Explain competition for limited resources
Competition can be indirect when organisms need the same scarce resource.
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Use the stated case, sample and assumptions. Diagrams and numerical records in this pathway are original teaching models; written answers are self-checked.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which example describes indirect competition?
What you will learn
- Identify a limiting resource in a stated environment
- Explain competition without implying purposeful change
Original selection schematic. Population counts and scenarios are supplied teaching models; they are not field observations.
| Stage or record | Meaning |
|---|---|
| Case | Dense seedbed |
| Limited resource | Light reaching lower leaves |
| Mechanism | Upper leaves intercept light |
| Not established | A heritable population shift |
Identify a limiting resource in a stated environment
Competition occurs when organisms need a resource that is limited in the environment. Seedlings may draw on the same light, water, mineral ions and space; young animals may use the same food, shelter or nest sites. They need not attack one another. One individual can reduce the amount available to another simply by using part of a shared resource.
State the resource and why it is limited in the case. In a shaded woodland patch, light at ground level may be reduced by leaves above it. If water is scarce, plants may also share a finite water supply. A vague statement that organisms “compete to be strongest” does not identify the environmental constraint or explain how it affects growth and reproduction.
Explain competition without implying purposeful change
Competition does not make an organism develop a desired allele. Individuals already differ; environmental conditions can influence which survive and reproduce. A taller seedling may intercept more light in one patch, but height alone is not proof of a survival advantage in every habitat. Use the specified resource and evidence.
Competition is one element of natural selection, not the complete process. A full account also needs population variation, many offspring, a greater chance of reproduction for better-adapted individuals in that setting, and transmission of alleles to offspring. A single contest for light does not establish that whole population-level sequence.
Sources for this lesson
Pause and explain
What is the best explanation for seedlings competing in a shaded patch?
Worked example
In an invented dense seedbed, 40 seedlings share a small illuminated area. State the limited resource and explain how competition may occur without direct contact.
Show the worked solution
- Name the shared resource: light reaching the seedlings.
- More leaves above can intercept light before it reaches lower seedlings.
Answer Light is limited in the stated patch. Seedlings compete indirectly because one may reduce the light available to another; no direct fight is required.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
In a crowded garden tray, leaves overlap and less light reaches lower leaves. Identify the resource and give one plausible effect without claiming an evolutionary outcome.
Give me a hint
Name what the upper leaves intercept.
Compare my reasoning
- The shared resource is light.
- Lower leaves may receive less light for photosynthesis and growth.
Light is the limited resource; lower seedlings may grow less in this condition, but this alone does not demonstrate inherited change or later reproduction.
Look for these in your work
- Resource identified
- Effect bounded to stated evidence
Two shore crabs feed on the same limited mussel bed at different times. Explain why they can compete without meeting.
Give me a hint
Ask whether their use changes the resource left for the other.
Compare my reasoning
- Both depend on the same finite food source.
- Earlier feeding can reduce the food remaining for the later crab.
They compete indirectly for mussels because the shared food is limited; physical contact is unnecessary.
Look for these in your work
- Shared limited resource
- Indirect mechanism
An unshaded field has abundant water but little nesting space for birds. A student says the birds compete for water. Correct the resource claim and describe what evidence would strengthen an explanation of reproductive differences.
Give me a hint
Use the stated limiting resource, then connect to recorded outcomes.
Compare my reasoning
- Water is stated as abundant; nest sites are limited.
- Compare access to nest sites with breeding success while considering other differences.
The likely limiting resource is nest space, not water. Records linking access with reproductive outcomes would help, while a correlation alone would still require caution about other factors.
Look for these in your work
- Correct limitation
- Evidence and causal caution
Common mistakes
- Saying competition always means fighting
- Claiming limited resources deliberately change genes
- Calling a resource limiting without identifying it
What can you explain now?
What is the best explanation for seedlings competing in a shaded patch?
Compare with the explanation
Their leaves share limited access to light
The stated resource is limited and used by both groups.
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Make it stick
Without your notes, identify a limiting resource in a stated environment and explain competition without implying purposeful change. Explain the mechanism, use the given population or breeding records and state what the evidence does not establish.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.