Final answer:
Island biogeography asserts that an island closer to the mainland typically has higher biodiversity due to more frequent migration and a greater number of ecological niches.
Step-by-step explanation:
The theory of island biogeography suggests that the closer island should have a higher biodiversity. This theory, developed by Robert H. MacArthur and Edward O. Wilson, indicates that biodiversity is influenced by immigration and emigration, speciation, and extinction events. As such, islands that are closer to the mainland tend to have higher migration rates and are more likely to receive new species. In addition, islands that are far from a mainland have lower immigration rates, which may lead to fewer species establishing populations on these remote islands. Greater geographic diversity and more available niches can also influence the speciation rate on larger islands.