Which value of Simpson’s D indicates maximum diversity?
Under the commonly used dominance definition, Simpson’s D is calculated as Σpᵢ², where pᵢ is the proportional abundance of species i. It estimates the probability that two individuals drawn at random from a community belong to the same species. D approaches 1 when one species dominates, because nearly every pair is conspecific. It approaches 0 as richness increases and abundances become more evenly distributed, because a random pair is increasingly likely to contain different species. Among the listed values, 0 therefore represents the theoretical direction of maximum diversity. For a finite community, the exact minimum is usually greater than zero, so zero is best understood as a limiting value. Confusion arises because “Simpson’s index” is also reported as 1 − D or 1/D. In the 1 − D convention, values near 1 indicate high diversity; in the reciprocal convention, larger values do so. The keyed value relies specifically on D as a dominance index, consistent with nearby items. Always identify the formula before interpreting whether a high numerical value means high or low diversity.
Ref: NCERT Biology Class 12, Ch. 15 Biodiversity and Conservation