Lesson focus: competitionWhen living things try to get the same thing that is in short supply, such as food, light or space. occurs when organisms require the same limited resource, while adaptationA feature of an organism, produced by natural selection over many generations, that helps it survive and reproduce in its environment. affect survival and reproduction in a particular environment.
Compare competition within and between species and explain adaptations without implying that individuals acquire traits because they need them.
Build on earlier learning
EcosystemsSampling describes abundance and distribution. Competition and adaptation help explain why those patterns arise.
You will be successful when you can…
- Identify resources that can be limiting.
- Distinguish intra- and interspecific competition.
- Classify structural, behavioural and physiological adaptations.
- Explain that adaptation is population-level and environment-specific.
Words that carry the science
- competition
- An interaction in which organisms reduce each other’s access to a limited resource.
- intraspecific
- Occurring between members of the same species.
- interspecific
- Occurring between members of different species.
- adaptation
- An inherited feature that increases reproductive success in a particular environment.
- selection pressure
- An environmental factor that affects survival or reproduction differently among variants.
- niche
- A species’ ecological role and its use of resources and conditions.
Connect limited resources to selection without purpose language
01Resources become limiting when demand exceeds supply
Plants may compete for light, water, mineral ions and space. Animals may compete for food, water, shelter, territory and mates. competitionWhen living things try to get the same thing that is in short supply, such as food, light or space. can occur without direct fighting because using a resource leaves less for others.
intraspecificBetween members of the same kind (species), such as two robins competing for the same space. competition is often strong because members of one species have very similar requirements. interspecificBetween different kinds (species) of living things, such as foxes and owls competing for mice. competition can also be strong where nicheThe role a living thing has in its habitat: what it eats, where it lives and how it fits in. overlap.
02Adaptations take several forms
Structural adaptationA feature of an organism, produced by natural selection over many generations, that helps it survive and reproduce in its environment. include insulating fur or specialised roots. Behavioural adaptations include migration or nocturnal activity. Physiological adaptations include concentrated urine or antifreeze proteins.
One feature can have costs as well as benefits. Thick fur reduces heat transfer in cold conditions but can increase overheating risk in a warmer environment.
03Populations become adapted across generations
Inherited variation exists before a particular selective event. Individuals with variants that improve reproductive success tend to leave more offspring, so associated alleles can become more common.
An individual may acclimatise or learn, but it does not genetically adapt because it needs to. Adaptation describes inherited population change or a feature shaped by past selection.
Competition for resources
Organisms compete for limited resources: plants for light, water, space and minerals; animals for food, mates and territory. When two species need the same resource, each holds the other back. If the overlap is large, the better competitor can drive the other out.
Each shape stands for about 10 individuals.
Controls
Overlap 0: they need different things and do not compete. Species A is the slightly stronger competitor. Numbers are illustrative (a Lotka–Volterra model).
Explain resource partitioning
Two bird species feed on insects in different parts of the same tree.
- Both species require insect food, so their potential niches overlap.
- Feeding in different tree zones reduces direct overlap in resource use.
- Reduced overlap can weaken interspecific competition.
- The pattern may reflect behaviour, morphology and selection, but observations are needed to identify the mechanism.
How to make the reasoning visible: Resource partitioning describes reduced niche overlap; it does not mean competition has disappeared.
Analyse adaptations as trade-offs
For each feature, connect benefit, environment and possible cost.
| Feature | Environment | Likely benefit | Possible cost or limit |
|---|---|---|---|
| Thick insulating fur | Cold climate | Reduces thermal transfer | Overheating in warmth |
| Deep roots | Dry soil | Accesses deeper water | High construction cost |
| Large ears with blood supply | Hot climate | Increases heat loss | Heat loss in cold conditions |
| Nocturnal activity | Hot desert | Avoids daytime heat | Lower visibility or colder nights |
| Antifreeze proteins | Cold seawater | Reduce damaging ice formation | Energy and material cost |
Why is “a camel grew long eyelashes to keep out sand” scientifically weak?
Why can the same feature be advantageous in one habitat and disadvantageous in another?
Check your understanding
Answer from memory, then check against the suggested answer.
What is intraspecific competition?
Name three broad types of adaptation.
What makes a resource limiting?
Explain why planting crops closer together can eventually reduce yield per plant.
Explain why competition can promote niche divergence over evolutionary time.
Exam Question Practice
Exam Question Practice
Mark points shown after marking
Polar bears are adapted to the Arctic.
Explain how one structural adaptation helps a polar bear survive in the Arctic.
(3)Explain why the same adaptation could reduce success in a different environment.
(2)Total for this question: 5 marks
Command word: For explainA command word: say how or why something happens, giving reasons with words like "because" or "so"., use one specific feature and build two causal chains: benefit in one context and cost in another.