Predator/Prey Lab
Names______________________________________________
Problem: How do the numbers of predators and prey in an ecosystem affect each other from
generation to generation?
Materials:
Petri dish
100 beads
Spoon
Data sheet
Assumptions:
1. The surviving mice of each generation always double their numbers.
2. In each generation at least 10 mice are initially present in the meadow (by immigration if
necessary).
3. The maximum number of mice that the meadow can support is 100.
4. In each generation at least one weasel is initially present in the meadow (by immigration
if necessary).
5. In order for a weasel to survive in the meadow, it must capture at least 5 mice. (If a
weasel does not capture at least 5 mice, it will either starve or move to another meadow
to search for food.)
6. For each 5 mice that a weasel captures, it will produce 1 offspring. (If 1 weasel captures
7 mice and a second captures 2, the first weasel will survive in the meadow and produce
1 offspring, but the second will neither survive in the meadow nor produce offspring.)
Procedure:
Generations 1-4 Data
Generation 1- Begin with 10 mice, scoop once through the dish for each weasel present (1 to
begin). Do not capture any mice. Record your data in the charts together with your instructor.
Generation 2- Double your remaining mice from generation 1 (20 mice), another weasel has
moved into the meadow. Scoop once through the dish and capture 4 mice. Record your data in
the charts together with your instructor.
Generation 3- Double the remaining mice from generation 2 (32 mice). Another weasel has
immigrated into the meadow. Scoop once through the dish and capture 7 mice. Record your
data in the charts together with your instructor.
Generation 4- Double the remaining mice from generation 3 (50 mice). There is 1 surviving
predator from generation 3 and 1 predator offspring, so scoop 2 times through the dish.
Capture 13 mice for the first predator and 7 mice for the second predator. Record your data in
the charts together with your instructor.
All other generations- continue as we have been doing in the first 4 generations. Remember DO
NOT LOOK AT THE DISH WHILE SCOOPING. Remember the mice total never falls below 10 and
the predators never fall below 1. When table 2 is complete graph your data as directed on the
data sheet.
Results: See data sheet
Questions:
1. Which population (predator or prey) shows the first increase in numbers?
2. Does a peak in the weasel population come at the same time or after a peak in the mice
population? Why?
3. What factor seems to determine the size of the weasel population in the meadow at any
given generation?
Weasel and mice data sheet 1
Initial
Predators
Initial Prey
Prey survivors
Predator
Survivors
Predator
offspring
PART B
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
G1
C O
G2
C O
G3
C O
G4
C O
G5
C O
G6
C O
G7
C O
G8
C O
G9
C O
G 10
C O
G 11
C O
G 12
C O
G 13
C O
G 14
C O
Graph Results- After the table is complete; plot the results on the graph below. Use an X for the
amount of initial prey in each generation and an O for the amount of initial predators in each
generation. Connect the X points and then the O points. Use different colors for X and O.