Evolution in Action

Evolution in Action Questions 1. a. What observations can you make about the overall shape of each graph? (Imagine that you are drawing a line that connects the tops of the horizontal bars.) i. They all look like normally distributed bell curves when drawing a line across the top of the bars b. What do the shapes of the two graphs indicate the distribution of beak depth measurements in these two groups of medium ground finches? i. The beak depth trait among all the birds is extremely variable. Most beak depth values are around the mean 2. Compare the distribution of beak depths between survivors and nonsurvivors. In your answer, include the shape of the distributions, the range of the data, and the most common measurements. a. Both graphs appear to be similar shapes but they aren't distributed in the same way, the groups have a different range than each other. The nonsurvivors had a range of 7.25mm to 11.25mm while the survivor's range was 8 to 11.25. The mean beak depth of birds that did not survive was 9.11mm while the ones who did survive had a mean of 9.67mm. 3. Based on what you saw in the film, think about how changes in the environment may have affected which birds survived the drought. Propose a hypothesis to explain differences in the distribution of beak depths between survivors and non-survivors. a. The birds experienced a drought forcing them to change their food source. Birds with larger beaks were better able to use these large seeds as food, so they are better adapted, than were birds with smaller beaks 4. Let’s look in more detail at the mean beak depths in the two groups of birds to understand the meaning of standard deviation. a. How do the mean beak depths and standard deviations of the mean beak depths compare? i. The mean beak depth for the surviving birds was 9.67 mm versus the mean beak depth for the non-surviving birds being 9.11 mm. Also, the standard deviations for the two groups were nearly the same: 0.88 and 0.84. b. If the standard deviations of the two samples were vastly different, what would you conclude about the two groups? i. If the standard deviations are vastly different, the data set that has the larger standard deviation always has more variability compared to its mean. 5. For each sample, calculate the mean beak depth and standard deviation (s) and add those numbers to the tables. a. Nonsurvivors i. 5: Mean- 8.78, SD- 1.15 ii. 15: Mean- 9.11, SD- .98 b. Survivors i. 5: Mean- 9.78, SD- 1.06 ii. 15: Mean- 9.56, SD- .90 6. Record the means for each sample of survivors and nonsurvivors from Figure 1 in Part B (50 birds) and Table 1 in Part C (5 and 15 birds) in Table 2 below. a. 50 Finch Sample i. Non- Survivors 1. 9.11 ii. Survivors 1. 9.67 b. 15 Finch Sample i. Non- Survivors 1. 9.11 ii. Survivors 1. 9.56 c. 5 Finch Sample i. Non- Survivors 1. 8.78 ii. Survivors 1. 9.78 7. Compare the means for each sample size (5 birds, 15 birds, and 50 birds) within each group of survivors and nonsurvivors a. Are the means in smaller samples different from the means in larger samples? Explain why you think that is i. Not including the non-survivor sample size of 15, none of the means match the mean beak depths of the 50-bird samples. I think this is because of the sets of birds being randomly selected from the large group 8. Which results (i.e., from 5, 15, or 50 birds) do you think are closer to the means of the entire population of medium ground finches on the whole island? Explain your answer. a. The larger the sample the more accurate it is compared to the population as a whole 9. What are one advantage and one disadvantage of calculating the mean from a sample of a population rather than the entire population? a. Advantage- less cost lower time, disadvantage- doesn't reflect the population as a whole 11. Based on the graphs you have drawn, how does wing length compare between survivors and non-survivors? What about body mass? a. The surviving medium ground finches have larger body masses and longer wings then the ones that didn't survive 12. What do the results illustrated by your graphs indicate the effects of the drought on birds with particular wing lengths and body masses? a. This suggests that these traits that helped them survive (larger mass, longer wings) were an advantage in the drought. 13. The Grants say in the film that a key trait that made the difference in survival for the birds during the drought was beak depth. Is that conclusion consistent with the data presented in this activity (including Part B)? a. Yes, beak depth, body mass, and wing length were obviously key features for the birds survival 14. Explain why the Grants concluded that beak depth may have played a more important role in survival during the drought than wing length or body mass. Correctly use the terms natural selection, adaptation, and fitness in your answer. a. The major problem the birds faced was needing to adapt to a new food source, The larger beaks were necessary to allow the birds to use these large seeds as food, so they are better adapted, than were birds with smaller beaks. This shows that the birds who have larger beaks were more fit to face this drought. Due to this, Natural Selection now plays the part of eliminating the birds with smaller beaks as well as the ones that did not include all the advantageous features to survive in a new environment. 15. Explain the role of variation in important traits (like beak depth) in a population for the survival of a species. a. Variation is extremely important among individuals to allow them to survive in a constantly changing environment.