Student Exploration Rainfall and Bird Beaks

Student Exploration: Rainfall and Bird Beaks Directions: Follow the instructions to go through the simulation. Respond to the questions and prompts in the orange boxes. 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. 1. Which species do you think is best adapted to a diet of small, delicate seeds? Explain why you think so. I think the Geospiza fortis would be better for small delicate seeds because the beak is smaller which allows them to get a hold of the seeds easier/ 2. Which species do you think is best adapted to a diet of large, tough-to-crack seeds? Explain. I think the Geospiza Magnirostris would be better for tough to crack seeds because the beak is much bigger and stronger. 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? 10.0 B. Select the HISTOGRAM tab. Do all the finches have the same beak depth? No, they do not have the same depth 2. Click Play ( ) and let the simulation play for five years with average rainfall (10 inches/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 goes down B. Does the beak depth change significantly? It doesn’t really only towards the end does it start to go up some. 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 five inches 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 10 inches, click Play, and then Pause ( passed. Select the TABLE tab and look at the Month and Finches columns. ) after one year has A. How did the finch population change over the course of one year? The population goes up then goes back down. 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? During month 5 2. Analyze: Click Reset, and choose the HISTOGRAM tab. 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? 10.09 B. What is the range in beak depths in the population? 5 C. Do most of the finches have beak depths near the lower extreme, the middle, or the higher extreme of the range? most of them are in the middle 3. Experiment: Click Play, and observe the histogram as the simulation plays for five years. A. What is the average beak depth now? 9.98 B. What is the current range of beak depths? 2 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 medium beaks because at average rainfall it is 10.34 so medium beaks are more likely to survive the average rain. Activity B: Get the Gizmo ready: ● Click Reset. Drought Introduction: In years of extreme drought, Galápagos plants don’t produce new seeds. The small, delicate seeds get eaten up quickly, leaving behind only the largest, toughest seeds. Question: How does drought affect the finch population and average beak depth? 1. Form hypothesis: What type of beak do you think will be best for finding food in a drought? A bigger/stronger beak that can crack through the tougher seeds. 2. Predict: Select the HISTOGRAM tab. On the left side below, sketch the current histogram and list the average beak depth and range of beak depths. On the right side, sketch what you think the histogram will look like after five years of drought. Explain your prediction. Initial beak depths Beak depths after 5 years (predicted) Initial number of finches: 1000 Initial average depth: 10.06 Initial range of beak depths: 2 Explanation: The beak depth will increase because they need stronger beaks in order to survive 3. Experiment: Use the sliders to set the Rain to 2 inches for each of the five years in the simulation. Click Play, and wait for five years. Observe the beak of the finch. A. How does the beak depth change over time? It decreases B. What is the final average beak depth? 13.38 C. What is the final range of beak depths? 3 4. Describe: Compare the final histogram to the initial histogram. How have the finches been affected by drought? Describe at least two changes that you notice. The number of finches decreased because of the drought. The beak depth is from 10 to 13. 5. Analyze: Was the increase in the average beak depth caused by an increase in large-beaked finches or a decline in small-beaked finches? Explain your answer. I think it's a decline of small-beaked finches because of how the population decreased. 6. Draw conclusions: What do you think caused the changes in the finch population and average beak size during the drought? Some of the finches were not able to survive or find who and the ones that did had a bigger beak size during the drought 7. Interpret: Directional selection occurs when individuals at one end of a range are more likely to survive than intermediate individuals or individuals at the opposite end of the range. Stabilizing selection occurs when intermediate individuals are the most likely to survive. Is directional selection, stabilizing selection, or both operating in this example? Explain. Directional because the small beak finches were unable to survive. but the bigger beak finches were able to crack through the tougher seeds. 8. Think and discuss: Evolution is the process by which populations of organisms can change over time. How is directional selection related to evolution? At first, the small beaks were thriving but because of the drought, they weren’t able to survive so they evolved into bigger beaks. Activity C: Rainy days Get the Gizmo ready: ● Click Reset. Introduction: In years of abundant rainfall, there can be 20 inches or more of rain. In these years, plants produce an enormous number and variety of seeds. Question: How does plentiful rainfall affect the finch population and average beak depth? 1. Form hypothesis: What beak shape do you think will be best for finding food in a period of abundant rainfall? I think a small beak would be best for this environment 2. Predict: Select the HISTOGRAM tab. On the left side, sketch the current histogram and list the average beak depth and range of beak depths. On the right side, sketch what you think the histogram will look like after five years of abundant rain. Explain your prediction. Initial beak depths Beak depths after 5 years (predicted) Initial number of finches: 1000 Initial average depth: 10.13 Initial range of beak depths: 4 Explanation: I think that the beak depth will decrease because the smaller beaks are better for a lot of water 3. Experiment: Click Reset. Use the sliders to set the Rain to 20 inches for each of the five years in the simulation. Click Play, and wait for five years. Observe the beak of the finch. A. How does the beak depth change over time? it decreases B. What is the final average beak depth? 7.25 C. What is the final range of beak depths? 3 4. Describe: Compare the final histogram to the initial histogram. How have the finches been affected by abundant rain? Describe at least two changes that you notice. The number of finches increased a lot and the depth of the beak decreased. 5. Analyze: Was the decrease in the average beak depth caused by an increase in small-beaked finches or a decline in large-beaked finches? Explain your answer. It was an increase of small beaked finches because they thrived in that environment 6. Draw conclusions: What do you think caused the changes in finch population and average beak size during the period of abundant rain? because the rain caused the small beak finches to succeed and thrive. The bigger beaks were unnecessary 7. Extend your thinking: Most scientists think that a small group of finches colonized the Galápagos Islands thousands of years ago. They would have been the only seed-eating birds on the islands. Suppose one island was very dry and another had plentiful rainfall. A. How would the finch populations on these islands change over time? The rainy island would have many finches over time while the drier environment would have less of a population. B. What might happen to the finch populations after millions of years? They could increase a lot on the rainy island because that is where they are able to thrive and have plenty of food and nutrients.