Explain how an invasive species can alter the realised niche of a native species within a community.

IB DP Biology Standard Level (2023 syllabus) — B4.2 Ecological niches · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

An invasive species can alter the realised niche of a native species by competing for the same resources. The invasive species uses the same food, shelter or nesting sites, which increases competition. The native species is then forced to use a smaller or different set of resources, so its realised niche becomes smaller or shifts. If it cannot adapt or shift its niche, its population may decline or it may be locally extinct, showing competitive exclusion.

Examiner tips

Use the definition of realised niche first
Show the competition mechanism clearly
Explain the consequence for the native species
Mention competitive exclusion if the native cannot adapt

Common mistakes

Confusing realised niche with fundamental niche
Failing to mention the resource overlap
Not linking the competition to a change in the niche

Mark scheme (4 marks)

The realised niche is the actual set of conditions and resources a species uses when biotic interactions (such as competition) are present.
An invasive species competes with the native species for overlapping resources (e.g. food, shelter, nesting sites).
Increased competition forces the native species to use a smaller or different set of resources, reducing / shifting its realised niche.
If the native species cannot adapt or shift its niche sufficiently, it may face population decline or local extinction, demonstrating competitive exclusion.

Key terms in this question

invasive species · realised niche