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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.

The Iberian Peninsula is a primary entry point for non-native species (NNS) into Europe via maritime routes, and is a significant tourist destination. This positions the highly diverse Spanish National Parks at high risk from invasive species, necessitating proactive adaptation and mitigation strategies. We present a comprehensive analysis of the risks posed by NNS to the network of 15 continental and marine National Parks in Spain under climate change, aiming to align management strategies with international Global Biodiversity Framework (GBF) targets. We identified 200 NNS across the network of National Parks, including 78 listed in national NNS regulations. Park managers helped identify 22 priority NNS, including the water hyacinth, American mink, Cape fig and wakame, among others. Over half of the 22 priority NNS (55%) were classified as having a “Major” impact on native biodiversity according to EICAT standards, with another 23% considered “Massive”. Distribution models suggest that rising minimum temperatures could enable NNS to expand in altitude within the parks, particularly in high-mountain parks. Species like the barbary sheep, water hyacinth and largemouth bass may particularly benefit from global warming. Our findings prioritize national parks most vulnerable to the double threat posed by climate change and invasive species, such as Islas Atlánticas, Doñana and Archipelago de Cabrera. We conclude that, in order to progress towards achieving GBF goals, it is essential to: (i) coordinate NNS management efforts across administrations (national and regional), (ii) integrate resources and expertise in a unified strategy against invasion across the network and (iii) enhance public awareness about the risks of introduction and impact of NNS.

Protected areas underpin global biodiversity conservation and sustainability goals, but remain at risk from biological invasion impacts. Anticipated expansions of protected lands and waters towards 2030 under the Kunming-Montreal Global Biodiversity Framework (GBF) will concurrently increase the burden of biological invasions within and from these newly protected areas. To prioritise management efforts and assess the potential risks of current and future designations to address multiple GBF targets, it is essential to quantify impact patterns at large scales across contexts. Here, we provide the first comprehensive global assessment of non-native species impacts in protected areas using the Environmental Impact Classification for Alien Taxa (EICAT)—a semi-quantitative, standardised protocol for evaluating their environmental impacts. We analyse taxonomic, ecological, and spatiotemporal predictors of harm and compare the distribution of impact mechanisms across contexts, using 579 impact cases from a literature review. Harmful impacts from non-native species have been documented across all taxonomic groups and environments, including irreversible extinctions. In particular, non-native plants and fish most often affect native plants and insects. Competition, predation, and structural changes were the most impact mechanisms recorded. Studies have been biassed geographically towards Nearctic, Palearctic and Neotropical protected areas, reinforcing the need for regional strategies to mitigate impacts. Our findings culminate in a series of recommendations to directly and indirectly address GBF targets by managing biological invasion impacts. Overall, expanding the range of studies towards whole ecosystem levels across regions can enrich the understanding of how biological invasions affect protected areas. Based on our results, managers should seek to reduce invasion rates in general across all taxa, but especially prioritise those conferring impacts through consumptive and structural mechanisms.

Biodiversity impacts caused by alien species can be severe, including those caused by alien birds. In order to protect native birds, we aimed to identify factors that influence their vulnerability to the impacts of alien birds. We first reviewed the literature to identify native bird species sustaining such impacts. We then assigned impact severity scores to each native bird species, depending on the severity of the impacts sustained, and performed two types of analyses. First, we used contingency table tests to examine the distribution of impacts across their severity, type and location, and across native bird orders. Second, we used mixed‐effects models to test factors hypothesised to influence the vulnerability of native birds to the impacts of alien birds. Ground‐nesting shorebirds and seabirds were more prone to impacts through predation, while cavity‐nesting woodpeckers and parrots were more prone to impacts through competition. Native bird species were more vulnerable when they occupied islands, warm regions, regions with climatic conditions similar to those in the native range of the invading alien species, and when they were physically smaller than the invading alien species. To a lesser extent, they were also vulnerable when they shared habitat preferences with the invading alien species. By considering the number and type of native bird species affected by alien birds, we demonstrate predation impacts to be more widespread than previously indicated, but also that damaging predation impacts may be underreported. We identify vulnerable orders of native birds, which may require conservation interventions; characteristics of native birds that increase their vulnerability, which may be used to inform risk assessments; and regions where native birds are most vulnerable, which may direct management interventions. The impacts sustained by native birds may be going unnoticed in many regions of the world: there is a clear need to identify and manage them.

