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Risk assessments are fundamental to invasive species management and are underpinned by comprehensive characterization of invasive species impacts. Our understanding of the impacts of invasive species is growing constantly, and several recently developed frameworks offer the opportunity to systematically categorize environmental and socioeconomic impacts of invasive species. Invasive ants are among the most widespread and damaging invaders. Although a handful of species receives most of the policy attention, nearly 200 species have established outside their native range. Here, we provide a global, comprehensive assessment of the impacts of ants and propose a priority list of risk species. We used the Socioeconomic Impact Classification for Alien Taxa (SEICAT), Environmental Impact Classification for Alien Taxa (EICAT) and Generic Impact Scoring System (GISS) to analyze 642 unique sources for 100 named species. Different methodologies provided generally consistent results. The most frequently identified socioeconomic impacts were to human health. Environmental impacts were primarily on animal and plant populations, with the most common mechanisms being predation and competition. Species recognized as harmful nearly 20 years ago featured prominently, including Wasmannia auropunctata (little fire ant, electric ant), Solenopsis invicta (red imported fire ant), Anoplolepis gracilipes (yellow crazy ant), and Pheidole megacephala (African big-headed ant). All these species except W. auropunctata have been implicated in local extinctions of native species. Although our assessments affirmed that the most serious impacts have been driven by a small number of species, our results also highlighted a substantial number of less well publicized species that have had major environmental impacts and may currently be overlooked when prioritizing prevention efforts. Several of these species were ranked as high or higher than some of the previously recognized \"usual suspects,\" most notably Nylanderia fulva (tawny crazy ant). We compared and combined our assessments with trait-based profiles and other lists to propose a consensus set of 31 priority species. Ever-increasing global trade contributes to growing rates of species introductions. The integrated approaches we used can contribute to robust, holistic risk assessments formany taxa entrained in these pathways.

Compared to other facets of invasion science, the impacts of biological invasions have been understudied, but many studies have been published in the last decade. This paper reviews the growing body of evidence of impacts of invasions in South Africa. We classified information for individual species into ten ecological and four social categories of impact. We also reviewed studies that upscaled this information to larger spatial scales, as well as progress with assigning invasive species to impact severity categories. We identified 123 studies that documented the impacts of 71 invasive alien species, about 5 of the country’s naturalized alien biota. The most frequently reported impact category was species interactions (changes to habitat suitability, pollination networks or seed dispersal mechanisms), followed by direct competition, changes to ecosystem functioning (hydrology or nutrient dynamics), hybridization and predation. Trees and shrubs accounted for more than half of the species studied, but there were examples from most other groups of plants and animals. The social consequences of invasions have been less well studied at the level of individual species. Most studies (72%) considered the impacts of a single species, based on data collected on < 1 ha, and were completed in less than a year. Space-for-time substitution was widely used, but widespread collection of data from numerous small plots allowed for reporting impact over larger spatial scales. We also identified seven studies that either monitored impacts over longer periods (up to 40 years), or repeated surveys in the same area to assess change over time. Prominent landscape-scale impacts included reductions in water resources, the attrition of native biodiversity, reductions in rangeland productivity, predation of marine birds and freshwater fishes, and disease organisms affecting native mammals and trees. Nineteen studies at broader scales estimated substantial impacts on landscape-scale water yield, habitats and biodiversity, rangeland productivity, and the economic value of ecosystem services. Despite considerable progress, our understanding remains fragmentary. Impacts are expected to grow as invasions enter exponential phases of spread and densification and as the duration of invasions increases. A robust understanding needs to be developed to provide justification for management costs.

Species of the genus Acacia have been introduced worldwide and have negative environmental and socio-economic impacts in many introduced regions. This study makes use of environmental and socio-economic impact classification schemes for alien taxa (EICAT and SEICAT) to assess the impacts that 33 acacias introduced to South Africa have at a global scale. The aims of this study were: (1) to compare the EICAT impact categories which are based on literature with expert assessments; (2) to determine which environmental and socio-economic mechanisms underlie acacia impacts; and (3) to test if certain habitats experience higher impact magnitudes than others. Most acacias had a massive impact when evaluated by experts, while the impact was mostly major for EICAT. This could be due to the use of different definitions for the impact categories. It might also show that the data available is insufficient or inadequate in showing that such high impacts exist. Competition was found to be the most often recorded mechanism underlying acacia environmental impacts and was one of the mechanisms with the largest impact magnitude. Grassland, shrubland, marine-coastal and forest habitats were found to be impacted by acacias equally as much. Using impact scoring schemes as an evidence-based and transparent approach to determine the impact status of alien species provides a more robust method to aid management prioritisation and risk assessment than expert opinion alone. However, data quality and availability could limit their effectiveness, especially for less well studied species.

