Biodiversity Index Calculator

Measuring biodiversity is not just about counting species; it is about assessing the distribution of life. The Shannon diversity index H is derived from Claude Shannon's information entropy: H = -Σ p_i ln p_i. In ecology, this measures the uncertainty in predicting the species of a randomly chosen individual. If an ecosystem is dominated by a single species, uncertainty is low, and the Shannon index is close to zero. If species are equally abundant, uncertainty and diversity are maximized. Similarly, the Simpson index measures the probability that two randomly selected individuals belong to the same species. By translating biological diversity into thermodynamic and information-theoretic terms, ecologists can mathematically evaluate ecosystem stability, resilience to disturbance, and the impact of conservation efforts.

Two communities can list the same number of species yet be worlds apart. A plot with 90 individuals of one species and just one each of four others has the same richness (S = 5) as a plot with 20 of each — but far less real diversity, because one species drowns out the rest. That is why this tool reports evenness (Pielou's J) beside the raw count: diversity is about how evenly individuals are spread, not only how many species are present.

Simpson's dominance λ = Σpᵢ² is mathematically identical to the Herfindahl-Hirschman Index that economists use to gauge market concentration — regulators apply the very same sum of squared shares to decide whether a merger creates a monopoly. Low ecological diversity and a monopolised market are, arithmetically, the same thing. Fittingly, Edward Simpson introduced the index in 1949 after wartime service as a Bletchley Park codebreaker.