Answer:
Answer is A. this situation represents isolation by vicariance.
Explanation:
Isolation by vicariance is known to occur when a large population of an organism is divided or broken up, because a barrier suddenly appeared. This situation usually affect the flow of the genes, that is characters , which will occur through natural selection.
In this case, the flood that occurred, through the damming of the water, is the barrier that occurred suddenly, which separated the population of the ants, and will or may automatically prevent transfer of characters.