Lesson 7: Adaptive Radiation in the Galapagos Preview CT-STEM

What Causes Change in Finches?

The scientist that have collected this data have done so for over 40 years now, the first bar graph that you saw in section one contains finch data from 1973 -1981. Lets see what we can find if we look deeper into the data.

In this data set, "Last Year" is the record of the last year an individual finch was seen by the researchers. This typically means that the individual finch died during that year.

Use the methods you learned in the last activity to compare the finches that died during 1977 with the finches that survived 1977 and answer the questions below.

Questions

Please answer the questions below.

Question 4.1

What differences do you see between the group of finches that only lived until 1977 and the finches that lived to 1978 and beyond? Please discuss the position (i.e. mean, median) and shape (i.e. standard deviation, range) of the beak depth distributions in your response, along with any other information you think is relevant.

Question 4.2

The medium ground finch (Geospiza fortis) has a short, blunt beak which is adapted to picking up seeds from the ground. In 1976, seeds on the island were diverse and plentiful. During a drought in 1977, seeds became much harder to find. Once the finches had eaten all the small and medium-sized seeds, they had to turn to larger, spiny seeds that are hard to crack open. In your group come up with a reasonable hypothesis as to why there might be changes in how beak depths are distributed before and after 1977. Think about connecting past ideas like competition and natural selection. Be as specific as you can.

Question 4.3

During the drought, the beak depth with the greatest fitness increased, but the amount of variation in the trait did not. This is an example of directional selection. Directional selection is often the result of a change in environmental conditions. How does this compare to the stabilizing selection you saw in the previous lesson?

Notes

These notes will appear on every page in this lesson so feel free to put anything here you'd like to keep track of.