Since then, Darwin’s finches have been studied extensively for the insight they provide into the evolutionary questions of adaptation and speciation. However, the complex role of ecological and environmental factors (including competitive exclusion, cultural/behavioral differences, disturbances, reproductive barriers, etc. ) in the process of divergence is still not well understood. Using the finch species Geospiza difficilis and the islands Darwin and Santiago as the subjects of our study, we will address these questions, simultaneously filling in the gaps left in previous studies of these islands and species.
We are using the BIRDD database (Price, 1998) as the basis for our analysis of previously collected data concerning Geospiza difficilis on Darwin and Santiago. Analysis of the data indicated a significant correlation between beak size and island habitat (see table 1) suggesting island dissimilarity as a major influence in natural selection. Character displacement (i. e. divergence in body structure in allopatric populations as a result of niche competition) is one possible explanation for this variation (Campbell, 2010).
Gaps in the data provided and collection dates limited our ability to analyze specific characteristics (body length and beak width in particular).
Information concerning beak height and length for Darwin and Santiago Islands separately is found on tables 2 and 3. Collecting new data will provide further insight into the evolution of Geospiza difficilis. Based on our analysis, we have developed two hypothesis outlined in the following aims: Specific Aim 1: Test our hypothesis that the variations in island size and location of the islands Darwin and Santiago have influenced the process of natural selection in Geospiza difficilis.
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Specific Aim 2: Test our hypothesis that differences in Geospiza difficilis characteristics (body length, beak length and height, and genetic composition) are the result of character displacement. Methods To sample the finches, we will use a system of mist nets on the islands of Darwin and Santiago. We will have two mist net sites on Darwin and four mist nets on Santiago due to its larger size. Each site will be operated by two researchers who will open the net everyday fifteen minutes after sunrise and keep the net open for 3 hours.
They will then wait until the temperature cools down and then open the net for an additional three hours in the evening. We will also observe and record the bird’s behaviors and interactions during this time. This will be essential in determining the species occupied niche. The remaining two members of the team will make food at the camp and rest. A rotational system will be implemented so every team member will have equal opportunity to rest and participate in field work.
Once a bird has been caught, the species and sex of the bird will be identified, and its wing length, body length, body weight, tail length, beak width, beak height, upper beak length and lower beak length will all be measured. Also, blood samples will be taken from the birds to measure genetic diversity. To estimate population size of the species on each island and to track each individual, we will tag each bird captured. Even though our study is focused on the species Geospiza difficilis, we will take measurements on all birds we capture to add to the BIRDD database for future analysis.
