Based on Simpson’s index, which is true for communities X and Y?
Simpson-based comparisons incorporate both species richness and the distribution of individuals among species. In its dominance form, D = Σpᵢ², the index is the probability that two sampled individuals belong to the same species; smaller D therefore means greater diversity. In the complementary form, 1 − D, larger values mean greater diversity. A conclusion that community X has greater alpha diversity than Y is justified when X has the lower dominance value, or equivalently the higher 1 − D value, under the same sampling effort. This can occur even if both communities contain the same number of species, because a community with more even relative abundances is less likely to yield two conspecific individuals in a random pair. Species richness alone cannot establish the result: one community may contain more species yet be strongly dominated by one of them. “Alpha” here specifies that X and Y are each being assessed internally, rather than measuring turnover between them. The numerical abundance table or plotted Simpson values are absent from the text, so the ranking cannot be independently recalculated, but this is the interpretation supporting X.
Ref: NCERT Biology Class 12, Ch. 15 Biodiversity and Conservation