Invasive species cause incredible harm to the environment and cost billions of dollars to state and federal governments and private industry. Although many species introductions happen each year, only some will cause harm and become invasive.
An Ecological Risk Screening Summary, or Risk Summary, provides a rapid evaluation of a species’ potential invasiveness. These evaluations give us, as well as our natural resource stakeholders and the public, a quick way to determine which species are more likely (high risk) and less likely (low risk) to cause damage if they spread outside of their natural range, and which ones have insufficient information to make such a determination (uncertain risk).
Because we need to assess many species quickly, the standards set forth in the Standard Operating Procedures manual allow Risk Summaries to be prepared by a broad range of biologists, ecologists, and invasive species invasive species
An invasive species is any plant or animal that has spread or been introduced into a new area where they are, or could, cause harm to the environment, economy, or human, animal, or plant health. Their unwelcome presence can destroy ecosystems and cost millions of dollars.
Learn more about invasive species specialists trained in conducting literature searches and evaluating data according to the Standard Operating Procedures. Risk Summaries should not be considered as a substitute for in-depth risk assessment methods that rely on species-specific expertise. We encourage our stakeholders and the public to carefully consider what type of risk assessment best meets their needs.
- Introduced Species: A plant or animal species that has been transported by human activities, either intentionally or unintentionally, into a new region.
- Invasive Species: An introduced species that causes, or is likely to cause, economic or environmental harm or harm to human, animal, or plant health in the new area of introduction.
Review supporting documentation.
We evaluate risk based on similarity of climate and history of invasiveness.
Our Risk Summaries use similarity of climate and history of invasiveness to determine risk. Research has shown that these two factors are predictive of invasion risk across a wide range of plants and animals. However, other biological factors (predation, lack of prey, lack of habitat, etc.) could limit the ability of a species to become invasive. For some species, risk of introduction already may be limited by regulations that prohibit importation or trade, or by non-regulatory risk management options. Risk Summaries do not factor risk management options, which may reduce risk, into the risk category.
We use our Risk Assessment Mapping Program to compare air temperature and precipitation patterns within a species’ known range with climates across the United States. The results of this analysis include a map of the contiguous United States showing how the local climate compares to the climate where the species is distributed and an overall climate match score. Species that establish populations and spread successfully in the United States have, on average, higher climate match to the United States than species that do not establish and spread, so we use the overall climate score to evaluate the level of establishment concern warranted for a species. We assign the risk category for a species based on the current establishment concern for the contiguous United States as a whole. However, those interested in the climate match and establishment concern for a specific local area can view the climate match results map in the Risk Summary to estimate a local climate match, and those interested in possible future climate match can view the projections included in the Risk Summary appendix. If you are interested in climate matching for a non-contiguous area of the United States, please contact us at ais_risk_assessment@fws.gov.
There are limitations to the climate match, such as:
- Some species may have wider climatic tolerances than demonstrated by their native ranges. Geographic barriers, such as being on an island or blocked by a desert, mountain range, or large river can cause this. This will result in an underestimate of climate match.
- Special highly localized climatic situations are not factored in (for example, hot springs that can sustain tropical or subtropical animals and plants in cold climates).
We also look at where the species has been introduced in other parts of the world outside of its native range and whether it became established and caused harm. We call this the species’ history of invasiveness. There is a compelling body of evidence that invasion history is among the most useful variables to predict whether nonnative species introduced into new ecosystems may become invasive.
Finally, we look at how certain we are that the information used for the climate match and history of invasiveness is scientifically credible, reliable, and sufficiently documented to be used for the intended purpose. You can review all of our supporting documentation for more details on how each risk category is determined and how we establish certainty.
What are the risk categories?
High risk: Species that are considered high risk have a well-documented history of invasiveness in at least one location globally and are an establishment concern for the contiguous United States. While a high-risk species may not be an invasive risk to every locality in the United States, great caution is needed when trading or acquiring high-risk species, particularly in parts of the United States where environmental conditions in the wild have been identified as suitable for their survival. Please consider choosing an alternative species from the low-risk category for pets and other uses, rather than a high-risk species. If new species are being considered for trade, then we do not recommend high-risk species.
Low risk: Species that are considered low risk present a minimal risk of invasiveness because their establishment is doubtful within the contiguous United States AND there is no evidence of invasiveness globally.
Uncertain risk: Species that are considered uncertain risk need a more in-depth assessment beyond the Risk Summary to better define the species’ risk to U.S. environments. This additional information will help inform decisions on where, when, and how the species may be used to minimize risks of them becoming invasive.
Our process results in many species being classified as uncertain risk because strong evidence is required to place them in either the high-risk or low-risk categories. As a precaution, results are weighted toward an uncertain risk categorization when our rapid screening process shows conflicting signals about level of risk based on establishment concern and history of invasiveness, and may warrant additional evaluation. If a species is not yet in trade and is uncertain risk, we do not recommend its utilization without conducting or consulting a more in-depth assessment.
Risk Summaries are used to inform the public and help prevent future harm from invasive species.
Risk Summaries are publicly available to governments, industry, and other stakeholders as a readily available source of information to aid in making informed decisions about developing watch lists, and trading, transporting, or possessing a particular species. Uses include:
- Developing watch lists and selecting target species for invasive species early detection and rapid response programs.
- Finding species-specific information when a new species is detected within the United States.
- Making more environmentally responsible choices regarding pet and plant ownership.
- Developing agreements between industry and government for species within their jurisdictions.
- Informing management decisions for invasive species programs.
- Identifying which species may need additional assessments before informed decisions can be made on where, how, and when a species is utilized.
Certain species that have a high or uncertain overall risk may warrant additional detailed evaluations to determine if a proposal for listing as injurious wildlife is appropriate. The Service does not list species based solely on the Risk Summary. More detailed reviews are completed on species being evaluated for a proposed injurious wildlife listing.
Risk Summaries are updated as new information becomes available.
Because Risk Summaries are prepared relatively rapidly, it is possible some information was unavailable or missed at the time of preparation. Because new information could change the Risk Summary results, we periodically update Risk Summaries. Additionally, we periodically update the Risk Summary Standard Operating Procedures to ensure we are using the current best-available science to guide our screening process. Please check the Risk Summary website regularly to obtain the most current versions of the Risk Summaries, and recognize that older Risk Summaries may have been written to different standards than are currently in use. Please contact ais_risk_assessment@fws.gov to obtain older versions of our Standard Operating Procedures.
You can help improve our Risk Screenings. If you have information that could help improve the accuracy of our assessments please contact us at ais_risk_assessment@fws.gov.
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