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Axia College Material
Appendix P
PopEcoLab
Before beginning PopEcoLab:
1. Print out these lab experiment instructions. A printed copy of these instructions will aid in
completing the lab accurately and effectively, because you will not need to switch back
and forth between computer screens.
2. Disable your pop-up blocker. PopEcoLab and the PopEcoLab online notebook will open
in new browser windows. If you have a pop-up blocker, they will be blocked.
3. Read the online introduction and background information related to this lab
The experiment is divided into two sections: Self-Check Experiment and Exploration Experiment.
The Self-Check Experiment is designed to help you become familiar with the lab. The answers to
the Self-Check Experiment questions are given to you (in red text). Completing the Self-Check
Experiment and checking your answers will help you verify that you are completing the
experiments correctly.
The Exploration Experiment is the experiment you will be conducting and turning in to your
instructor for credit. You will report your findings for the Exploration Experiment in the PopEcoLab
report.
Getting to Know PopEcoLab
This following experiment is designed to help you become familiar with the operation of
PopEcoLab by studying the population growth of brown sparrows. The first screen that appears in
PopEcoLab shows you an input parameter page with a table listing the default parameters for the
laboratory conditions that you can manipulate when setting up your experiments.
Before you can set up an experiment in PopEcoLab, you must be familiar with the input
parameters that you can manipulate. You will study the effects of these different parameters in
future assignments. A brief description of each input parameter is provided below. Refer back to
this section as needed.
1. Click on the Change Inputs button to see all the parameters you can manipulate for this lab.

A new page will open with buttons for each of the input parameters located at the left side
of each page. Initial population size will be open as the first input parameter.
2. Click on each input parameter.
3. Read the descriptions below and change each parameter so that you can become familiar
with how each input parameter operates.

Initial Population: The initial population for brown sparrows is set at 200 birds while the
default value for blue sparrows and hawks is zero. Population size of each species can
be manipulated by clicking and dragging the slider bar.
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
Clutch Size: Clutch size is the number of eggs that a female bird lays in her nest. The
default value for brown sparrows and blue sparrows is three eggs while the default clutch
size for hawks is two eggs. Controlling clutch size is one way to influence the rate of
reproduction for all three species of birds.

Life Span: Brown and blue sparrows have a shorter life span than hawks. Notice that the
default life span for sparrows is one year while the life span for hawks is three years. This
feature allows you to manipulate mortality rates (independent of predation) to influence
life span.

Flight Speed: The ability of sparrows to avoid predation by hawks depends on their flight
speed. The default value for both brown and blue sparrows is 6 meters per second
(m/sec).

Competition: Although brown sparrows primarily eat seeds and blue sparrows primarily
eat insects, the two sparrows are potential competitors because brown sparrows can also
eat insects and blue sparrows can also eat seeds. The relative rates of consumption of
these "alternative resources" can be varied independently.

Resource Densities: Seed density and insect density directly influence the carrying
capacity of brown and blue sparrows, respectively. The default values are 100 seeds per
meter-squared (m2) and 100 insects/m2.
o
Carrying Capacity: The maximum population size that can be supported by the
available resources, symbolized as K.
After you have finished this introduction to the input parameters, click the Reset button at the left
of the screen to return all input parameters to their default values.
Self-Check Experiment: Single Species Population Growth
Population Growth of Brown Sparrows
Now that you are familiar with the basic parameters in PopEcoLab, set up the following
experiment to help you understand some of the factors that affect population growth of a single
species.
1. Leaving all input parameters at their default values, run a simulation of population growth
2. Click the Run Experiment button on the first screen.

Note: The number of years to run each experiment can be manipulated in 100-year
increments from 100 years to 500 years by using the drop-down menu in the lower left
corner of the input parameter page. The default value is 100 years.
3. When the experiment has finished running, a separate page will appear that presents the
results of your experiment.

