Download Keystone Species

Name ________________________________ Class _______ Date _________________
Keystone Species
Use the virtual Ecology lab bench to see how the
removal of predators can disrupt food webs.
Predation is one factor that can limit the growth of a
Lab Bench Used
population. When predation ceases, a prey population that
is normally somewhat stable can explode, causing effects to ripple out across the
entire food web. The predator doesn’t need to be an apex predator in order to have
this kind of effect on a community. In this lab activity, you will see what happens
when such a keystone species is removed from a marine ecosystem.
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.
Part A: Removing a Predator
At the virtual Ecology lab bench, click on the clipboard and choose “Keystone
Species” from the list of presets. Three species will appear in the Species Tracking
box: kelp, purple sea urchin, and sea otter. Read about these species in the Species
Selector to learn about where they live and what they eat. Their initial population
levels are set to approximate a simplified food web off the coast of the Pacific
Northwest, an area of North America that includes Oregon, Washington, northern
California, British Columbia (Canada), and the southern part of Alaska.
Click the play button on the Controller. Let the simulation run until 10 years have
passed, as displayed by the graphs that appear in the data window on the right side of
the screen, then pause the simulation. Save the data to the Lab Book, then click on
the red Lab Book to open the saved data. Change the data titled “Marine” to
“Normal.”
1. Using the graphs in the Lab Book or in the data window, describe any trends you
observed among kelp, purple sea urchin, and sea otter populations.
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Click the “Time” button on the Controller to reset the simulation. Run it again, but
this time, use the “Catastrophe” button in Species Tracking to wipe out 80% of the
otter population at the 5-year mark. Pause the simulation at Year 20 or until all the
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Virtual Bio Lab
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Biomes & Populations
Keystone Species
Name ________________________________ Class _______ Date _________________
populations collapse, whichever happens first. Again, save the data to the Lab Book.
Edit the data’s title to: “80% Otters Removed, Year 5.”
2. What happened to this food web when catastrophe struck the sea otters?
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3. Why do you think the removal of the otters caused the other two populations to
crash as well?
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Part B: Restoring Populations
Use the play button to continue the simulation from where you left off. Go to the “+/Population” area of the Species Tracking box. Set the value to “+100” (with no %
sign) and “All” and click the button. This will introduce 100 individuals of each
species to the habitat. Watch what happens to the populations in the data window.
Stop the simulation after about five years. Again, save the data to the Lab Book.
Change the data’s title to “All Replenished.”
4. What happened to the food web when 100 individuals of each species were
reintroduced to the habitat?
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5. What would have happened if you had only reintroduced the kelp and the urchin?
Explain.
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Virtual Bio Lab
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Biomes & Populations
Keystone Species
Name ________________________________ Class _______ Date _________________
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6. What if you had only reintroduced five individuals of each species? Would that
have worked to restore populations? Explain your hypothesis. Using the term
“limiting factor” in your answer.
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7. Click the “Time” button to reset the simulation. Test your hypothesis by setting
“+5” for all populations in the Species Tracking box. Run the simulation and
describe the results. Save your data to the Lab Book as “Small Populations.”
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Virtual Bio Lab
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Biomes & Populations
Keystone Species