Evolution can be observed directly, as in the famous example of natural selectio

Question

Evolution can be observed directly, as in the famous example of natural selection and adaptation to drought in Darwin’s finch populations on Daphne Major in the Galápagos archipelago. Answer the following questions, referring to these graphs:

a) What characteristics of the graphs show that there was variation in the population? Approximately how much variation was in the population in 1976? How much variation was in the population in 1978?

b) What happened to the population size between 1976 and 1978? What other changes occurred in the population?

It decreased?

c) Based on these limited data, which mode of selection seems to have operated on the finches? What evidence supports this idea?

I'm guessing this is something like geographic separation?

d) Assume the drought continues for another 2 years. If natural selection is occurring, what would you expect to see in future generations? If the changes in beak size are not due to natural selection, but to genetic drift, then what would you expect to see in future generations?

Thanks!

90 Before the drought 1976 All Daphne birds N=751 60 30 0 6 8 9 10 12 13 12 After the drought 1978 Survivors N=90 2 2 8 4 0 10 11 Beak depth (mm) 6 8 12 13 14

Explanation / Answer

a) The x- axis shows the variability in beak size,it indicates that some birds possessed small beaks, some birds possessed medium beaks and some possessed large beaks. In 1976 , there was a lot more variation.In that time period, small and larger beak depths were seen more commonly.

b) The population size dropped by around 82% between 1976 and 1978. Due to the drought there was a shortage of food, as a result of which there was death due to starvation.Birds with larger beaks were able to crack open hard seeds better than birds with small beaks.Birds with larger beaks were seen to having selective advantage.

c) Directional selection seems to have operated on the finches. There was a directional increase in the size of the beaks of the birds.

d) If the changes in beak size are not due to natural selection but due to genetic drift , then there would be random changes in the average beak size.There could be an increase in the beak size or a decrease or the beak size would not change , irrespective of the environmental conditions.

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