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Biology
Call of the Wild
EACH GROUP
calculator
computer
100 beans, individual
pinto
spoon, plastic
plate, paper
ABOUT THIS LESSON
T
his lesson is designed to introduce the concept
of predator/prey population cycles. One of the
main points of this activity is to help students
see that population sizes of predators and their prey
fluctuate according to the same pattern, but one is
offset in relation to the other. The data collected in this
activity can be used as a reference point for terms used
during presentations on community and ecosystem
ecology.
T E A C H E R
MATERIALS AND RESOURCES
P A G E S
Investigating Predator/Prey
Relationships
OBJECTIVES
Students will:
• Investigate how a wolf and an elk population
change over time in response to the other’s
presence and how each population relates to the
other
• Participate in a guided inquiry activity using a
computer simulation that is used to test studentcreated questions about the population cycles
of sheep and wolves under several populationlimiting factors
LEVEL
Biology
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i
Biology – Call of the Wild
NEXT GENERATION SCIENCE STANDARDS
COMMON CORE STATE STANDARDS
(LITERACY) RST.9-10.3
DEVELOPING AND
USING MODELS
ANALYZING AND
INTERPRETING DATA
Follow precisely a multistep procedure when
carrying out experiments, taking measurements, or
performing technical tasks, attending to special cases
or exceptions defined in the text.
(LITERACY) RST.9-10.7
CAUSE AND EFFECT
PATTERNS
Translate quantitative or technical information
expressed in words in a text into visual form (e.g., a
table or chart) and translate information expressed
visually or mathematically (e.g.in an equation) into
words.
Write narratives to develop real or imagined
experiences or events using effective technique, wellchosen details, and well-structured event sequences.
(LITERACY) W.4
Produce clear and coherent writing in which the
development, organization, and style are appropriate
to task, purpose, and audience.
(MATH) A-CED. 2
Create equations in two or more variables to represent
relationships between quantities; graph equations on
coordinate axes with labels and scales.
Copyright © 2013 National Math + Science Initiative, Dallas, Texas. All rights reserved. Visit us online at www.nms.org.
T E A C H E R
LS2: ECOSYSTEMS
P A G E S
(LITERACY) W.3
ii
Biology – Call of the Wild
CONNECTIONS TO AP*
AP
• Assessment of prior knowledge
• Discussions with students regarding proper
graphing technique
BIOLOGY
D.1
• Discussions with students regarding proper
interpretation of the graphs
ACKNOWLEDGMENTS
Wilensky, U., and Reisman, K. (1999). “Connected
Science: Learning Biology through Constructing
and Testing Computational Theories—An Embodied
Modeling Approach.” International Journal of
Complex Systems, M. 234, pp. 1–12. This model is a
slightly extended version of the model described in the
paper.
Wilensky, U., and Reisman, K. (2006). “Thinking like
a Wolf, a Sheep or a Firefly: Learning Biology through
Constructing and Testing Computational Theories—
An Embodied Modeling Approach.” Cognition &
Instruction, 24(2), pp. 171–209.
2
All biological systems from cells and
organisms to populations, communities
and ecosystems are affected by complex
biotic and abiotic interactions involving
exchange of matter and free energy.
AP
BIOLOGY
4
A.5
Communities are composed of populations
of organisms that interact in complex
ways.
A.6
Interactions among living systems and
with their environment result in the
movement of matter and energy.
B.3
Interactions between and within
populations influence patterns of species
distribution and abundance.
B.4
Distribution of local and global
ecosystems changes over time.
http://ccl.northwestern.edu/papers/wolfsheep.pdf
P A G E S
The following types of formative assessments are
embedded in this lesson:
T E A C H E R
ASSESSMENTS
*Advanced Placement® and AP® are registered trademarks of the
College Entrance Examination Board. The College Board was not
involved in the production of this product.
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iii
Biology – Call of the Wild
TEACHING SUGGESTIONS
Discuss how to properly use a two-cycle semi-log
graph.
This simulation utilizes the Java application.
Make sure that this application is updated to the
latest version. You will need to have the following
specifications to run the simulation.
• Windows users: Microsoft Windows XP/
Vista/2000/7 and Java 6 or later
• Mac users: OS 10.4 or later and Sun Java 6 or
later
http://ccl.northwestern.edu/netlogo/requirements.html.
