Identify factors affecting population growth
Food supply, competition, predation and disease can affect the rate of population growth; the direction depends on the organisms and evidence.
Core and Extended; Biology 0610, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked
Before you begin
- Know population, community and ecosystem terms and read the axis labels on a graph.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which four factors are specified for population growth in this syllabus section?
What you will learn
- Identify the four syllabus factors
- State a plausible effect on population growth using context
Use the four specified factors
The syllabus limits factors affecting population growth to food supply, competition, predation and disease. More available food can support survival and reproduction in a stated context. Competition for limited resources can reduce access to food, space or another resource. Predation removes prey organisms; disease can reduce survival or reproduction.
The size and direction of a population response depend on the organisms and conditions. A predator may also limit a competitor, and different prey may be available. Identify a direct link from the scenario rather than claiming every factor always causes the same population change.
Separate factor from evidence of effect
A graph showing a population decline identifies a change, not its cause. A causal explanation needs evidence connecting the factor with the population and should consider other changes. If a question states that food supply fell, explain a plausible route through survival or reproduction, but do not invent an unmeasured magnitude.
Use “may affect” when the prompt gives a possible factor without enough data to establish causation. The listed factors can influence growth rate even when the population is still increasing or decreasing.
Pause and explain
A population falls after food becomes scarce. What is a careful explanation?
Worked example
A disease spreads through a population and fewer individuals survive to reproduce. Identify the factor and explain its possible effect on growth.
Show the worked solution
- The stated factor is disease.
- Reduced survival to reproduction can reduce additions to the population.
Answer Disease may lower population growth because fewer individuals survive to reproduce. The effect size would need population data.
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.
A rabbit population has less available food after a drought. Identify the syllabus factor and give one possible effect.
Give me a hint
Name food supply and connect it to survival or reproduction.
Compare my reasoning
- Food supply is reduced.
- The rabbits may have lower survival or reproductive success.
The factor is food supply. Less food may reduce survival or reproduction and therefore lower the rate of population growth.
Look for these in your work
- Factor named
- Possible mechanism linked
More foxes are observed and a rabbit count later falls. What factor could be involved, and what evidence is needed before assigning the cause?
Give me a hint
Use the predator–prey link but avoid treating timing as proof.
Compare my reasoning
- Predation could affect rabbit numbers.
- Comparable counts and other factors should be considered.
Predation may be involved, but the observations do not by themselves prove it caused the decline. Comparable population data and information about food, disease and other changes are needed.
Look for these in your work
- Factor identified
- Causal limit stated
A disease reduces the number of breeding insects, but total insect count still rises. Can disease still affect population growth rate? Explain.
Give me a hint
A factor can slow growth without making the total decline.
Compare my reasoning
- Growth rate is the change over time.
- The population may still grow if additions exceed losses.
Yes. Disease may reduce the growth rate by lowering survival or reproduction even if births or recruitment still exceed losses and the total count continues to rise.
Look for these in your work
- Rate distinguished from direction
- Mechanism qualified
Common mistakes
- Adding unlisted factors as if required
- Assuming a factor always changes numbers in one direction
- Claiming a graph alone proves a cause
What can you explain now?
Which four factors are specified for population growth in this syllabus section?
Compare with the explanation
Food supply, competition, predation and disease
These are the listed factors.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Name the four factors listed in 19.4.4 and explain why a population trend alone does not prove which one caused it.
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.