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Name:_____________________________________________________ TOC#______ 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? Name:_____________________________________________________ TOC#______ 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. Name:_____________________________________________________ TOC#______ 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. Name:_____________________________________________________ TOC#______ 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). Name:_____________________________________________________ TOC#______ 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?