The model consisted of the following components:
 

Grasses	Rodents	Elk	Coyotes	Wolves

Our investigation consisted of examining the ecological construction of one small part of the Yellowstone National Park community.  Our chief  concern was how the  reintroduction of the wolves to the park might affect the coyote population. In the first simulation we constructed a food web that involved the wolves, coyotes , elk , rodents, and  grass. From the food web outline of the community we asked specific questions such as:

• Will the coyote population increase or decrease with the introduction of the wolves?
• Will the elk population decrease?

Using the EcoBeaker program, we developed  a stable ecosystem by manipulating variables such as: prey species, diet, movement, birth rate, immigration, and feeding behavior. Then we introduced the wolves.  We developed a model in which the wolves had little effect on any of the populations except the coyotes, which they reduced dramatically.  During the exercise, we removed the wolves from the community and found  they had a much larger effect than we expected.  We concluded that the wolves were a keystone species for this ecosystem because they determined the structure of the community. Without the wolves, there was no significant predator for the elk. The unchecked growth of the elk population would have seriously depleted the grass and the herbivore (elk and rodent) populations would have crashed. The wolf predation reduced the previous growth of the elk population which allowed the rodents to survive. The rodents were the food supply for the coyotes. The elk, rodent and coyote populations were stabilized shortly after the introduction of the wolves and diversity was maintained.
 
 

Note the changes in the elk population at the point of the wolf introduction (time step 200). The wolves' predation of the elk allowed the other species populations to stabilize at more predictable levels. Note also that the rodents' population does cycle during the period of elk growth (time step 50,) but each peak is smaller than the previous peak. Because the coyotes prey primarily on rodents in our model, their populations also cycle, but the cycles are less dramatic, and follow the rodent population peaks.
 

Main Page

Introduction

Situation 1

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