AP BIOLOGY Student Exploration: Rainfall and Bird Beaks Gizmo

AP BIOLOGY Student Exploration: Rainfall and Bird Beaks Gizmo Student Exploration: Rainfall and Bird Beaks Vocabulary: adaptation, beak depth, directional selection, drought, evolution, natural selection, range, stabilizing selection Prior Knowledge Questions (Do these BEFORE using the Gizmo.) During the voyage of the HMS Beagle (1831–1836), the young Charles Darwin collected several species of finches from the Galápagos Islands. Two of Darwin’s finches are shown below. Which species do you think is best adapted to a diet of small, delicate seeds? Explain why you think so. Geospiza fortis because it has a smaller, pointed beak that can help pick up small, delicate seeds. Which species do you think is best adapted to a diet of large, tough-to-crack seeds? Explain. The Geospiza magnirostris would probably be better at eating large, tough-to-crack seeds because its beak would help it crush the shells up more easily. Gizmo Warm-up Darwin’s finches are one of many types of animals on the Galápagos Islands that have unique adaptations, or traits that help an organism survive in its environment. The Rainfall and Bird Beaks Gizmo allows you to explore how rainfall influences the range of beak shapes found in a single finch species. 1. The beak depth of a finch is the distance from the top of the beak to the bottom, as shown. A. What is the current average beak depth in the Gizmo? 10.16 mm B. Select the HISTOGRAM tab. Do all the finches have the same beak depth? No, most are different. 2. Click Play ( ) and let the simulation play for five years with average rainfall (25 cm/yr). Select the GRAPH tab and view the Finches vs time and Beak depth vs time graphs. A. How does the finch population change? The population has some variation and change because it goes up in numbers then it goes down slightly again and climbs back up again with a decline following. This study source was downloaded by from CourseH on :38:43 GMT -06:00 B. Does the beak depth change significantly? No, the depth of the beaks decreases over time, but nothing dramatic. Over the timespan of 5 years, the beak of the finches went from 10.21- 10.05. This study source was downloaded by from CourseH on :38:43 GMT -06:00 Activity A: Normal years Get the Gizmo ready: ● Click Reset ( ). Introduction: The Galápagos Islands are very dry, with an average rainfall on some islands of only 12 centimeters per year. The amount of rainfall has a large impact on the abundance and types of seeds that are available to be eaten by finches. In the process of natural selection, only the finches that are best adapted to the available seed types survive and have offspring. Question: How is the finch population affected by a period of average rainfall? 1. Observe: With the Rain sliders set to 25 cm, click Play, and then Pause ( ) after one year has passed. Select the TABLE tab and look at the Month and Finches columns. A. How did the finch population change over the course of one year? The population decreased by 80, from 1000 to 920 over the course of one year. B. The finches have their young during the rainy season. Based on the table, which part of the year do you think is the rainy season? Through spring to mid-summer, March to July. 2. Analyze: Click Reset, and choose the HISTOGRAM. The bars represent the numbers of finches that have different beak depths. The range of beak depths is equal to the difference between the largest and smallest beaks. A. What is the average beak depth of the current finch population? 9.99mm B. What is the range in beak depths in the population? 7-13 mm=6mm C. Do most of the finches have beak depths near the lower extreme, the middle, or the higher extreme of the range? Middle 3. Experiment: Click Play, and observe the histogram as the simulation plays for five years. A. What is the average beak depth now? 9.83mm B. What is the current range of beak depths? 6-14mm C. Based on what you have seen, are finches with very small, medium, or very large beaks most likely to survive in times of normal rainfall? Justify your answer. The finches with large beaks are most likely to survive in normal rainfall due to their ability to obtain food in less accessible places because of thei