Although hummingbirds and house flies both use wings to fly, this similarity is not based upon closely shared ancestry but rather on evolution and adaptation as a result of survival and reproduction in a given environment. The term best describing such a phenomenon is

Analogous Structures

Explanation:

Defintion of Analogous Structures: body parts that share a common function, not structure. I wish there was multiple choice but hopefully this helps.

A lot of toxins in a coral reef could influence natural selection so it would become like survival of the fittest. Then the fish would develop certain traits to better protect themselves (less prey means predators would takes bigger measures to get food). This would also cause a decrease genetic variation because there wouldn't be as much fish left. Since the coral reef went from unique to dull from toxins.