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NAME ________________________________________ DATE __________________PERIOD________
PREDATOR/PREY LAB
PURPOSE
Illustrate a predator-prey relationship and analyze the effect this relationship has on the dynamics of a
population.
BACKGROUND INFORMATION
A population is all the individuals of the same species within a community. The maximum rate of
reproduction of a population is its biotic potential. This is the rate at which a population would produce
offspring if every new individual lived and reproduced at maximum capacity. Populations never achieve
their biotic potential because the environment can only support a limited number of organisms. The
maximum number of individuals of a species that can be supported by the environment is called the
carrying capacity. Populations tend to stabilize, or stop growing in size, when the carrying capacity of the
environment is reached. The environmental factors that limit the size of populations are called limiting
factors. Predators are considered limiting factors because they can limit the size of the prey populations.
Conversely, the availability of prey is a limiting factor on the populations of predators.
Populations in nature are often controlled by predation. The regulation of a population by predation takes
place within a predator-prey relationship, one of the best-known mechanisms of population control. The
relationship between mice and weasels is one example of a predator-prey interaction that affects population
growth. In this lab, a new meadow develops in a forest as a result of a fire. Mice migrate into the meadow
and begin to reproduce. As the mouse population increases, a weasel is also attracted to the meadow. In
the following exercise the meadow (habitat) is represented by a dish, the mouse population (prey) is
represented by popcorn kernels, and the weasel population (predator) is represented by a spoon.
MATERIALS (by group of 2)
Small plastic bowl (habitat)
100 popcorn kernels (mice/prey)
plastic spoon (weasel/predator)
calculator
graph paper
PROCEDURE
Rules
1. The surviving mice of a generation always double their numbers.
2. In each generation, at least 10 mice are initially present (by immigration if necessary).
3. The carrying capacity is 100 mice (there cannot be more than 100 mice).
4. In each generation at least one weasel is initially present (by immigration if necessary).
5. In order for a weasel to survive, it must capture at least 5 mice. For each 5 mice that a weasel
captures, it will produce one offspring.
Completing the Exercise: Continue until you have completed 12 generations. When simulating the
capture of mice by the predator, scoop the spoon through the dish and do NOT look at the dish while you
are doing this and do NOT try to scoop up all the kernels. Remember that the initial prey must never fall
below 10 and the initial predators must never fall below one. Complete the generations in the chart on your
student lab sheet.
Using the data table, graph the number of prey at the beginning of each generation. Make a second line
on the same graph to represent the number of predators at the beginning of each generation.
(Hint: it would be helpful if you placed all the prey captured by each predator in its own pile so that
you can easily determine which predator survived and which reproduced.)
DATA TABLE
Generation
Number
Initial
Prey
Total Prey
Captured
Prey
Survivors
Initial
Predators
Surviving
Predators
Predator
Offspring
1
2
3
4
5
6
7
8
9
10
11
10
1
Questions
1. Which population, predator or prey shows the first increase?
2. What is the relationship between peaks in population? Explain.
3. What was the determining factor for the size of the weasel population?
4. Give three other examples of predator-prey relationships.
5. Describe a predator-prey relationship that will follow a cyclic pattern like the weasel-mice
relationship.
12
6. Is the competition between weasels to obtain mice interspecific?
7. Give an example of an organism that competes interspecific with the weasel in catching mice.