Species diversity
Species diversity is the variety of species within a defined area or community, considered through both the number of species present and how individuals are distributed among them. It is one component of biodiversity, alongside diversity within species and of ecosystems, and its interpretation depends on taxonomy, sampling method, scale, season, and reference condition.
In simple terms
Two sites can contain the same number of species but differ in diversity if one is dominated by a single species and the other has a more even distribution. Measures may therefore combine species richness with relative abundance, and different indices emphasize these features differently. Results depend on which taxonomic groups are sampled, survey effort, detectability, habitat boundaries, and timing. A single index also does not show whether native, threatened, endemic, invasive, or functionally important species are present.
Why it matters
As one dimension of Biodiversity, species diversity helps describe ecological condition, compare sites, track pressures, and evaluate conservation or land-management outcomes. Poorly specified metrics can hide declines in sensitive species or create false comparisons between unlike surveys. Credible reporting states the area, taxa, methods, season, reference, uncertainty, and ecological meaning of observed change.
Example
A restoration team surveys plants and pollinators in treated and reference plots using the same seasonal protocol. It reports richness, evenness, native and invasive species, and sampling uncertainty. The analysis finds more species after restoration but also shows that a few disturbance-tolerant species still dominate the treated plots.
How it differs
Biodiversity
Biodiversity includes variation within species, between species, and among ecosystems, while species diversity focuses on the variety and relative abundance of species in a defined area or community.