Corresponding author: Sabrina Kumschick ( email@example.com )
Academic editor: Wolfgang Rabitsch
© 2017 Sabrina Kumschick, Giovanni Vimercati, F. Andre de Villiers, Mohlamatsane M. Mokhatla, Sarah J. Davies, Corey J. Thorp, Alexander D. Rebelo, G. John Measey.
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: Kumschick S, Vimercati G, Villiers FA, Mokhatla MM, Davies SJ, Thorp CJ, Rebelo AD, Measey GJ (2017) Impact assessment with different scoring tools: How well do alien amphibian assessments match? NeoBiota 33: 53-66. https://doi.org/10.3897/neobiota.33.10376
Classification of alien species’ impacts can aid policy making through evidence based listing and management recommendations. We highlight differences and a number of potential difficulties with two scoring tools, the Environmental Impact Classification of Alien Taxa (EICAT) and the Generic Impact Scoring System (GISS) using amphibians as a case study. Generally, GISS and EICAT assessments lead to very similar impact levels, but scores from the schemes are not equivalent. Small differences are attributable to discrepancies in the verbal descriptions for scores. Differences were found in several impact categories. While the issue of disease appears to be related to uncertainties in both schemes, hybridisation might be inflated in EICAT. We conclude that GISS scores cannot directly be translated into EICAT classifications, but they give very similar outcomes and the same literature base can be used for both schemes.
Environmental Impact Classification for Alien Taxa (EICAT), Generic Impact Scoring System (GISS), prioritisation, listing, alien species, biological invasions
Alien species can cause a variety of changes to the areas in which they are introduced (
The two impact scoring schemes we chose for the comparison are the Generic Impact Scoring System GISS (
In this study, we use the same literature as source information to assess all alien amphibian species with EICAT and GISS. We ask (i) whether the two impact scoring schemes produce complementary maximum classifications, (ii) whether GISS total scores correlate with EICAT assessments, and (iii) under which conditions anomalies occur. Furthermore, it is well known that some taxa receive more research attention than others (e.g.,
We assessed all alien amphibians established anywhere outside of their native range. They comprised of a list provided by
Both schemes applied here rely on published literature. We used the species' scientific (scientific binomial) name as search term on Web of Science and Google Scholar and subsequently manually filtered through the titles and abstracts to find publications relevant with regards to impacts of alien populations. We incorporated articles published until August 2015. In the case that the scientific species name had changed recently (since 2000; e.g. Bufo marinus changed to Rhinella marina), we also searched under the older name. In addition, we consulted the references in the relevant publications for suitable references.
GISS and EICAT both aim to produce a comparative score for different alien taxa based on published evidence. Both schemes have five levels of impact, and discriminate between no impact and a lack of available data which results in a Data Deficient status (in EICAT) and no score (in GISS), respectively. Table
Summary of GISS and EICAT scores applied across mechanisms (e.g., competition, hybridisation, etc.). See
|EICAT/GISS score||Massive (MV)/5||Major (MR)/4||Moderate (MO)/3||Minor (MN)/2||Minimal concern (MC)/1|
|EICAT||Causes at least local extinction of native species, and irreversible changes in community composition; even if the alien taxon is removed the system does not recover its original state||Causes changes in community composition, which are reversible if the alien taxon is removed||Causes population declines in native species, but no changes in community composition||Causes reductions in individual fitness, but no declines in native population sizes.||No effect on fitness of individuals of native species|
|GISS||Major large-scale impact with high damage and complete destruction, threat to species including local extinctions||Major impact with high damage, major changes in ecosystem functions, decrease of species||Medium impacts, large-scale, several species concerned, relevant decline, relevant ecosystem modifications||Minor impacts, more widespread, also on rarer species||Minor impacts, only locally, only on common species|
GISS and EICAT differ in (i) the number of categories (i.e., mechanisms) and (ii) the details of what is required to score a species in any category. The details of both schemes are published elsewhere (
The schemes also differ in that GISS provides categories for economic as well as environmental impact assessments whereas EICAT only includes environmental impacts. Here we only use scores that relate to environmental assessments of both schemes, because economic assessments were poorly populated for amphibians (see
In addition to the maximum GISS score (1 to 5), GISS gives sums which are totals of all scores across all categories (1 to 30), but EICAT uses only the maximum scores. However, EICAT assessments assign a confidence level to each assessment ranging from low to high as described in
We used a paired Wilcoxon signed rank test to assess how similar the maximum and total scores obtained in GISS were to those scored in EICAT. For this we assigned numerical values to EICAT assessments, namely 1 for MC to 5 for MV, respectively: we refer to this as nEICAT. We used a non-parametric (Kendall’s tau) correlation test to assess the relationship between the number of publications found per species and (i) nEICAT, (ii) the maximum GISS score and (iii) the sum of all GISS scores for each species respectively. All analyses were performed in R v3.2.1 (
We found that the maximum scores produced by the two impact scoring systems were not equivalent, but the paired Wilcoxon signed rank test was significant, suggesting that they are similar (V = 25; P < 0.0001; Figure
Boxplots showing how a GISS maximum scores and b the sum of all GISS environmental scores are related to EICAT classifications. Individual data points represent different species (with a jitter effect to prevent overlapping), and show the entire range of data in all groups.
