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Name ________________________________ Class _______ Date _________________
Competition
Use the virtual Ecology and Microscopy lab
benches to see how the removal of a predator
can affect competition at lower trophic levels.
Lab Benches Used
Predation affects populations at lower trophic levels
both directly and indirectly. In this activity you will determine why the removal of a
predator causes the decline of a population that is not on the predator's menu.
Enter the Virtual Bio Lab and select the title of this lab activity from the “Biomes and
Populations” menu on the whiteboard. You will be taken to the virtual Ecology lab
bench. Later, you will use the virtual Microscopy bench.
Part A: Removing a Predator
At the virtual Ecology lab bench, go to the clipboard and click on the "Competition"
preset. You will see scenery and settings for a marine biome. In the Species Tracking
box, you will see listed the purple sea star, California mussel, and white acorn
barnacle. Read the descriptions in the Species Selector to learn about these organisms
of the intertidal zone.
1. Run the simulation for about 20 years to track the three populations under normal
conditions. (Save your results to the Lab Book as "Normal.") When these
populations interact under normal conditions, what are their growth patterns like?
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2. Reset the simulation by clicking the "Time" button on the Controller. This time,
use a catastrophe to remove the sea stars from the habitat at the 5-year mark. Stop
the simulation at the 10-year mark. Save your results as “Sea Stars Removed”.
What happens when the sea stars are removed?
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Virtual Bio Lab
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Biomes & Populations
Competition
Name ________________________________ Class _______ Date _________________
3. Why does the removal of the sea stars cause the mussel population to change in
this way? Use the term "limiting factor" in your answer.
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Neither the California mussel nor the acorn barnacle preys upon the other. Rather,
both of these invertebrates are sessile filter feeders, meaning they stay in one place—
on the rocks they live on—and filter the water to get their food. So, how do they
affect each other’s populations?
4. Why does the exploding mussel population seem to be correlated with a steep
decline in the population of white acorn barnacles? If the mussels aren’t eating
barnacles, how else could they be reducing the barnacle population?
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5. Open the Lab Book and review the population data after the point of sea star
removal. How would you describe the mussel’s population growth rate? How
would you describe the barnacle’s decline?
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6. Is there anything about your answer to Question 5 that seems odd?
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Virtual Bio Lab
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Biomes & Populations
Competition
Name ________________________________ Class _______ Date _________________
Part B: Microscopy
To determine why the white acorn barnacle population is managing to hang on
despite the explosive population growth of its competitor, the California mussel, exit
the virtual Ecology lab bench. Head to the Microscopy bench on the far right side of
the main lab room. Select the barnacle (“Barnacle, White Acorn”) from the Species
Selector, and look at the images that are available in the field scope. Save any
relevant images to the Lab Book.
7. Do any of the images give you any clues as to how the barnacle population could
persist even though the mussel population is exploding at an exponential rate and
depriving the barnacle of space on the rocks? Explain.
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8. If you were managing a marine conservation zone that saw a huge increase in
California mussels after people collected a large number of sea stars, how would
you try to restore balance to the intertidal community? Explain.
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9. Would you call the purple sea star a keystone species? Why or why not?
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Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Virtual Bio Lab
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Biomes & Populations
Competition