CourseCourseQ BankQuestion BankDocsDocuments

C4.1.10—Community

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

Syllabus
First assessment 2025
Objective
C4.1.10
Level
HL

Exam analysis

Chance of appearing1%of analysed past papers
Latest appearanceMay 2021
Most common paperPaper1
Typical marks1

Common command terms

  • Identify
  • State
  • Suggest
  • Evaluate
  • Compare
  • Contrast
  • Describe
  • Explain

Scoring notes

Common mistake
Including abiotic factors in the definition of community instead of reserving them for ecosystem.

Recent exam appearances

May 2021Paper1 ["HL"] · TZ113[ 1 ]C4.1.10—Community
Practice this objective

Coverage 2021–2021 · Updated 16 Jul 2026

A community contains interacting populations

A community contains interacting populations.

A community is the populations of different species living and interacting in one area. Its composition and structure depend on abiotic conditions and biotic relationships.

list populations; define boundary; identify interaction and environmental filter.

A pond community includes algae, plants, fish, bacteria and invertebrates interacting under the pond’s chemistry and light.

A community is not the same as an ecosystem: an ecosystem also includes abiotic stores and flows.

Community exam focus

Assessment in practice

1 marks
How it is assessed

This objective is assessed through structured response, commonly using Identify / State / Suggest.

Command terms

Identify / State / Suggest / Evaluate / Compare / Contrast / Describe / Explain

What earns marks

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

Watch for

Including abiotic factors in the definition of community instead of reserving them for ecosystem.

Representative question

Question 1

[Maximum number: 3]

Compare and contrast the community structure within and outside the marine protected area.

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

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