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C4.1.13—Endemic vs. invasive species

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

Syllabus
First assessment 2025
Objective
C4.1.13
Level
HL

Exam analysis

Chance of appearing10%of analysed past papers
Latest appearanceNovember 2023
Most common paperPaper3
Typical marks2–6

Common command terms

  • State
  • Discuss
  • Suggest
  • Identify
  • Outline
  • Describe
  • Explain
  • Evaluate
  • Define
  • Analyse

Scoring notes

Common mistake
Naming an alien species without explaining competition, predation, disease or biodiversity impact.

Recent exam appearances

November 2023Paper3 ["HL"] · TZ220[ 6 ]C4.1.13—Endemic vs. invasive species
May 2023Paper3 ["HL"] · TZ116(a)[ 2 ]C4.1.13—Endemic vs. invasive species
November 2020Paper3 ["HL"] · TZ015(c)[ 1 ]C4.1.13—Endemic vs. invasive species
May 2019Paper3 ["HL"] · TZ214(c)[ 2 ]C4.1.13—Endemic vs. invasive species
November 2018Paper3 ["HL"] · TZ013(d)[ 2 ]C4.1.13—Endemic vs. invasive species

Coverage 2014–2023 · Updated 16 Jul 2026

Introduced Does Not Automatically Mean Invasive

Term Meaning
native occurs in an area without human introduction
endemic native and restricted to a particular geographic area
alien / introduced moved outside its native range by human activity
invasive introduced, spreads rapidly and causes ecological harm

In Britain, introduced grey squirrels can digest acorns earlier and use a wider diet than red squirrels. Their niches overlap, so more grey squirrels compete for hazelnuts, pine cones and habitat while also carrying squirrelpox that strongly affects red squirrels.

Escape from predators or pathogens, rapid reproduction and broad resource use can expand an introduced species' realized niche. The native competitor may then lose resources and occupy a smaller realized niche.

Explain Community Change with Signs, Mechanism and Evidence

Question What a strong explanation identifies
Who interacts? populations and whether each gains or loses
What is transferred or limited? food, habitat, nutrients, protection, disease or a chemical
Where does change begin? individual pair, predator level, producer/resource level or introduced species
How does it propagate? competition, feedback, trophic cascade or niche restriction
What supports causation? manipulation, control, replication and a predicted response
What supports association? representative sampling, expected counts and a statistical decision

Use observations to find a pattern, statistics to judge whether it is unlikely under a null model, and experiments or field manipulations to test the proposed mechanism.

Community structure emerges from many population interactions. Naming a relationship is only the start; explanation requires its mechanism, direction of effect, feedback through the network and the limits of the evidence.

Endemic vs. invasive species

[ 6 ]

Discuss, giving an example, the possible effects of the introduction of an alien species into an ecosystem.

Concept essentials

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