The Atlantic blue crab ( Callinectes sapidus ) is an invasive alien with recent populations developing along the Mediterranean shoreline of Morocco's Oriental region. This study evaluates its ecological and socio-economic impacts, with a special emphasis on artisanal fisheries, in three Ramsar-designated sites, i.e., Cap-de-l’Eau–Saïdia, Nador–Marchica Lagoon, and Al Hoceima–National Park. Field observations, questionnaires, and semi-structured interviews with fishing operators and restaurant owners were used to obtain data. Results show that blue crab presence peaks in the summer and its habitat is connectivity-dependent: higher abundances occurred in semi-open marine systems such as lagoons and estuaries. The enormous majority of fishermen (91%) consider the species as harmful because it preys on native fauna. Changes in benthic community inventories have been documented through ecological assessments. Impacts were assessed using the Environmental Impact Classification for Alien Taxa (EICAT) and the Socio-Economic Impact Classification for Alien Taxa (SEICAT), showing major disturbances to ecosystems and local economies. Although there is some recognition of commercial potential among fishermen and restaurant owners, they often face hurdles such as limited demand, low market prices, lack of culinary knowledge and absence of specific fishing gear. We conclude on the multifaceted challenges that the blue crab invasion presents, and highlight the necessity of an integrated management approach, that accounts for the invasive impacts while investigating the blue crab’s value as a fishery resource.

Alien species can be damaging to native biodiversity, human well‐being and the economy. Identifying the complete range of impacts they cause, and the ways that these impacts are connected, may inform the prioritisation of management actions to mitigate impacts. Using datasets on the biodiversity impacts and monetary costs (damage and management costs) of alien birds, we aimed to establish whether species with the most severe biodiversity impacts also had the highest costs; whether types of biodiversity impact were associated with high costs; and whether specific factors associated with alien species are linked to both damaging biodiversity impacts and high costs. We identified a positive relationship between a specific type of biodiversity impact (predation) and costs, possibly because predation by alien birds can be severely damaging to native species and therefore attracts management actions. However, predation impacts are likely to occur more frequently and to be easier to identify than some other impact mechanisms such as hybridisation and transmission of diseases, and they are therefore likely to be more frequently managed and hence to have costs. We identified a specific species characteristic (generalism) to be associated with severe biodiversity impacts and high costs, probably because generalist species have greater opportunity to cause impacts, whether they be on biodiversity or the economy, or both. We also found widely distributed alien birds to be associated with high costs, probably because these species also have greater opportunity to cause impacts. Management interventions that prevent the introduction of both predatory and generalist alien bird species, or that reduce their geographic distribution at early stages of invasions, may have significant biodiversity and economic benefits. Read the free Plain Language Summary for this article on the Journal blog. Les espèces exotiques envahissantes peuvent nuire à la biodiversité indigène, au bien‐être des humains et à l'économie. L'identification de l'ensemble des impacts qu'elles provoquent et de la manière dont ces impacts sont liés peut permettre de hiérarchiser les mesures de gestion visant à atténuer ces impacts. En utilisant des ensembles de données sur les impacts sur la biodiversité et les coûts monétaires (dommages et coûts de gestion) des oiseaux exotiques, nous avons cherché à établir si les espèces ayant les impacts les plus importants sur la biodiversité avaient également les coûts les plus élevés ; si certains types d'impacts étaient associés à des coûts élevés ; et si des facteurs spécifiques associés aux espèces exotiques étaient liés à la fois à des dommages sur la biodiversité et à des coûts élevés. Nous avons identifié une relation positive entre un type spécifique d'impact sur la biodiversité (la prédation) et les coûts, peut‐être parce que la prédation par les oiseaux exotiques peut être très préjudiciable aux espèces indigènes et nécessite donc des mesures de gestion. Cependant, les impacts de la prédation sont susceptibles de se produire plus fréquemment et d'être plus faciles à identifier que d'autres mécanismes d'impact tels que l'hybridation et la transmission de maladies, et ils sont donc susceptibles d'être gérés plus fréquemment, et donc d'entraîner des coûts. Nous avons identifié une caractéristique spécifique des espèces (le généralisme) comme étant associée à des impacts forts sur la biodiversité et à des coûts élevés, probablement parce que les espèces généralistes ont plus de possibilités de causer des impacts, que ce soit sur la biodiversité ou sur l'économie, ou sur les deux. Nous avons également constaté que les oiseaux exotiques largement répandus étaient associés à des coûts élevés, probablement aussi parce que ces espèces ont plus de chances d'avoir un impact. Les interventions de gestion qui peuvent avoir les plus forts avantages en termes de biodiversité et d'économie sont ceux qui préviennent l'introduction d'espèces d'oiseaux exotiques prédatrices et généralistes, ou qui réduisent leur distribution géographique aux premiers stades des invasions. Read the free Plain Language Summary for this article on the Journal blog.

Impact scoring schemes are useful for identifying to what extent alien species cause damage. Quantifying the similarity and differences between impact scoring schemes can help determine how to optimally use these tools for policy decisions. Using feral mammals (including rats and mice) as a case study, environmental and socio-economic impacts were assessed using three schemes, namely the Generic Impact Scoring System (GISS), Environmental Impact Classification for Alien Taxa (EICAT) and Socio-Economic Impact Classification for Alien Taxa (SEICAT). The results show that socio-economic impacts scores differ between the respective schemes (GISS and SEICAT) possibly because they assess different aspects of social life and economy. This suggests that both scoring schemes should ideally be applied in concert to get a complete picture of socio-economic impacts. In contrast, environmental impact scores are correlated between GISS and EICAT assessments and this similarity is consistent over most mechanisms except for predation and ecosystems, suggesting that one scoring scheme is sufficient to capture all the environmental impacts. Furthermore, we present evidence for the island susceptibility hypothesis as impacts of feral mammals were found to be higher on islands compared to mainlands.