Fig. 1 shows a small island where medium ground finches feed mainly on seeds. In one dry year, most small soft seeds failed to form. A conservation team mea...
Question 1 Report
Fig. 1 shows a small island where medium ground finches feed mainly on seeds. In one dry year, most small soft seeds failed to form. A conservation team measured the beak depth of adult birds that survived until the following breeding season. The same team recorded the seeds available in two areas of the island.
| seed type | mean seed width / mm | number found before drought | number found after drought |
|---|---|---|---|
| small, soft | 2.1 | 840 | 90 |
| large, hard | 5.8 | 170 | 150 |
Beak depth varies between individual finches and is inherited. Finches with deeper beaks can crack hard seeds more easily. No finch changes its inherited beak depth because it needs food. The team plans to return in 20 years to compare the population.
(a) Use Table 1 to describe the change in the availability of the two seed types. [2]
(b) Suggest which finches were more likely to survive the drought. [1]
(c) Describe how the mean beak depth of the population may change over several generations. [3]
(d) What evidence would support the idea that beak depth is inherited? [2]
Answer Details
Labelled answer diagram:
(a) Small soft seeds decreased greatly from 840 to 90 [1]. Large hard seeds changed little, from 170 to 150 [1].
(b) Finches with deeper or larger beaks were more likely to survive [1].
(c) Deeper-beaked finches can obtain more hard seeds and are more likely to survive [1]. They reproduce more successfully and pass alleles for deeper beaks to offspring [1]. Over generations, mean beak depth increases [1].
(d) Evidence would be that offspring of deep-beaked parents tend also to have deep beaks [1]. This pattern should remain when offspring are raised under similar conditions, or beak depth should be associated with parental genotype [1].
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