Research Article |
Corresponding author: Dewidine Van der Colff ( d.vandercolff@sanbi.org.za ) Academic editor: Sven Bacher
© 2020 Dewidine Van der Colff, Sabrina Kumschick, Wendy Foden, John R. U. Wilson.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Van der Colff D, Kumschick S, Foden W, Wilson JRU (2020) Comparing the IUCN’s EICAT and Red List to improve assessments of the impact of biological invasions. In: Wilson JR, Bacher S, Daehler CC, Groom QJ, Kumschick S, Lockwood JL, Robinson TB, Zengeya TA, Richardson DM. NeoBiota 62: 509-523. https://doi.org/10.3897/neobiota.62.52623
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The IUCN recommends the use of two distinct schemes to assess the impacts of biological invasions on biodiversity at the species level. The IUCN Red List of Threatened Species (Red List) categorises native species based on their risk of extinction. Such assessments evaluate the extent to which different pressures, including alien species, threaten native species. The much newer IUCN Environmental Impact Classification for Alien Taxa (EICAT) categorises alien species on the degree to which they have impacted native species. Conceptually, the schemes are related. One would expect that: 1) if a native species is assessed as threatened under the Red List due to the impacts of alien species, then at least one alien species involved should be classified as harmful under EICAT; and 2) if an alien species is assessed as harmful under EICAT, then at least one native species impacted should be assessed as threatened by alien species under the Red List. Here we test this by comparing the impacts of alien gastropods, assessed using EICAT, to the impact on native species as assessed based on the Red List. We found a weak positive correlation, but it is clear there is not a simple one-to-one relationship. We hypothesise that the relationship between EICAT and the Red List statuses will follow one of three forms: i) the EICAT status of an alien species is closely correlated to the Red List status of the impacted native species; ii) the alien species is classed as ‘harmful’ under EICAT, but it does not threaten the native species with extinction as per the Red List (for example, the impacted native species is still widespread or abundant despite significant negative impacts from the alien species); or iii) the native species is classified as threatened under the Red List regardless of the impacts of the alien species (threatened species are impacted by other pressures with alien species potentially a passenger and not a driver of change). We conclude that the two schemes are complementary rather than equivalent, and provide some recommendations for how categorisations and data can be used in concert.
Aichi Target 9, documenting impacts, Gastropods, invasive alien species, invasion frameworks, species population declines, threatened species
The role of biological invasion as a driver of global change (
EICAT provides a simple, objective, and transparent tool for systematically documenting the impacts of alien species that occur anywhere in the world (
A summary of the IUCN Red List and the IUCN EICAT schemes showing areas of potential interaction between them. These are based largely on direct comparisons between the Red List guidelines (IUCN 2019) and EICAT standards and guidelines (
Sections | Red List | EICAT | Interaction between schemes |
---|---|---|---|
Purpose | To estimate the risk of extinction of specific native species and the drivers contributing to this risk. | To identify the type and magnitude of impacts that specific alien species have on native species. | The schemes have different purposes but share some outputs, for example, documenting alien species impacts. |
Scheme categories | Not Evaluated (NE) | Not Evaluated (NE) | With increasing threat levels of the impacted species on the Red List, the impact severity of the alien may also increase on EICAT. This may not be true for all cases. |
Data Deficient (DD) | No Alien Populations (NA) | ||
Not-threatened | Data Deficient (DD) | ||
Least Concerned (LC) | Non-Harmful | ||
Near Threatened (NT) | Minor (MN) | ||
Threatened | Minimal Concern (MC) | ||
Vulnerable (VU) | Harmful | ||
Endangered (EN) | Moderate (MO) | ||
Critically Endangered (CR) | Major (MR) | ||
Extinct | Massive (MV) | ||
Extinct in the Wild (EW) | |||
Extinct (EX) | |||
Geographical scope | Global, regional or national. | Global, regional or national. | For the Red List, the global population is the entire distribution of the species within its native range. All levels of assessment are related to the global population (e.g., regional adjustments). For EICAT, the global scope refers to impacts recorded where there are alien populations present, and impacts are not related to the global population of the impacted native species. |
Population declines | Population decline is recorded against specific thresholds per category. It is also assessed across different time frames (past, present, and future). | Harmful categories indicate decline, MO is for a population; MR is a reversible loss of a population; MV is an irreversible loss of a population. Only past declines are considered. | There are different thresholds of decline and methods and time frames of recording population decline. |
Which species are explicitly specified | Native species and the species causing impacts (e.g., alien species, unless the native species is LC). | Alien species and native species being impacted. | Need to identify the same impacted taxa to enable the linkage of schemes. |