EICAT classification versus maximum environmental GISS scores for all 40 amphibian species for which data was available.
GISS total scores do not correlate with EICAT assessments (V = 315.5; P = 0.315; Figure
In total, we found 242 relevant publications for 40 species, with an average of 5.9 publications per species (excluding the 65 species for which no data was available). A full reference list can be found in
This paper presents the first systematic EICAT assessment for amphibians detailing species-specific classifications.
Our study shows that for alien amphibians, EICAT assessments are not equivalent to maximum or total scores under GISS. This means that we cannot simply adopt GISS assessments under IUCN instead of performing full EICAT assessments. However, we found that the scores were very similar, and, where they did differ, they differed by a single level of impact. The broad agreement between these two impact scoring schemes is encouraging as it suggests that each is managing to provide a comparative measure of impact, despite having different sets and numbers of criteria. Moreover, as both schemes rely on the same type of data, namely published evidence, once literature has been amassed for making a GISS score, the same data sources can be productively used for an EICAT assessment. The detailed EICAT assessments for each species will be externally reviewed and published under the IUCN umbrella on the Global Invasive Species Database (GISD; http://www.iucngisd.org/gisd/) after acceptance by the EICAT Unit (
Of particular note are species which score the highest possible in the one system but not the other: 5 in GISS but MR in EICAT, or MV in EICAT but 4 in GISS. This is the case for three species (Table
The two Pelophylax species scoring highest in EICAT but not in GISS had demonstrated impacts related to hybridisation, predation and competition with native species. The two schemes have in common that for low to medium impact levels of 1-3 (GISS) or MC to MO (EICAT) respectively, hybrids of the native and alien species need to be sterile. However, in the distinction of the two highest impact levels, EICAT and GISS differ. Higher impacts through hybridisation in GISS are determined by the relative quantity of hybrid populations (
Hybridisation should be carefully considered in amphibians, especially frogs and salamanders, as some of these species readily hybridise through polyploidy and may have done so for many decades (e.g.,
Furthermore, in some cases, species previously imbedded under the same species name were split into two species, which “creates” a hybridisation impact of one species on another which was previously unrecognised. An example thereof is the hybridisation of tiger salamanders (Ambystoma tigrinum) with the California tiger salamander (Ambystoma californiense) (e.g.,
Summing impact scores can potentially be biased towards species with higher research efforts, as it is more likely for various mechanisms to be studied for these species. Our data on the number of publications to make an assessment are not atypical (
The adoption of a single impact scoring scheme under an international umbrella such as IUCN is necessary, yet we show the potential pitfalls of converting scores between two widely used schemes: GISS and EICAT. These schemes are largely congruent, but do present some challenges where one might borrow from the other to resolve apparent discrepancies for amphibians which we feel are likely to manifest in time for other taxa. Levels of impact assigned in general, but specifically on disease transmission and hybridisation require detailed background information backing up the classification, and additional guidelines should be considered to make classifications more unified in this regard.
SK acknowledges financial support from the South African National Department of Environment Affairs through its funding to the Invasive Species Programme of the South African National Biodiversity Institute. We also thank the DST-NRF Centre of Excellence for Invasion Biology for its support.