What factors affect the likelihood a species will migrate from the mainland to an island?

The factors that might affect the likelihood a species will migrate from the mainland to an island are the distance to the mainland and the island´s size.

Explanation:

Ecologists MacArthur and Wilson took the term island biogeography theory to refer to the predictions about the number of species that could inhabit an island.  

Island biogeography theory establishes that the two factors that affect species richness in natural communities on an island are the distance to the mainland and the island´s size.

At the same time, these factors affect immigration and extinction rates. According to the theory, islands that are closer to the continent have higher possibilities of receiving immigrants than those located farther from the mainland. This is the effect of distance.

The effect of size is reflected in the relation between island size and species diversity.  In smaller islands, the probability of extinction is higher than in bigger islands. Bigger islands can have more species than smaller ones.

In the case of two islands of the same size and different distance to the mainland, both of them will have the same extinction rate, but the one closer to the continent will have a higher immigration rate, and so, a higher amount of species. The S value will be higher on the island closer to the continent.

the correct answer is:

a population changes in response to a change in the environment.