<em>A) The biodiversity will decrease because there are fewer species on the newly formed island.
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<em>D) The species on the island will likely have lower genetic diversity than the species on the mainland.</em>
Explanation:
When a larger population is broken down and a smaller population is formed, the genetic diversity in the smaller population will be lower as it has fewer species. As a result, options for genetic variations will be lesser. Hence, the landmass which drifted away will have lower biodiversity than the mainland. There will be more number of species on the mainland hence the genetic diversity will be more there.
