Species richness

Definition

The count of distinct species present in a defined ecological unit—such as a community, habitat patch, landscape, or region—without regard to their relative abundances or population sizes. As a raw tally, it differs from species diversity, which incorporates both richness and evenness (the distribution of individuals among species).

Etymology

Example

A Malaise trap sample from a tropical forest canopy might yield 847 morphospecies of Hymenoptera, giving a species richness of 847 for that sampling event, even if 90% of individuals belong to a single abundant braconid wasp species.

Synonyms

• species count
• taxonomic richness

Related Terms

• Species diversity
• species evenness
• alpha diversity
• beta diversity
• gamma diversity
• rarefaction
• species accumulation curve
• community ecology

Usage Notes

Specialists distinguish sharply between richness (a count) and diversity (a composite measure). Richness increases with sample size and effort, so comparisons require standardized sampling or rarefaction. In arthropod surveys, morphospecies counts often substitute for true species richness when taxonomic expertise is limited. Contrast with species evenness, which describes how equally individuals are distributed among those species.