C4.1 Populations and communities

Populations and communities describe abundance, sampling, growth limits, species interactions and trophic controls that shape ecological patterns across habitats and ecosystems.

What you’ll learn

18 learning objectives

Choose one objective for a focused lesson, or study the complete topic.

Exam analysis

An aggregate view of how the complete C4.1 Populations and communities appears across past papers.

Chance of appearing42%of analysed past papers

Latest appearanceNovember 2025

Most common paperPaper3

Most tested objectives

C4.1.13—Endemic vs. invasive species15 questions
C4.1.11—Interspecific relationships14 questions
C4.1.12—Mutualism as interspecific relationship12 questions

Common question formats

Definition or recall
Structured response
Data analysis
Experimental design
Evaluation
Diagram interpretation
Calculation
Process explanation
Comparison

Exam question appearances

November 2025Paper2 ["HL"] · TZ15(a)[ 2 ]C4.1.5—Carrying capacity

November 2025Paper1A ["HL"] · TZ336[ 1 ]C4.1.17—Top-down vs. bottom-up control

November 2025Paper1A ["HL"] · TZ136[ 1 ]C4.1.12—Mutualism as interspecific relationship

November 2025Paper2 ["HL"] · TZ31(c)[ 2 ]C4.1.2—Population size estimation

May 2025Paper2 ["HL"] · TZ35(b)[ 2 ]C4.1.11—Interspecific relationships

Practice this topic

19 original exam-style questions based on the patterns above.

Coverage 2012–2025 · Updated 16 Jul 2026