LAB ACTIVITY:Predator-Prey Simulation: Population Growth

Neil Sheard, Sarah Donnelly, Colleen Rapaich



Objectives:

To investigate how populations are affected by predator-prey relationships over several generations.

Materials:
- Sixty, 6cm x 6cm squares cut from stiff coloured paper:  the wolves.
- 400, 2cm x 2 cm squares cut from a different color of paper:  rabbits.
- One sheet of green paper (approx. 43 x 28 cm):  the meadow
- Graph Paper

Procedures:

1.  Read the following rules of the game:  
-The game contains a meadow and stacks of reserve cards for wolves and rabbits.  Active wolves and rabbits are taken from this reserve.
-The meadow is the playing field.
-To start the game, the rabbit managers distribute three rabbits evenly on each meadow.   The rabbit managers add active rabbits by spreading them evenly in the meadow and remove rabbits when they are caught.
-The wolf managers throw active wolf cards and add or remove active wolves from the meadow.
-All animals that are removed from the meadow are placed back in the reserve stacks.
-The following represents one round of the game and produces one generation:
          a.  The wolf managers toss each active wolf square into the meadow  in an effort to catch rabbits.  The toss must leave a wolf manager's hand outside the meadow area.  As long as the wolf  square touches a rabbit square, that rabbit is considered to be caught.
          b.  Each wolf that can catch three rabbits with one toss has enough  energy to reproduce, so the wolf managers double the surviving wolf population in the next round.
          c.  After the caught rabbits are removed, the remaining rabbit population is doubled for the next round.
          d.  If a wolf cannot catch three rabbits in a round, the wolf starves and is removed from the meadow by the wolf managers.
-If there are no surviving rabbits, a new round is begun with three new rabbits, which immigrate into the meadow.
-If there are no surviving wolves, a new round is begun with a new wolf, which immigrates into the meadow, and double the number of rabbits left at the end of last round.

2.  Play the game in groups of four.  Work in pairs.  One pair manages the prey  (rabbit population), and the other pair manages the predators (wolf population).

3.  Begin the game with one wolf and three rabbits.  Record these numbers as rabbits and wolves in the meadow.  Continue to record their counts at the beginning of each round for the 25 generations in the game.

4.One of the wolf managers should toss a wolf card into the meadow in an attempt to land on at least three rabbits.  Probably, the first wolf catches fewer than three rabbits and starves.  There will be no surviving wolf or new baby wolf.  (How do you explain this?)

5.  The rabbit managers should double the rabbit population and place them in the meadow.

6.Complete the data table for this generation.

7.The wolf managers too a new wolf into the meadow.

8.If the wolf catches three rabbits, remove three rabbits, add a wolf, and double the remaining rabbits for the next round.  If the wolf was unsuccessful, begin the next round with a new immigrant wolf, and continue to double the remaining rabbits.

9.  Continue additional rounds.  Eventually, the rabbit population will increase to a level that allows the wolf to catch three rabbits in a single toss. If the wolf catches three rabbits, it not only survives but also reproduces.  It has one baby wolf for each three rabbits that it catches.  Therefore if it catches six rabbits, it will have two babies.

10.Continue to play the game for up to 25 generations, recording data at the beginning of each generation.  By this time your meadow may be full of rabbits.  Toss as many wolf cards as are in their populations.


Interpretations:

1.  Graph your data using the number of individuals as the dependant variable and the number of generations as the independent variable.  Us a separate line on the same page for rabbits and wolves.

2. Study your graph lines for the two populations.  How are the wolf and rabbit populations related to each other?  How do the sizes of each population affect each other?

3.  Under what modifications can both populations continue to exist indefinitely?

4.  What do you think would happen if you introduced an additional predator, such as a coyote, which requires fewer rabbits to reproduce?

5.  What would happen if you introduced another type of rabbit, one that could run faster and escape its predators?  (In the game, you could give the new type of rabbit a chance to escape by tossing a coin after it is caught and letting it live if you got heads.)  Which type of rabbit would predominate after many generations of predation?

Applications:

1.  How does this simulation relate to the human population and its interaction with its environment?  Are there any predator-prey relationships?

2.  What predator-prey relationships have you observed in your community?

3.If a population biologist visited your classroom, what are some questions about the human population you could ask?