# The Predator-Prey Simulation

Dorothy Reardon
1991 Woodrow Wilson Biology Institute

## Objectives:

The student simulates the interactions between a predator population of lynx and a prey population of rabbits in a meadow. After collecting the data, the student graphs the data and then extends the graph to predict the populations for several more generations.

## Background:

Before playing this game students should be able to define a food chain, population, immigration, predator and prey.

## Materials:

• one 7.5 cm cardboard square (the lynx); about 250 2.5 cm construction paper squares (the rabbits); a 61 cm square section of table top (the meadow); masking tape (to mark off the meadow); data table; graph paper.

## Procedure:

1. Distribute 3 rabbits in the meadow.
2. Toss the lynx square once in an effort to catch a rabbit. (At this point in the activity there is no way that the lynx can catch the 3 rabbits that it needs to survive and reproduce. The lynx is not allowed to skid and the rabbits should be distributed in the field.)
3. Complete the data table for generation #1. The lynx will starve and there will be no surviving lynx or new baby lynx.
4. At the beginning of generation #2 double the rabbits left at the end of generation #1. A new lynx immigrates into the meadow. Be sure to disperse the rabbits in the meadow.
5. Eventually the rabbit population increases to a level that allows the lynx to catch 3 rabbits in a single toss. If the lynx catches 3 rabbits it not only survives but it reproduces too! It has one baby lynx for each 3 rabbits that it catches. Therefore, if it catches 6 rabbits it will have 2 babies. Lynx are not allowed to cheat, but they should try to be efficient. Stupid lynx result in an overabundance of rabbits.
6. As the number of lynx increases throw the cardboard square once for each lynx. Record the number of rabbits caught by each lynx. The simulation is more realistic if the number of new baby lynx is based on each lynx`s catch rather than merely the total number of rabbits caught in a generation.
7. There are always at least 3 rabbits at the beginning of a generation. If and when the entire rabbit population is wiped out, then new rabbits immigrate into the meadow.
8. Remember that the number of rabbits in the meadow needs to be correct at all times. Remove the rabbits caught and add new ones as indicated by your data table.
9. Model about sixteen generations and predict nine more or up to a total of 25 generations. Base the prediction on the pattern observed during the first sixteen generations.

## Analysis:

Graph the data for 25 generations. Place both the rabbit and the lynx data (the first two columns of the data table) on the same graph so that the interrelationship can be easily observed. Label the vertical axis "Number of Animals" and the horizontal axis "Generations." Use one kind or color of line for rabbits and another for lynx.

## Resources:

This simulation is a classroom adaptation of a game produced for home use by Urban Systems Inc. many years ago. Other versions in use include owl and mice, etc. If your students are unable to run the simulation at their own workstations then it may be played on an overhead projector. You may wish to introduce disturbances in the cycle such as killing off the lynx or starving the rabbits. This activity serves as a good introduction to computer models.

### Predator-Prey Simulation

GenerationRabbitsLynxRabbits
Caught
Lynx
Starved
Lynx
Surviving
New Baby
Lynx
Rabbits
Left
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5

6

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9

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25

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