Natural Selection and Predator-Prey Evolution
Name
Objectives
1. Describe the factors that influence
the survival of prey organisms
2. Describe the factors that influence
the survival of predator organisms
3. Explain how natural selection
provides for the evolution of a
population
4. Explain how the populations of
predators and prey are intertwined
Introduction
This exercise simulates a population of
predators, or consumers that feed on other
species. It also simulates a population of
prey, or the food species of the predator.
Both the predator and prey show variation
within their populations, and we will
simulate this variation in our exercise. The
Theory of Natural Selection states that the
characteristics of organisms in a population
will tend to change over time in response to
the environment. This is because:
1. A population of organisms shows
variation among its members
2. Individuals in a population compete with
each other for food, shelter, etc.
3. Those individuals who have variations
and characteristics that help them compete
better will reproduce more often and leave
more offspring
4. Subsequent generations of this population
will have a greater proportion of individuals
with strong competitive characteristics for a
given environment.
You will discover in this exercise that a
change in “the environment” includes
changes in the food supply, changes in the
ease of catching food, changes in the
background that an organism might try to
“hide” on, and changes in the numbers and
efficiency of organisms that eat others. All
these factors alter the nature of the
competition between prey organisms,
between predator organisms, and between
both populations. These factors therefore
promote evolutionary change, or alterations
in the numbers of certain variations (allelic
frequencies) in a population. Because
changes in the predator population also
effect the prey population, and vice versa,
the two groups coevolved.
If the allelic frequencies (proportion of
certain variations) changes in a population,
it could be due to directional, stabilizing, or
disruptive selection. In directional
selection, individuals in subsequent
generations become more like one extreme
variation in the population. In stabilizing
selection, intermediate variations become
more common and the extremes are lost
over time. In disruptive selection, two
extreme variations become common and
intermediate variations die out. You will be
asked about the type of selection you see in
the predator-prey exercise today.
When the last member of a predator or
prey population dies, that species becomes
locally extinct. This occurs when the
predator or prey does not have the variations
necessary to cope with the pressure of eating
or escaping. It is probably easier to envision
how an increase in predators could wipe out
all the prey, but an equal change in the
ability of prey to escape capture can wipe
out all the predators by starvation. Changes
in predator and prey populations can be
caused by the actions of humans, disrupting
Bios 140 Biology Lab Manual
pg. 1
the ecological balance between these
species.
PROCEDURE
The prey in this exercise will be colored
beans or beads or some other small objects.
The prey will be carefully counted, with
different variations among them, and strewn
randomly over the Hunting Ground.
Your instructor will designate you as a
certain type of predator. There will be an
equal number of each type of predator at the
beginning of the game. Predators in this
exercise have a mouth (a paper cup) and a
capturing structure (a fork, chopsticks, spoon,
tweezers, etc). To capture and eat prey, a
predator must lift the prey off the ground and
drop it into its mouth. Predators may not
scrape prey along the ground into their cup
(illegal move).
Your instructor will ask you to stand
around the edges of the Hunting Ground with
your “tool” touching your nose. When the
signal is given, you can hunt for only a short
time (like 10 seconds). During this time, you
should eat as much as you can. You may
compete with other predators for the same
prey (no bumping) and you cannot disturb
any of the prey already “eaten” in another
predator’s cup.
After hunting, we will count and tabulate
how many prey were eaten by which
predators. Be sure you write down the
data we collect together on your own
sheet. If you don’t eat at least 10 prey in a
hunt, you’re dead. You might be reborn
again as another predator type however in a
later hunt.
Every prey and predator alive after a
hunt will be allowed to reproduce with a
single offspring. In this game, we are
keeping the reproductive rate of all the
organisms constant for simplification. In
nature, reproductive rate and the number of
individuals born at the same time vary
between parents.
Your instructor may have you play up to
four generations of prey and predators
before having you sit down and complete
the questions at the end.
