainer Video
Check out this @JoeDoesBiology video that explains intraspecific and interspecific competition or read the full notes below. Once you've gone through the whole note, try out the practice questions!
What Is Competition?
Competition occurs when organisms attempt to access the same resources that are in limited supply. This is a key biotic factor that influences population size and distribution in ecosystems.
Types of Competition
1. Intraspecific Competition
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Definition: Competition between individuals of the same species for the same resource.
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Example – Animal: Red deer stags compete for mates during rutting season.
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Example – Plant: Beech trees compete for sunlight in dense woodland by growing taller and broader canopies.
Result: Intraspecific competition leads to cyclical fluctuations in population size. When resources are scarce, population falls; when competition decreases, population can rise again.
2. Interspecific Competition
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Definition: Competition between individuals of different species for shared resources.
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Example – Animal: Red and grey squirrels in the UK compete for food. Grey squirrels often outcompete red squirrels due to better fat storage and digestion.
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Example – Plant: Grass and dandelions compete for light and water in a lawn ecosystem.
Result: Interspecific competition can lead to the exclusion of one species if the other is more efficient at using the resources (known as the competitive exclusion principle).
Competition & Population Dynamics
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Limiting Factors: The availability of food, water, space, or nesting sites can limit population growth.
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Species Interactions: Competition influences natural selection, where better-adapted individuals outcompete others and survive to reproduce (passing on the advantageous alleles).
Key Terms
- Competition: The struggle between organisms for limited resources.
- Intraspecific Competition: Competition between individuals of the same species.
- Interspecific Competition: Competition between individuals of different species.
- Limiting Factor: A factor that restricts the size of a population.
- Competitive Exclusion: When one species is outcompeted and eliminated from a habitat by another.
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Exam Tip
Command words matter:
If the question asks for "explain the effect of intraspecific competition on population size", don’t just define it. You must explain the rise and fall pattern and link back to resource availability.
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Explain how intraspecific competition can lead to fluctuations in population size. (4 marks)
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Intraspecific competition occurs between individuals of the same species.
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When population size increases, more individuals compete for the same limited resources, such as food.
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This leads to a decrease in population as fewer individuals survive and reproduce.
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With fewer individuals, competition is reduced, resources become more available, and the population can increase again.
Practice Question 1
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!
Practice Question 2
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!