Download Part A-2. Colonization by First Generation

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Island Evolution Experiment
The Effects of Island Size and Distance from the Mainland on Island Evolution
Introduction
In Integrated Science 2, you conducted a simple simulation of natural selection by looking at color changes in a
population of mythical 'punch bug' organisms. The results showed evolutionary change towards traits that best
camouflaged the punch bugs in their environment. The only factor that affected the punch bugs was predation by the
simulated birds. That simulation did not account for conditions that make isolated island environments different from the
mainland. Also, in that simulation only predictable (deterministic) factors of predation were considered; random
(stochastic) disturbances were not.
In Charles Darwin’s theory of natural selection, predictable factors – predation, size, speed, camouflage, et. al –
influence the survival/reproduction of individual organisms. Since then, scientists have noted that many traits exist that
are not explained by natural selection. Evolution is shown occurring, even in the absence of natural selection. This
happens when populations (with their particular traits) change over time due to chance or random events.
Two scientists, Edward O. Wilson and Robert H. MacArthur, developed an important model to explain and predict
how specific random events influence island evolution. Their model, called the theory of island biogeography, predicts
the number of species found on any given island.
This prediction is based on two factors that determine the species number: immigration, which adds species and
extinction, which removes them. The rates of extinction and immigration are, in turn, influenced by two other factors:
distance from the mainland and island size. Both of which determine the likelihood that random events will play a crucial
role in the evolution of that island’s organisms.
How do distance and size influence island evolution? Distance has a critical effect on immigration. Islands closer to
the mainland have a greater chance of immigration/emigration than islands that are farther away. Island size influences the
extinction rate by determining the population size that an island can support. Smaller islands support smaller populations
while larger islands have larger populations. Smaller populations, importantly, are much more susceptible to random
events such as storms, volcanoes and disease. The theory of island biogeography is quantitative and is most easily
visualized using the graph below and to the right. The immigration curve of the graph shows that the chance of
immigration decreases as distance from the mainland increases, while the extinction curve shows the chance of extinctions
increasing with decreasing island size.
The point at which the two curves cross defines the theoretical equilibrium number
of species an island can support. This theory has been supported with field studies,
most importantly from the re-colonization of Krakatoa following its dramatic eruption
of 1883.
The Effects of Distance and Size
on Immigration and Population
Size
The purpose of this new simulation is to provide a better model for evolution as
it occurs on islands. We will compare island and mainland evolutionary models by
conducting three simulations using the same ‘environment.’ We will measure
evolution by comparing the number and populations of color variations in punchbugs
over time in our three experimental treatments. We will also look to see if the island
simulations develop the same color/camouflage patterns as the mainland simulation.
Additionally, this experiment will include a variety of random/stochastic events,
allowing us to test the hypothesis that these events have a greater effect on islands.
Focus Questions:
What are the important differences between island environments and the mainland environments?
What factors influence the populations of both islands and the mainland?
How the difference between islands and the mainland effect the process of natural selection and the evolutionary
results of that process?
How can those differences, between island and mainland environments, be effectively simulated?
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Procedures:
Read ALL procedures and then complete the hypothesis on page X BEFORE starting lab):
Each group in the class will conduct some aspect(s) of our experiment (A-1/2/or 3as instructed by your teacher. Data will
be shared with the class so work correctly and carefully. Complete Part A-1/2/or 3 and then follow Part B- H.
Mainland Environment Treatment
Part A-1. Establishment of First Mainland Generation
1. The ‘mainland’ has 6 punchbug variations represented by different colors. Choose a cloth (the ‘environment’) and
pick up 6 jars of different colored of punchbugs. 3 of the color variations match the cloth and 3 do not.
2. Count out 10 of each of the six punchbug color variations (60 punchbugs total). Record the starting population of
(which should be 10) for each color on your Raw Data Table (separate handout). Also note the pattern of the cloth
and which punchbug colors match the cloth.
3. Using the cloth “environment,” unfold the cloth to its full size and scatter the First Mainland Generation
populations evenly.
Near or Far Island Environment Treatments
Part A-2. Colonization by First Generation
1. Choose a cloth (the ‘environment’) and 6 jars of punchbug variations (from the mainland) to populate the “island.”
2. To be populated, an island must be colonized by organisms from the mainland. Colonization, from the mainland, is
largely a chance occurrence. The ‘mainland’ environment – your source of immigration/colonization – has 6
punchbug variations as represented by different colors. The probability of a given variation colonizing a given island
is largely dependent on the island’s distance from the organism’s habitat.
• If you have a ‘far’ island, only 3 colors will successfully colonize your island. Place one punchbug of each color
variation on the table. Close your eyes and have a partner shuffle the 6 colors. With your eyes closed, randomly
select 3 of the punchbug colors. The 3 selected colors represent successful colonizers—the remaining 3 colors did
not make it to the island.
• If you have a ‘near’ island, the probability of colonization is greater. Place one punchbug of each color variation
on the table. Close your eyes and have a partner shuffle the 6 colors. With your eyes closed, randomly select 5 of
the punchbug colors. The 5 selected colors represent successful colonizers—the remaining 1 color did not make it
to the island.
3. Count out (10) of each color variation that successfully colonized your island (a total of 50 punchbugs if a near island;
30 if a far island). Record the starting population of (10) for each successfully colonizing color on your Raw Data
Table (separate handout). Also note which punchbug colors match the cloth.
4. Unfold the cloth to its full size and scatter the First Generation populations evenly on the cloth.
Large or Small Island Environment Treatments
Part A-3. Colonization by First Generation
1. Choose a cloth (the ‘environment’) and (6) jars of different colored of punchbugs. Three (3) of the color variations
should match the cloth and three (3) should not match.
