Priority Score, S-Ranks and G-Ranks

Source: wildlifearkansas.com (03SGCN.pdf)

To best prioritize the efforts directed by the CWCS, Arkansas developed a protocol
to evaluate all species on the Species of Greatest Conservation Need (SGCN) list and manage the information in a database.

A “Species Priority Score” for SGCN makes it possible to prioritize projects to
address the most pressing needs of species and groups of species included in the
database.

Calculating the Species Priority Score

G Ranks (Table 2.3) are used to determine the range of vulnerability or security of
a species worldwide. Several factors are considered in assessing conservation status:
total number and condition of populations; population size; range extent and area
of occupancy; short- and long-term trends; scope, severity and immediacy of threats;
number of protected occurrences; and intrinsic vulnerability and environmental
specificity. (Source: Natureserve 2005). For the CWCS, the global conservation
condition of a species is weighted more heavily than is state condition.

In calculating the Species Priority Score, Arkansas assigned a numeric value to the
G Rank from 1 to 16 which represents an exponential progression. This emphasizes
scores of species that are imperiled across their entire range, and de-emphasize
species that are relatively more common but are rare or imperiled only in Arkansas.

A higher number represents a more imperiled status. Generally:

Combination G Ranks, for example, G3G5, that fell between the values assigned
were given an average value. Subspecies were treated in the same manner as species.
Where a determination needed to be made for a score value, the more conservative
one was selected.

Similarly, the S Ranks (Table 2.4) were assigned a numeric value:

Combination S Ranks, for example, S2S3, that fell between the values assigned
were given an average value. Subspecies were treated in the same manner as species.
Again, where a determination needed to be made for a score value, the more conservative
one was selected.

Table 2.3. Key to G Rank Scores

Table 2.4. Key to S Rank Scores

Factoring in Population Trend

After the G score is added to the S score, the resulting raw score is multiplied by
0.75 if the species is increasing or multiplied by 1.25 if the species is declining so
that the score will reflect trend data. The raw scores of stable populations or instances
where trend data were not available were not manipulated. Population trend
was determined by Taxa Association Teams using information derived from literature
reviews, expert opinion or recent survey data.

The resulting number is divided by 0.2625 to scale it to a hundred point scale. The
final score, the Species Priority Score, is presented on the first page of species reports
and in Tables 2.6-2.14. The entire list of SGCN, ranked by Species Priority
Score, is provided in Appendix 2.1, pages 1684-1691.

Revising the SGCN list

The process for adding a species to the list is as follows: Any person or group may
petition to have a species listed. This request is first taken to the species’ Taxa Association
Team for approval or denial.

If approved, the species is added to the SGCN database and information is captured
about its conservation status. If the species is rejected by the Taxa Association
Team (Table 2.2), the person or group may appeal to the Species team (Table 2.1).
However, the conservation status of a species, and whether it is increasing or in
decreasing, will determine the Species Priority Score and the potential to have associated
research and conservation actions funded.

Table 2.5. Evaluation of Species Priority Scores by taxa association.

Below are averages of Species Priority Scores within each taxa association. A higher
score implies the taxa association has a higher degree of conservation need.