Precipitation Levels and the Affects to Beak Size

Dixie Woodard

BIO/101

November 22, 2010
Alison Barrett

Precipitation Levels and the Affects to Beak Size

The experiment demonstrates the affect of precipitation levels to the beak size of finches on Darwin Island and Wallace Island. The levels of rainfall not only affect the beak sizes of the finches but also the population over time. The experiments were conducted over a period of three hundred years. The parameters remained constant over the three hundred year span to determine the effect of more or less precipitation on the food sources for the finches. The level of rainfall controls the types of seeds the birds eat. More rainfall creates smaller, softer seeds. Less
The lower levels of precipitation create harder, larger seeds. The birds’ beaks must become larger and stronger to eat the seeds. The population of the birds on Wallace Island is much lower than Darwin Island in the first 148 years in the first run. It takes the birds that long to adapt to their new environment. Then, in the year 2145, there is only 80 bird’s difference between the island populations. The chart below shows the results of years of adaptation of the finches and the correlation to population. [pic] The results of the experiments demonstrate the effect of rainfall levels has on beak sizes of birds. The data supports the hypotheses that over time the birds can adapt to less or more levels of precipitation in their environment. The population is adversely affected until the birds become adapted. After many years of evolving, the birds are able to increase their population under the same conditions that first impacted the population. The most striking fact discovered was that the greater the rainfall level, the smaller the beak size. However, the beak size does increase for both island populations over time. The experiments ran were interesting and unexpected. Considering the fact with less precipitation, the Wallace Island finches were not only able to survive but also increased their population under the same conditions. The Darwin Island finches had more rainfall that had little or no impact on population or beak size over time.