2. Resource availability is limited by environment size. The size of a population on a given island is dependent on the
island’s size.
• If your island is ‘large,’ assign a starting population of (6) for each of the (6) color variations.
• If your island is ‘small,’ assign a starting population of (3) for each of the (6) color variations.
3. Count out to appropriate number of each of the eight punchbug color variations (36 total punchbugs if a large island;
18 if a small island). Record the starting population of 6 (if large island) or 3 (if small island) for each color on your
Raw Data Table (separate handout). Also note which punchbug colors match the cloth.
4. For a large island, unfold the cloth to its full size. For a small island, unfold to full size then fold in half one time.
Scatter the First Generation populations evenly on the cloth.
After completing Part A-1/2/ or 3 with your group, do Part B-Part H.
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Part B. First Generation Predation and Reproduction
Predation
1. One team member will feed like a hungry bird. Feed as quickly as possible standing up above the table while looking
at the cloth when selecting each bug, until one half of your total population has been eaten. As the bugs are collected,
another team member should keep count.
2. Subtract the number of bugs eaten of each color from the starting number to get the number of survivors of each color
left on the cloth. Record survivors in your Raw Data Table.
Reproduction
3. Each surviving bug will reproduce. For each bug that survived the first feeding, place (1) additional bug of the same
color on the cloth (in other words, double the surviving population). Be sure to scatter the new bugs evenly. "Dead"
bugs (eaten bugs) from the first feeding should be saved for returning to the stock bottles.
4. Record the new starting population in your Raw Data Table for the next (Second) Generation. The total number
of punchbugs will still be the same as your total starting number from Part A.
Part C. Second Generation: follow all of the procedures for predation and reproduction from Part B.
Part D. Stochastic Factor #1
1. Random events such as disease and natural disasters will often effect populations in unpredictable ways. One such
stochastic factor is about to occur in your environment: a volcanic eruption. This eruption kills all punchbugs in a 10
cm. radius from the center of the cloth.
2. Remove the punchbugs indicated by the stochastic factor and record the new starting population for the next
(Third) Generation in your Raw Data Table.
Part E. Third Generation Follow all of the procedures for predation and reproduction from Part B. Remember to
record survivors then calculate the new population and record the new starting population in your Raw Data
Table for the next (Fourth) Generation.
Part F. Fourth and Fifth Generations: follow all procedures for predation and reproduction from Part B for 4th and 5th
Part G. Stochastic Factor #2
1. Another stochastic factor is about to occur: this time it is a drought that kills 50% of all punchbugs of each colors
variation.
2. Remove the punchbugs indicated by the stochastic factor and record the new starting populations for the next
(Sixth) Generation in your Raw Data Table.
Part H. Sixth Generation: follow all procedures for predation and reproduction from Part B. Your final reproduction
following this generation will be your Final Population. Record this on your Raw Data Table.
• Repeat procedures Part A-Part H for additional trials.
Hypothesis
1. Read the Procedures and complete the hypothesis statement by predicting the experimental outcome for each treatment.
If six punchbug variations are exposed to evolutionary forces (deterministic and stochastic), then populations on island
environments will have (1) a greater chance of extinction and/or a lesser chance of colonization, and (2) less
predictable evolution as compared to mainland environments.
Number of Variations (colors) that will Remain in Final
Percent of Remaining Variations that will Match
Treatment/
Population in comparison to the Mainland.
Environment.
Environment
(Write: FEW, SOME, or MANY variations remaining)
(Write: FEW, SOME, or MANY percent matching)
Mainland
Near Island
Far Island
Mainland
Large Island
Small Island
2. Explain your predictions.
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Analysis of Data
• Summarize your Raw Data then record data on the Class Data Table. Class Data will be compiled
Summary Tables
Table 1: Your Data
Number of Variations (colors) Remaining in Final Population
Treatment/
Mean
Std. Dev.
Trial 2
Trial 3
Trial 4
Environment
Trial 1
(for # of
(for # of
variations)
variations)
Percent of Remaining Variations that Match Environment
Treatment/
Environment
Trial 1
Trial 2
Trial 3
Trial 4
Mean
Std. Dev.
Record data for each trial from your Table 1 on the board for the class and the record all Class Data below. Find the
mean for the whole class data.
Table 2: The Effect of Area and Distance from Mainland on the Number of Variations Remaining in Final Population
Number of Variations (colors) Remaining in Final Population
Treatment/
Mean (of all trials)
Trial 2
Trial 3
Trial 4
Environment
Trial 1
(for # of variations)
Mainland/
Control
Near Island
Far Island
Large Island
Small Island
Table 3: The Effect of Area and Distance from Mainland on the Percent of Remaining Variations that Match the
Environment
Percent of Remaining Variations that Match Environment
# of matching variation s that remain
 100
# of remaining variation s
Treatment/
Environment
Mainland/
Control
Near Island
Trial 1
Trial 2
Trial 3
Trial 4
Mean (of all trials)
Far Island
Large Island
Small Island
Graph: construct graphs showing mean for each treatment shown on Table 2 and Table 3 (two graphs).
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Discussion and Conclusion
1. How does distance from the mainland affect evolution on islands? Was your hypothesis correct? Use actual data in
your answer.
2. How does island size affect evolution on islands? Was your hypothesis correct? Use actual data in your answer.
3. Explain why what happened (especially why the number of variations remained in each population and why these
variations did or did not match the environment). To demonstrate your understanding, correctly use and underline the
following terms in discussing your data: variation, natural selection, genetic drift, evolution, deterministic factor,
stochastic factor, island size, island distance from mainland.
4. How would your results have been different if only natural selection had been at work (stochastic factors not
considered)?
5. How valid is the model this simulation provides for evolution? How could the simulation be improved?