Abundance and Distribution

Biology Unit 4

Abundance and Distribution Experiment

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Biology Unit 4
Revision Notes
Topic 5: On the wild side
11. Describe how to carry out a study on the ecology
of a habitat to produce valid and reliable data
(including the use of quadrats and transects to assess
abundance and distribution of organisms and the
measurement of abiotic factors, eg solar energy
input, climate, topography, oxygen availability and
edaphic factors).
How can we practically investigate where organisms live (distribution) and how many there are
(abundance)? The answer depends on what kind of habitat we are in and what we want to find out.
If there appears to be a change across the area, a transect is the preferred method.
If two areas appeared different and we want to compare them, we could take random
samples within each area.
In either case, the usual methods to estimate abundance would be:
Either count the individuals in a quadrat ­ this is not easily done with many plants, such as
grasses, but quite possible with organisms such as limpets.
Or find the percentage cover of each species ­ this is the most common method with plants.
These estimates are best made using a quadrat that is divided up into smaller squares and
counting the number of squares or part squares occupied by each species in turn.
In order to answer questions about the distribution and abundance patterns you have found in the
habitat you are studying, you will also need to measure a number of factors:
Abiotic factor Measurement technique
Solar energy input Use a light metre.
climate Information about rainfall and temperature can be obtained from published
Topography Topographical surveys measure the shape of the land.
Oxygen Availability Use an oxygen probe
Edaphic pH Use a pH probe or soil pH kit
Minerals Gardeners test kits can test the levels of important nutrients such as NPK
Water Soil sample can be weighed, dried slowly in an oven and reweighed to give the
mass of water.

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Biology Unit 4
Revision Notes
Organic The dry soil sample can be weighed, burnt in a crucible and reweighed. Any
matter organic matter is burnt off, which accounts for any difference in mass.
Soil Soil texture charts can be used to assess if the soil is mainly clay, silt or sand.
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