Which of the following alternate hypotheses could explain Yoel's results that on some islands, green anole lizards live higher in the trees and have larger toe pads?

• A. A mutation in the green anole that increased toe pad size spontaneously occurred on one island.
• B. The brown anole lizards began to migrate to higher trees on all islands.
• C. Climate change reduced insect availability, causing lizards to move up.
• D. The introduction of a predator that lives on the ground caused the green anole lizard to evolve.

Answer: (D)

A key idea here is that natural selection can couple where a species lives with how it’s built. If a predator that hunts on the ground appears on some islands, green anoles that stay higher in the trees are less likely to be eaten. Those individuals tend to survive and leave more offspring. Over generations, traits that help climbing become more common—such as larger toe pads—so lizards living up high end up with bigger toe pads. This explains why, on islands with the new ground predator, you’d see green anoles living higher and having larger toe pads, while this pattern might not appear on islands without the predator.

The other ideas don’t fit as neatly. A single random mutation on one island could create larger toe pads, but that wouldn’t readily explain the repeatable pattern of higher perch use and bigger toe pads across multiple islands. If brown anoles moving to higher trees were the cause, you’d expect a broader, cross-island shift tied to them, not a local adaptation in green anoles tied to a ground predator. And while climate changes could push lizards upward for reasons related to prey, it doesn’t directly justify a consistent increase in toe pad size without a specific climbing-related selective pressure.