Essex Red Data rarity statuses
It is impracticable at present to address most of the problems associated with varying coverage and comparability of fieldwork but here regional rarity categories are based on distribution are defined by the number of 1km records as a percentage of the total number of 1km squares in the county with records for the taxonomic group. This provides some measure of comparability with other counties for the factors of recording coverage and area.
These definitions based on HARVEY, P R, 1998. The modern distribution of ants (Hymenoptera: Formicidae) in Essex with their regional rarity and threat status. Essex Naturalist (New Series) 15: 61-111.
HARVEY, P R, 1999. The modern distribution of harvestmen (Arachnida: Opiliones) in Essex with their regional rarity and threat status. Essex Naturalist (New Series) 16: 125-144.
Watsonian Essex Rarity categories
These Watsonian Essex Rarity categories are 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 1km squares in the county covered for all the species in the group. 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 1km squares covered.
Essex Local post-1980 records from more than 5% to 15% of the 1km squares covered. It is almost inevitable that these species will have a restricted status confined either 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 30% of the 1km 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 Rarity categories
These Watsonian Essex Rarity categories are 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 1km squares in the county covered for all the species in the group. 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 1km squares covered.
Essex Local post-1980 records from more than 5% to 15% of the 1km squares covered. It is almost inevitable that these species will have a restricted status confined either 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 30% of the 1km 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.