The Evolution and Survival of the Galápagos Medium Ground Finch

A Carolina Essentials™ Activity

Total Time: 35-45 mins

Prep: 15 mins | Activity: 20-30 mins

Life Science

9-12

High School

Overview

This activity is a data-driven analysis lesson that uses information collected in the late 1970s by Peter and Rosemary Grant of Princeton University. The Grants collected data on Medium Ground Finches, Geospiza fortis, on Daphne Major, one of the Galapagos Islands. During 1977 there was a drought on Daphne Major that resulted in a higher than normal mortality rate for the finches, so the Grants investigated finch characteristics that may have contributed to the survival of the remaining birds.

 

Students will use this data to construct frequency distribution graphs as evidence of the process of evolution, leading them to identify those birds that are better able to survive and reproduce during a drought period.

Phenomenon

Below is a stamp commemorating Darwin and two of the Galapagos Islands finches he observed. How does this represent and explain the theory evolution?

 

charles darwin stamp

Essential Question

What kind of evidence is necessary to explain the process of evolution?

Activity Objectives

  1. Create frequency distribution graphs of finch survival after drought.
  2. Use distribution graphs as evidence to explain which finches are better able to survive and reproduce during drought conditions and how this relates to the process of evolution.

Next Generation Science Standards* (NGSS)

PE HS-LS4-2: Construct an explanation based on evidence that the process of evolution primarily results from four factors: (1) the potential of the species to increase in number, (2) the heritable genetic variation of individuals in a species due to mutation and sexual reproduction, (3) competition for limited resources, and (4) the proliferation of those organisms that are better able to survive and reproduce in the environment.

 

HS-LS4-4: Construct and explanation based on evidence for how natural selection leads to adaption of populations.

Science & Engineering Practices

Constructing Explanations and Designing Solutions

Disciplinary Core Ideas

LS4.C: Adaptation

Crosscutting Concepts

Cause and Effect

Materials

Safety Procedures and Precautions

No PPE is required for the activity.

Teacher Preparation and Disposal

Copy or upload student activity page. There is no disposal of waste materials.

Student Procedures

  1. Prepare a survivability table by year and the number of finches that survived and died.
  2. Construct a frequency distribution histogram of the finch survival data.
  3. To the survival data, add the average beak depth to the table.
  4. Construct a frequency distribution histogram of beak depth and survival.
  5. Select one of the other variables in the data table that you think may impact the survival of the finches during a drought and complete the same analysis as above. Generate a survivability data table and frequency distribution histogram.

Teacher Preparation and Tips

  1. If these tables are new to students, go through the first table with them. See the keys below.
  2. Students may graph by hand or use a computer program. Excel is easy to use.
  3. Calculations may be done by hand, calculator, or using a computer.
  4. You may wish to assign the remaining variables yourself to ensure that all other variables are tested.

Data and Observations

Individual Finch Survival and Mortality Measurements

individual finch survival and mortality measurements graph

 

Procedure 1

finch survivability graph

 

Procedure 2

frequency distribution of surviving finches graph

 

Procedure 3

average beak depth of survivors/nonsurvivors graph

 

Procedure 4

average depth of finch beaks and survival graph

 

Procedure 5

additional variables and weight graphs

 

Procedure 5 (continued)

additional variables and wing length graphs
 

Analysis & Discussion

Knowing the drought occurred in 1977, interpret the frequency distribution histogram of survival data.

50% of the birds died in 1977. 1978 also showed a large decrease in finch population. From 1979 -1981 birds within the 100-bird sample continued to die within their expected life span. You may wish to add statistical calculations to this question.

Knowing the drought occurred in 1977, interpret the frequency distribution histogram of beak depth and survival data.

The birds that continued to survive had a noticeably larger beak depth. Increased beak depth for survivors is true for every year past 1977 for which data was supplied. You may wish to add statistical calculations to this question.

Using your frequency distribution histograms as evidence, make a claim about the evolutionary trend in beak depth.

It appears that birds with deeper beaks were better able to survive after the drought. Since birds with deeper beaks survived every year past 1977 they could reproduce and potentially pass on their genes for deeper beaks. The evolutional trend appears to favor the survival of finches with deeper beaks.

Using your all 3 frequency distribution histograms as evidence, make a claim about the evolutionary trend and adaptations in the Medium Ground Finches that make those birds better able to survive and reproduce during a drought period.

Answers will vary depending on which additional variables students select. Generally, the additional variables did not show strong evidence of impacting survival, so beak depth is the trait driving the evolutionary trend. You may wish to add statistical calculations to this question.

Assuming there are no droughts, what would you predict the average depth of finch beaks will be? Use your data to justify your prediction.

The average beak depth of the surviving finches after the 1977 drought is 9.82 mm so I would expect that those birds continued to reproduce and pass on the genes for a deeper beak. The range of average beak depth after the drought was 9.67 mm- 10.01 mm, with the largest beak depth occurring in 1979. In subsequent years the beak depth decreased slightly. You may wish to have students generate a line graph and calculate the slope of the best fitting line, (regression line), to predict beak depth.

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*Next Generation Science Standards® is a registered trademark of Achieve. Neither Achieve nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of, and do not endorse, these products.

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