Several lessons in this curriculum use computational models designed using a piece of software called NetLogo. In this lesson, we will try to understand what computational models are and how to use them.

This lesson specifically focuses on learning science with computational models of emergent natural phenomena. Emergent phenomena are ones in which simple interactions between agents and their environment result in complex patterns. For example, a flock of birds (see below). 

In a flock of birds, most people assume that the "head" bird is a leader of the flock. However, flocks actually emerge from each bird following a simple set of rules regarding how close and how far they should be from their neighbors as well as general direction of travel. This means that the shape of a flock is emergent and not directed by any particular leader bird.

We can use computational models to study and make predictions about emergent behaviors as long as we have a realistic understanding of the rules followed by the individual agents. 

Learning Goals - 

• In this lesson, we will use a NetLogo model about Forest Fires to learn about how to computationally study a scientific phenomenon.
• We will learn how to engage in the scientific inquiry practices of constructing knowledge.
• We will learn how to engage computational thinking practices.

We will focus on four computational thinking practices: data practices, modeling and simulation practices, computational problem solving practices, and systems thinking practices.

Let's get started!

Scientists use scientific modeling approaches to construct knowledge about the world. In this section, we explore the ideas behind scientific models.

Let's investigate how the density of the trees affects the spread of a forest fire. We will first generate some data using the Fire model and then visualize that data using another computational tool called CODAP.

Follow the experimental design that is described below:

Research Question: How does the density of trees in a forest affect the spread of a forest fire?

Hypothesis: As the density of trees in the forest increases, the percentage of forest burned will increase "linearly". (That means, if density of trees doubles, the percentage of forest burned will also double)

Let's test our hypothesis using the model.

Change the values of density systematically (plan out a series of different values to try). Record the value of 'percentage burned' in the data table for each density. Make sure that you press the 'setup' button every time you do a trial. Make sure to run each different value of density twice (2 trials) and finally, make sure you record values for each experimental trial. 

CODAP will automatically graph the average of the two trials that you will record. 

In this lesson, you will build and explore computational models of living systems. A special type of scientist called computational biologists, use computational models to study biological systems.

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

NetTango is a block-based coding environment. It uses blocks to create a code for a computer program to perform certain tasks.  

NetLogo is text-based coding environment. It uses text to write code for creating computational models.

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 down any of the forests. 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 over the course of the next few days will be to build a scientific model that can 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. 

Let's start with building a simple model.

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

Try the following challenges:

1. Get the wolf to move around the field.
2. Get the wolf to move around the field more realistically (hint: think about how wolves might move in real life)
3. Get the wolf to draw a dashed line or another pattern.

The poor defenseless moose should be allowed to move as well! Start by setting up realistic movement for both wolves and moose and then move on from there.

Try the following challenges:

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

Now that we have a basic model, let's try to use it to predict what might happen in the future to Isle Royale.

Recently the Isle Royale ecosystem has been suffering. Since it has been isolated for a very 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 what will happen in the future to Isle Royale.

In this lesson, you will use an advanced model of the ecosystem on Isle Royale to make a prediction.

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%. These two "sliders" will help us model the fact that the wolves on Isle Royale are sick. They have a harder time staying healthy and a harder time having baby wolves.

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.

In this lesson, you will study a phenomenon about a population of rock pocket mice. You will explore a computational model of a population these mice and observe changes in the population over time. By the end of the lesson, you'll be able to explain how the color of fur coat of mice changed over time and how it may have been affected by the change in their environment.

The American Southwest is a fantastic place to study rock pocket mice with different fur coat colors. Ancestral pocket mice had light-colored fur coats that blended in with the rocks and sandy soil that was prevalent in the region. This kept the mice hidden from their predators (mainly owls).  Then, a series of volcanic eruptions spewed a river of black lava more than 40 miles long that wove right through the middle of pocket-mouse territory. Lava flows created huge patches of dark rock among the surrounding light-colored sand.

Today there are now two forms of pocket mice:

• light-colored mice that live on sandy soil
• dark-colored mice that live on black lava rock

Researchers noticed that rock pocket mice with a dark fur coat were more common on the dark lava flows, whereas the mice with light colored fur coat were more common on the light-colored sand. How might this have happened? 

In orer to investigate this mystery, we're going to investigate this case of pocket mice evolution using computational models.

Let's start by watching a video developed by HHMI Biointeractive about this phenomenon.

Below is a computational model of a population of pocket mice. 

Each clock tick in the model is a mouse-generation and in each generation, male and female mice move around randomly, search for a partner, and reproduce if they find a partner. The fur-coat-color of the mice is a trait that is passed down from one generation to the next.

Play around with the model. It is totally okay if you don't understand everything mentioned in the model. Just explore the model for a few minutes and then try your best to answer the questions below.

In this lesson, you will continue to explore our computational model of pocket mice further. Today, you'll be investigating the concept of inheritance of a trait across generation and how it affects evolution of a population in the model.

Remember that in this model, there are mice with two types of fur coat colors: light and dark. Observable characteristics (also called as traits) like fur color, eye color, or blood type are referred to as phenotypes. These phenotypes, including the color of fur coats is determined by the genes that a mouse has. 

There are two kinds of genes in this models that affect the fur coat color of mice. 

While answering the following questions, make sure that the "PREDATION?" box is unchecked. 

In this lesson, you will investigate how natural selection affects a population of mice over time. You will design and perform an experiment about natural selection in the case of rock pocket mice by using a computational model to test your hypothesis.

In the previous lesson, you experimented with the concept of predation. In other words, you investigated how the mice being eaten by predators affected the population of mice differently in different types of environments. In nature, some individuals with certain traits (like fur color) have better fitness to survive and create offspring that can inherit those traits. In the case of our models, mice with certain phenotypes might have a advantage over other mice in different environmental conditions. Traits that gives an advantage would get passed to the next generation. As these traits are passed from each generation to the next, this process causes populations to change over time. We call these sorts of changes in populations natural selection.