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Wyoming Natural Diversity Database

State Status

NSS Rank and Tier Rank

WGFD_NSS
Below is an abbreviated version of the Wyoming Game and Fish Department's NSS ranking procedure. For more detailed information, click on the links provided.

Element 1 of the Congressional guidelines for State Wildlife Action Plans (SWAPs) specifies that each state must provide “information on the distribution and abundance of species of wildlife, including low and declining populations as the state wildlife agency deems appropriate, that are indicative of the diversity and health of the state’s wildlife.” These species have been termed Species of Greatest Conservation Needs or SGCN.

The Wyoming Game and Fish Department's (WGFD) SGCN designation process is based upon its Native Species Status (NSS) classification system, which also includes a description of their method of assigning Tier ranks. During the early 1980's, the WGFD conducted a series of analyses to identify species of special concern. A system was developed that used a matrix to evaluate a species’ status in relation to population (y-axis) and habitat variables (x-axis). In the 2005 Comprehensive Wildlife Conservation Strategy (CWCS),1 a 16-cell matrix was used for birds and mammals and a 9-cell matrix for fish, reptiles, amphibians, and invertebrates. An NSS rank was assigned for an individual species based on the intersection of the two most appropriate population and habitat conditions. For the purposes of the 2005 CWCS, species identified as NSS1, NSS2, NSS3, or NSS4 were considered to be SGCN.

Since that time, it was determined that using a separate matrix for fish, reptiles, amphibians, and invertebrates was too cumbersome, and a revised approach was created for the 2010 SWAP. The revised NSS matrix has 16 cells (see table below). The y-axis consists of population variables, which range on a continuum from populations declining with extirpation possible (row A) to populations that are widespread and expanding (row D). After identifying the appropriate row for a species population, the most appropriate limiting factor column is selected from the x-axis, ranging from limiting factors that are severe and worsening (column a) to limiting factors that are moderate and not likely to increase (column d). Limiting factors include habitat, human activity levels, genetics, invasive species, disease, environmental contaminants, and climate change.

This system cannot be used for classifying some species because necessary information is lacking. These species are placed in a separate status category as NSS Unknown (NSSU) until additional information is obtained. Species that receive an NSS rank of NSS1, NSS2, NSS3, NSS4, or NSSU were recommended to the Wyoming Game and Fish Commission to receive SGCN designation for the 2010 SWAP. NSSU species were recommended to receive the SGCN designation because obtaining a greater understanding regarding population numbers and distributions of these species is necessary in determining their conservation status, including responding to petitions for listing under the Endangered Species Act. Some species with naturally low numbers and limited distributions were not recommended to receive SGCN status if both the following qualifications were met:

1. The species in Wyoming is not experiencing known population declines or increasing threats, and
2. The species’ population is abundant and secure throughout its range.

Only species that are legally considered wildlife in Wyoming were evaluated for SGCN status. Wyoming Statute 23-1-101 (a) (xiii) defines “wildlife” as all wild mammals, birds, fish, amphibians, reptiles, crustaceans and mollusks, and wild bison designated by the Wyoming Game and Fish Commission and the Wyoming Livestock Board within Wyoming. Plants and invertebrates (excluding crustaceans and mollusks) are outside the jurisdictional authority of the WGFD and were not considered for SGCN status. To increase understanding about Wyoming’s invertebrates, a cooperative agreement was signed between the WGFD and the Wyoming Natural Diversity Database (WYNDD) in May 2010.


Limiting Factors
a.
EXTREME
Limiting factors are severe and continue to increase in severity
b.
SEVERE
Limiting factors are severe and not increasing significantly
c.
MODERATE
Limiting factors are moderate and appear likely to increase in severity
d.
MINIMAL
Limiting factors are moderate and not likely to increase in severity

 P
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 S
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A.
IMPERILED
Population size or distribution is restricted or declining and extirpation is possible
Aa
NSS1
Ab
NSS2
Ac
NOT APPLICABLE
Ad
NOT APPLICABLE
B.
VULNERABLE
Population size or distribution is restricted or declining but extirpation is not imminent
Ba
NSS2
Bb
NSS3
Bc
NSS4
Bd
NOT APPLICABLE
C.
STABLE
Population size and distribution is stable and the species is widely distributed
Ca
NOT APPLICABLE
Cb
NSS4
Cc
NSS5
Cd
NSS6
D.
EXPANDING
Populations are expanding in number and/or distribution and the species is widely distributed
Da
NOT APPLICABLE
Db
NOT APPLICABLE
Dc
NSS6
Dd
NSS7

 

WGFD_Tier
Numerical scores were assigned to each of the above variables and summed to provide a total score. SGCN were placed into one of three tiers based on their total score: Tier I – highest priority, Tier II – moderate priority, and Tier III – lowest priority. Prioritization scores were assigned by two or more WGFD biologists who have considerable knowledge about the SGCN. If the difference in total scores by any two individual s resulted in a species being placed in different tiers , then the relevant variables were discussed to reach consensus about the appropriate tier for the species.  The tier for any SGCN may be reviewed annual if circumstances change or new data becomes available.

Species ranked NSS1-NSS4 were treated differently than NSSU species.  This was due to the lack of sufficient information about NSSU species to adequately assess some prioritization variables and also because of an absence of a numerical NSS rank.  The prioritization system for NSS1-NSS4 and NSSU is as follows:

NSS1-NSS4

  1. The NSS rank of the species is subtracted from 5 and multiplied by 6: [(5-NSS)x6].  This would result in scores of NSS1 = 24, NSS2 = 18, NSS3 = 12, NSS4 = 6.
  2. The species is assigned a score of 1-10 based on the variable "Wyoming's contribution to the species' overall conservation"; 10 being the highest contribution and 1 being the lowest contribution. The WYNDD G rank (global chance of extinction) and Wyoming Conservation Contribution score were consulted in determining this score.
  3. The species is assigned a score of 1-5; 5 being the highest and 1 the lowest for each of the following variables:
    1. Regulatory/monetary impacts of the species' listing under the Endangered Species Act.
    2. Urgency of conservation action.
    3. Ability to implement effective conservation actions.
    4. The species' ecological or management role as a keystone, indicator, or umbrella species.


A species ranked NSS1-NSS4 has a maximum of 54 points.  Species with a total score of 1-18 are Tier III, 19-36 are Tier II, 37-54 are Tier I.


NSSU

  1. NSSU species are assigned a score of 1-12 based on the variable "Wyoming’s contribution to the species’ overall conservation"; 12 being the highest contribution and 1 being the lowest contribution.
  2. Next, a score of 1-6 is assigned for each of the following variables ; 6 being the highest and 1 the lowest :
    1. Regulatory/monetary impacts of the species’ listing under the Endangered Species Act.
    2. Urgency of conservation action


An NSSU species can have a maximum of 24 points.  Species with a total score of 1-8 are Tier III, 9-16 are Tier II, and 17-24 are Tier I.

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