Effect of allowing only impact evidence from the invaded area under assessment (orange lines) versus also including evidence from other geographical areas (brown lines) on impact assessment outcomes for ring-necked (left) and monk parakeets (right) introduced to Europe. Impacts were scored according to the GISS protocol (Nentwig et al. 2016), whereby the magnitude of impact is quantified with six levels ranging from 0 (no impacts known) to 5 (the highest possible impact, see Table 2 in Nentwig et al. 2016). Spider graphs are drawn using maximum scoring (i.e. based on the worst recorded impact for each impact mechanism) based on data from White et al. (2019).

  Part of: Strubbe D, White R, Edelaar P, Rahbek C, Shwartz A (2019) Advancing impact assessments of non-native species: strategies for strengthening the evidence-base. NeoBiota 51: 41-64. https://doi.org/10.3897/neobiota.51.35940