A Pielou index value of 1 indicates:
A Pielou value of one occurs when every species has the same relative abundance. Under that distribution Shannon entropy reaches ln(S), its maximum for S species, so the ratio H′/ln(S) equals one and represents perfect evenness. 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, Perfect evenness, 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.
Ref: NCERT Biology Class 12, Ch. 15 Biodiversity and Conservation