Non-native, invasive plants are projected to shift their ranges with climate change, creating hotspots of risk where a multitude of novel species may soon establish and spread. The Northeast U.S. is one such hotspot. However, because monitoring for novel species is costly, these range-shifting invasive plants need to be prioritized. Preventing negative impacts is a key goal of management, thus, comparing the potential impacts of range-shifting invasive species could inform this prioritization. Here, we adapted the environmental impacts classification for alien taxa protocol to evaluate potential impacts of 100 invasive plants that could establish either currently or by 2050 in the states of New York, Massachusetts, Connecticut, or Rhode Island. We searched Web of Science for each species and identified papers reporting ecological, economic, human health, or agricultural impacts. We scored ecological impacts from 1 (‘minimal concern’) to 4 (‘major’) and socio-ecological impacts as present or absent. We evaluated 865 impact studies and categorized 20 species as high-impact, 36 as medium-impact, and 26 as low-impact. We further refined high-impact invasive species based on whether major impacts affect ecosystems found in Northeast U.S. and identified five high-priority species: Anthriscus caucalis, Arundo donax, Avena barbata, Ludwigia grandiflora, and Rubus ulmifolius. Additional research is needed for 18 data-deficient species, which had no studies reporting impacts. Identifying and prioritizing range-shifting invasive plants provides a unique opportunity for early detection and rapid response that targets future problem species before they can establish and spread. This research illustrates the feasibility of using impacts assessments on range-shifting invasive species in order to inform proactive policy and management.

Risk maps are a useful tool to prioritise sites for management and allocate resources where they are most needed as they can show us where impacts of biological invasions are most likely to happen or expected to be largest. Given the pace of global changes, we need to understand not only the risks under current conditions, but future risks taking these changes into account. In this study, we use Australian acacias alien to South Africa as a case study to model their potential distribution under future climate change to map their potential impacts at the middle and end of the century and the uncertainty related to three socio-economic pathways and five climatic models. The resulting risk maps across South Africa are a pioneering attempt to combine impacts of alien species with potential future distributions. We found that although climatic suitability and therefore the risk is predicted to decrease under climate change in 51,4% of the country’s area, the opposite is predicted for 26% of the area and the highly vulnerable fynbos biome remains an area with high projected impacts. Such risk maps can help us prioritise management actions and aid the development of suitable plans to protect biodiversity under current and future climate conditions. However, they have to be interpreted with caution and we highlight some shortcomings around species distribution models in general, vulnerability of ecosystems to the potential impacts, data gaps on impacts, as well as currently benign or unknown invaders, which are not included in the projections.

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.

Aim Anthropogenic environmental modifications such as climate or land‐use change are causing species to move on their own beyond their native ranges. As this phenomenon will increase in the near future, it is crucial to determine whether range‐expanding species, or neonatives, are more or less likely than native and alien species to impact their recipient ecosystems. Here, we compared impact magnitudes of bark beetle species from their native, neonative and alien ranges, simultaneously. Location Global. Methods We formulated four general scenarios about the magnitude of environmental impacts in different ranges (native, neonative and alien) based on hypotheses commonly used in invasion biology. We tested these scenarios globally on Dendroctonus bark beetles, asking whether they have the most harmful impacts in their native, neonative or alien ranges. Impacts reported in the literature were assessed with the IUCN Environmental Impact Classification for Alien Taxa (EICAT). Results We found that bark beetles cause the most harmful impacts in their native ranges, followed by the neonative ranges, while impacts in their alien ranges are the lowest. This indicates that the more dissimilar the environment is from that in the native range, the lower the probability of high‐impact magnitudes. Our results align with several non‐exclusive hypotheses, e.g. pre‐adaptation and habitat filtering, while they do not support others, e.g. enemy release or Darwin’s naturalization. The results are also in contrast with previous studies on vertebrates and plants, which found no or mixed differences in impact magnitudes with biogeographic origin. Main conclusions Our analysis suggests that bark beetles, like other species that are keystone and abundant in their native ranges, have generally lower impacts when introduced to novel environments due to biotic resistance or lack of pre‐adaptation. Research and management implications regarding the impacts of neonative and alien populations are also discussed.