Dr. Houghton – Environmental Science
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Predator – Prey Simulation
Purpose:
 Simulate and analyze the interactions between a predator population of coyotes and a
prey population of mice.
 Organize and graph data from the simulation, predicting future populations over
several generations
 Compare simulation results to data taken from nature
Background
Population dynamics is influenced by biotic and abiotic factors. Abiotic factors include climate,
soil, water, sunlight and air. Biotic factors include predation, disease, birth rate, and mortality
rate. In predation members of one species feed directly on another species. In this interaction, the
predator benefits and at the individual level the prey is clearly harmed. At the population level
the prey species can benefit because predators help to reduce competition for food amongst the
prey species and also sick and aged animals can be removed. Some species that interact as
predator and prey undergo cyclic changes in their numbers, with sharp increases and periodic
crashes. For example the snowshoe hare and its predator the Canadian lynx show this cycle very
clearly. The Lynx population rises, eats the hares which experience a decline in numbers. Then
there are few hares to eat so the lynx numbers decline. This is called top-down population
control. The other theory is that the numbers of hares determine how many lynxes there will be
and that factors that determine hare population are more important than the number of lynxes.
This is called bottom-up population control. In reality it is probably a combination of both.
Materials:
1) 1 small bowl – representing a field (habitat)
2) 100 beans - representing a population of mice (prey)
3) 1 spoon – representing - a population of coyotes (predators)
4) 4 colored pencils – Blue (coyote line on graph), Red (mice), Green (added pressure on
the predator population), Black (fire wipes out prey population)
Rules:
1. Surviving mice of each generation always double in number (if you have 5 left, add 5
more).
2. There must be at least 10 mice at the beginning of each generation (if there are not 10
left, add mice via immigration up to the number 10).
3. There must be at least one coyote at the beginning of each generation, by immigration if
necessary (if all the coyote die, none caught 5 mice, then add 1 via immigration).
4. The maximum number of mice is one hundred (if you go over 100, take mice out until the
number reaches 100 via starvation, disease, and old age).
5. Each coyote must catch at least 5 mice to survive (if you do not get 5 beans in the spoon,
that coyote dies of starvation, the population of coyotes is reduced in the next
generation).
6. Each coyote must catch at least 5 mice to reproduce. (1 offspring per 5 mice, if the coyote
doesn’t catch 5 mice it dies, if it does, it lives and one coyote is added to the next
generation via reproduction).
Dr. Houghton – Environmental Science
Name:
Date:
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Methods:
1. Start with 10 mice (beans) and 1 coyote (spoon) and 1 field (bowl).
2. Randomly place 10 mice in the field (drop 10 beans in the bowl, notice if the beans are
clumped, which is not uncommon among species, they are more likely to be eaten in
larger numbers).
3. Record the starting number of mice (10) and coyotes (1) on the data table.
4. Make 1 pass through the field with the spoon catching as many mice as possible
(remember, if the coyote doesn’t catch at least 5 mice, the coyote starves to death, if he
catches 5-9 mice, he lives and adds one young to the next generation, if he catches 10
mice he adds 2 young to the next generation).
5. Add more coyotes and mice according to the rules (you must always have at least 1
coyote per generation, even if you add one via immigration, you must also always have at
least 10 mice, even if you add some via immigration).
6. Record the starting number of mice and coyotes on the data table.
7. Repeat the predation, with each coyote representing 1 pass through the field. For example
if you have 3 coyotes, then you make three passes through the field with each pass
representing each coyote.
8. Continue to record the starting number of mice and coyotes on the data table until the
mice and coyote have passed through 15 generations.
9. Use a piece of graph paper to make one graph. On the x-axis of the graph put “Time in
generations” (Generation 1, 2, 3 etc). On the left side of the y-axis put number of mice
(starting number) and on the opposite side (the right side) label the y-axis number of
coyotes. The range on both sides of the y-axis will be different, but we want the
information for both animals on one graph so that we can see the relationship. Draw the
line for coyotes in blue and the line for mice in red.
Table 1. The number of mice (beans) and coyote (passes with the spoon) present at the
beginning of each generation.
Generation #
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Mice (starting number)
Coyote (starting number)
Dr. Houghton – Environmental Science
Name:
Date:
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Analysis
1. What do you predict would happen to the prey cycle if some coyotes died of disease or
were killed by humans? Explain your answer and on your graph use a green pencil to
show your prediction. Start your prediction after your last cycle on the graph and
continue three more generations.
2. What would happen to the coyotes on your graph if fire killed the prey population?
Explain and show on the graph with black pencil how the graph would change. Start after
your last cycle and continue three generations.
3. How would it matter at what point in your simulation such disturbances occurred?
4. What is carrying capacity? What happens to a population that overshoots its carrying
capacity?
Dr. Houghton – Environmental Science
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Read the article on the Moose of Isle Royal (pg . 83 of your textbook)
5. How does the predator population vary when the prey numbers change?
6. Are the populations in phase with one another? Explain.
7. Are the population curves for the moose and the wolves similar in shape? How do the
curves differ from one another?
8. Describe how your simulation data are similar or different from the Isle Royal data. If
your results are similar, explain what could account for this occurrence. If your results
from your simulation are very different explain what could account for this.
Dr. Houghton – Environmental Science
Name:
Date:
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More Questions about your lab
9. In this investigation you examined only the simple relationship between changing prey
populations and the number of predators. What other factors affect the number of prey
and predators in a population?
10. Describe an example of a predator being used to control a prey population that is
considered a pest. Explain scientifically why you think this is a good idea or not.
Dr. Houghton – Environmental Science
Name:
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Conclusion - follow the conclusion protocol below
The following information is very general and should be used as a guide when writing out your
conclusions. It is important to keep in mind that with any research there may be special
procedures/observations and other relevant information that may not be listed in the following guidelines,
but will be necessary to be included in a conclusion.
3 section conclusions
Often, it is easiest to use a 3-section system for writing conclusions. We will use the following format in
Earth Science. You may need to use more than 3 paragraphs to conclude your work. This is a general
outline of how to write a scientific conclusion.
First “section”: Answers the question: What did you do?
1) Briefly restate the purpose
2) Summarize the experiment or your observations – do not re-write the procedure
Second “section”: Answers the question: What happened?
1) Describe your data and observations. Do not simply repeat your results – only write up your most
important results in the conclusion – summarize the most important details.
2) Describe the most relevant class results, observations, or outside sources when applicable
3) Compare and contrast your data with the class and other data sources
Third “section”: Answers the question: Why?
1) Why did your data look the way it did?
a. What problems/errors did you and/or your classmates encounter that may have skewed
the results
b. What key processes/principles were highlighted by the data? These processes/principles
are often addressed in the purpose and introduction sections of your report.
2) Readdress the purpose – did you succeed in meeting the objectives of the lab? Do not write: We
met our objectives. Instead, write “The objective of the study was to … we were able or not able
to …” If the purpose of the lab was to answer a question such as; can minerals be identified by
their density? Be sure to answer that question.
3) Include other relevant observations such as things you found challenging about the lab, i.e. time
constraints, lab equipment, etc. Don’t write “I thought it was challenging when we…, instead write,
“The measuring device was broken”. If you encountered difficulties in the experiment, what were
their sources? How might they be avoided in future experiments?
4) End with a concluding statement, similar to an abstract, which summarizes the significant aspects
and results of your experiment. It should tell the reader why the experiment is significant and what
implications its results have for your field of study. If your experiment confirms or contradicts an
established principle or theory, this should be stated clearly.