Note: Any of the following data views can be saved by clicking the Export button.
Clicking on this button will open a separate window with your plot or table. From this
window you can then save your data.

The following data can be examined:
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o
Population Size—represented as a plot of the number of birds in the population
versus years of the experiment.
o
Phase Space—a plot of the number of one species (e.g., blue sparrows) against
another (e.g., brown sparrows) as population numbers change over time. This
type of plot is valuable for examining relationships between species. You can
select the species for each axis.
o
Textual Data—text columns of raw data for population size of brown sparrows,
blue sparrows, and hawks.
o
Input Summary—a summary table of the input parameters for the experiment
that you carried out.
4. Answer the following question:

Examine the population size plot. What is your estimate of the carrying capacity for the
population of brown sparrows?
The carrying capacity will be approximately 1000 birds
5. Repeat this same experiment at least three or four times manipulating the number of years to
determine if the results from this experiment are consistent.
Changes in Mean Clutch Size of Brown Sparrows
1. Formulate a hypothesis to predict the effects of a decrease in clutch size on the population
number of the brown sparrow.
You should hypothesize that decreasing clutch size will reduce population size.
2. Prove or disprove this hypothesis by carrying out three different experiments with mean
clutch size set to different values such as 0, 0.5, 1.0, 1.5, and so on, up to the maximum of 10
eggs, keeping all other parameters at their default values.
3. Repeat each experiment several times. Study the plots of population size.
4. Answer the following questions:





What did you discover?
Did the results agree with your hypothesis? Why or why not?
Is there a threshold clutch size needed to keep the population from going extinct?
What happens to the variability in population numbers as clutch size gets smaller?
If you were a conservation biologist, what would you say about your ability to predict
population numbers when clutch size decreases?
The hypothesis that decreasing clutch size will reduce population size is correct. The threshold
clutch size needed to keep the population from going extinct is approximately 2 eggs. In some
simulations, extinction will occur with a clutch size of 1 or 2. Because this is an experimental
simulation, be aware that the same conditions can produce extinction for one experiment but not
another. Population numbers become much more variable as clutch size decreases (fewer new
birds replacing birds that die and fewer birds in the population to reproduce). You should predict
that as reproductive capacity decreases, predicting population numbers becomes more difficult.
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5. Formulate a hypothesis to predict the effects of an increase in clutch size on population
number, then design and carry out experiments to test your hypothesis.
You should hypothesize that an increase in clutch size will increase population number (shortterm). You may also hypothesize that long-term increases in clutch size can lead to a decrease in
population number as carrying capacity is exceeded.
6. Answer the following questions:



What happens to population size as clutch size gets larger?
What happens to populations with very large clutch sizes?
What do you think is causing the pattern that you see?
As clutch size increases you will start to see large oscillations in the population. With very large
clutch sizes, the oscillations may be so large that the population eventually fails to recover from
one of the crashes and it goes extinct. An increase in clutch size creates these patterns in part
because populations reproduce so fast that they reach numbers that exceed what the
environment can support, then they crash. If the population does not go extinct, population
numbers will increase again (until the next crash). This creates boom and bust cycles over
periods of time.
Mortality Rates of Brown Sparrows
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Investigate the effects of increasing mortality rates.
Click on New Experiment.
Click on Change Inputs.
Click on Reset.
Click on Life Span and decrease the life span of brown sparrows.
Keep all other parameters at their default values.
Click Done.
Click Run Experiment.
Examine the plots of population size.
Answer the following question:

Is there a threshold life span needed to keep the population from going extinct? Explain
this result.
The threshold life span is approximately 0.7 years. Essentially, birds must survive this long to at
least reproduce and maintain population size.
11. Repeat the steps above to investigate the effects of decreasing mortality rates by increasing
life span. This time increase the life span of the brown sparrow, instead of decreasing the life
span.
12. Answer the following questions:


