The graph below shows the average tail length of a population of deer mice. The first graph shows the tail length of the mice while living in a prairie ecosystem, and the second shows the tail length many generations after a group of mice moved into a forest ecosystem. Which of the following types of natural selection describes this scenario, and what conclusion could you draw from these data?

• A. Stabilizing selection: shorter-tailed mice had increased fitness in the forest ecosystem.
• B. Stabilizing selection: longer-tailed mice had increased fitness in the forest ecosystem.
• C. Directional selection: shorter-tailed mice had increased fitness in the forest ecosystem.
• D. Directional selection: longer-tailed mice had increased fitness in the forest ecosystem.

Answer: (D)

Verified step by step guidance

1. Examine the graphs: The first graph represents the tail length distribution of deer mice in a prairie ecosystem, showing a normal distribution centered around a specific tail length. The second graph represents the tail length distribution after many generations in a forest ecosystem, showing a shift in the distribution.
2. Identify the type of selection: In the prairie ecosystem, the tail length distribution is centered around a mean value. In the forest ecosystem, the distribution has shifted, indicating a change in the average tail length. This shift suggests directional selection, where one extreme of the trait is favored over others.
3. Determine the favored trait: The shift in the distribution towards longer tail lengths in the forest ecosystem suggests that longer-tailed mice had increased fitness in this environment. This is because the distribution has moved in the direction of longer tails.
4. Understand directional selection: Directional selection occurs when environmental pressures favor one extreme phenotype over others, leading to a shift in the population's trait distribution over generations. In this case, longer tails are favored in the forest ecosystem.
5. Draw a conclusion: Based on the shift in tail length distribution, the scenario is best described by directional selection, where longer-tailed mice had increased fitness in the forest ecosystem. This conclusion aligns with the observed data and the principles of natural selection.