Assume two habitats have the same number of species. One habitat is predominantly one species with just a few of the other species. The other habitat has equal numbers of all the different species. Which will have the highest diversity index?

Base on your question where as the two habitat have the same number of species and one is predominantly on species and with just a few the other species the other one is equal number of all different species and the highest diversity index is the habitat with equal number of species.