Hon Env Science
2013-14
Name ______________________________ Per _____
Date _____________
Predator Prey Simulation
Background Information
Interactions between predators and their prey are important in 1) determining the populations
of both predators and prey and 2) determining and maintaining the structure of a community.
Many factors enter into the ultimate outcome of the predator-prey interactions. A predator
must have the skills and appropriate physical structure to be able to find, recognize, capture,
and consume its prey. Prey, in turn try to avoid predators by employing a variety of adaptations
including physical, chemical, and behavioral strategies. Habitat also plays an important role in
determining the number of prey that can be supported, whether the predator is present or not.
Predator-prey interactions in a population are usually a feedback system. The prey population
has a positive effect on the predator numbers, but the predator population has a negative
effect on the prey numbers. The predator-prey relationship can be represented as changing
cyclically with a phase diagram as shown below.
In the lower right quadrant, as the predator
population rises, the prey population also rises.
But, as the predator numbers reach a particular
size, the prey population starts to decrease,
followed by an eventual decrease in the predator
population as well. (seen in the upper left
quadrant).
In time the predator population becomes small enough for the prey numbers to rebound and
the process continues into another cycle. In nature, the cycles are more complex that is
indicated in the diagram, as there are many factors that influence populations in the wild. In
this investigation, the factors will be confined simply to just the predator-prey pressures.
Hon Env Science
2013-14
Name ______________________________ Per _____
Date _____________
Objectives

Simulate and analyze the interactions between a predator population of coyotes and a
prey population of mice.

Organize and graph data from the simulation, predicting future populations over several
generations.
The Situation
A field that had once been planted in corn has now been temporarily abandoned. The field is
now undergoing early stages of succession. Mice, as well as other herbivores, are moving into
the field in search of food and shelter. As the mouse population increases, due to immigration
and reproduction, coyotes and other carnivores in search of food are attracted to the area.
Procedure
In this simulation, the field (habitat) is represented by a shallow paper plate, the mouse
population (prey) is represented by beans, and the coyote population (predator) is represented
by spoons. You need to follow the rules of the community listed below to take the coyotes and
mice through many generations, simulating the effects of each on the population of the other
over time.
Rules:

There must be a minimum of 10 mice at the start each generation.

At the end of each generation, the surviving mice double in number due to reproduction
and immigration.

There can be no more than 100 mice to start each generation. So, 100 mice is the
carrying capacity.

There must be at least 1 coyote at the start of each generation.

Coyote must capture 5 mice to survive in a generation and reproduce 1 offspring. Less
than 5 mice = coyote death, but 1 new coyote will emigrate into the habitat (following
the 1 coyote rule).
Hon Env Science
2013-14
Name ______________________________ Per _____
Date _____________
Data & Graphing
1. Record all data in the data table attached at the end of the lab handout.
2. Graph the following data
a. Initial mice and coyote population size vs. generation number
b. Surviving number of mice and coyote vs. generation number
c. Number of captured mce and surviving coyote vs. generation number
Analysis Questions. For full credit, type your answers to the following questions in complete
sentences on a separate sheet of paper.
1. Which population (mice or coyote) shows the first increase in numbers? Why?
2. Describe the change in the mice population over the course of the 20 generations.
3. Describe the change in the coyote population over the course of the 20 generations.
4. Describe the relationship between changes in the mice population relative to changes in the
coyote population over the course of the 20 generations.
5. Which of the three graphs best illustrates the relationship between changes in the mice
population relative to changes in the coyote population and why?
6. What do you predict would happen to your results if your system was disturbed by some
unforeseen, outside force? Explain and Illustrate your predictions graphically if some of the
predators died of disease, and if the prey population experienced a wildfire, or another
natural disaster.
7. What could you do to adjust the community rules to better model natural patterns?
8. Consider predator-prey relationships in an aquatic ecosystem. How might an excess
nutrient like nitrogen affect population sizes? How might a decrease in nitrogen levels affect
population sizes?
9. Describe three adaptations of predators that make hunting easier and three adaptations of
prey that help them escape predation.
10. How could a predator-prey simulation be used to model the spread of disease such as
measles, SARS, ebola, or the flu, in a large population center? Explain.