Cambridge International A Level Biology Revision Guide

Chapter 18: Biodiversity, classification and conservation
QUESTION
Figure 18.5 These snails all belong to the same species,
Cepaea nemoralis. The differences between them are the
result of different alleles for shell colour and banding.
Assessing species diversity
Collecting organisms and making
species lists
Imagine you are in an ecosystem like that in Figure 18.6.
The most obvious species are the large plants and maybe
some of the larger animals, particularly bird species. The
first task when assessing species diversity is to identify and
catalogue the types of organism and build a species list.
18.2 a The snails in Figure 18.5 look very different from
one another. Explain why they are all members of
the same species.
b Explain the term genetic diversity.
c Suggest and explain the effect of the following
on genetic diversity: artificial selection (selective
breeding), habitat destruction and the release of
farmed fish into the wild.
Biologists use identification keys to name the
organisms that they find. There are different forms of key
– some have drawings or photographs with identifications;
others ask a series of questions. The most common of these
is a dichotomous key; in your own fieldwork you may use
one of these to identify some plant species. Identification
requires good skills of observation.
At first, it is a good idea to do a timed search
throughout the area you are studying to see how many
species you can collect and then identify. If you cannot
identify particular species, take photographs of them
and name them as species A, species B, and so on. Some
animals will be hard to find and collect, especially small
ones such as tiny beetles. A pooter is a simple piece of
apparatus that is used to collect these animals (Figure
18.7). Breathing air into the mouth sucks up small animals
into a plastic container. They can then be removed and
studied and identified using a hand lens and then returned
to their habitat.
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Figure 18.6 How would you start to investigate and catalogue
the biodiversity of an area like this?
Figure 18.7 This ecologist is using a pooter to collect small
animals from high in the tree canopy in a Yungas forest, along the
eastern slopes of the Andes in Argentina.