The question is incomplete. The complete question is:
Question: Imagine a population of Galápagos finches that vary for bill size. If the population mean is near the optimum size for eating the seeds found on the island, what would we expect to occur if their main seed resource goes extinct, and another plant with much larger seeds replaces it?
a) Stabilizing selection maintaining the population average
.
b) Directional selection increasing bill size towards a new optimum
.
c) Extinction of the new plant as finches each all its seeds
.
d) Disruptive selection increasing phenotypic variance for bill size
.
e) Correlational selection between seed size and bill size.
Answer:
b) Directional selection increasing bill size towards a new optimum
.
Explanation:
Directional selection occurs when there is a change in the environmental conditions and includes gradual replacement of one phenotype with another. The changes in the environmental conditions favor one of the extreme phenotypes.
According to the given information, there is a change in the seed size available as food for the finches. The extinction of the main seed and availability of larger seeds would favor the bill size that allows the finches to feed on the larger seeds. Directional selection would favor this beneficial bill size and gradually, the bill size of the population would change in favor of the new optimum bill size.
