State one example of the accidental release of an alien species that has had a significant impact on an ecosystem.

Discuss the impact of alien species on ecosystems.

Answer needs to be specific giving name of organism, where it was released and where it came from. If unsure, check answer with Google, but examples must be accidental releases.

e.g. zebra mussel (Dreissena polymorpha) originally from Russia/Caspian carried in ships’ ballast water and introduced into Great Lakes / rats accidentally introduced to mainland of New Zealand from visiting ships / Africanized honey bees introduced to Brazil (“killer bees”)

inter-specific competition/alien species have characteristics that may enable them to out-compete native species;
lack of predators may allow alien species to reproduce more rapidly;
alien species may utilize areas or resources that native species cannot;
predation by invasive species can cause loss of biodiversity;
can lead to species extinction, especially of endangered species;
alien species may introduce new diseases;
use of alien species for biological control can be ineffective or negative;

This was a difficult question, and many examples given were not accidental releases of alien species. Where correct examples were given, they were not accompanied by enough detail to gain the mark.

The majority of candidates could gain one or two marks in this question, but some answers were generalised and vague. This was a “discuss” question, so candidates should have been able to expand their answers beyond a reference to competition.