Table 1.

Differences in methodology applied in the two impact scoring studies

	Kraus	Kumschick et al.
Search terms	Literature from before 2007 was extracted from Kraus (2009). That list was updated up to late 2014 using Zoological Records searches limited to the years 2007–2014 with assorted combinations of search terms like: “alien species” or “invasive species” plus “impact” done for various taxonomic names such as “frog”, “amphibian”, etc.	Literature from before 2007 was extracted from Kraus (2009). Additionally, literature up to August 2015 was searched using each species’ scientific name (current and previous taxonomic iterations) in Web of Science and on Google Scholar. The results were filtered manually for relevant data on impacts by selecting publications according to the information provided in titles and abstracts, and by scanning the selection in more detail. References cited within the selected publications were screened and included as appropriate, as was gray literature. This was supplemented by more specific searches for the species name and the name of each country (according to Kraus, 2009) in which it is known to be alien. Only the primary source of information or study regarding the impacts was included on the score sheet
Magnitude	Only species for which impacts MO or higher were expected or found given the search strategy outlined above; species with lower impacts or no reports with medium or high confidence (see below) were excluded	All impacts found ranging from MC to MV were recorded (according to Hawkins et al., 2015)
Confidence	A confidence rating was not explicitly included, but only reports with medium to high confidence were used according to the assessor's interpretation	Low, medium, or high confidence (according to Hawkins et al., 2015) was attached to every single impact record, as well as the final classification per species
Initial number of species assessed	Not specified due to nature of search strategy	105 (all alien species listed in Kraus, 2009 with at least one established population plus few additional according to IUCN Red List)
Expertise on taxon	All assessments made by a single assessor with long‐term expertise on taxon	Assessments made by a team, some of whom were not experts in the taxon