Distribution of populations
Density
Density
of a population is the number of organisms in 1m2 found using a
quadrat of sides 1m.
Average
number of organisms inside the quadrat on ten throws is the density.
E.g.
|
Quadrat
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
8
|
9
|
10
|
|
Organisms
|
10
|
5
|
6
|
7
|
10
|
11
|
10
|
13
|
8
|
10
|
Total
number of organisms = 90
Average = 90/10
= Density
of 9 organisms per m 2
Species
Frequency
The
percentage frequency of a species is the percentage of sample units (usually
quadrats) in which the species occurs. The quadrat is thrown randomly and a
record is kept of what particular species is present or not. The number of
times a species is present is divided by the number of throws and the
percentage calculated.
E.g.
If a X occurs in 10 out of 25 quadrats thrown randomly, what is its frequency?
Answer:
10/25 * 100 = 40 %
References:
1. June Mitchelmore, Biology. Macmillan CXC revision guides 2005.
2. CXC, Biology Resource Materials for Teachers, Book 5, 1997.
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