Species diversity

Definition

A composite measure of how many different species occur in a community and how evenly individuals are distributed among them; commonly expressed as species richness (the raw count of species), species evenness (the relative abundance distribution), or combined indices such as the Shannon or Simpson index. Unlike species richness alone, species diversity weights rare and common species to reflect both variety and equitability.

Etymology

Example

A temperate meadow with 30 butterfly species represented by roughly equal population sizes has higher species diversity than a comparable meadow with 40 butterfly species where one or two dominant species comprise 90% of all individuals.

Synonyms

• biological diversity (in narrow usage)
• taxonomic diversity

Related Terms

• Species richness
• species evenness
• alpha diversity
• beta diversity
• Shannon index
• Simpson index
• community ecology
• biodiversity

Usage Notes

Often conflated with species richness in casual speech, but specialists distinguish them: richness counts species regardless of abundance, whereas diversity integrates abundance. The 'effective number of species' offers an intuitive alternative—expressing diversity as the equivalent number of equally common species that would produce the same heterogeneity index. In insect surveys, species diversity is frequently estimated from light-trap or Malaise-trap samples, where sampling completeness and rarefaction curves must be considered before comparing across sites.