Question

which is the best example of a community responding to an external factor?
plants and animals thrive on the forest floor after the fall of a white pine causes an opening in the canopy.
many species of raptors fly alongside each other during the autumn migration to warmer climates.
elephants use their tusks to dig the salt needed in their diets from the wall of a cave.
adult musk oxen in a herd surround their young to protect them from wolves.

Explanation:

The fall of a white - pine creating an opening in the canopy is an external factor. The plants and animals thriving on the forest floor as a result is a community response. Migration is a seasonal behavior not a response to a specific external factor in the moment. Elephants digging for salt is a feeding behavior. Musk - oxen protecting their young is a defensive behavior against a predator, but not a response to a general external environmental factor like the canopy opening.

Answer:

Plants and animals thrive on the forest floor after the fall of a white pine causes an opening in the canopy.