Note that the data published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution. For the most recent data, purchase the 2008 Report from Island Press.

This indicator also applies to

• At-Risk Native Forest Species
• At-Risk Native Freshwater Species
• At-Risk Native Grasslands and Shrublands Species

The Indicator

The species reported here are those in groups (such as mammals, birds, and fish) that are considered sufficiently well known that the conservation status, habitat, and location (by state) can be assigned with some degree of confidence for all members of the group. The conservation status assessment for each species is an attempt to determine the relative susceptibility of a species to extinction. The assessment process is based on consideration of up to 12 factors that relate to a species’ degree of imperilment or risk of extinction throughout its range. Rare species are particularly vulnerable to extinction and so several aspects of rarity are characterized in the assessment process including population size and number of populations, and range extent and area of occupancy. However, trends in population and range size as well as magnitude and immediacy of threats are also important considerations in assessing a species’ overall vulnerability or risk of extinction. Additional information on this ranking process can be found at http://www.natureserve.org/explorer/ranking.htm and in Master (1991).

There is general recognition among experts that both status information (as presented here) and trend information (whether a species is increasing, decreasing, or stable) are critical to understanding the condition of species. If and when trend information for large numbers of species becomes widely available, revising the current measure by incorporating trend information or substituting trend information for status should be considered.

The Data

Data Source: NatureServe (www.natureserve.org) and its member programs in the network of Natural Heritage programs develop and maintain information on each of the species reported here.

Data Collection Methodology: On an ongoing basis, NatureServe research biologists gather, review, integrate, and record available information about species taxonomy, status, and use of different habitats or ecological system types. They are assisted in this work by scientists in the network of Natural Heritage programs as well as by contracted experts for different invertebrate taxa. NatureServe staff and collaborators assign a conservation status by using standard Heritage ranking criteria (see http://www.natureserve.org/explorer/ranking.htm) and by using the best information available to them.

The Heritage ranking process considers five major status ranks: critically imperiled (G1), imperiled (G2), vulnerable (G3), apparently secure (G4), and demonstrably widespread, abundant, and secure (G5). In addition, separate ranks are assigned for species regarded as presumed extinct (GX) or possibly extinct (GH).

Critically imperiled species are often found in five or fewer locations, imperiled species are often found in 20 or fewer locations, and vulnerable species are often found in 80 or fewer locations. Apparently secure species are uncommon but not rare, and secure species are common—meaning they are both abundant and widespread. Presumed extinct species have not been located despite intensive searches, and possibly extinct species are missing and are known only from historic records, although there is some hope of their rediscovery. See Stein (2002) for further details on ranks.

These data are not from a site-based monitoring program, but rather from a census approach that focuses on the location and distribution of at-risk species. For other species, the dataset incorporates information from a wide variety of observations and sources.

Data Manipulation: NatureServe has summarized the actual global ranks into “rounded ranks” for the purposes of presentation and analysis. For example, an actual rank may express the bounds of uncertainty, noting for instance that a given species falls somewhere in the range of “critically imperiled” to “imperiled.” In such cases, the rounded rank reflects the more imperiled designation, in this instance, critically imperiled. Such rank rounding applies to between 10-20% of species included here. The analysis of the percent of at-risk species by region is based on all species that are known to occur within one or more states in each region.

For the core national indicator, only species groups for which sufficient information is available on the entire group are reported. Thus, mammal status is reported because data are available on the status of all mammals, but the status of mayflies and stoneflies is not included because data on all species in these two groups are not available. Groups reported for the national measure are mammals; birds; reptiles; amphibians; freshwater fishes; freshwater mussels; freshwater snails; crayfishes; fairy, clam, and tadpole shrimp; butterflies and skippers; giant silkworm and royal moths; sphinx moths; underwing moths; papaipema moths; tiger beetles; stoneflies; grasshoppers; mayflies; dragonflies and damselflies; ferns/fern allies; gymnosperms; and flowering plants.

For the forest, freshwater, and grassland/shrubland indicators, species were first identified as “forest species” or “freshwater species” or “grassland/shrubland species.” In this process, species were assigned to an ecosystem if they live in that ecosystem during at least part of their life cycle and depend on access to that ecosystem type for their survival. This was a generally conservative approach; in preparing these lists, only species that are strongly associated with a habitat type were included. This means that some species that make frequent use of forest, or grasslands/shrublands, or fresh water may be excluded, but also that the group of species reported for each of these systems here is quite representative of species that are dependent upon those habitats for their survival. Groups reported for the forest and grassland indicator are mammals, birds, reptiles, amphibians, grasshoppers, and butterflies and skippers. Groups reported for the freshwater indicator are freshwater and anadromous fishes; amphibians; reptiles; butterflies and skippers; freshwater mussels; freshwater snails; crayfishes; fairy, clam, and tadpole shrimp; dragonflies and damselflies; mayflies; stoneflies; and caddis flies.

At present, it is not possible to use the data presented here to distinguish naturally rare species from those that have been depleted in number. Increases in the number of at-risk species over time, however, would generally be interpreted as an increase in the number of depleted species after accounting for changes due to changes in taxonomy or to discovery of new species.

Data Quality/Caveats: Heritage conservation status ranks are updated on an ongoing basis through literature review and feedback from users of the network’s databases, and also through periodic review of all statuses. Uncertainty about conservation status of a species is captured in part through the use of range ranks (see “Data Manipulation” above). A species’ status may change over time due to several reasons, and not solely due to a species becoming more or less at risk of extinction. For example, more populations may be found than were known to exist, or a species may be split taxonomically into two species, such that the two new species may individually be at greater risk of extinction than their single parent species. Because status may change for reasons other than an actual change in condition, and because a species may experience a significant increase or decrease in population size without an incremental change in status, trend is itself a particularly useful measure to use in addition to conservation status and may be reported in future editions of this report if and when data on trends become available.

These data are not from a site-based monitoring program, but rather from a census approach that focuses on at-risk species; for more common species knowledge has been incorporated from a wide variety of observations and sources.

Data Access: Updated and more detailed information on all species is available at http://www.natureserve.org/explorer/. For more customized data requests, contact jason_mcnees@ natureserve.org.

The Data Gap

Data are not currently available on the status of most coastal and marine species. However, NatureServe will be incorporating status assessments for marine fishes into their databases. NatureServe already reports the status of nearly 150 coral species found off the coast of southern Florida. NatureServe expects to broaden its coverage of marine species to include many more invertebrates and, hopefully, Hawaiian fishes, which is a large challenge given that these are largely different varieties than those found in coastal regions of the mainland United States.

Data on the status of vascular plants exist (and are reported here), but for the most part, these plants have not been classified according to their habitat associations, in the manner that the animals reported here have been (i.e., animals that are dependent upon forests, or grasslands/shrublands, or fresh water). This is primarily a resource issue—there are far more vascular plants than vertebrate animals, and the size of the workload involved in categorizing them has prevented this work from taking place.

See the indicator for Status of Animal Species in Farmland Areas for further discussion of the data gap with respect to species in agricultural landscapes.

See the indicator and technical note for urban/suburban Species Status (pp. 191 and 269) for discussion of the data gap with respect to species in urban/suburban areas.

References

Master, L.L. 1991. Assessing threats and setting priorities for conservation. Conservation Biology 5(4):559–563.

Stein, B.A. 2002. States of the Union: Ranking America’s biodiversity. NatureServe, Arlington, VA. 25 p.