Biodiversity and species richness

Biodiversity describes the variety of living organisms in an area. The area being considered can be small, such as a local habitat, or as large as the whole Earth. The scale must therefore be clear when describing biodiversity.

Within a community, species richness is the number of different species present. To find it, count each species once, regardless of how many individuals belong to it.

For example, a community with 90 individuals of one species and 5 individuals of each of two other species has a species richness of 3. A community with 34, 33 and 33 individuals of three species also has a species richness of 3.

The two communities have the same species richness, even though their individuals are distributed differently among the species. Species richness tells us how many species are present, not how individuals are shared among them.