1. Caroline and Conrad’s Theory
The Finch Module
Caroline and Conrad’s Theory

2. Overview of Explanation
Initial variation evident in beak size
Change in environment causes selective pressure
Resulting shift in food available
Natural selection for longer beak

3. Initial Variation in Beak Size

4. Change in Environment: Drought

5. Food Supply
Plants used as food:
Chamae
Portulaca
Cactus
Tribulus

6. Effects of Drought
Tribulus becomes most prevelant

7. How is a longer beak significant to the tribulus plant?
Longer beak allows for more of the seed to fit into the finch’s mouth, making it easier for the finch to crack open the shell and eat the seed.

8. Changes in Beak Length
Dry 76
Wet 77

9. Small Beak Length
Example: mm

10. Large Beak Length
Example: mm