Evaluate the use of indicator species in monitoring environmental changes.

indicator species sensitive to/need specific environmental conditions to survive;
monitor population size of indicator species over time;
biotic index can be calculated;
low overall score when abundance of tolerant species / lack of indicator species / vice versa;
represent summation of factors/overall assessment of environmental conditions;
time consuming / species not easy to identify (need keys) / species may not be present for other reasons such as season / another disadvantage;
methodology is simple / minimum equipment needed;
needs a reference study/guide to compare;
example of variable e.g. oxygen level / temperature / heavy metals / sulphur dioxide in air / other;
example of appropriate indicator species e.g. Tubifex to heavy metals / Chironomis to low oxygen levels / lichens to sulphur dioxide / other;

This question was very poorly answered by the majority of candidates with many not actually knowing what an indicator species was.  The answers were very general, lacking in any detail. Some wrote about migration and changes in weather. Those that knew an indicator species did not link it with a specific environmental factor.