Practice question

Pielou's evenness is calculated as J = H′/ln(S), where H′ is Shannon entropy and S is species richness. Dividing observed Shannon diversity by its maximum possible value at that richness isolates how uniformly individuals are apportioned among species. Community indices compress abundance data, so their assumptions and mathematical conventions must remain explicit. Shannon entropy gives weight to both common and uncommon species, Simpson measures are more strongly influenced by dominant species, and Sørensen similarity usually uses presence–absence overlap. Equal abundance provides useful benchmarks: Shannon reaches ln(S) and Pielou reaches one. These properties allow the numbers to be interpreted biologically rather than treated as isolated arithmetic results. In this context, the keyed term, Shannon’s H, identifies the relevant mechanism or quantitative relationship and links the observed pattern to its underlying ecological cause. The distinction is testable by measuring changes in organisms, resources, or process rates through time rather than relying on the label alone.