Download 14. Natural Selection

14. Natural Selection
A. Natural Selection Simulation:
Predator and Prey
Objectives
At the end of this lab you should be able to:
1. Define the concepts of natural selection and genetic drift.
2. Differentiate between natural selection and genetic drift
with respect to how they influence evolutionary change in
small populations.
Introduction
Have you ever wondered how it happened that many
In this simulation, a predator will visually “hunt” and “kill”
its prey. Two important factors in determining the environmental “fitness” of organism will be studied. The first factor
is the genetically determined ability of an organism to see
various shapes, colors and movements. The second factor,
camouflage, is the structural adaptation that allows potential
prey to blend in with their environment, thereby avoiding
detection by potential predators.
organisms are so well suited for their environment? Consider
Materials
how night vision in nocturnal animals allows them to find
food or how a deer’s quickness allows it to avoid many
Each group needs:
predators. These variations that help an organism survive
•
A container of with 40 mixed beads, 10 beads in each of
4 colors
•
A piece of multicolored fabric with a complex pattern
(about 50 cm x 30 cm)
•
4 small containers, each with beads of one of the four
colors (about 40 beads in each container)
•
Colored markers in the same colors as the beads
•
2 labeled petri dishes: “survivor” dish and “graveyard”
dish
•
Masking tape, sticky side out, wrapped around 3 pencils
are called adaptations. Organisms have developed many
different kids of adaptations that help them survive in their
environments.
Charles Darwin observed many species of animals and plants
in the Galapagos Islands that were unique to the islands,
but still similar to species he had seen elsewhere. Darwin
developed a theory called natural selection to explain how
species change over time. He described natural selection as
the process by which populations change in response to their
environment. As individuals better adapted to their environment survive, they are able to reproduce and pass their
variations on to the next generation.
Evolution can be a difficult subject of study in real time.
Evolutionary change generally occurs at extremely slow rates.
This simulation is designed to speed up the process, so we can
get a glimpse of the process in a shorter time frame.
Procedure
1. Spread the fabric out on the lab bench. This will act as
your habitat. The beads will act as the prey.
2. Assign roles in your group so that you have a “habitat
manager” who manages the fabric and bead counts, a “data
recorder” and “chip collectors” that will act as predators.
14. Natural Selection
3. Answer the question below and then finish the If…Then
hypothesis by predicting which colors will be left in the
largest number after 3 rounds.
What colors are found on your material?
Data Analysis
Table 14.1: Sample Data
Hypothesis:
If natural selection occurs then…..
4. All group members should turn their backs on the habitat
while the habitat manager sprinkles the 40 beads onto the
fabric and spreads them evenly.
5. The “predators” pick out 30 beads one at a time in the
following manner: look at the fabric and select a “prey” by
only using eyesight to locate the bead. Take the first bead
that stands out - look away between each “hunt”.
Table 14.2: Natural Selection Simulation Results
Round One
Survivors
6. Put the bead victims in the “graveyard” dish. The habitat
manager should count them carefully as they are hunted,
until 30 are removed from the fabric and placed in the
dish.
Offspring
(Survivors x 3)
Offspring
+
Survivors
Totals
Offspring
(Survivors x 3)
Offspring
+
Survivors
Totals
Offspring
(Survivors x 3)
Offspring
+
Survivors
Totals
7. Stop hunting when 10 survivors are left on the fabric.
8. Remove the remaining 10 bead survivors from the fabric
and place them in the “survivor” dish. Count the number
of each color and record the data in Table 14.2 (see sample
data in Table 14.1).
Round Two
Survivors
9. Assume that each survivor produced three offspring.
Multiply the number of each survivor by 3 and put the
results in the data sheet. The four totals should add up
to 30.
10. Add the number of survivors of each color to the corresponding total from step 9 and record the results in
the Totals column of Table 14.2. Make sure the total
number of all four colors is 40.
11. Take the number beads of each color shown in the Totals
column from the four single-color bead contains and once
again have the habitat manager scatter 40 beads onto the
fabric to start round 2.