If you have computers and internet readily available,
encourage your students to do the Challenge at the end
of the activity.
If you do not have access to the Internet in your
classroom, the simulation can be downloaded to your
computer or multiple computers in order to facilitate
the lesson. If you only have one computer, you could
project the image on a screen and facilitate Part II as a
classroom discussion. This would also be a good idea
for students who are struggling to get started with Part
II. You could go through one or two of the prompts
with them until they understand the methodology and
then let them start asking their own questions.
If you need to raise the rigor for students who can be
pushed further than the parameters of this lesson, you
might try the following suggestions:
• Participate in the Challenge at the end of the
lesson.
• Have the students investigate other ecological
disturbances due to density-independent and
density-dependent factors.
Copyright © 2013 National Math + Science Initiative, Dallas, Texas. All rights reserved. Visit us online at www.nms.org.
P A G E S
This activity should be conducted in a classroom
setting rather than a laboratory setting since the
students will be simulating predation by eating the
prey (beans). Be sure to check for food allergies
before conducting this activity. As an alternative, you
may choose to use a non-food item for this simulation.
For example, you could use colored beads as the prey.
If you have any technical issues, please refer to
troubleshooting page on the website
T E A C H E R
T
he students pretend to be the wolves with their
spoon. The students can decorate their spoons
to look like wolves. Prior to the activity, you
will need to set out each group’s materials.
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Biology – Call of the Wild
HYPOTHESIS
The elk population and wolf population will rise and fall at the same rate.
DATA AND OBSERVATIONS
PART I: PREDATOR/PREY CYCLES
Initial Elk
Population
Elk
Eaten
Elk
Survivors
Initial Wolf
Population
Wolf
Survivors
Wolves
Born
1
10
3
7
1
0
0
2
14
3
11
1
0
0
3
22
5
17
1
1
1
4
34
6
28
2
1
1
5
56
18
38
2
2
2
6
76
42
34
4
4
4
7
68
46
12
8
8
8
8
24
24
0
16
4
4
9
10
10
0
8
2
2
10
10
8
2
4
1
1
11
10
5
5
2
1
1
12
10
4
6
2
0
0
13
12
5
7
1
1
1
14
14
4
10
2
0
0
15
20
4
16
1
0
0
16
32
5
27
1
1
1
17
54
19
35
2
2
2
18
70
36
34
4
4
4
19
68
50
18
8
8
8
20
36
36
0
16
7
7
21
10
10
0
14
2
2
22
10
9
1
4
1
1
23
10
4
6
2
0
0
24
12
4
8
1
0
0
25
16
A N S W E R
Generation
K E Y
Table 1. Elk and Wolf Data
1
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Biology – Call of the Wild
ANALYSIS
Figure A. Wolf vs. elk population sizes over time
Copyright © 2013 National Math + Science Initiative, Dallas, Texas. All rights reserved. Visit us online at www.nms.org.
A N S W E R
K E Y
GRAPH 1: WOLF VS. ELK POPULATION SIZES OVER 25 GENERATIONS
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Biology – Call of the Wild
ANALYSIS (CONTINUED)
PART II: WOLF/SHEEP PREDATION
Question #1
What would the affect be on the three different
populations if the field consisted of four times as many
wolves as sheep?
Answers may vary depending on the data that the
students collect. For example, the students should
include all of the following criteria:
E. Conclusion: As seen in Figure B, at the very
beginning the wolf population had very little food
and thus many of them died off. Eventually, there
were not enough sheep to keep any of the wolves
alive, and they all perished or left the area.
A. Question: What would the affect be on the three
different populations if the field consisted of four
times as many wolves as sheep?
D. Results: In a relatively short amount of time,
all the wolves died off and the sheep and grass
populations exhibited the same “predator/prey”
cycles exhibited as the wolf and elk in Part I.
Figure B. Wolf, sheep, and grass populations
However, there were a few sheep left at this time,
which began to repopulate. The sheep population
rose whereas the grass population fell. There was
a point where there was not enough grass to feed
all of the sheep, and the sheep population began
to decline.
