Final answer:
Under the Island Biogeography Theory, a large, close island will have the highest equilibrium number of species owing to greater habitat diversity and higher immigration rates.
Step-by-step explanation:
According to the Island Biogeography Theory (IBT), the equilibrium number of species on an island is determined by various factors including the size of the island and its distance from the mainland. Larger islands can support more species due to more varied habitats and larger populations which lower the chance of species extinction. Proximity to the mainland also affects the immigration rates of new species. Therefore, a large, close island would have the highest equilibrium number of species due to higher immigration rates and larger habitats, while a big, far island would also have comparatively high biodiversity, but slightly less due to lower immigration rates.