12. Repeat steps 5-11 two more times for a total of three
rounds.
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Round Three
Survivors
14. Natural Selection
3. Did any bead colors become extinct? If so, which ones and
why do you think this happened?
Graphing
Display your results in a graph with the vertical (Y) axis being
the total number of beads after each round for each of the
four colors (include also the starting populations, 10 of each
color) and the horizontal axis (X) being the three rounds
plus “round zero”, the starting point. Use Graph 14.1 or the
graph paper provided.
Review Questions
1. Was one bead color represented more than others in the
first generation of survivors?
4. Which colors had the greatest surviving populations?
Why?
2. Did the population of this bead increase or decrease in the
second generation?
Graph 14.1: Natural Selection Simulation Results
Number of Beads after each Round
40
30
20
10
0
Start
Round 1
Round 2
Round 3
Rounds
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14. Natural Selection
B. Genetic Drift Simulation
In this simulation, the “prey” will be killed by a falling tree
that smashes into their habitat.
Data Analysis
Table 14.3: Genetic Drift Simulation Results
Round One
Procedure
Survivors
1. Identify your roles in the team: The Falling Tree “smashes”
a pencil onto the fabric. The Habitat Manager manages
the fabric and bead count. The Recorder records the data
in the data tables.
Offspring
(Survivors x 3)
Offspring
+
Survivors
Totals
Offspring
(Survivors x 3)
Offspring
+
Survivors
Totals
Offspring
(Survivors x 3)
Offspring
+
Survivors
Totals
2. The habitat manager sprinkles 40 beads onto the fabric
and spreads them evenly.
3. With eyes closed, the Falling Tree gently rolls or drops the
taped pencil randomly onto the habitat and removes the
prey that stick to it. Be sure to watch for escapees that get
knocked off the fabric! Put them back on the fabric!
Round Two
Survivors
4. Put the beads from the pencil in the “graveyard” dish,
counting them carefully as they are “killed” until all 30 are
removed. It may take a few rolls of the pencil to achieve
the precise number of 30 beads. If a roll yields a cumulative number “killed” larger than 30, beads from that roll
should be put back on the fabric and the pencil re-rolled,
if necessary repeating this procedure of replacing and rerolling until exactly 30 beads have been removed.
5. Check to make sure there are 10 survivors left in the
habitat.
6. Remove the remaining 10 bead survivors from the fabric
and place them in the “survivor” dish. Count the number
of each color and record it in Table 14.3.
Round Three
Survivors
7. Multiply the number of each survivor by 3 and put the
results in Table 14.3. The total of all four colors should
add up to 30.
8. Add the number of survivors of each color to the corresponding total from step 8 and record the results in the
Totals column of Table 14.3. Make sure the total number
of all four colors is 40.
9. Then, take the number of beads of each color shown in the
Totals column from the four single-color bead containers
and once again scatter 40 beads onto the fabric to start
round 2.
10. Obtain a new taped pencil and repeat steps 3-9 two more
times for a total of three rounds.
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Graphing
Display your results in a graph with the vertical (Y) axis being
the total number of beads after each round for each of the
four colors (include also the starting populations, 10 of each
color) and the horizontal axis (X) being the three rounds
plus “round zero”, the starting point. Use Graph 14.2 or the
graph paper provided. Use colored markers for the beads.
14. Natural Selection
Review Questions
1. What does each of the simulation components represent
in nature?
2. What are at least two other variables that affected how
the simulation played out? Do these same variables exist in
nature?
The bead:
The pencil:
The step of increasing the 10 survivors to 40:
3. What if the two mechanisms, natural selection and genetic
drift, were both operating in the simulation? Predict the
outcome.
The fabric:
4. Compare and contrast the graphs of the Natural Selection
Simulation and the Genetic Drift Simulation.
The bead colors:
The elimination of bead colors:
The different rounds:
Number of Beads after each Round
Graph 14.2:
40
Genetic Drift Simulation Results
30
20
10
0
Start
Round 1
Round 2
Round 3
Rounds
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