Factors Considered in Ranking
CDCs use element occurrence (EO) as the mapping unit.
An EO is defined as an area of land or water on/in which an element (plant,
or animal species, or ecological community) is, or was, present. It is
a physical location important to the conservation of a species or community.
(Species are used in the examples below, but similar information has been
collected and will soon be available for communities.). For a species
it is generally the habitat occupied by a local population. What constitutes
an occurrence also varies among species (e.g., breeding ponds where adults,
egg masses or larvae have been identified; hibernacula; den sites; etc.).
Some species have more than one type of occurrence, for example breeding
and wintering occurrences.`
Status ranks for species and communities are based on a combination
of eight primary factors. Assuming adequate information, a letter, A to
D, is assigned to each factor. As for the eight factors will be ranked
S1 (rare) whereas a species or community assigned all Ds will be ranked
S5 (common). Where there is a mixture of letter ranks, the ranking team
assigns weights to each factor. The criteria below are used to determine
ranks (S) for the four Atlantic provinces.
Abundance - is measured in different
ways depending on the class and species. For animals it is usually the
number of individuals, for plants it usually the area occupied by a population,
for aquatic invertebrates it could be the stream length or area occupied.
Range - an estimate of the percentage
of a province that is occupied
Abundance trend - an estimate of change,
based on long-term monitoring, historical accounts, and ignoring natural
fluctuations, the density of mature individuals over time
Distribution trend - characterizes
the trend in the species' distribution over its provincial range. (When
a species' distribution is extremely limited and there are very few site
occurrences, it is highly susceptible to ecological disturbances. Distribution
is therefore an important factor influencing S-rank when the number of
occurrences is low. If the letter code for this field is A or B, the species
usually qualifies for a rank of S1 or S2.)
Element occurrences (EOs) – the estimated
number of occurrences in the province
Protected occurrences - the estimated number of adequately
protected occurrences in the province
Population threats - observed, inferred, or projected
due to: 1) direct exploitation, 2) harassment, or 3) ecological interactions
with predators, competitors, pathogens or parasites - which may result
in population declines. General threats may arise from natural or human
causes
Habitat threats - observed, inferred, or projected (loss,
conversion, degradation, or fragmentation) that may result in population
declines or loss of element occurrences
Other considerations – includes components other than
those outlined above, used to determine rank. Generally, those considerations
will increase, rather than decrease, the rank (e.g., never reproduces
sexually or all occurrences are in developing farmland or suburbs)
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