Cambridge International A Level Biology Revision Guide

Cambridge International A Level Biology
Answers to self-assessment questions
compete with the existing herbivores in
the ecosystem. If they are plants, they will
compete with existing species for resources
such as light, minerals, water and space.
They may introduce disease that the existing
species have not experienced so have no
immunity. They will compete with native
species for space and breeding sites, etc.
They may change the environment so that
native species cannot survive.
b Find two areas: one invaded by an alien
species and one that has not. Carry out
random sampling. Count the number of
different species / make a species list. Record
the abundance of the different species.
Use an appropriate method, e.g. species
frequency, species density, percentage cover
or an abundance scale. Use Simpson’s Index
of Diversity to compare the different areas. If
this is repeated in several places, where the
alien species is present then Spearman’s rank
correlation coefficient could be calculated
to see if there is a correlation between the
abundance of the alien species present in the
areas sampled and the index of diversity for
each area.
Cambridge International AS and A Level Biology © Cambridge University Press 2014