The lab was designed to introduce us to computer modeling by using the Yellowstone National Park ecosystem, and the recent wolf introductions there, as the situation to model. Each sub-group looked at a different aspect of the ecosystem interactions.

One of the few remaining wilderness areas in America is Yellowstone National Park.  It is a large ecosystem with millions of acres of diverse mountain wilderness. (Map of wolf pack locations in Yellowstone) In Yellowstone National Park nearly every species of plant and animal life that explorers found 200 years ago still flourishes. Careful management by the National Park Service is important for the biological community to remain as undisturbed as possible while still allowing a human presence in the park.

In our lab we worked with a computer program called EcoBeaker.  EcoBeaker is a program that lets  you design and manipulate a wide variety of ecological models. EcoBeaker is an ecological simulation program, designed primarily for use in the classroom, although it can also be useful for researchers interested in quickly constructing ecological models. EcoBeaker gives you a two-dimensional world in the computer upon which you can place creatures whose behaviors you design. You can then watch as the creatures eat, reproduce, move around, die, and do all the other things that creatures normally do, producing patterns that you can compare against the real world and against theoretical predictions. You can also make graphs of many different statistical measurements from the EcoBeaker world and sample the populations using a variety of common sampling techniques.
 
 

This is an example of a species grid in which all of the model action takes place. The different colors represent different species. The green squares are vegetation, peach are small mammals, red are elk, yellow are deer, blue are foxes and purple are coyotes.  The seven species included in this picture are frozen at a particular time step. As the program runs, the number and distribution of the species changes based on the parameters selected by the experimenter. These include settlement procedures (the rates of immigration and reproduction of the species) and predation parameters (the food values, preferences and movement ability of the pedators and their prey.) The changes over time can be shown on various types of graphs -- again, as selected by the experimenter.

Our first task was to learn a bit about the Ecobeaker program. We began by going through a tutorial that illustrated the concepts of competition and predation on the simulation program. We then used the Keystone Predator simulation provided by the software package to look at some of the features of the Ecobeaker program. This simulation shows a rocky substrate ecosystem which includes nine species. There are three algae, several competing herbivores and planktivores, and a top level carnivore. The model includes both direct competition for food as well as competition for space on the hard substrate. After watching the program run, and making careful observations of the species' gut contents, movements, and competitive replacements, we attempted to diagram the competition interactions which we "discovered" in the model ecosystem. The food web that resulted from these observations is below.

For the diagram above, the rocky intertidal zone simulation called Keystone Predator was used. Pisaster is a starfish, K.tunicata is a chiton, Mytilus is a mussel, Mitella and Balanus are barnacles, Nucella is a snail and Corralina, Porphyra and Neorhodamela are attached algae.
 

After diagraming the situation on paper, we predicted what would happen if we removed particular species. We then tested these predictions by using the computer to remove individual species to see what the effects would be. We found that the starfish, Pisaster, is a keystone species for this model. Removing this species from the simulation resulted in a collapse of the entire ecosystem. The removal of the starfish allowed the mussel Mytilus to crowd out the algae as well as the other attached organisms. Then the barnacle-eating snail, Nucella, died off for lack of food. This left only the mussel, Mytilus, remaining on the rocks.

The simulations we ran in the lab gave us a feel for how even a small number of  individuals in a particular species can change their environment. By running these models and graphing the population changes, we developed a better understanding of how to design a stable ecosystem using the program.

Our next job was to learn as much as possible about the Yellowstone Park ecosystem in order to design our own simulations. These simulation activities can be used by teachers and students to learn about modeling ecosystems. We scanned the government research report  Wolves For Yellowstone? A Report to the United States Congress, May 1990 which was prepared before the release of the wolves into the Yellowstone ecosystem. We also examined reports on the ecology of the wolf populations of Minnesota, Alaska and Canada in order to better understand some of the components in this type of ecosystem.

Based on our research, attempted to draw food webs  illustrating several of the major components of the Yellowstone ecosystem. We divided into three sub-groups where each sub-group selected a part of the food web and designed a model to represent their respective components for the simulations.

Using EcoBeaker, we set parameters for each species based on our research.  We were able to manipulate variables such as settlement and birth rates, the amount of habitat available, and the dietary and energy requirements necessary for survival and reproduction.  We added one species at a time to see how that species would survive in the environment that we had created.  As each species was added, we were able to observe its population fluctuations as it interacted with the other species that already existed there.  We were able to observe a running model of these interactions by viewing a Species Grid and a variety of population graphs. The computer models were adjusted to maintain stability. Each of our models focused on how different parts of the ecosystem would behave both in the presence and absence of wolves, to demonstrate the far-reaching effects of this top predator.
 
 

Main Page

Situation 1

Situation 2

Situation 3

Resources: Wolves

Resources: Modeling

 
 

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The Woodrow Wilson National Fellowship Foundation CN 5281, Princeton NJ 08543-5281 - Tel:(609)452-7007 - Fax:(609)452-0066 Technical contact: lpt@woodrow.org