What happens to the variability in population numbers over time as life spans get longer?
If you were a conservation biologist, what would you say about your ability to predict
population numbers as life span changes?
Population numbers over time show less variability as life span increases. Population numbers
show less variability, in part, because the population experiences strong reproduction over time
as individuals live longer and the population does not suffer as much from cycles created by the
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effects of early mortality vs. new births. As a result, predicting population numbers as life span
increases is easier because populations are more stable over time.
Influence of Resource Density on Brown Sparrows
1. Repeat the steps above to investigate the effects of decreasing and increasing seed density.
2. Run experiments with a decreased resource density for seeds and separate experiments with
an increased resource density for seeds. For both experiments, keep all other parameters at
their default values.
3. Examine the plots of population size.
4. Answer the following questions:

How does changing the amount of available resources affect population size? Why is this
so?
Recall that the carrying capacity of a population is directly proportional to the density of available
resources.
Exploration Experiment: Two Competing Species
As you learned in the background text for PopEcoLab, interactions between populations of two or
more different species (inter-specific interactions) can affect population size and population
density in a number of ways that can benefit or harm one or several species.
This experiment is designed to help you learn about interactions that result in competition by
following the population growth of both the brown and blue sparrow.
Activity 1: Carrying Capacity
1.
2.
3.
4.
5.
Investigate the population growth of the brown and blue sparrow.
Click the New Experiment button.
Click on the Change Inputs button.
Click on the Reset button.
Under the Initial Population view.


Set the initial number of hawks to zero.
Set the initial population numbers for both the brown and blue sparrow equal to 200 birds.
6. Click on the Competition button.

Set the relative insect consumption by the brown sparrow equal to zero, and set the
relative seed consumption by the blue sparrow equal to zero.
7. Keep the remaining parameters at their default values.
8. Run several simulations and get an estimate of the carrying capacity of each species.

Note: You can run ten independent simulations by going to the Initial Population view and
clicking the Multiple Run Mode button. With this mode, set the number of runs to 10,
then run the experiment.
9. Export your data by clicking the Export data button.
10. Copy and paste your data into Appendix Q: PopEcoLab Report.
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11. Answer the following question in Appendix Q: PopEcoLab Report:

What did you observe for the carrying capacity of each species?
Activity 2: Increased Insect Consumption of Brown Sparrow
1. Run a new experiment by clicking the New Experiment button.
2. Click the Change Inputs button.
3. Go to the Competition view and use the slider to increase the relative insect consumption by
the brown sparrow
4. Click Done.
5. Click Run Experiment.
6. Run several simulations of this experiment, increasing the relative insect consumption of the
brown sparrow until one of the two species goes extinct.
7. Answer the following questions in Appendix Q: PopEcoLab Report:


What happened to the density of the two sparrows?
What is the point at which one of the two species goes extinct?
Activity 3: Increased Insect Consumption of Blue Sparrow
1. Reverse the situation and keep the relative insect consumption by the brown sparrow equal
to zero while increasing the relative seed consumption by blue sparrows.
2. Before you run this experiment, formulate a hypothesis to predict the results of this
experiment.
3. Answer the following question in Appendix Q: PopEcoLab Report:

What happened to the density of the two sparrows? Is that what you expected? Explain
your results.
Activity 4: Increased Insect Consumption of Both Sparrows
1. Keep the two consumption rates of resources equal, but gradually increase both.
2. Make sure you run several simulations for each set of consumption rates.
3. Answer the following question in Appendix Q: PopEcoLab Report:

What happens as you increase the amount of competition between the two species of
sparrows? Explain these results.
References
PopEcoLab assignments and answers were adapted with permission from Pearson Education,
Inc.
Biology Labs On-Line is a collaboration between the California State University system and
Benjamin Cummings.
© 2002 California State University and Benjamin Cummings, an imprint of Pearson Education,
Inc. Development was partially supported by a grant from the U.S. National Science Foundation.
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