Unit B

Module 4 ~ Lesson 1

 Finch Beak Lab

Environmental factors, adaptation, variation, and mutation all play a role in the struggle for survival among individuals in a population. Charles Darwin based his theories of natural selection primarily on his observations of finches in the Galapagos Islands. In this lab you will determine the effect of environmental conditions on finch beak depth.
  1. Open or print the lab activity sheet. If you do not have access to a printer open the Word or Google doc.
  2. Open the Rainfall and Bird Beaks Gizmo.
  3. Follow the directions in the lab activity sheet.
  4. Complete the analysis questions below.

Image by minka2507 from Pixabay


Analysis

Answer these questions. Then compare your answers with those below.

    How did the finch population size and beak depth respond to drought years? What about in years of heavy rainfall? 

  1. During years of drought, the smaller, softer seeds are quickly eaten up, leaving behind only the larger, tougher seeds that are harder to crack and more difficult to find under the baked soil. What kinds of beaks are more useful in these conditions? Why? 

  2. Assuming that beak depth is a genetic trait, and that an individual finch cannot change the shape of its own beak, how did the change in average beak depth actually occur during the drought? Be able to explain in detail. 

  3. What selection pressure caused the change in beak depth?
1. The average beak length is less in times of greater precipitation.
2. Larger stronger beaks are able to break these tough seeds. They are also better adapted to finding seeds in the soil.
3. Finches with smaller beaks did not survive to reproduce due to lack of food. The reproduction of finches with larger beaks increased the frequency of this trait in the population.
4. A change in the availability of soft seeds due to drought.