Non-indigenous speciesSpec 9.9
In short
A non-indigenous species is one brought, deliberately or accidentally, into an area where it does not naturally live. It may have no natural predators, so its population grows quickly, and it can compete with, eat or spread disease to native species. Biodiversity falls as native species decline, although some are introduced for food or to control pests.
A non-indigenous species (also called an introduced or invasive species) is one that has been brought, deliberately or accidentally, into an area where it does not naturally live.
- It may have no natural predators in the new area, so its population can grow quickly.
- It can compete with native species for food and space, so native species decline.
- It may eat native species or carry diseases that native species cannot resist.
- The result is that biodiversity falls, as native species decline or die out.
Positive effects are possible. Some non-indigenous species are introduced to provide food or other products, or to control pests. But the risk to native species means that introductions need careful control.
Written and checked against the Edexcel GCSE Combined Science (1SC0) specification · Updated October 2026
Frequently asked questions
What is eutrophication and what causes it?
Eutrophication is caused by too many nutrients, such as nitrates from fertilisers or sewage, running into lakes and rivers. Algae grow quickly and block light, so plants below die. Decomposer bacteria feed on the dead material and use up the oxygen for aerobic respiration, so fish and other aquatic animals die and biodiversity falls.
Why is biodiversity important to ecosystems?
Biodiversity is important because ecosystems with high biodiversity are more stable. Species depend on each other, so the loss of one is less likely to cause others to fail. Biodiversity also gives humans food, materials and medicines, and species help maintain the conditions we depend on, such as pollination of crops and cycling of materials.
What are the advantages and disadvantages of fish farming?
Fish farming provides a reliable food supply, reduces overfishing of wild stocks, and lets conditions be controlled so fish grow quickly. However, waste and uneaten food pollute water and can cause eutrophication, disease and parasites can spread to wild fish, and escaped fish may compete or interbreed with wild fish, reducing their genetic variety.
All 4 questions on Human impacts, biodiversity and food security
