Prioritization is indispensable for the management of biological invasions, as recognized by the Convention on Biological Diversity, its current strategic plan, and specifically Aichi Target 9 that concerns invasive alien species. Here we provide an overview of the process, approaches and the data needs for prioritization for invasion policy and management, with the intention of informing and guiding efforts to address this target. Many prioritization schemes quantify impact and risk, from the pragmatic and action-focused to the data-demanding and science-based. Effective prioritization must consider not only invasive species and pathways (as mentioned in Aichi Target 9), but also which sites are most sensitive and susceptible to invasion (not made explicit in Aichi Target 9). Integrated prioritization across these foci may lead to future efficiencies in resource allocation for invasion management. Many countries face the challenge of prioritizing with little capacity and poor baseline data. We recommend a consultative, science-based process for prioritizing impacts based on species, pathways and sites, and outline the information needed by countries to achieve this. This should be integrated into a national process that incorporates a broad suite of social and economic criteria. Such a process is likely to be feasible for most countries.

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The abundance and distribution of an invasive species is influenced by its relative ability to find resources under a variety of conditions. We examined the exploitative ability of the Argentine ant (Linepithema humile (Mayr)), in comparison with two common New Zealand ant species Monomorium antarcticum (Fr. Smith) and Prolasius advenus (Hymenoptera: Formicidae) (Fr. Smith), using maze trials under different temperature and starvation regimes. Our results showed temperature significantly affected the mean time to discover food resources, but different species responded differently to changes in temperature. A change in temperature from 23°C to 13°C resulted in an approximately 8‐fold increase in the time to discover food for native P. advenus, but discovery times remained relatively similar for invasive Argentine ants. Starvation did not significantly influence the ability of species to find food. Argentine ants consistently located and recruited to food faster than the native species. We examined for variation in walking speed under the experimental conditions as a mechanism for our results. The results revealed Argentine ants and P. advenus to have similar walking speeds at each temperature‐starvation treatment and both were faster than M. antarcticum. However, Argentine ants had rates of turning or returning to the nest that were lower than the native species. This result suggests that Argentine ants show greater ‘exploratory willingness’ or ‘novelty seeking’ behaviour. Our results suggest that Argentine ants are able to discovery and exploit resources more efficiently than these native species under a wide spectrum of environmental and physiological conditions. Such relative efficiencies have likely contributed to the success of this invader.

Impact assessment is a widely used and cost-effective tool for prioritising invasive alien species.With the number of alien and invasive alien species expected to increase, reliance on impact assessment tools for the identification of species that pose the greatest threats will continue to grow. Given the importance of such assessments for management and resource allocation, it is critical to understand the uncertainty involved and what effect this may have on the outcome.Using an uncertainty typology and insects as a model taxon, we identified and classified the sources and types of uncertainty when performing impact assessments on alien species. We assessed 100 alien insect species across two rounds of assessments with each species independently assessed by two assessors. Agreement between assessors was relatively low for all three EICAT components (mechanism, severity, confidence) after the first round. For the second round, we revised guidelines and gave assessors access to each other's assessments which improved agreement by between 20-30%. Of the 12 potential reasons for assessment discrepancies identified a priori, 11 occurred. The most frequent sources (and types) of uncertainty (i.e. differences between assessment outcomes for the same species) were: incomplete information searches (systematic error), unclear mechanism and/or extent of impact (subjective judgment due to a lack of knowledge), and limitations of the assessment framework (context dependence). In response to these findings, we identify actions to reduce uncertainty in the impact assessment process, particularly for assessing speciose taxa with diverse life histories such as Insecta.Evidence of environmental impact was available for most insect species, and (of the non-random original subset of species assessed) 14 or 29% of those with evidence were identified as high impact species (with either 'Major' or 'Massive' impact). Although uncertainty in risk assessment, including impact assessments, can never be eliminated, identifying and communicating its source and variety is a first step toward its reduction and a more reliable assessment outcome, regardless of the taxa being assessed.