# Explain how an invasive species can cause the competitive exclusion of a native species, and suggest one long-term consequence for ecosystem function.

> IB DP Biology Higher Level (2023 syllabus) — B4.2 Ecological niches · Explain · 4 marks

> Invasive species are non-native organisms introduced to a new environment, often in the absence of the predators and parasites that regulated their populations in their native range.

## Mark scheme (4 marks)

1. The invasive species occupies a niche that overlaps substantially with that of the native species, leading to direct competition for the same limiting resources (e.g. food, shelter, nesting sites).
2. The invasive species has a competitive advantage (e.g. absence of natural enemies, broader tolerance, faster reproduction), allowing it to acquire a greater share of resources, reducing the fitness and population size of the native species.
3. According to the competitive exclusion principle, two species cannot indefinitely occupy the same niche; the inferior competitor (native species) is eventually eliminated locally or driven to extinction.
4. Loss of the native species can disrupt ecosystem function; for example, if the native species was a pollinator, seed disperser, or keystone predator, its absence can destabilise food webs, reduce biodiversity, or alter nutrient cycling.

## Key terms

- [invasive species](https://www.gradenine.co.uk/glossary/invasive-species)
- [ecosystem function](https://www.gradenine.co.uk/glossary/ecosystem-function)

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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