Each element is ranked at two levels: global (G)
and provincial, or "subnational" (S). The global rank
is based on the status of the element throughout its entire range
whereas the provincial rank is based solely on its status within
British Columbia. The global rank is established by a biologist
assigned to that element by The Nature Conservancy; the provincial
rank cannot exceed the global rank.
The status of an element is indicated on a scale
of one to five; the score is based primarily on the number of extant
occurrences of the element, but other factors such as abundance,
range, protection, and threats are also considered if the information
is available. Generally speaking, the Conservation Data Centre will
track only those species with ranks of 1-3. In addition to the ranks
1-5, there are several letter ranks; all are defined below.
1 = Critically
imperilled because of extreme rarity (5 or fewer extant occurrences
or very few remaining individuals) or because of some factor(s)
making it especially vulnerable to extirpation or extinction
2 = Imperilled
because of rarity (typically 6-20 extant occurrences or few remaining
individuals) or because of some factor(s) making it vulnerable to
extirpation or extinction
3 = Rare or
uncommon (typically 21-100 occurrences); may be susceptible to large-scale
disturbances; e.g. may have lost extensive peripheral populations
4 = Frequent
to common (greater than 100 occurrences); apparently secure but
may have a restricted distribution; or there may be perceived future
threats
5 = Common
to very common; demonstrably secure and essentially ineradicable
under present conditions
H = Historical
occurrence; usually not verified in the last 40 years, but with
the expectation that it someday may be rediscovered
X = Apparently
extinct or extirpated, without the expectation that it will be rediscovered
U = Status
uncertain, often because of low search effort or cryptic nature
of the element; uncertainty spans a range of 4 or 5 ranks
R = Reported from the province, but without persuasive
documentation for either accepting or rejecting the report
RF = Reported in error, but this error has persisted
in the literature
? = Limited information is available or the number
of extant occurrences is estimated
A = An element (usually an animal) that is considered
accidental or casual in province; a species that does not appear
on an annual basis
E = An exotic or introduced species to the province
Z = Occurs in the province but as a diffuse, usually
moving population; difficult or impossible to map static occurrences
In addition to the above ranks, there are four
letter qualifiers sometimes used in conjunction with them:
T = Designates a rank associated with a subspecies
B = Breeding; the associated rank refers to breeding
occurrences of mobile animals
N = Non-breeding; the associated rank refers to
non-breeding occurrences of mobile animals
Q = Taxonomic validity of the element is not clear
or in question
Each
"element" (for example, a species) on the Conservation
Data Centre's list is ranked using the system developed over the
past 25 years by The Nature Conservancy (U.S.). This system is now
in use in six Canadian provinces, all U.S. states and a number of
Latin American countries. Most government agencies within these
jurisdictions have also adopted this ranking system.