Biodiversity & Conservation

Species richness

The number of species in a given habitat, biotope, community or assemblage. The following scale is used to judge the likely response of species richness to an external factor.

Rank Definition
Major decline The number of species in the community is likely to decrease significantly (>75% of species) in response to the factor, probably because of mortality and loss of habitat. For example, a change from very rich to very poor on the NHAP scale (Hiscock 1996).
Decline The community is likely to loose some of its species in response to the factor by either direct mortality or emigration.
Minor decline The community is likely to loose few species (<25% of species) in response to the factor. For example, a decrease of one level on the NHAP scale (Hiscock 1996).
No change The factor is unlikely to change the species richness of the community
Rise The number of species in the community may increase in response to the factor. (Note the invasion of the community by aggressive or non-native species may degrade the community).
Not relevant It is extremely unlikely for a factor to occur (e.g. emergence of a deep water community) or the community is protected from the factor.
Insufficient Information

References:

Hiscock, K., 1996. Interpretation of data. In Marine Nature Conservation Review: Rationale and methods, ed. K. Hiscock, p.73-84. Peterborough, Joint Nature Conservation Committee.