Ranking Methodology

Natural Heritage programs, including Nevada Natural Heritage, and NatureServe evaluate the conservation status of all elements (species, subspecies, varieties, ecological communities) using standard methods to help set conservation priorities and goals. These methods are straightforward, repeatable and can be applied to all elements across taxonomic groups and have supporting documentation. Conservation status assessments seek to evaluate the extinction risk of species at global (Grank), national (Nrank) and state (Srank) levels. Assigned status ranks are based on best current knowledge of the species which rely on using field surveys, collected data (e.g., museum records), expert opinion, and remote sensing information.

Species are assessed using 8-10 core status rank factors (depending on knowledge of element) based on the three categories of rarity, threats, and trends. Rank factors include:

Factor Category Factor
  • Range Extent
  • Area of Occupancy
  • Population
  • Number of Occurrences
  • Number of Occurrences or Percent Area with Good Viability/Ecological Integrity
  • Environmental Specificity
  • Threats
  • Intrinsic Vulnerability
  • Short-term trend
  • Long-term trend

Each factor is rated using a scale of values. Based on these values, a conservation status is assigned on a scale of 1-5, with 1 being critically imperiled and 5 being common and widespread. See our Data Glossary.

Ranks are assigned at multiple geographic scales. Global ranks (Grank) evaluate the element based on the entire range of the element throughout the world. National ranks (Nrank) evaluate the element based on the range of the element within the country (e.g., Canada, United States, Mexico, etc.) while subnational rank (Srank) evaluations are based on the range of the element within a particular state or province (e.g., Nevada, Yukon Territory, etc.). By assigning ranks at multiple scales, we are able to get a more complete picture of the entire conservation status of an element which can help us prioritize conservation actions. 

For example, the Phainopepla (Phainopepla nitens) is ranked as G5S3. This rank indicates that Phainopepla are globally common, abundant and widespread (G5) and Vulnerable within Nevada (S3). Qualifiers can be added to a rank including breeding (B), non-breeding (N), or migrant (M) populations as well as questionable taxonomy (Q).   

In addition, ranks can be applied to subspecies or varieties and are indicated using a T before the numeric rank. For example, the Jaeger beardtongue (Penstemon thompsoniae ssp. jaegeri) is ranked G4T2S3. This rank is interpreted as the species Penstemon thompsoniae is globally Apparently Secure (G4) but the subspecies jaegeri is globally Imperiled (T2) and state Vulnerable (S3). T-ranks are always used in conjunction with Granks; the Srank applies to the subspecies within the jurisdiction (e.g., Nevada).