Question

Imagine you are studying leaf size in a large population of plants over several years. In one year of your study there is a below-average amount of rainfall, and the following year the average leaf size in the population is smaller than before. However, the amount of variation in leaf size is the same and the population size doesn't change. Other scientists have done experiments showing that small leaves are better adapted to dry conditions than large leaves. What has most likely occurred?

A) genetic drift
B) directional selection
C) stabilizing selection
D) the founder effect
E) disruptive selection

Answer 1

The decrease in average leaf size in response to drier conditions, with the variation in leaf size remaining consistent, indicates that directional selection has occurred in the plant population.

Step-by-step explanation:

The scenario described where a population of plants with large leaves adapts to drier conditions by developing smaller leaves suggests that directional selection has most likely occurred.

This type of natural selection shifts the average phenotype in the population because the environment favors individuals with traits that are better suited to the new conditions—in this case, smaller leaves that conserve water better during dry conditions.

Since the variation in leaf size remains the same but the average leaf size decreases, it supports the idea that the population is responding to a change in the environment rather than genetic drift, the founder effect, stabilizing selection, or disruptive selection.