The Evolution of Finches on Darwin and Wallace Islands
Angela Vaughn
BIO/110
December 9, 2013
Heather Browning

The Evolution of Finches on Darwin and Wallace Islands
In the 1800s, Charles Darwin, a brilliant scientist and naturalist, observed that an organism’s traits allowed it to adapt to an environment. These organisms would produce offspring that possessed abilities to survive in their environment. Those that did not possess these traits were less fit and were unable to survive the environment. This was the beginning of the study of evolution and natural selection.
“Evolution is the study of how modern organisms have descended from the earliest life-forms and of the genetic, structural, and functional modifications of a population that occur from generation to generation. The ability of a population of organisms to respond to change in their environment and survive and reproduce by developing the characteristics or modifications necessary for survival is known as adaptation.” (University of Phoenix, 2013)
House Finches live in dry desert, grasslands, stream sides and open coniferous forests at elevations below 6,000 feet. They eat seeds, buds and fruits. (House Finch, n.d.)
The purpose of the experiment is to test my hypothesis, “Precipitation does not cause natural selection to act upon beak size.”
Materials
To complete the experiment, I will need access to a computer and the Evolution Lab simulation at the University of Phoenix website. The Evolution Lab will allow me to simulate tests by changing the input values or parameters. The results should show the effect of natural selection, and how these changes may influence the beak sizes and population of the finches in the Darwin Island and Wallace Island over various time periods. Methods and Procedure
In the Evolution Lab, there are different variables to test. The variables are beak size (12 millimeters), variance (1.00), heritability (.70), clutch size (10 eggs), island size (0.5 kilometers), population, precipitation and the time intervals.
To conduct the experiment, I first tested by keeping all the variables in the simulation the same except the precipitation amount. I observed how the finch population was affected on both Darwin Island and Wallace Island with precipitation levels at 0, 10, 20, 30, and 60 centimeters at a 100 year period. Next I observed how the finch population was affected on both Darwin Island and Wallace Island with precipitation levels at 0, 10, 20, 30, and 60 centimeters at a 200 year period.
To see if there was a comparable difference, I changed the beak size of the finches. I observed how the finch population was affected on both Darwin Island and Wallace Island by observing the beak sizes at 10, 12, and 20 millimeters with the precipitation level at a constant of 20 centimeters at a 100 year period. Last I observed and recorded the data for the finches on both Darwin Island and Wallace Island by observing the beak sizes at 10, 12, and 20 millimeters with the precipitation level at a constant of 20 centimeters at a 200 year period.

Data
Precipitation Level – 0 centimeters Precipitation Level – 60 centimeters Figure 1: Average Beak Size of Finches over 100 Year Period with Zero Precipitation
Figure 2: Average Beak Size of Finches over 100 Year Period and 60 Centimeters of Precipitation Figure 3: Finch Population Over 100 Year Period and Zero Precipitation
Figure 4: Finch Population Over 100 Year Period and 60 Centimeters of Precipitation

Figure 5: Number and Types of Seeds Over 100 Year Period and Zero Precipitation
Figure 6: Number and Types of Seeds Over 100 Year Period and 60 Centimeters of Precipitation

10 mm Beak Size
100 Year Time Period 10 mm Beak Size 200 Year Time Period

Figure 7: Average Beak Size Over 100 Years with 20 centimeters of precipitation Figure 8: Average Beak Size Over 200 Years with 20 centimeters of precipitation Figure 9: Finch Population over 100 Years with 20 centimeters of precipitation
Figure 10: Finch Population over 200 Years with 20 centimeters of precipitation

20 mm Beak Size – 100 Years
20 mm Beak Size – 200 Years

Figure 11: Average Beak Size Over 100 Years with 20 centimeters of precipitation Figure 12: Average Beak Size Over 200 Years with 20 centimeters of precipitation

Figure 13: Finch Population over 100 Years with 20 centimeters of precipitation Figure 14: Finch Population over 200 Years with 20 centimeters of precipitation

Figures 1 – 6 illustrate how the finches’ beak sizes and populations change over a 100 year period. The number and types of seeds available as a food source on both Darwin Island and Wallace Island are also illustrated. Notice as the precipitation level is decreased to zero centimeters the beak sizes and population of the finches steadily and comparably increase. The beak sizes of the finches on both islands are enlarged, and the food source is only hard seeds.
Notice as the precipitation level is increased to 60 centimeters the beak sizes and population of the finches do not increase and are balanced at a steady and comparable level. Figures 5 – 6 illustrates how the food source levels change. When the precipitation level is at 60 centimeters, the number of hard seeds are decreased, and the number of medium and soft seeds are increased. In a separate test, Figures 7-14 illustrate the precipitation levels remaining at 20 centimeters, and the beak sizes change from 10 millimeters to 20 millimeters and the data illustrate the evolution over at 100 – 200 year period.

Discussions and Results
At closer examination of the data, the results show that over the 100 year period when there was a zero precipitation level, the finches on Darwin Island beak sizes began at 12 millimeters and grew to 18 millimeters. The food source was only hard seeds. The finch’s population dropped from 200 to 93 in year 2017. In 2018, the population began to grow on Darwin Island to over 400 birds during year 2096. Meanwhile on Wallace Island, the beak sizes shrunk and the population died in year 2020.
When the precipitation level was at 60 centimeters, on both islands, the beak sizes were an average of 11 - 13 millimeters. The finches had a variety of food source options, there were more medium and soft seeds available. The population began at 200 and rose as much as 700 birds. On either island the species did not completely die.
I did another test to see if I changed the beak size and kept the precipitation constant. When the precipitation level remained at 20 centimeters and the beak size was at 10 millimeters, over 200 years, the beak size doubled to near 20 centimeters on both islands, but the population also grew from 200 to nearly 650 finches.
When the precipitation level remained at 20 centimeters and the beak size started at 20 millimeters, over a 200 years period, the beak size grew an additional 5 millimeters and the population grew to 800 finches on both islands.
My hypothesis was incorrect. The precipitation does cause natural selection to act upon beak size, as the birds on Darwin Island survived with larger beak sizes and increased population with no precipitation on the island. However, the birds on Wallace Island beak sizes shrunk and died when there was no precipitation on the island. The experiment would have been more improved if there were more food sources on the island besides seeds, for instance, berries and insects to determine if the beak size would grow or if the food source would diminished.
Conclusion
After conducting the experiment with multiple simulations, increasing and decreasing the precipitation levels on both Darwin and Wallace islands, my hypothesis is rejected, and precipitation does cause natural selection to act upon beak size. The precipitation also affects the available food source and the evolution of finch population.
References
House Finch. (n.d.). Retrieved December 8, 2013, from All About Birds: http://www.allaboutbirds.org/guide/HOUSE_FINCH/lifehistory#at_habitat

University of Phoenix. (2013). Evolution Lab [Multimedia]. Retrieved from University of Phoenix, BIO101 - Principles of Biology website.