Question

the fossil record shows that the average size of black bears was large during cold glacial periods and got smaller during warmer time periods. what is this an example of?
directional selection
disruptive selection
ecosystem selection
stabilizing selection

Explanation:

Directional selection favors phenotypes at one extreme of a trait distribution. Here, black - bear size changes in a single direction (larger in cold, smaller in warm) in response to environmental changes. Disruptive selection favors extreme phenotypes over intermediate ones. Ecosystem selection is not a standard evolutionary term. Stabilizing selection favors intermediate phenotypes.

Answer:

A. directional selection