A N S W E R
C. Methodology: I started the simulation by pressing
Setup. Then I turned on “grass?” so that the
simulation would keep track of its population. I
then set the initial wolf population to 100 and the
initial sheep population to 25, and then pressed
the “go” button. I let the simulation run for 20
seconds and then observed what happened.
K E Y
B. Hypothesis: The wolves would kill all of the
sheep and then, without any food, the wolves will
either leave or die off.
The rest of the graph shows the rise and fall
cycles of the sheep and grass populations slightly
offset from each other, which is indicative of
predator/prey relationships.
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vii
Biology – Call of the Wild
CHALLENGE
Find three ways in which your group can manipulate
the simulation so that both populations die off. When
you figure this out, describe the limiting factors
involved in creating this situation, and then explain
why both populations were not able to survive.
There are many ways in which students could create
a situation where both the sheep and wolf populations
would die off. One example is setting the “grassregrowth-time” very low (Figure C). This type of
situation would be caused by a drought. The sheep
population rises drastically, which consequently
causes the grass population to drop. The grass has
a tough time repopulating, which causes the sheep
population to decrease to zero. With no food left, the
wolf population also drops to zero.
CONCLUSION QUESTIONS
1. Write a statement describing the relationship
between a predator population and a population
of its primary prey.
The population of the prey rises due to the low
number of predators. Increased prey population
causes the predator population to rise drastically.
However, when there is not enough prey for
the rising predator population, the number of
predators begins to decline. This cycle continues
if all other variables are held constant (adequate
food for the prey, for example).
2. Look at the peaks and troughs seen in both
populations. Explain how they relate to each
other.
The two populations have peaks and troughs that
correlated to each other but are slightly offset of
each other.
K E Y
ANALYSIS (CONTINUED)
A N S W E R
3. Describe a density-independent factor that might
affect the elk population size. What effect would
this have on the wolf population?
A hurricane hits the area and kills off all but a
few elk. This drastic decrease in the number of
elk might cause the population to die off due to
predation. This would consequently cause the
wolf population to die off or emigrate to a new
area due to a lack of food.
Figure C. Wolf and sheep populations dying off
This challenge could be a competition between
individuals or teams.
4. Describe a density-dependent factor that might
affect the elk population size. What effect would
this have on the wolf population?
Increased temperature due to a drought might
cause the elk population’s food source to become
less plentiful. This would drastically decrease the
number of elk, which might cause the population
to either die off or emigrate to another place. This
would consequently cause the wolf population to
either die off or emigrate form that area as well.
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viii
Biology – Call of the Wild
CONCLUSION QUESTIONS (CONTINUED)
6. Describe the relationship between the grass and
sheep populations over the time period indicated
by the simulation. Justify your answers with
evidence from the graph.
As seen by the graph in the simulation, the sheep
and the grass populations follow the same pattern
as the wolf and sheep populations. However, in
this case the sheep are the predators and grass is
the prey.
7. What indirect effect does grass have on the wolf
population? Justify your answer with evidence
from the graph.
When the grass population is rising, this
will inevitably initiate in a rise in the sheep
population. This would inevitably cause a rise in
the wolf population. On the other hand, a decline
in the grass population would initiate a decline
in the sheep population, which would initiate a
decline in the wolf population.
Answers will vary. One example is the lynx and
snowshoe hare populations of the boreal forest in
Canada.
9. Contrast the different effects that occur between
when all of the sheep die off and when all of the
wolves die off.
If all of the sheep die off, there will not be any
food left for the wolves, and therefore they will
either die off as well or emigrate to a new place.
If all of the wolves die off, the sheep population
with adequate amounts of food will continue to
grow.
10. The brown tree snake still thrives on the island of
Guam. Why is it still able to thrive while so much
of its food has been eliminated?
The brown tree snake also feeds on other
organisms like small mammals and lizards.
Therefore, even though the bird population has
been drastically depleted, there are still other
types of food of which the brown tree snake can
feed.
K E Y
As seen by the graph in the simulation, the wolf
and sheep populations follow the same patterns
as the wolf and elk populations in Part I of the
activity. The population of the sheep rises due
to the low number of wolves. Increased sheep
population causes the wolf population to rise
drastically. However, when there are not enough
sheep for the rising wolf population, the number
of wolves begins to decline. This cycle continues
if all other variables are held constant (adequate
food for the prey, for example).
