Lesson #3: Communities and Field Techniques

Question 1

Evaluating Communities

Answer 1

A community is formed by populations of different species interacting
in an ecosystem.

In order to determine the species that exist in an ecosystem,
ecologists use transects.

A transect is a method used to ensure that there is no bias in sample
selection. Samples must be used because ecosystems are often too
large to count all the member of each species.

Question 2

Transects

Answer 2

There are a number of types of transects including;

Line transect – a tape is laid down between two poles. Sampling can be
confined to organisms that touch the line or distance from the line can
be recorded.

Belt transect – sampling occurs between two lines separated by a fixed
distance.

Point transect – used in studies of bird populations, a point is randomly
selected and the researcher stands at that point and makes
observations within a certain radius.

Question 3

Quadrat sampling

Answer 3

A quadrat is a frame used to isolate a standard unit of area for study of the distribution of an organism over a large area.
The position of a quadrat can be chosen randomly or placed along a transect.
Quadrat sampling allows for estimation of population numbers, frequency and distribution.
The quadrat method is best used for plants.

Question 4

Associations between species

Answer 4

If the presence or absence of more than one species is recorded in every quadrat during sampling it is possible to test for associations between them.

To determine the association, a chi-squared test is performed.
The association can be;
Positive – two species occur together
Negative – if one is present the other is not
Independent – the two species do not affect each other.