Outline changes in species diversity during primary succession.

Describe a method used to estimate the size of a mouse population.

(i)  Describe the environmental impact of a named invasive alien species.

(ii)  State an example of biological control of the invasive alien species named above.

few colonizing species establish themselves in harsh conditions/volcanic ash/ sand/areas devoided of life/bare rock;
e.g. moss/lichens/marram grass/bacteria;
more organic material accumulates/soil develops;
increasing species diversity;

capture-mark-release-recapture / OWTTE;
mice are trapped in a given area, counted, marked and released (without damage);
a second capture is made in the same area and marked and unmarked mice counted;
use of Lincoln index /

(accept valid alternatives for equation)
assumes marked mice randomly distributed / other valid comment on limitations;

(i)  name of invasive alien species and impact
e.g.:
water hyacinth is an invasive plant with explosive growth that blocks waterways/kills other aquatic organisms

(ii)  example of biological control organism e.g.: weevils/moths/fungus/mites have been used to control the water hyacinth growth Do not award the mark if the example of the control does not correspond to the species named. 

Most candidates gained all the marks in part (a), although many answers demonstrated a poor understanding of primary succession and did not relate to an increase in species diversity.

The majority of candidates answered part (b) in terms of recapturing marked mice, but many answers missed out on a few details, mainly counting the mice; a limited number of candidates confused methods, mainly with quadrats or diversity indices and rare were the candidates commenting of methodological details or limitations of the method.

Part (c) was usually well answered, but some candidates lost marks because of imprecise organism name (for the invasive species and/or the control method), not stating the impact, or stating an unrelated control method with the named species; most candidates used textbook examples, but there were also valid regional examples and a certain number of plausible "creative" examples that were dismissed by examiners after some time wasted searching for their validity.