Evidence sources | Projected, inferred, estimated or suspected. | Observed (estimated) and inferred. | The Red List makes allowance for the use of projections and suspected evidence, while these are not included on EICAT. Data included in Red List assessments may not be accepted under EICAT. |
Responsiveness of schemes | Assessments are due every 10 years or as resources and/or new information becomes available. Additionally, new species are described regularly, so there are always more assessments to be conducted. | As a new scheme, only few groups have been assessed. Additionally, impacts must have been recorded before an assessment can be conducted or the species will be assessed DD or NE. | Two sources of delays in detecting change. First is due to processes of the assessment schemes (e.g. resource availability, expert time, assessment information). Second is the role of invasion debt resulting in, for example, delay in the detection of impacts. |
Taxonomy | An updated taxonomic backbone is used, but is dependent on the experts to prompt updates. | Uses the same taxonomic backbone as the Red List; however, primary references may include outdated taxonomy of alien and impacted native species. | Both schemes are in principle using the same taxonomic backbone; however, primary literature sources may differ. This is a procedural difference and will need management as assessments are conducted. |
Final status selection | The highest threat status selected based on supporting data as a precautionary method. | The highest impact status selected corresponding to the maximum threat level. | Both schemes make use of the highest status obtained. |
Measure of uncertainty | No specific categories. Specify best estimate or range of plausible values and document all information used and process of calculation. | Three different levels: high, medium, and low. | Not directly comparable. Primary literature needs to be examined to determine how the uncertainties relate. |
Sources of uncertainty | Natural variability and semantic uncertainty (vagueness in terms and definitions used in the criteria). | Presence of confounding effects, study design, data quality and type, spatial and temporal scale, and coherence of evidence. | Not directly comparable. Primary literature needs to be examined to determine how the uncertainties relate. |
Threshold bases | Quantitative (e.g. range size, number of individuals). | Qualitative (e.g. categories of decline from individual performance to populations and species). | Not applicable. |
The Red List assigns species to categories of extinction risk using quantitative criteria and relevant species information, enabling species to be classed as threatened or not-threatened (IUCN 2019). As part of the process of assigning an extinction risk, the Red List identifies and documents the pressures on native species. These pressures include the five major biotic and abiotic pressures as defined by the CBD, namely invasive alien species, habitat loss and degradation, climate change, over-exploitation, and pollution (
In this paper, we examine the relationship between EICAT and the Red List using alien gastropods as a case study. We predict that: 1) if a native species is assessed as threatened under the Red List due to the impact of alien species, then at least one alien species involved should be classified as harmful under EICAT; and 2) if an alien species is assessed as harmful under EICAT, then at least one native species impacted should be assessed as threatened by alien species under the Red List. We then consider the relationship between the two schemes more broadly, responding to the World Conservation Congress (Hawaii 2016) resolution (WCC-2016-Res-018-EN) which urges the incorporation of EICAT assessment results into Red List assessments (
The choice of which taxa to use for comparison purposes was limited primarily by the availability of EICAT assessments (as a relatively new scheme, there are far fewer EICAT assessments than species with Red List assessments). EICAT assessments are available for alien birds (
Given that the data are categorical, we used a Pearson Chi-squared test to assess, across all species interactions, whether harmful or non-harmful alien species tended to be associated with threatened or not-threatened native species (see Table
Most impact evidence was recorded in Australia (n = 48), Hawaii (n = 12), and New Zealand (n = 10). The publication dates of the impact studies ranged from 1976 to 2016. All threatened species that were impacted had small distribution ranges and were endemic to the Hawaiian Islands, except for the fountain darter Etheostoma fonticola (EN), which is restricted to two locations in central Texas (extent of occurrence less than 100 km2) (
Of the 101 interaction records, only 18 had harmful EICAT statuses (17 Moderate impacts and one Major). This is not surprising as few alien species cause severe negative impacts and biological invasions is one of several interacting threats (
Harmful alien species tended to be associated with threatened native species, and non-harmful alien species with not-threatened species (chi-squared value = 35.6, P < 0.001). Similarly, an increase in Red List status was associated with an increase in the EICAT status (LR test = 28.0, df = 3, P < 0.05), although none of the individual transitions was significant (e.g. MO–MR or EN–CR), probably due to the low sample sizes (Fig.
