You are studying leaf size in a natural population of plants.The second season is particularly dry,and the following year the average leaf size in the population is smaller than the year before.But the amount of overall variation is the same,and the population size hasn't changed.Also,you've done experiments that show that small leaves are better adapted to dry conditions than are large leaves.Which of the following has occurred?

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Quizplus · Accepted Answer

The dry conditions during the second season selected for smaller leaves, which are better adapted to the arid environment. This is an example of directional selection, where one extreme phenotype is favored over another. The fact that the population size hasn't changed and the amount of variation has remained the same suggests that genetic drift and disruptive selection are not occurring. Stabilizing selection would favor the mean or intermediate phenotype, but in this case, the selection pressure was towards smaller leaves.

You Are Studying Leaf Size in a Natural Population of Plants.The