Student Exploration: Prairie Ecosystem (ANSWER KEY)

Student Exploration: Prairie Ecosystem
Vocabulary: carnivore, consumer, ecosystem, equilibrium, extinct, food chain, herbivore, organism, population, prairie, producer
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
An ecosystem consists of all organisms (living things) in an area, plus the natural landscape. 
A prairie is flat or gently rolling grassland with few trees, such as in parts of central United States and Canada.
Organisms often found in a prairie ecosystem include prairie dogs, swift foxes, black-footed ferrets, and of course the grass itself.
Which organism (grass, prairie dog, ferret, or fox) do you think is a producer (does not depend on other organisms for its food)?.
Organisms that depend on other organisms for food are consumers. Which consumer you think is a herbivore (eats plants only)?.
Which consumers are carnivores (eat meat)?. 
Gizmo Warm-up: Life on the Prairie 
The population of prairie dogs is all the prairie dogs living in the village. In the Gizmo, what are the starting numbers of
Click Advance year 10 times. On the Data tab, look at the Bar graphs and the Line graph. Do the populations change very much, or are they in equilibrium (stable)? Explain.
Activity A:

Grass
Get the Gizmo ready:
  • Click Reset.
  • Be sure Show population is selected.
 
Question: How is grass important to a prairie ecosystem?
Observe: Remove ALL animals from the prairie by clicking the minus (–) button next to each animal many times. Click Advance year 20 times. Does grass survive by itself? Explain.
Because grass does not depend on other organisms for food, it is a producer. Grass gets what it needs from the Sun, air, and soil.
Predict: Click Reset. Predict what will happen to the prairie dogs, ferrets and foxes if half of the grass were removed. Write “increase” or “decrease” in each blank below.
Experiment: Remove about half of the grass by clicking the minus – button. There should now be about 2,000 tons of grass. Click Advance year once, and look at the Bar graphs or the Line graph. What happened to each population—increase or decrease?
Prairie dogs:         Ferrets:           Foxes:
Think about it: What do you think will happen if you continue advancing years?
Experiment: Test your prediction by clicking Advance year until 20 years have passed.
What do you notice?.
Does the ecosystem return to equilibrium?
How do you know.
Extend your thinking: Suppose a fire swept through the prairie. The animals ran away, but about half the grass was burned. What would be the long-term results of this natural event?
Activity B:

Making a food chain
Get the Gizmo ready:
  • Click Reset.
 

Question: How do animals affect the prairie ecosystem?
Form hypotheses: What do you think each animal in the food chain eats? (Experiment with the Gizmo to help you make your hypotheses.)
Prairie dogs eat.   Ferrets eat.     Foxes eat.
Predict: Based on your hypotheses, predict how the changes below will affect the other animals. Write either “increase” or “decrease” next to each “P” (for “prediction”) in the table.
Test: Click Reset. Add as many prairie dogs as the Gizmo allows. Click Advance yearonce. Record the effects on the other three organisms in the table next to “A” (for “actual”). Then click Reset and do the same with ferrets, and then again with foxes.
Analyze: In a food chain, each animal eats only one other animal or plant. Based on your experiments, what is the food that each animal eats? Explain how you know.
Prairie dogs eat.   Ferrets eat.     Foxes eat.
Explain:.
Apply: Now complete the Prairie Ecosystem food chain. Arrows point toward the animal that is eating. For example, “Mouse ® Hawk” would mean that the mouse is eaten by the hawk.
Activity C:

Long term changes
Get the Gizmo ready:
  • Click Reset.
 
Introduction: Once common, the black-footed ferret is an endangered animal. In 1986 there were only 18 black-footed ferrets alive; today there are almost 1,000.
Question: What would happen to the ecosystem, long-term, with no black-footed ferrets?
Form a hypothesis: Based on what you have seen so far, what do you think would happen if black-footed ferrets died out, or went extinct? Explain in detail.
Experiment: Click Reset, and remove all the ferrets from the prairie dog town. Click Advance year for 12 years. What happens?
Analyze: Why did removing ferrets have such a powerful effect on the prairie ecosystem?
On your own: Investigate other major changes to the prairie ecosystem. Run each experiment for 20 years to see what the long-term results would be.
Give an example of a change that the ecosystem could recover from and return to equilibrium
Give an example of a change that the ecosystem was not able to recover from. Can you explain why?.

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