Where does diversity collide?

The variety of species in a biological community, combining how many species are present (richness) with how evenly individuals are spread across them (evenness): a community of ten equally common species is counted as more diverse than one where a single species dominates. Simpson's 1949 note Measurement of diversity set out an index for this, and the Shannon index is the other common measure of the same idea. The referent is a property of a whole community, computed from species counts and their relative abundances, and it is unrelated to a mix of workers in a firm, a spread of assets in a fund, or the variety of alleles in a population.[1]

Unit

A community's species variety, as an index of richness and evenness

Recovery means

Not applicable

Measured by

Computed as the Simpson or Shannon diversity index from species counts and their relative abundances in a sample

The extent of differences among the members of a work group or organization: these can be surface-level attributes such as age, sex, and race that are readily observed, or deep-level attributes such as attitudes, values, and beliefs that emerge only over time. Harrison, Price, and Bell's 1998 study Beyond relational demography drew that distinction and showed the two kinds of difference act on a group in different ways as members work together, a finding at the centre of the long debate over whether diversity helps or hurts performance. The referent is the spread of people within a social unit, indexed from member attributes, and it has nothing in common with species counts in a community, correlations among assets, or allele frequencies in a gene pool.[2]

Unit

A work group's spread across member attributes, surface-level or deep-level

Recovery means

Not applicable

Measured by

Indexed from member attributes, as demographic spread for surface-level difference or as dispersion in attitudes and values for deep-level difference

The variety of alleles and genotypes carried by the individuals of a population: a population where many alleles occur at appreciable frequency is more diverse than one fixed on a single variant, and this variation is the raw material on which selection and drift act. Nei's 1973 paper Analysis of gene diversity in subdivided populations defined a general measure, gene diversity, as the probability that two alleles drawn at random from the population differ, and partitioned it within and between subpopulations. The referent is a property of a gene pool, computed from allele frequencies, and it is separate from the variety of species in a community, the mix of members in a firm, or the spread of assets in a fund.[3]

Unit

A population's allelic variety, as the chance two random alleles differ

Recovery means

Not applicable

Measured by

Computed as Nei's gene diversity, equivalently expected heterozygosity, from observed allele frequencies