Answer:
<em>The correct option is limited food and water resources favored the survival of smaller deer.</em>
Explanation:
The islands where the Key deer lived had limited food and water resources. As migration was not possible for these species because the white-tailed deer had more adaptations as compared to them, hence they had to somehow survive in these areas with limited food and water resources. Limited food resources were the reason that the Key deer could not grow properly and hence evolved to have very little weight.
Long term I think because it takes a while for forest to be filled again
A gene pool changes throughout evolution this could be natural selection, genetic drift or a mutation. A gene pool does this to adapt with the needs of the environment it is in