After the Drought of 1977, Researchers on the Island of Daphne

question 28

Multiple Choice

After the drought of 1977, researchers on the island of Daphne Major hypothesized that medium ground finches that had large, deep beaks survived better than those with smaller beaks because they could more easily crack and eat the tough Tribulus cistoides fruits. If this hypothesis is correct, what would you expect to observe if a population of these medium ground finches colonizes a nearby island where T. cistoides is the most abundant food for the next 1000 years? Assume that (1) even the survivors of the 1977 drought sometimes had difficulty cracking the tough T. cistoides fruits and would eat other seeds when offered a choice; and (2) food availability is the primary limit on finch fitness on this new island.

• A) evolution of yet larger, deeper beaks over time
• B) evolution of smaller, pointier beaks over time
• C) random fluctuations in beak size and shape
• D) no change in beak size and shape

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