# Explain why invasive alien species are considered one of the greatest threats to biodiversity, with reference to the ecological mechanisms by which they reduce native species populations.

> IB DP Biology Higher Level (2023 syllabus) — A4.2 Conservation of biodiversity · Explain · 4 marks

## Mark scheme (4 marks)

1. Invasive species often lack natural predators, parasites or pathogens in the new environment, allowing unchecked population growth.
2. Invasive species outcompete native species for limiting resources such as food, space or light, reducing native species' reproductive success or survival.
3. Invasive species can act as novel predators or herbivores, causing disproportionate mortality in native populations that have not evolved defences against them.
4. Invasive species can introduce novel diseases or parasites to which native species have no immunity, or hybridise with closely related natives, reducing genetic integrity and potentially leading to extinction.

## Key terms

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

## 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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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-invasive-alien-species-are-f862afdf) · Published by Druglandscape Ltd.