Bios 140 Biology Lab Manual
pg. 2
LAB REPORT
Predator/Prey Evolution
Name
FIRST GENERATION
Number of
prey at start
Prey type
Number of
prey caught
% of total prey
caught
Number of
surviving prey
Number of
prey after
reproduction
% of total prey
in field after
reproduction
White
Sky-blue
Sapphire (transparent)
Royal blue (dark)
Black
TOTAL
Predator type
Number of
predators at start
Number of
predators died
% of total
predators died
Number of
surviving
predators
Spoon
Spork
Fork
Forceps
Chopsticks
TOTAL
Calculations:
Bios 140 Biology Lab Manual
pg. 3
Number of
predators after
reproduction
% of total
predators alive
after
reproduction
SECOND GENERATION
Number of
prey at start
Prey type
Number of
prey caught
% of total prey
caught
Number of
surviving prey
Number of
prey after
reproduction
% of total prey
in field after
reproduction
White
Sky-blue
Sapphire (transparent)
Royal blue (dark)
Black
TOTAL
Predator type
Number of
predators at start
Number of
predators died
% of total
predators died
Number of
surviving
predators
Spoon
Spork
Fork
Forceps
Chopsticks
TOTAL
Calculations:
Bios 140 Biology Lab Manual
pg. 4
Number of
predators after
reproduction
% of total
predators alive
after
reproduction
THIRD GENERATION
Number of
prey at start
Prey type
Number of
prey caught
% of total prey
caught
Number of
surviving prey
Number of
prey after
reproduction
% of total prey
in field after
reproduction
White
Sky-blue
Sapphire (transparent)
Royal blue (dark)
Black
TOTAL
Predator type
Number of
predators at start
Number of
predators died
% of total
predators died
Number of
surviving
predators
Spoon
Spork
Fork
Forceps
Chopsticks
TOTAL
Calculations:
Bios 140 Biology Lab Manual
pg. 5
Number of
predators after
reproduction
% of total
predators alive
after
reproduction
FOURTH GENERATION (Optional if time allows)
Number of
prey at start
Prey type
Number of
prey caught
% of total prey
caught
Number of
surviving prey
Number of
prey after
reproduction
% of total prey
in field after
reproduction
White
Sky-blue
Sapphire (transparent)
Royal blue (dark)
Black
TOTAL
Predator type
Number of
predators at start
Number of
predators died
% of total
predators died
Number of
surviving
predators
Spoon
Spork
Fork
Forceps
Chopsticks
TOTAL
Calculations:
Bios 140 Biology Lab Manual
pg. 6
Number of
predators after
reproduction
% of total
predators alive
after
reproduction
LAB REPORT QUESTIONS
Natural Selection and Predator-Prey Evolution
Name
***Turn in your data tables with this worksheet portion
1. Which prey variant was the best adapted, and why?
2. Which prey variant was the least adapted and why? Which species, if any, went extinct?
3. Which predator variant was best adapted, and why?
4. Which predator variant was the least adapted and why? Which species, if any, went extinct?
5. Describe how you think the changes in the prey population was affected by simultaneous
changes in the predator population.
6. How might the introduction of an alien predator species into Puget Sound affect:
a. the number and makeup of the prey that this predator can eat?
b. the number and makeup of other predators which also eat the same prey?
7. Describe in your own words why certain prey variants became more common over several
generations, using the principles of natural selection.
8. Name a simple change in the Hunting Field or the predator population (i.e. the “environment”)
which would alter the proportion of prey variants in a different way than that seen in this
particular exercise. Hypothesize about the results.
Bios 140 Biology Lab Manual
pg. 7

Determining the Type of Natural Selection for Prey
 Review the prey colors in this exercise and organize them in order of lightest to darkest.
Assign a number from 0 to 4 to each color of prey, from lightest to darkest. Using the
graph paper on the next page, plot the Color Value of each prey color versus the
Number of Prey at Start for the First Generation. Draw a smooth curved line between
the points.
 Then complete an ending graph by plotting the Color Value versus the Number of Prey
After Reproduction for the last generation you played in lab. If you only did three
generations, this graph shows the number of prey at the start of the fourth generation.
Use the same scaling on the x-axis for both of these graphs to facilitate comparison.
First Generation
Last Generation
 What type of selection (directional, stabilizing, or disruptive) was seen in this game for the
prey?
Bios 140 Biology Lab Manual
pg. 8

Determining the Type of Natural Selection for Predators
1. Review the predator types in this exercise and organize them in order of wide-solid to
thin-long-disconnected. Assign a number from 0 to 4 to each type of predator, from widesolid to thin-long-disconnected. Using the graph paper on the next page, plot the WidthLength Value of each prey color versus the Number of Predators at Start for the First
Generation. Draw a smooth curved line between the points.
2. Then complete an ending graph by plotting the Color Value versus the Number of
Predators After Reproduction for the last generation you played in lab. If you only did
three generations, this graph shows the number of predators at the start of the fourth
generation.
Use the same scaling on the x-axis for both of these graphs to facilitate comparison.
First Generation
Last Generation
3. What type of selection (directional, stabilizing, or disruptive) was seen in this game for
the predators?
Bios 140 Biology Lab Manual
pg. 9