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Activity 10: Experiment with Ecosystems
Introduction
Scientists observe the world around them and ask questions about what they see. Scientists do lots of different experiments. Scientists start experiments by making a hypothesis, which is a guess about how the world works. Scientists use computer models to test a hypothesis. With models, scientists can predict the weather, test new designs for bridges or airplanes, or even explore an ecosystem.

The Virtual Ecosystem is a computer model. In this activity, you will set up your own experiments using the Virtual Ecosystem model.


Balancing an ecosystem
Before we start new experiments, let's review! In the picture below, you see the hawk, rabbit, and grass populations living together in a balanced ecosystem where all the populations can survive well.







You might have questions about how plants and animals live when the environment is not balanced. Removing a plant or animal population is one way to change the balance in an ecosystem.
1. What does the grass need to survive? Sunlight Water Soil All of the above 2. What do rabbits eat? Grass Hawks Foxes None of the above 3. What do hawks eat? Worms Grass Rabbits None of the above
Think like a scientist



Just like a scientist, you can make a hypothesis about what might happen if there are changes in the Virtual Ecosystem. Think about removing a population from the Virtual Ecosystem. Are you curious about what would happen if an ecosystem did not have any producers? What about an ecosystem that did not have any predators?

Before you design your experiment, you have to think like a scientist. You will make a hypothesis about why something happens in the Virtual Ecosystem. Then plan and do an experiment with the model. Finally, you will observe what happens and think about the data.

Testing a hypothesis is exciting! Will your guess be correct? We will see!
The missing grass experiment
You know that rabbits in the Virtual Ecosystem need to eat grass to survive. But do hawks need grass to survive? What will happen to the hawk population if the grass is removed from the field? You can test this question using the Virtual Ecosystem model!

Instructions


1. Add grass, rabbits, and hawks to set up a balanced ecosystem.

2. Run the model. Watch the model and graph for a few seconds.
3. Remove the grass from the field using the button.

4. Try this experiment a few times!

Your Challenge: Run the model and test your hypothesis!



Choose a hypothesis below for the grass experiment:
Was your hypothesis correct?




4. What happened to the hawk population when the grass was removed from the Virtual Ecosystem? The hawk population increased when there was no grass. The hawk population decreased when there was no grass. The hawk population stayed the same when there was no grass. The hawk population died when there was no grass. 5. Why do you think that happened?
Enter the fox population
Adding a new animal population to an ecosystem is a way to change the balance.

We will add a new predator to the Virtual Ecosystem -- a fox . Foxes also eat rabbits. And foxes have an advantage over hawks -- they can catch more rabbits! Will there be enough food for both the hawks and the foxes to survive?


The fox experiment
Hawks and foxes both eat rabbits. Will there be enough rabbits for both the hawk and the fox populations to survive? You can test this question using the Virtual Ecosystem model!

Instructions


1. Add grass, rabbits, hawks, and foxes to set up a balanced ecosystem.

2. Run the model. Watch the model and the graph.

Your Challenge: Determine if both hawks and foxes can survive in the field together.


Choose a hypothesis below for the fox experiment:
Competition between predators
When a new predator population moves into an already balanced ecosystem, the predators that are already living there might have trouble finding food. It is hard to be a predator! In most balanced ecosystems there are many more prey animals than predators.




6. What happened when there were foxes AND hawks in the Virtual Ecosystem? The fox population survived and the hawk population died. The hawk population survived and the fox population died. The hawk and the fox populations both survived. The hawk and the fox populations both died. 7. Why do you think this happened?
Your own experiment
Do you have your own questions about the Virtual Ecosystem? Think about what you would like to test. Play with the model and see what you learn!

Instructions

1. Add plants and animals to the model.
2. Run the model. To remove a population from the field, use the buttons.

3. When you are done experimenting, go on to the next page.





Results of your experiment
 Great job, scientist!








8. What did you learn in the last experiment? 9. Is it easy to keep an ecosystem in balance? No Yes 10. How does adding or removing a plant or an animal from an ecosystem affect the other organisms living there?
Conclusion
Congratulations, scientist! You have run many experiments in the Virtual Ecosystem and have learned lots about the plants and animals that live there.

The planet Earth contains many connected ecosystems. There is a lot to learn about all the different ecosystems on Earth! Remember to keep exploring, observing, and asking questions when you go out into the real world! Click the X at the top of this window to close the activity and save your work.