How is camouflage an adaptive advantage? Lab 11 atural selection can be described as the process by which those organisms best adapted to the environment are more likely to survive and reproduce than are those organisms that are poorly adapted. Organisms have developed many different kinds of adaptations that help them survive in their environments. These include adaptations for finding food, such as keen night vision in nocturnal animals, as well as adaptations for avoiding predators. Some organisms use camouflage as a way to escape predation from other organisms. Camouflage allows them to blend in with the background. O BJECTIVES In this investigation, you will use an artificial environment to model the concept of natural selection. hypothesize what will happen if natural selection acts over time on organisms exhibiting camouflage. construct bar graphs to show the results of the Investigation. compare the model of natural selection in the Investigation to real examples of natural selection. hole punch colored paper (1 sheet each of purple, brown, blue, green, tan, black, orange, red, yellow, and white) plastic film canisters or petri dishes (10) P ROCEDURE 1. Work in a group of four students. 2. Punch 20 dots from each sheet of colored paper and place each color dot in a different plastic container. 3. Spread out the floral cloth on a flat surface. 4. Spread 10 dots of each color randomly over the cloth. See Figure 1. 5. Select a student to choose dots. That student must look away from the cloth, turn back to it, and then immediately pick up the first dot he or she sees. 6. Repeat step 5 until 10 dots have been picked up. Be sure the student looks away before a selection is made each time. 7. Record the results in Table 1. Return the 10 collected dots to the cloth in a random manner. piece of brightly colored, floral fabric (80 cm X 80 cm) graph paper (2 sheets) Spread 10 dots of each color Figure 1 Assume that the dots represent individual organisms that, if allowed, will reproduce more of their own type (color). Also assume that the selection of dots represents predation. 8. Write a hypothesis to predict what will happen over time if selected dots are not returned to the cloth and the remaining dots reproduce. Write your hypothesis in the space provided. 35
P ROCEDURE continued Figure 2 9. Each student in the group must, in turn, pick up 20 dots following the method in steps 5 and 6. Place the dots in their original containers. Remember to look away each time before making a selection. 10. After each student has removed 20 dots, shake the remaining 20 dots off the cloth onto the table. See Figure 2. 11. Count and record in Table 2 the number of dots of each color that remains. 12. Give each of the surviving dots four offspring of the same color by adding dots from the containers. You may need to punch out more of certain colors. Return all of the dots to the cloth in a random manner. This will bring the total number of dots on the cloth back to 100. See Figure 3. 13. Repeat steps 9 12 three more times. Each repetition represents the survival and reproduction of a single generation. Continue to record the results of each repetition in Table 2. 14. Make a bar graph in the space below to show the number of dots of each color that were on the cloth at the beginning of the Investigation. Label the horizontal axis with the names of the 10 colors and the vertical axis with the number of dots. Bar Graph Figure 3 Bar Graph Total of 100 dots 20 surviving dots Add 4 offspring for each surviving dot 15. Make a second bar graph in the space to the right to show the number of dots of each color that were on the cloth at the end of the fourth generation. Label the axes as on the first graph. 36
D ATA AND A Table 1 Table 2 Color Purple Selection of Dots Number of dots selected Color Number of Dots After Each Number remaining after Brown Blue Green Blue Tan Black Orange Red Yellow White Red Yellow White 1. Hypothesis 2. Which colors were picked up from the floral background? 3. Which colors, if any, were not picked up? Why not? 4. If the dots represent food to a predator, what is the advantage of being a color that blends in with the background? 35
D ATA AND continued 5. Give two examples of real organisms that use camouflage to avoid predation. 6. As the dots on the cloth passed through several generations, what trends in frequency of colors did you observe? 7. How would the outcome of this Investigation have differed if the predator was color-blind? Explain. 8. How would the outcome of this Investigation have been affected if dots that were subject to predation (those picked up) tasted bad or were able to harm the predator in some way, such as by stinging it? 9. Describe an example of natural selection that is similar to the model of natural selection in this Investigation. 10. Was your hypothesis supported by your data? Why or why not? 36
37