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Lab 4: Isopod Natural Selection – Figure Instructions
Follow the steps below to create your frequency distribution graphs for your assignment. Your graphs and
figure captions MUST be computer generated (using Excel or some other graphing software).
I. Your TA will email you the raw data collected during your lab.
II. Organizing your data:
The example here is only for ONE trait and an original sample size of 30 isopods. You
will have to deal with 2 traits (length and speed) and a much larger original population
(because you are using the pooled class data).
You should make TWO separate tables (one for body length and one for speed) to
make it easier to visualize and manipulate your data.
Your tables should look something like Sample Data Table I. I have used “weight”
as my trait – you will be using “length” and “speed” as your traits.
III. Determine an appropriate value range for your phenotypic classes:
Phenotypic classes can be used to categorize our measured independent variables into
specific ranges.
To find an appropriate value range for each phenotypic class, I can divide my
maximum value by the number of phenotypic classes that I would like to plot.
In my example, the maximum weight value for the entire population is 0.011g.
I’d like to plot a total 6 phenotypic classes. You should probably aim for about
the same number of phenotypic classes (i.e., 6 classes) to divide your data into.
…So 0.011g/6 = 0.0018333g….You should round this number up or down to
make it a bit easier to work with. After looking at the rest of my data, I think
I’ll use a range of 0.002g. The range should be the same for all of your
phenotypic classes. The phenotypic classes for my example are shown in
Sample Data Table II.
IV. Counting the number of individuals in each phenotypic class:
Count how many individuals of the total population (victims +
survivors) and survivors fall into each of the classes/ranges as
shown in Sample Data Table III.
Victim (V)
Survivor (S)
Weight (g)
S 0.001
S 0.0015
S 0.002
S 0.002
S 0.0025
S 0.003
S 0.003
S 0.0035
S 0.004
S 0.004
S 0.0045
S 0.005
S 0.005
S 0.005
S 0.0055
S 0.007
S 0.008
S 0.0085
V 0.003
V 0.0045
V 0.0055
V 0.006
V 0.006
V 0.0065
V 0.0075
V 0.008
V 0.009
V 0.0095
V 0.01
V 0.011
Sample Data Table I.
1 0.0000-0.0020
2 0.0021-0.0040
3 0.0041-0.0060
4 0.0061-0.0080
5 0.0081-0.0100
6 0.0110-0.0120
Wt Range (g)
Phenotypic
Class
Sample Data Table II.
1 0.0000-0.0020 4 4
2 0.0021-0.0040 7 6
3 0.0041-0.0060 9 5
4 0.0061-0.0080 5 2
5 0.0081-0.0100 4 1
6 0.0110-0.0120 1 0
Wt Range (g)
Phenotypic
Class
Total Population
(before predation)
Survivors (after
predation)
Sample Data Table III.
