In this unit, you will build and explore computational models of living systems. A special type of scientists called computational biologists, use such kind of computational models to study biological systems.

This units focuses on prey-predator interactions in an ecosystem. It uses two computational modeling environments - NetTango and NetLogo.

NetTango is a block-based coding environment, whereas NetLogo is text-based coding environment.

As you spend your time learning about how to construct computational models of prey-predator ecosystems, you will learn a bit about coding using blocks as well as text.

Isle Royale

Ecosystems are often difficult to understand because they usually include interactions between a large number of species. Isle Royale is different. It is a relatively simple island ecosystem, located 24 km from the shore of Canada in Lake Superior.

While there are many types of small animals on the island, and almost 20 types of mammals, only two species of the mammals that live on the island are relatively large. These are the wolves and the moose. On this island, wolves are the only predator of moose, and moose are essentially the only food for wolves.

To understand nature, it helps to observe an ecosystem where human impact is limited. On Isle Royale, there are no towns and people do not hunt wolves or moose or cut the forest. It is a very rare place on the planet where wolves, their prey, and the plants that support the prey are all left unharvested by humans. Isle Royale is remarkable, because nature runs wild there.

Your challenge will be to build a scientific model that can more realistically simulate the interactions of wolves and moose on Isle Royale, in order to help make predictions about how these two populations may change over time. 

1. Scroll down the page and interact with the setup and go (play) button.
2. Drag blocks over to tell the wolf and moose how to behave. Anytime you make changes click on the "recompile" button followed by setup and go (play).
3. Blocks can be used multiple times.
4. Blocks can be dragged to the trash to take them out of the code.

Challenges:

1. Get the wolf to move around the field.
2. Get the wolf to move around the field  more realistically.
3. Get the wolf to draw a dashed line or another pattern.

The poor defenseless moose should be allowed to move as well. Let's see how we can make this a more realistic model. Start by setting up realistic movement for both wolf and moose and then move on from there.

Challenges:

1. Wolves and moose move around the field in a realistic way.
2. Make the wolf appear to eat a moose when it runs into one.
3. Make the moose slowly multiply.
4. Come up with a challenge of your own!

In this lesson you will take a closer look at the underlying code that is generated when you drag the blocks. You will see that there are some parts of the code that are outside of the blocks, but are needed to get the model up and running.

Now we will look at the computer code produced from your blocks.

1. Scroll down and click on the triangle next to "NetLogo Code" 
2. Set up the blocks that you used before to have the wolf move around.
3. Look at the code that is generated when you recompile.
4. Answer the questions below.

Now that you have a more realistic model of wolves and moose, what can you transform to make it more interesting?

Here are a couple of ideas:

1. Try to make it even more realistic

2. Try to change to an extremely alien ecosystem 

Challenge:

Use any combinations of blocks below to make your own world of wolves and moose. Explain your process below.

In this unit you will build a computer model of a simple ecosystem involving wolves and moose based on Isle Royale National Park.  You will later evaluate that model using real data from the Isle Royale ecosystem and use it to make predictions about the future of the island.

We will transfer the code that you generated in NetTango to the new NetLogo model. This will give us the basic functions that you worked on before but allow us to make more direct changes.  If you need help with any of the steps listed below, click here to see a video of the process.

1. Set up a model similar to the one you completed in the earlier lesson using NetTango.  Make sure you click "Recompile" after you finish making changes.

2. Scroll down and click on the 'NetLogo Code' arrow below the block areas to see the full code of the first model written out.  Select all of this code and copy it.

3. Scroll down to the second model lower on the page.  These instructions will continue below.

4. Click the "NetLogo Code" button in the second model and paste the code there.

5. Click the "Recompile Code" button in the second model.

6. Click setup and go in the second model.

7. Answer the questions below.

Right now, our ecosystem is very small, with only a handful of moose and wolves.  In order for it to be more useful for studying places like Isle Royale, we need to make the ecosystem bigger.  Open the NetLogo code tab and make the changes need to transform your basic NetTango model into a model that shows interactions on much wider scale.

Before we work with a more realistic model of wolves and moose, go ahead and mess around again and create your own world? Although this time you will make your changes directly in the code. Don't forget to click the "recompile code" button after you make your changes.

Explain your process below.

In this lesson, you will look at a version of the model you have been building in the earlier lessons. You will evaluate the accuracy of the model based on data from the real world. 

In this lesson we will look at the wolf and moose ecosystem on Isle Royale again. In an earlier lesson, you thought about why the numbers of wolves and moose might change over time. Now, we will make more predictions about this ecosystem.

Look at this table showing the wolf and moose population sizes in 2011 and answer the questions below.

In earlier lessons, we tried to think about how a wolf or a moose might behave in the wild. We also thought about how the populations of wolves and moose might change on Isle Royale. You have used this to build a model ecosystem, but we don't know how good of a model it is yet. In this activity we will try to figure that out.

The model below is very similar to the model you have been working with in earlier lessons. The wolves and moose follow all of the same rules as before, except that now there are plants for the moose to eat. If the wolves or moose don't eat enough food, they will die. Look at how the size of the populations changes over time.

We have also added sliders to the model that allow you to change parts of the code without having to go back into the code tab.

Scientists have studied the wolf and moose populations on Isle Royale for decades. This means we have detailed data on how these populations have changed over time. We can see how good our model is by comparing it with these data.  When a scientist ran the model from the last activity with the default settings, they got the graph on the left.  The data from Isle Royale is on the right.
 

In the last lesson, you saw that your ecosystem model matches the real world pretty well. Now that we have some confidence in it, we will try to use this model to make predictions about the future of Isle Royale.

Recently the Isle Royale ecosystem has been suffering. Since it has been isolated for a long time, inbreeding has made the wolves less healthy. Also, there are very few wolves left on the island even though there are a lot of moose. We can use our model to try to predict the future of Isle Royale.

First we need to set the model up so that it starts close to the current state of the island. There are very few wolves left and a lot of moose, so set the initial wolf population to 2 and set the initial moose population to about 200. Because the wolves are unhealthy, decrease the WOLF-GAIN-FROM-FOOD slider from 20 to 13 and decrease the WOLF-REPRODUCE slider from 5% to 3%.

Answer the first two questions below before running the model.

Many scientists think that the wolf population on Isle Royale will probably die out in the near future. However, it may be possible to save them through some human intervention. We can use our model to test how good different interventions might be.

Answer the first two questions below before you start using the model.