The relationship between EICAT and Red List assessments for interactions between alien gastropods and native species that were recorded as impacted (n = 102). In order of increasing impact, the EICAT categories are: Minimal Concern (MC), Minor (MN), Moderate (MO), Major (MR), and Massive (MV). In order of increasing extinction risk, the Red List categories are: Least Concern (LC), Near Threatened (NT), Vulnerable (VU), Endangered (EN), Critically Endangered (CR), and Extinct (EX). Extinct in the Wild is included in the EX category. Points are jittered to avoid overplotting. Margin bars indicate the numbers of interactions per Red List and EICAT category. The EICAT scores are based on the study by
We found a positive but weak correlation between the EICAT status of alien species and the Red List status of impacted native species. However, the relationship between the two schemes is not a simple one-to-one correlation. We hypothesise that the relationship between Red List and EICAT statuses will follow one of three general forms.
Firstly, a linear relationship will occur when there is a positive correlation between the EICAT status of an alien species and the Red List status of an impacted native species (general form i in Fig.
The proposed three forms of the relationship between assessments using the EICAT and the Red List schemes.
The different forms of the relationship arise, we argue, due to structural differences between the Red List and EICAT. Specifically, the schemes differ in the geographic coverage of assessments, the type of evidence used in assessments, their responsiveness to change, the mechanisms of impact, the specification of the alien species causing the impact, and the approach to taxonomic changes. We discuss these in turn.
Both assessment schemes have a global scope, but how underlying assessment data are interpreted is very different. EICAT assessments make use of all known impacts of an alien within its introduced range(s). However, impacts are recorded at the scale of a specific subpopulation or locality and the impacts often relate to only part of the global population of the impacted native species (
First, there is likely to be a closer correlation between EICAT and the Red List for alien species that impact native species that are range-restricted. For example, Cyanea grimesiana is an island endemic plant assessed as Critically Endangered (CR) in 2015, with biological invasion listed as a major pressure (
Second, native species that are widespread and assessed as of Least Concern (LC) in the Red List can be impacted by alien species with a wide range of EICAT statuses. This can be due to the range of scales at which impacts are recorded in EICAT and/or higher impacts relative to the local populations, not global ones, as in the Red List [e.g. Major (MR) impacts are described as reversible local population extinction]. An alternative explanation is that the native species might have a large global population, and a decline in the local populations is not sufficient to trigger a threatened category on the Red List. For example, the attenuate fossaria snail (Galba truncatula) is widespread across southwest Asia, southern Europe, and Mediterranean North Africa, and is predated upon by Draparnaud’s glass snail (Oxychilus draparnaudi) (
Even though the native species was not threatened overall, such impact information is valuable for inclusion in a Red List assessment. It can become useful, for example, if the widespread species becomes threatened and can be used as evidence to track impacts over time. Additionally, this information can be used to highlight potential future threats to a species, even if it is currently not threatened (IUCN 2019). When including this information in the Red List the threat score would most likely be low, with severity classified as negligible. However, an assessor can also decide on the impact score by considering the primary source of the EICAT assessment, particularly the date of assessment and the type of evidence. This information can be used to determine the timing, severity, and scope of the impact, which determine the threat score in the Red List. Similarly, data collected on impacts of aliens identified in the Red List without an EICAT assessment could be used as a starting point for the EICAT assessment.
