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Microevolution & Mechanisms of Evolution Activity
Station One: Skittlebugs
A population of Skittlebugs live in Bottle Forest. Skittlebugs have 5 different
color variants: yellow, green, orange, red, and purple. In the current
environmental conditions, all colored Skittlebugs have approximately the
same chance of surviving and reproducing.
1. The population of Skittlebugs in Bottle Forest has 20 of each color Skittlebug
(total of 100 Skittlebugs). What is the percent composition of the population of each
color Skittlebug?
Color
% of population
Yellow
20/100 X 100 = 20%
One day, a flash flood comes through the forest and kills all but 6 Skittlebugs
that just happened to be high up on a rock when the flood came through.
2. Pour 6 Skittlebugs from the Bottle Forest to represent the new population after
the flood. Examine your new population. What is the percent composition of the
population of each color Skittlebug in the new population?
Color
% of population
______/6 X 100= __________%
3. What happened to the variation & genetic diversity of the Skittlebug population
after the flood? Did it increase or decrease? Refer to your data table.
4. Which of the following mechanisms of evolution does this simulate (more than
one may be correct; if so, identify both): gene flow, genetic drift, bottleneck effect,
founder effect? How do you know?
Station 2: Owl Island
Think about the population of Bensalem High School. Record what phenotypes
exist within Bensalem HS for the following traits (be as specific as possible, i.e.
light brown, dark brown, etc.):
Hair color:
Eye color:
You and your group members decide to leave the population of Bensalem High
School. You move to Owl Island and start your own population. Record what
phenotypes exist within your new population:
Hair color:
Eye color:
1. What happened to the variation & hence genetic diversity of the population of Owl
Island compared to the initial population?
2. Which of the following mechanisms of evolution does this simulate (more than
one may be correct; if so, identify both): gene flow, genetic drift, bottleneck effect,
founder effect? How do you know?
Station 3: Skittlebug meets Skittlebug
Hamlin Forest has two populations of Skittlebugs: 20 purple Skittlebugs live
on the west side and 20 yellow Skittlebugs live on the east side. The two
groups are separated by a small river (Skittlebugs can’t swim). One day, a tree
falls across the river, creating a bridge for the Skittlebugs to travel back and
forth from the west side to the east side. 5 yellow Skittlebugs move to the west
side from the east side. Demonstrate this by moving 5 yellow Skittlebugs from
the east side beaker to the west side beaker.
Analyze the percent composition of each allele in the west side of the forest before
and after the yellow Skittlebugs joined this population.
Allele
Number in West Side
population Before
Number in West Side
Population After
Purple
Yellow
1. Did the variation in the west side of the forest increase or decrease after the
Skittlebugs were able to move between populations? (Think about how many alleles
existed in the population before versus after)
2. Which of the following mechanisms of evolution does this simulate (more than
one may be correct; if so, identify both): gene flow, genetic drift, bottleneck effect,
founder effect? How do you know?
3. If the tree had never fallen, the two populations of Skittlebugs would have
remained separate. If they were separate for long enough, do you think they could
eventually evolve into different species? Explain.
Station Four: Microevolution
Scenario 1: Pick the graph that shows a change in the population of giraffes after
reading the scenario. Giraffe’s will be successful in an environment with large trees
if the giraffe has a long neck. There was a selection pressure against short necks,
since individuals with short necks could not reach as many leaves on which to feed.
As a result, the distribution of neck length shifted to favor individuals with long
necks.
Question 1: What graph matches the scenario and why?
Scenario 2- Plant height might be acted on by stabilizing selection. A plant that is
too short may not be able to compete with other plants for sunlight. However,
extremely tall plants may be more susceptible to wind damage. Combined, these two
selection pressures select to maintain plants of medium height. The number of
plants of medium height will increase while the numbers of short and tall plants will
decrease.
Question 2: What graph matches the scenario and why?
Scenario 3- Imagine a plant of extremely variable height that is pollinated by three
different pollinators, one that was attracted to short plants, another that preferred
plants of medium height and a third that visited only the tallest plants. If the
pollinator that preferred plants of medium height disappeared from an area,
medium height plants would be selected against and the population would tend
toward both short and tall, but not medium height plants.
Question 3: What graph matches the scenario and why?