Define indicator species.

Outline, with a named example, biological control of invasive species.

species sensitive to certain environmental conditions / species used to monitor environmental change / species used to determine environmental conditions

name of species to be controlled;
method of biological control with species name of predator/parasite/pathogen;

e.g. rabbits (introduced into Australia);
controlled by release of myxoma virus / myxomatosis (from South America);
Allow any other verifiable example. Reject cane toads as a biological control agent and other unsuccessful cases.

Part (b) was well answered by most.

Many invalid answers were given, including cane toads. Although the purpose of their release in Australia may have been biological control, they are now better classified as an invasive species in their own right, rather than a biological control. Other answers were too vague to score marks. With topics such as the biological control of invasive species, teachers are encouraged to give their students a real and paradigmatic example, rather than atypical or dubious ones. Some candidates even suggested that rats had been introduced to New Zealand to control invasive birds.