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C4.1.9—Competition vs. cooperation

Competition versus cooperation explains how ecological evidence links organisms, resources and interactions to population size, distribution or community structure in a habitat.

Syllabus
First assessment 2025
Objective
C4.1.9
Level
HL

Exam analysis

Chance of appearing2%of analysed past papers
Latest appearanceMay 2014
Most common paperPaper3
Typical marks1–2

Common command terms

  • Discuss
  • State
  • Describe
  • Outline
  • Suggest
  • Compare
  • Contrast

Scoring notes

Common mistake
Describing overlapping niches without explaining that one competitor is displaced or restricted.

Recent exam appearances

May 2014Paper3 ["HL"] · TZ24(e)[ 1 ]C4.1.9—Competition vs. cooperation
November 2012Paper3 ["HL"] · TZ0E1(d)[ 2 ]C4.1.9—Competition vs. cooperation
Practice this objective

Coverage 2012–2014 · Updated 16 Jul 2026

Competition occurs when organisms share a limited resource

Competition occurs when organisms share a limited resource.

Competition lowers access to food, space, light or mates when demands overlap. Cooperation can instead improve group performance when individuals gain from working together.

name shared resource; show effect on each participant; include cost and context.

Two plant species competing for light may each grow less tall when planted together than when grown alone.

Competition is not defined by aggression; it is a reduction in resource access caused by overlap.

Competition vs. cooperation

Assessment in practice

1–2 marks
How it is assessed

This objective is assessed through structured response, commonly using Discuss / State / Describe.

Command terms

Discuss / State / Describe / Outline / Suggest / Compare / Contrast

What earns marks

Build the answer around this relationship: Competition versus cooperation must be linked to the correct ecological unit, method or species interaction.

Watch for

Describing overlapping niches without explaining that one competitor is displaced or restricted.

Representative question

Question 1

[Maximum number: 2]

Compare and contrast the frequency of monopoly and fighting when there is a change from two trays to one tray of food.

Populations and Communities

  • A population is one species in an area; a community is all interacting populations there.
  • Estimate abundance with unbiased sampling: quadrats for sessile organisms and capture–mark–release–recapture for mobile animals, checking each method’s assumptions.
  • Density-dependent competition, predation, disease and waste create negative feedback around carrying capacity; exponential growth slows into a sigmoid curve as limits strengthen.
  • Classify interspecific relationships by costs and benefits: predation, herbivory, competition, mutualism, parasitism and pathogenicity.
  • Invasive species may escape controls and displace endemic species. Removal experiments can reveal competition and fundamental versus realized niches.
  • Chi-squared tests assess species association from observed and expected quadrat counts.
  • Predator peaks usually lag prey peaks; top-down control begins with consumers, while bottom-up control begins with resources or producers.

Concept essentials

  • Competition versus cooperation must be linked to the correct ecological unit, method or species interaction.
  • The evidence for competition versus cooperation depends on measurable abundance, distribution, survival or resource patterns.
  • Competition versus cooperation is clearest when cause, ecological process and population outcome are kept distinct.
  • Field or graph evidence for competition versus cooperation needs biological interpretation, not values alone.
ConceptIB Biology HL