8. Describe another predator/prey relationship that
might follow a similar pattern as the ones seen in
this lesson.
A N S W E R
5. Describe the relationship between the wolf and
sheep populations over the time period indicated
by the simulation. Justify your answers with
evidence from the graph.
11. Hypothesize what other community and
ecosystem consequences have most likely
occurred due to the introduction of the brown
tree snake. Explain how each might affect the
community and ecosystem.
Answers may vary. One example is an increased
population size of the bird’s prey, such as spiders.
The spider population on Guam has significantly
increased since the bird population decreased.
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ix
Biology – Call of the
Biology
Wild
Call of the Wild
Investigating Predator/Prey Relationships
I
n the 1940’s, the island of Guam experienced one of the worst ecological
disasters ever recorded. The brown tree snake (Boiga irregularis) was
accidentally introduced to the island sometime between the end of the World
War II and 1952. It was originally native to Australia and the South Pacific.
MATERIALS
calculator
computer
spoon, plastic
100 beans, individual pinto
plate, paper
The brown tree snake feeds mainly on birds, lizards, and small mammals. When
it was introduced to the island of Guam, it started feeding primarily on the
native bird population. To date, ten of the twelve native bird species have been
completely decimated by the brown tree snake. The other two species are heavily
protected to conserve their numbers.
The effects of this invasive species are still being felt today on both community
relationships and the ecosystem as a whole.
PURPOSE
In this activity, you will investigate predator/prey relationships. In the first part
of this lesson, you will investigate how a wolf and an elk population change
over time in response to the other’s presence, and how each population relates
to the other. In the second part, you will get to ask your own questions regarding
a similar scenario, and use a computer simulation to experimentally test your
hypotheses.
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1
Biology – Call of the Wild
FOR THE SIMULATION
This activity shows the predator/prey relationship between wolves and the elk that
they feed on in a field habitat.
The following rules must be followed in this simulation:
• The field will only sustain up to 100 elk.
• After predation has occurred, the remaining elk population will double.
• Due to immigration, the habitat will always contain at least 10 elk.
• Due to immigration, the habitat will always contain at least 1 wolf.
• Each wolf must eat up to 5 elk or it will die or emigrate (leaves the habitat in
search of food somewhere else).
• For every 5 elk that a wolf eats, it has enough energy to produce 1 wolf cub.
FOR THE GRAPH
When displaying your data on a two-cycle semi-log graph, make sure that you
follow the following rules:
• Label the y-axis starting with 1, not 0, at the bottom.
• Number each line increasing by 1 individual (2, 3, 4…) until you reach 10
individuals.
• After 10 individuals, each line represents 10 more individuals than before
(20, 30, 40…). Label the rest of the y-axis until you get to 100 individuals.
Give the y-axis a title.
• The x-axis represents the 25 generations. Give this axis a title as well.
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2
Biology – Call of the Wild
PROCEDURE
PART 1: PREDATOR/PREY CYCLES
1. How do you think that, over many generations, the wolf the elk population
size relate to each other? Write your hypothesis on your student answer page.
2. Set up the habitat by placing 10 elk (beans) in a petri dish. One swipe of your
spoon represents 1 wolf. Enter your initial populations of elk and wolf into
Table 1.
3. With your eyes closed and one continuous swipe through the dish, pick up as
many beans as you can with your spoon. Set the beans on the table beside the
plate and count them.
The number of beans represents the amount of elk that the wolf was able to
consume. Record this number in Table 1.
4. Determine the number of surviving elk, surviving wolves, and if the
wolves were able to reproduce or not, and record these numbers in Table 1.
Remember that each wolf must consume at least 5 elk for 1 cub to be born.
5. Record the initial populations for the next generation. Remember that the
surviving elk population will double. Count the number of surviving wolves
and do not forget to add the number of new wolves to the starting population,
as they will need to consume 5 elk as well.
6. Repeat Step 2 through Step 5 until you have 25 generations of data. When
you have multiple wolves, then you will swipe that many times through the
dish to generate your prey count. Do not forget to abide by the six rules as
stated previously.
