Status Definitions And Criteria For Invertebrates

by P.J.Hodge

Criteria for the selection of species into the Red Data Book categories follow Shirt (1987), with minor modifications that are italicised. Categories RDB K (insufficiently known) and RDB I (indeterminate) are based on the criteria used by Wells, Pyle & Collins (1983). Criteria for the selection of Nationally Notable species follow Eversham (1983).

STATUS CATEGORIES

Red Data Book category 1 (RDB 1) - Endangered

Definition.

Taxa in danger of extinction in Great Britain and whose survival is unlikely if the causal factors continue operating.

Included are those taxa whose numbers have been reduced to a critical level or whose habitats have been so dramatically reduced that they are deemed to be in immediate danger of extinction. Also included are some taxa that are possibly extinct.

Criteria.

Species which are known or believed to occur as only a single population within one 10 km square of the National Grid.

Species which only occur in habitats known to be especially vulnerable.

Species which have shown a rapid or continuous decline over the last twenty years and are now estimated to exist in five or fewer 10 km squares

Species which are possibly extinct but have been recorded this century and if rediscovered would need protection.

Red Data Book category 2 (RDB 2) - Vulnerable

Definition.

Taxa believed likely to move into the endangered category in the near future if the causal factors continue operating.

Included are taxa of which most or all of the populations are decreasing because of over-exploitation, extensive destruction of habitat or other environmental disturbance; taxa with populations that have been seriously depleted and whose ultimate security is not yet assured; and taxa with populations that are still abundant but are under threat from serious adverse factors throughout their range.

Criteria.

Species declining throughout their range.

Species in vulnerable habitats.

Red Data Book category 3 (RDB 3) - Rare

Definition.

Taxa with small populations in Great Britain that are not at present endangered or vulnerable, but are at risk.

These taxa are usually localised within restricted geographical areas or habitats or are thinly scattered over a more extensive range.

Criterion.

Species which are estimated to exist in only fifteen or fewer 10 km squares. This criterion may be relaxed where populations are likely to exist in over fifteen 10 km squares but occupy small areas of especially vulnerable habitat

Red Data Book category 4 (RDB 4) - Out of Danger

Definition.

Taxa formerly meeting the criteria of one of the above categories, but which are now considered relatively secure because effective conservation measures have been taken or the previous threat to their survival in Great Britain has been removed.

Red Data Book category 5 (RDB 5) - Endemic

Definition.

Taxa which are not known to occur naturally outside Great Britain. Taxa within this category may also be in any of the other RDB categories or not threatened at all.

Red Data Book Appendix (RDB app.) - Extinct

Definition.

Taxa which were formerly native to Great Britain but have not been recorded since 1900.

Red Data Book category I (RDB I) - Indeterminate

Definition.

Taxa considered to be Endangered Vulnerable or Rare in Great Britain but where there is not enough information to say which of the three categories (RDB 1 to 3) is appropriate.

Red Data Book category K (RDB K) - Insufficiently Known

Definition.

Taxa in Great Britain that are suspected but not definitely known, to belong to any of the above categories, because of lack of information.

Criteria.

Taxa recently discovered or recognised in Great Britain which may prove to be more widespread in the future.

Taxa with very few or perhaps only a single known locality but which belong to poorly recorded or taxonomically difficult groups.

Species known from very few localities but which occur in inaccessible habitats or habitats which are seldom sampled.

Species with very few or perhaps only a single known locality and of questionable native status, but not clearly failing into the category of recent colonist, vagrant or introduction.

Nationally Scarce Category A - Notable A (Na)

Definition.

Taxa which do not fall within RDB categories but which are none-the-less uncommon in Great Britain and are thought to occur in 30 or fewer 10 km squares of the National Grid or, for less well recorded groups, within seven or fewer vice-counties.

Nationally Scarce Category B - Notable B (Nb)

Definition.

Taxa which do not fall within RDB categories but which are none-the-less uncommon in Great Britain and are thought to occur in between 31 and 100 10 km squares of the National Grid or for less well recorded groups, between eight and twenty vice-counties.

Nationally Scarce - Notable (N)

Definition.

Taxa which do not fall within RDB categories but which arc none-the-less uncommon in Great Britain and are thought to occur in between 16 to 100 10 km squares of the National Grid. Species within this category are often too poorly known for their status to be more precisely estimated.

References

EVERSHAM, B., 1983.

Defining Rare and Notable species – a discussion document. Invertebrate Site Register Report No. 49. Peterborough: NCC.

SHIRT, D. B. (Ed.), 1987.

British Red Data Books : 2 : Insects. Peterborough : NCC.

WELLS, S.M., PYLE, R.M. & COLLINS, N.M., 1983.

The IUCN Invertebrate Red Data Book. Gland: International Union for Conservation of Nature and National Resources.