This figure shows a population of island finches before and after a dry year. The finches feed mainly on seeds. During the dry year, small soft seeds became...
Question 1 Report
This figure shows a population of island finches before and after a dry year. The finches feed mainly on seeds. During the dry year, small soft seeds became rare and many of the remaining seeds had hard coats. Researchers measured beak depth, from top to bottom, for every adult finch caught briefly in nets. Beak depth is a continuous characteristic. Birds with deeper beaks were more likely to crack hard seeds and survive. The researchers checked that the same type of net and the same measuring method were used in both years.
(a) Describe the change in the distribution of beak depth shown in Fig. 1. [2]
(b) Suggest why beak depth is continuous variation. [2]
(c) Use the information to describe how natural selection changed the finch population. [5]
(d) Suggest why some finches with shallow beaks may still have survived the dry year. [2]
(e) Describe one reason why measuring all captured adult finches is better than measuring only 10 finches. [1]
(f) What environmental change acted as the selection pressure? [1]
(g) Suggest one other continuous characteristic that could be measured in these birds. [1]
Answer Details
Labelled answer diagram:
(a) After the dry year, the peak is shifted towards deeper beaks [1]. There are fewer birds with shallow beaks, so the mean beak depth is greater [1].
(b) Beak depth can be measured [1] and has many possible values between the smallest and greatest measurements [1], so it is continuous.
(c) Natural selection requires inherited variation. Finches had inherited variation in beak depth [1]. During drought, small soft seeds became rare and hard seeds became more important [1]. Finches with deeper beaks obtained food more easily and were more likely to survive [1]. They reproduced and passed alleles for deeper beaks to offspring [1]. Over generations, these alleles became more common, increasing mean beak depth [1].
(d) A shallow-beaked finch may have found some soft seeds [1] or eaten another food source [1]. Moving to another area, reduced competition, or chance survival are also acceptable.
(e) Measuring all captured adults gives a larger, more representative sample and reduces the effect of chance [1].
(f) The selection pressure was the reduced availability of small soft seeds, making hard seeds more important [1].
(g) Wing length is another acceptable continuous characteristic [1].
Download The App On Google Playstore
Everything you need to excel in your exams