7. Graph the initial populations for both the elk and the wolves in Graph 1
(two lines). Graph 1 is a two-cycle semi-log graph that allows us to see both
populations despite the large discrepancy in both values for wolves and elk.
PART II: WOLF/SHEEP PREDATION
Now it’s your turn!
For this activity, you will use a computer simulation as a tool to perform
predator/prey experiments on a population of wolves and sheep.
1. Navigate to http://ccl.northwestern.edu/netlogo/models/WolfSheepPredation.
Click on the link, “Run Wolf Sheep Predation in your browser.”
2. Click on the red tab in the box that says “grass?” to turn on the grass.
3. Click on “setup,” then click “go” and let it run for 20 seconds.
4. After 20 seconds, click on “go” again to stop the simulation.
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3
Biology – Call of the Wild
HYPOTHESIS
DATA AND OBSERVATIONS
PART I: PREDATOR/PREY CYCLES
Table 1. Elk and Wolf Data
Generation
Initial Elk
Population
Elk
Eaten
Elk
Survivors
Initial Wolf
Population
Wolf
Survivors
Wolves
Born
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
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4
Biology – Call of the Wild
ANALYSIS
GRAPH 1: WOLF VS. ELK POPULATION SIZES OVER 25 GENERATIONS
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5
Biology – Call of the Wild
ANALYSIS (CONTINUED)
PART II: WOLF/SHEEP PREDATION
1. Besides the presence of grass, what other variables are you able to
manipulate in this simulation?
RESEARCH QUESTIONS
Following the steps of the scientific method, use the simulation to perform the
following “investigations” to answer the questions or problems. After you have
completed each investigation and have gathered the data, communicate your
results in a brief paragraph using the following format:
A. State the question.
B. State your hypothesis.
C. Briefly describe how you manipulated the simulation to run your
“investigation.” Include in your description the following factors:
• Limiting factors
• Control groups
• Experimental groups
• Independent variables
• Dependent variables.
Make sure that you write precise enough descriptions of your methodology
so that other students could follow your exact procedure and get the same
results.
D. Make a screenshot of the generated graph to show your results. You might
have to increase the size of the picture.
E. Using data from the graph, describe what changes occurred to the wolf,
sheep, and grass populations in the simulation. Explain why these changes
occurred.
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6
Biology – Call of the Wild
ANALYSIS (CONTINUED)
Question #1
What would the affect be on the three different populations if the field consisted
of four times as many wolves as sheep?
Now it’s your turn!
Create your own questions and then use the simulation to investigate each
one. Write your question in the space provided and then write your conclusion
paragraph as outlined in Steps A–E previously.
Question #2
Question #3
CHALLENGE
Find three ways in which your group can manipulate the simulation so that
both populations die off. When you figure this out, describe the limiting factors
involved in creating this situation, and then explain why both populations were
not able to survive.
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7
Biology – Call of the Wild
CONCLUSION QUESTIONS
1. Write a statement describing the relationship between a predator population
and a population of its primary prey.
2. Look at the peaks and troughs seen in both populations. Explain how they
relate to each other.
3. Describe a density-independent factor that might affect the elk population
size. What effect would this have on the wolf population?
4. Describe a density-dependent factor that might affect the elk population size.
What effect would this have on the wolf population?
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8
Biology – Call of the Wild
CONCLUSION QUESTIONS (CONTINUED)
5. Describe the relationship between the wolf and sheep populations over the
time period indicated by the simulation. Justify your answers with evidence
from the graph.
6. Describe the relationship between the grass and sheep populations over the
time period indicated by the simulation. Justify your answers with evidence
from the graph.
7. What indirect effect does grass have on the wolf population? Justify your
answer with evidence from the graph.
8. Describe another predator/prey relationship that might follow a similar
pattern as the ones seen in this lesson.
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9
Biology – Call of the Wild
CONCLUSION QUESTIONS (CONTINUED)
9. Contrast the different effects that occur between when all of the sheep die off
and when all of the wolves die off.
10. The brown tree snake still thrives on the island of Guam. Why is it still able
to thrive while so much of its food has been eliminated?
11. Hypothesize what other community and ecosystem consequences have most
likely occurred due to the introduction of the brown tree snake. Explain how
each might affect the community and ecosystem.
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10