Simulating Evolution on Islands: Island Punchbugs
Integrated Science
Name___________________________ Per._________
04/07
Introduction
Scientists have recently begun to observe the results of natural selection in the wild. This was long assumed to be an
impossible undertaking because the pace of change directed by natural selection was felt to be too gradual. But, the study of
finches in the Galapagos Islands by Rosemary and Peter Grant has produced an effective model for studying the evolution. While
they have clearly been able to demonstrate results, and the surprisingly fast pace of natural selection, their study is a vast
undertaking. Without an extensive travel budget, let alone the 10 to 20 years necessary to document the evolutionary changes, we
must resort to constructing simulations that model the processes of natural selection. These simulations can get around the
problems of travel and time necessary for studies of real populations.
This laboratory activity will enable you to enable you to simulate natural selection by looking at color changes in a
population of mythical 'punchbug' organisms. This simulation will take in to consideration isolated populations, which increase
the impact of natural selection on populations. Additionally, you will consider the predictable (deterministic) factors of predation
as well as random (stochastic) disturbances that impact the population..
The purpose of this simulation is to provide a better model for natural selection as it occurs on islands by determining the
effect of distance from mainland, size of island, and stochastic disturbances on the evolution of island life.
1.
What is genetic drift? Give two examples of disturbances or conditions that could lead to genetic drift.
Procedures
Record the distance (near or far) and size (small or large) of islands A-D in the table below. Predict the relative number of
variations (more or less) and population sizes
Number of
Populations
(large or small) for each island based on its
Island
Distance/Size
Variations
Size
distance/size characteristics.
A
Mainland
1.
A
C
C
B
2.
3.
B
D
The two islands that will be tested in this
simulation are:
Island #1
D
Island #2
Construct two hypotheses predicting how the population of 'punchbugs' will change over time in terms of population size and
genetic diversity.
Island #1:
Island #2:
4. Complete simulation as described below:
Part A. Colonization by First Generation
1. The ‘mainland’ environment – your source of immigration/colonization – has six punchbug0 variations as represented by
different colors.
2. Colonization is a largely chance occurrence. 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, the numbers 1–2 will represent a successful colonization, while the numbers 3–6 will
represent no colonization.
• If you have a ‘near’ island, the probabilities are reversed, where 3–6 represents a successful colonization and 1–2
representing no colonization.
Now, roll a die to determine, for each variation, whether or not it will colonize your island. Record your results in
the data table as follows:
• If a color successfully colonizes and your island is ‘large,’ assign a starting population of (18).
• If a color successfully colonizes and your island is ‘small,’ assign a starting population of (6).
• If a color does not colonize, assign a starting population of (0).
In the interest of experimental design, your island simulation must have a minimum of (2) colonizing variations. If
you end up with only (1) colonizing variations, re-roll the die until you have at least two variations.
3. Now, you are ready to test your populations in an island environment. Collect a cloth (to represent the environment) and
the starting population of 'punchbugs'. Scatter the First Generation populations evenly on the cloth.
Part B. First Generation Predation and Reproduction
Predation
1. One team member will feed like a hungry bird. Feed as quickly as possible, looking away from the cloth after 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. Record the number of each color of bug eaten in your Data Table.
3. Calculate the number of bugs left on the cloth and record survivors in your Data Table.
Reproduction
4. Each surviving bug will reproduce. For each bug that survived the first feeding, place (1) additional bug of the same
color on the cloth. 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.
5. Record the new starting population in your Data Table for the next (Second) Generation.
Part C. Second Generation
For the second generation, follow all of the procedures for predation and reproduction from Part B.
Part D. Third Generation
Stochasitc Factors
1. Random events will often affect island populations in unpredictable ways. Roll the die to determine which stochastic
factor will occur on the island:
•
(1) and (6) will indicate that no random events have occurred this generation.
•
(2) will indicate a disease which kills 90% of two punchbug colors (your choice).
•
(3) will indicate a volcanic eruption that kills all punchbugs in a 6 cm. radius from the center of your island.
•
(4) will indicate a hurricane that kills all punchbugs located within 6 cm. of the island’s shoreline.
•
(5) will indicate a drought that kills 75% of all punchbug colors.
2. Remove the punchbugs indicated by your random event. Record the new punchbug populations.
Predation and Reproduction
3. Follow all of the procedures for predation and reproduction from Part B after the random event has occurred. Record
survivors then calculate the new population and record the new starting population in your Data Table for the next
(Fourth) Generation.
Part E. Fourth and Fifth Generations
For the fourth and fifth generations, follow all procedures for predation and reproduction from Part B.
Part F. Sixth Generation
For the sixth generation, follow all procedures for stochastic factors, predation and reproduction from Part D. Your final
reproduction following this generation will be your Final Population. Record this on your Data Table.
Part G. The Other Islands
1. Repeat all procedures, from Parts A – F, for your comparison island simulation (Island #2)