Biological invasions are one of the major drivers of biodiversity decline and have been shown to have far‐reaching consequences for society and the economy. Preventing the introduction and spread of alien species represents the most effective solution to reducing their impacts on nature and human well‐being. However, implementing effective solutions requires a good understanding of where the species are established and how biological invasions develop over time. Knowledge of the status and trends of biological invasions is thus key for guiding research efforts, informing stakeholders and policymakers, for targeted management efforts, and preparing for the future. However, information about the status and trends of alien species is scattered, patchy, and highly incomplete, making it difficult to assess. Published reports for individual regions and taxonomic groups are available, but large‐scale overviews are scarce. A global assessment therefore requires a review of available knowledge with careful consideration of sampling and reporting biases. This paper provides a comprehensive global assessment of the status and trends of alien species for major taxonomic groups [Bacteria, Protozoa, Stramenopila, Alveolata, and Rhizaria (SAR), fungi, plants, and animals] for Intergovernmental Panel of Biodiversity and Ecosystem Services (IPBES) regions. The review provides irrefutable evidence that alien species have been introduced to all regions worldwide including Antarctica and have spread to even the most remote islands. The numbers of alien species are increasing within all taxa and across all regions, and are often even accelerating. Large knowledge gaps exist, particularly for taxonomic groups other than vascular plants and vertebrates, for regions in Africa and Central Asia, and for aquatic realms. In fact, for inconspicuous species, such as Bacteria, Protozoa, and to some degree SAR and fungi, we found records for very few species and regions. Observed status and trends are thus highly influenced by research effort. More generally, it is likely that all lists for alien species of any taxonomic group and region are incomplete. The reported species numbers therefore represent minima, and we can expect additions to all lists in the near future. We identified six key challenges which need to be addressed to reduce knowledge gaps and to improve our ability to assess trends and status of biological invasions.

Invasive non‐native species (INNS) are recognized as a major threat to island biodiversity, ecosystems, and economies globally. Preventing high‐risk INNS from being introduced is the most cost‐effective way to avoid their adverse impacts. We applied a horizon scanning approach to identify potentially INNS in the United Kingdom Overseas Territories (OTs), ranging from Antarctica to the Caribbean, and from the Pacific to the Atlantic. High‐risk species were identified according to their potential for arrival, establishment, and likely impacts on biodiversity and ecosystem function, economies, and human health. Across OTs, 231 taxa were included on high‐risk lists. The highest ranking species were the Asian green mussel ( Perna viridis ), little fire ant ( Wasmannia auropunctata ), brown rat ( Rattus norvegicus ), and mesquite tree ( Prosopis juliflora ). Shipping containers were identified as the introduction pathway associated with the most species. The shared high‐risk species and pathways identified provide a guide for other remote islands and archipelagos to focus ongoing biosecurity and surveillance aimed at preventing future incursions.

Aim: Our aims were: (1) to study the shape of the species richness–elevation and abundance–elevation relationships (SRERandAER, respectively) in epigaeic mountain beetles; and (2) to analyse how richness and abundance of the beetles vary across the full gradient and within the forests and steppes in association with environmental variables representing productivity, thermal limitation, water–energy dynamics, environmental heterogeneity and soil characteristics.Location: Five mountains at temperate latitudes in north‐western Patagonia, Argentina.Methods: We collected beetles using 486 pitfall traps arranged in fifty‐four 100 m² grid plots of nine traps, established at intervals of about 100 m of elevation from the base to the summit of each mountain. We used multi‐model selection and the Akaike information criterion to find the best ecological explanation for species richness and abundance variation.Results: TheAERwas hump‐shaped in four mountains and negative in one;the SRERwas negative in one case, humped in two cases, and either low‐plateau or humped in the remaining two. Across the full gradient, the increase in vegetation cover, mainly associated with the presence of forests, predominately accounted forSRERs andAERs. In the forests, energy variables combined with precipitation, soil attributes and environmental heterogeneity accounted for richness and abundance. In the steppes, potential evapotranspiration and plant productivity were important.Main conclusions: We confirmed different forms in the shape ofSRERs, and the predominance of hump‐shaped patterns inAERs. Vegetation type (forests versus steppes) accounted for most of the variation in species richness and abundance on all mountains. Associations with local environmental factors were rather more variable and changed with the spatial extent of analysis, thus confirming the spatial dependence of the species richness/abundance–environment relationships.