Despite our expectations, the schemes did not consistently draw from the same evidence sources in our case study on gastropods. This was partly an issue of timing (see responsiveness to change below), but the schemes also differ in the types of evidence considered. The Red List includes evidence that is observed, estimated, projected, inferred or suspected (IUCN 2019). When conducting Red List assessments, detailed data are not always available across the entire global range of a species, but the Red List allows the use of different data sources, enabling assessments to be conducted in the absence of complete data (IUCN 2019). For EICAT, only observed and inferred evidence from the introduced range of alien species may be included, while projected and suspected sources are excluded (
Given the two systems are currently independent, updates of assessments might happen at different times and so scores may diverge. For example, Pua ʻala (Brighamia rockii), a Critically Endangered (CR) plant species, is only known from three subpopulations within the Hawaiian Islands and is currently experiencing population declines (
Under both schemes, there will be time lags between impacts occurring, the recording of impacts, and the incorporation of such data into assessments (IUCN 2019;
Moreover, the status of a species on the Red List can improve or deteriorate from assessment to assessment (IUCN 2019). For EICAT, however, the impact status of alien species can only ever be up-listed to a more severe impact level. Thus, even if an alien species is no longer threatening a particular native species, it can still be categorised as harmful due to past impacts recorded (
Classification of the mechanisms of impact is similar between the schemes, but there are some key differences (Fig.
As part of an EICAT assessment, impacted native species are identified, and supporting documentation is recorded. By contrast, in the Red List, the alien species affecting native species are only required to be identified and recorded if the native species are assessed as threatened or Near Threatened (NT). For other classifications this information is optional.
Both schemes allow for the impacting species to be identified at whatever taxonomic level is appropriate or available. If a specific alien species is not identified in the assessment (e.g., only as a “slug” rather than as L. flavus), then further information is needed to improve the assessment. In this study, we found seven interactions for which the same alien species or groups of species were identified in both schemes. The majority of these assessments were for threatened species, with the exception of a single native species that was categorised as of Least Concern (LC) (
The Red List’s taxonomy is updated regularly when new classifications become available and when prompted by experts. EICAT refers to the Red List for taxonomy. However, the taxonomy used in primary references can differ. This may be particularly relevant for species with many synonyms that result from different taxonomic revisions. Information on synonyms captured in the Red List helps maintain this link, though the situation can be complicated. For example, Bulinus natalensis is part of a species complex that is widespread across Africa. It was assessed as Least Concern (LC) on the Red List under the currently-accepted name Bulinus truncatus (
The EICAT and Red List schemes will benefit each other if information underpinning their assessments is made available and shared. Making such supporting information available in appropriate formats will improve the generation of sound evidence-based assessments, and help to identify data gaps and research needs. For example, alien species noted to cause impacts under the Red List which are assessed on EICAT as Data Deficient (DD) or are Not Evaluated (NE) should be prioritised for further research and EICAT evaluation (and vice versa).
Each scheme should link to relevant corresponding data in the other. The Red List uses a well-organised data management platform, the Species Information System (SIS), to gather, organise, and store data. The development and use of a similar data management platform for EICAT would aid assessments and could be tailored to enable data exchange between the two schemes. Our study shows that the types, extent, and frequency of information overlap between the two schemes depend on a range of factors, including geographical scope, population trends, evidence sources, scheme responsiveness, mechanisms of impact, and the taxonomic systems used. Further, as assessments under either scheme are updated, corresponding assessments need to be examined and potentially revisited.
In summary, while the Red List and EICAT are conceptually related, they have different purposes and methods. We are keen to see similar evaluations for other taxonomic groups and habitats, but we predict that the results will be similar to those outlined in Fig.
We thank Avril Castelle Subramoney for collecting information on impacted species from the