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These Watsonian Essex Rarity categories arc defined as:
County Extinct species not recorded in the county for more than 50 years and believed
extinct. This belief may be due to the loss of the known sites, the loss
of suitable habitat in the county or the result of a documented steady
decline.
Essex Rare
post-1980 records from 1% or less of the lkm squares in the county
covered for harvestmen species (i.e. 5 or less lkm square records).
This category is approximately equivalent to the Dorset Scarce and
Yorkshire Rare Species used by Mahon & Pearman (1993 and Archer
(1998) respectively.
Essex Scarce
post-1980 records from more than 1% to 5% of the lkm squares
covered.
Essex Local post-1980 records from more than 5% to 15% of the lkm squares
covered.
It is almost inevitable that these species will have a restricted status
confined cither to a particular habitat type or to a particular
geographical area within the county, or will be species with a
widespread distribution but whose populations are isolated by habitat
fragmentation.
Essex Common
post-1980 records from more than 15% to 25% of the lkm squares
covered.
On the assumption that there is reasonable county coverage, this
category will consist of widespread and numerous species.
Essex Ubiquitous post-1980 records from more than 30% of the 1km squares covered.
Watsonian Essex Threat categories
Increasingly our wildlife is threatened by liabitat degradation, destruction and fragmentation.
National Red Data Book categories should already provide assessment of the threat at a national
level. The following regional threat categories assess threat at a regional level but also with a
national perspective.
These Watsonian Essex threat categories are defined as:
Essex Endangered species which are known as a single extant population within a single
post 1980 one km square or from a single threatened or vulnerable
site in the county.
species believed extinct in the county but which if rediscovered would
need protection.
Essex Naturalist (New Series) 16 (1999)