Finch Beak Adaptation & Form: Natural Selection in Action

Introduction

In this activity, you will use the Finch Beak Adaptation & Form simulation to investigate how changes in the environment influence the physical traits of a population over time. You will observe a population of finches and see how their beak sizes change in response to different rainfall levels, which determine the size and hardness of the available seeds.

Your Goal: Use evidence from the simulation to construct an explanation for how natural selection leads to adaptation in the finch population.

Procedure

Part 1: Baseline Population

  1. Open the simulation. Set the Rainfall Level to Normal (50%).
  2. Run the simulation for 10 generations by clicking “Next Generation” or using the “Run” button.
  3. Pause the simulation.
  4. Record the Average Beak Size in the data table below for Generation 10.
  5. Sketch the shape of the Beak Size Distribution graph.

Part 2: Environmental Change - Severe Drought

  1. Do not reset the population.
  2. Change the Rainfall Level to Severe Drought (0-20%).
    • Notice what happens to the seeds in the environment.
  3. Run the simulation for another 10 generations (until Generation 20).
  4. Pause the simulation.
  5. Record the new Average Beak Size in the data table.
  6. Sketch the new shape of the Beak Size Distribution graph.

Part 3: Environmental Change - Heavy Rain

  1. Do not reset the population.
  2. Change the Rainfall Level to Heavy Rain (80-100%).
    • Notice what happens to the seeds in the environment.
  3. Run the simulation for another 10 generations (until Generation 30).
  4. Pause the simulation.
  5. Record the final Average Beak Size in the data table.
  6. Sketch the final shape of the Beak Size Distribution graph.

Data Collection

Generation Environmental condition Average Beak Size (mm) Description of Seed Availability (Small/Soft vs Large/Hard)
10 Normal Rainfall    
20 Severe Drought    
30 Heavy Rain    

Analysis & Sensemaking

  1. Describe the Pattern: How did the average beak size of the population change when the environment shifted from normal rainfall to severe drought?

  2. Cause and Effect: What caused this change in the beak size distribution during the drought? Explain your reasoning using the concepts of seed availability, feeding efficiency, and survival.

  3. Construct an Explanation: Using evidence from your data table and the simulation, construct an explanation for how natural selection led to adaptation in this finch population during the drought. Your explanation must include the four principles of natural selection:
    • Variation: What trait varied in the population?
    • Inheritance: Are beak sizes passed from parents to offspring?
    • Differential Survival and Reproduction (Selection): Which birds were more likely to survive and reproduce during the drought? Why?
    • Adaptation: How did the population change over time as a result?
  4. Predicting the Future: Based on your observations from Part 3 (Heavy Rain), predict what would happen to the average beak size if the heavy rain continued for 100 generations. Justify your prediction using your understanding of natural selection.