Name
Date
Teacher
Assessment type: Extended response
Task: Natural selection modelled
In this task you will simulate natural selection by means of a model and observe the
consequences of a selective force.
Evolution by natural selection is a slow process which takes place over a long period of
time with many generations involved. This makes direct observation difficult, however the
process can be simulated by means of a model as you will discover in the Beetle card
activity.
Materials

30 beetle cards or 30 rectangles of paper (10 marked red, 10 marked blue and 10
marked yellow to represent the beetles)

special die or a regular die with two numbers allocated to each colour (eg 1 and 3
equal red, 2 and 4 equal blue, 5 and 6 equal yellow).
Beetle card activity
Starting with a population of 30 beetles, represented using cards, it is possible to
demonstrate the consequence of a selective force over several generations.
There are three varieties of beetle colour in the population.
Read the following information, assumptions and instructions carefully, before you begin
this activity.
Assumptions
There are 30 beetles in the original population, 10 of each colour.
Each year, beetles mate at random and produce one offspring per pair.
The colour of the offspring is determined by these rules:

red x red equals red

red x blue equals 50% chance of red, 50% chance of blue

yellow x yellow equals yellow

yellow x red equals 50% chance of yellow, 50% chance of red

blue x blue equals blue

blue x yellow equals 50% chance of blue, 50% chance of yellow.
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After mating, a predator kills one third of the total population each year.
There are no other causes of death and there is no migration.
Instructions

Set up a population using 30 beetle cards, 10 of each colour and divide these
randomly into pairs.

To represent the offspring, add one card to each pair using the rules on the previous
page.

Where the offspring colour is 50 : 50, use the die numbers to decide the colour.

When blue x red or blue x yellow cross, let even numbers represent blue offspring.

When red x yellow cross, let even numbers represent red offspring.

Simulate predation by rolling the die and remove a beetle matching the colour rolled.
Repeat this until 15 beetles are removed from the population.

Record the colours of the remaining/surviving group in the table below.

Repeat the procedure of mating and predation until you have simulated 10 years.
Table of results
Year
Red
Blue
Yellow
Total
1
10
10
10
30
2
30
3
30
4
30
5
30
6
30
7
30
8
30
9
30
10
30
You will need to complete the table above before you answer the following questions.
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Questions
1.
What changes to the beetle population were observed during successive years?
2.
What selective pressure caused these changes?
3.
Examine the kit die and suggest the assumed predation rate for this model as a ratio.
4.
Under what circumstances in nature might a predator feed on red beetles more often
than on blue or yellow beetles?
5.
Does the chance of survival of any individual beetle vary from year to year? Explain
your answer.
6.
If the intensity of predation against beetles was altered to 4 red : 2 blue : 0 yellow,
predict what changes you would expect in the results.
7.
What assumptions given in this model would need to be altered for the population to
become homogenous red?
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8.
a)
If the intensity of predation against the beetles was 1 red : 1 blue : 1 yellow,
would there be any change in the ratio of colours from one year to the next?
Explain.
b)
Would this be an example of natural selection?
Additional question
9.
Myxomatosis, a viral disease of rabbits, was introduced
into Australia in 1950 to control the rabbit population.
The rabbit population declined rapidly as a result of this
disease. However, in recent times the rabbit population
has recovered.
From your knowledge of evolution and natural selection
explain, in a series of steps, how the rabbit population
was able to recover from this deadly disease.
Adapted from Web of Life Students Manual (11th Edition) with the permission of the Australian Academy of Science.
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