Download Camouflage: A Model of Natural Selection

Camouflage: A Model of Natural Selection
Introduction
Natural selection operates on the principle of survival of the fittest. Fitness can be defined as
the suitability of an organism to a given environment. One might ask if one set of features
favourable in one environment might prove unfavourable in another environment. In this lab you
will test the following hypothesis: If survival is related to specific characteristics in a given
environment, then altering the environment will decrease the survival rate. Once you have
formed a conclusion to this hypothesis and how it relates to the adaptation of camouflage, you
will apply this information to the peppered moths of Manchester, England. You will predict the
direction of an adaptive shift and the resulting gene frequencies.
In this experimental model, the features studied will be the adaptation of camouflage in two
very different environments. You will act as the predator and your prey will be two types of
paper circles, one with a plain colour and the other with a printed pattern. Their environment
will be either a sheet of plain coloured paper (butcher paper) or a sheet of paper with a printed
pattern (newspaper want ads).
Materials and Equipment: per team of two students:
1 page of newspaper want ads
1 sheet of butcher paper of the same size
Envelope with 100 each of butcher paper circles and want ads circles cut with a paper punch
Suitable timer
Procedure
Work with a partner. One of you must always be the predator while the other will supervise
the experiment so as to not introduce an uncontrolled variable. The experimenter’s job is to
spread out the prey (paper circles) randomly for each trial making sure they are not piled up
and that they thoroughly cover the sheet of paper. Also the experimenter will time each trial
and record the data.
The predator’s rile here is to locate (count them, do not pick them up) as many prey of a
particular colour as possible in 10 second trials. With the predator standing with his/her back
to the hunting area, the experimenter will give a signal, the predator then quickly turns around
and begins to spot and count the plain circles until the experimenter tells him to stop (at 10
seconds). The predator calls out his total. On the next trial, the predator attempts to spot and
count just the printed circles for 10 seconds. These trials are each repeated two more times
and then the environmental background will be changed to a printed pattern. Again three trials
will be made attempting to spot and count each type of circle in 10 seconds this time starting
with the printed circles first.
Important Notes:
1. The particular predator, in this problem, only hunts for prey just before sunrise and just
after sunset, therefore, the light in the room will be very subdued.
2. After each trial the experimenter should rearrange all paper circles on the paper to make
sure the population is randomly distributed. When all data is recorded compute your
average and report the results to your teacher.
3. Before you begin make a prediction.
Prediction:
State in the hypothesis format (If…….. then …….)
Which circle on which background will get the lowest count? Why? (2 marks)
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Observations: (3 marks)
Trial#
1
2
3
Team
Average
Class
Average
%
died
%
survived
%
advantage
Plain background
# plain circles # printed circles
Printed Background
# plain circles # printed circles
% advantage = % survived in population with most survivors
% survived in population with less survivors
Only fill in the % advantage in the space for the population with the most survivors.
What other observations did you make as a predator?
What other observations did you make as an observer?
(2marks)
Questions:
1. Darwin observed that there was great variability within a species. How did we illustrate this
observation in our activity? (1 mark) _________________________________________
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2. In natural selection, selective pressure is the factor that reduces the frequency of a
particular phenotype more than another phenotype. In this model the phenotypes are plain
and printed. What was the selective pressure on this population?(1 mark) ______________
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3. Some circles went uncounted and thus escaped predation. Why do some escape? (1 mark)
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4. Is survival equal for each phenotype? Explain why or why not. (2 marks) _______________
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5. Darwin believed that the characteristics that contribute to superior survival will increase in
frequency. If this experiment were to go on for generations, which phenotype do you think
will become dominant? Why?
(1 mark) _____________________________________________________________
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Discussion: (4 marks)
What was your prediction and was it correct?
How is this related to the peppered moth in England?
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