Swimming performance is a key feature that mediates fitness and survival in aquatic animals. Dispersal, habitat selection, predator–prey interactions and reproduction are processes that depend on swimming capabilities. Testing the critical swimming speed (U_crit) of fish is the most straightforward method to assess their prolonged swimming performance. We analysed the contribution of several predictor variables (total body length, experimental water temperature, time step interval between velocity increments, species identity, taxonomic affiliation, native status, body shape and form factor) in explaining the variation ofU_crit, using linear models and random forests. We compiled in total 204 studies testingU_critof 35 inland fishes of the Iberian Peninsula, including 17 alien species that are non-native to that region. We found that body length is largely the most important predictor ofU_critout of the eight tested variables, followed by family, time step interval and species identity. By contrast, form factor, temperature, body shape and native status were less important. Results showed a generally positive relationship betweenU_critand total body length, but regression slopes varied markedly among families and species. By contrast, linear models did not show significant differences between native and alien species. In conclusion, the present study provides a first comprehensive database ofU_critin Iberian freshwater fish, which can be thus of considerable interest for habitat management and restoration plans. The resulting data represents a sound foundation to assess fish responses to hydrological alteration (e.g. water flow tolerance and dispersal capacities), or to categorize their habitat preferences.

The Anthropocene is characterised by a continuous human‐mediated reshuffling of the distributions of species globally. Both intentional and unintentional introductions have resulted in numerous species being translocated beyond their native ranges, often leading to their establishment and subsequent spread – a process referred to as biological invasion. Biological invasions are associated with profound changes in the composition, structure, and functioning of recipient ecosystems, plus substantial financial losses and disruptions to society, culture, and human well‐being. These ecological, economic, and socio‐cultural impacts are interrelated, ubiquitous, and detrimental, yet they are often subjectively perceived or inaccurately quantified. Persistent knowledge gaps remain, however, which limit our understanding of the complex and multifaceted causes and mechanisms of invasion impacts. To overcome these gaps and comprehensively capture all related facets pertaining to the nature and diversity of invasion impact, this scoping review of academic studies, grey literature, and expert reports provides a conceptual model for interpreting invasion impacts, structured around three interrelated pillars: impact domains, challenges in the study of impacts, and available risk‐ and impact assessments. We initially explore the various mechanisms and consequences of ecological, economic, and socio‐cultural invasion impacts and their temporal dynamics, substantiating these with relevant empirical examples. We then review common challenges and fallacies in studying invasion impacts, including context specificity and inter‐comparability of impact magnitudes, challenges associated with quantifying non‐ecological impacts, and research biases, before synthesising how risks are analysed and impacts assessed, and how these assessments ultimately inform management decisions. Our review underscores the multifaceted and complex nature of invasion impacts, and that effectively addressing biological invasions requires more than isolated, reactive interventions; it calls for globally coordinated, proactive action underpinned by reliable scientific knowledge, sincere political commitment, and broad public engagement. Drawing on nearly a century of literature and global expert contributions, this work offers a comprehensive, nuanced, and timely overview of the potential consequences of biological invasions, providing a valuable foundation for informing future research directions, management interventions, and policy development.

Invasive alien species have widespread impacts on native biodiversity and ecosystem services. Since the number of introductions worldwide is continuously rising, it is essential to prevent the entry, establishment and spread of new alien species through a systematic examination of future potential threats. Applying a three-step horizon scanning consensus method, we evaluated non-established alien species that could potentially arrive, establish and cause major ecological impact in Spain within the next 10 years. Overall, we identified 47 species with a very high risk (e.g. Oreochromis niloticus, Popillia japonica, Hemidactylus frenatus, Crassula helmsii or Halophila stipulacea), 61 with high risk, 93 with moderate risk, and 732 species with low risk. Many of the species categorized as very high or high risk to Spanish biodiversity are either already present in Europe and neighbouring countries or have a long invasive history elsewhere. This study provides an updated list of potential invasive alien species useful for prioritizing efforts and resources against their introduction. Compared to previous horizon scanning exercises in Spain, the current study screens potential invaders from a wider range of terrestrial, freshwater, and marine organisms, and can serve as a basis for more comprehensive risk analyses to improve management and increase the efficiency of the early warning and rapid response framework for invasive alien species. We also stress the usefulness of measuring agreement and consistency as two different properties of the reliability of expert scores, in order to more easily elaborate consensus ranked lists of potential invasive alien species.

Aim: Unravelling the ecological and historical factors that underlie species distributions has challenged ecologists for a long time. Thus, our objective is to understand the role of environmental variables explaining the distribution of three major eco‐evolutionary groups of inland fishes (Darlington's divisions: primary, i.e. strict freshwater; secondary, i.e. salt‐tolerant; and peripheral, i.e. diadromous and marine origin), and how these variables are related to fish traits.Location: Iberian Peninsula.Taxon: 51 native and 17 alien inland fish species from the Iberian Peninsula.Methods: We modelled distributions of the most common inland fish species across the Iberian Peninsula to compare the importance of different predictors among the three Darlington's divisions and between native and alien species. To explore the importance of specific environmental variables in determining the distribution of different traits of inland fish, variable importances obtained from species distribution models were subjected to a redundancy analysis.Results: Darlington's divisions differ significantly in salinity tolerance, in distribution overlap, in the importance of distribution predictors and associated life‐history traits. Topographic and climatic variables were generally more important than land use and anthropogenic factors in explaining fish distributions. We found significant differences in the importance of variables explaining the distribution of native vs. alien species and especially among Darlington's divisions. River basin was most important for primary native and many alien species. Increasing mean temperature and damming were positively associated with the presence of tolerant, large‐bodied and warm‐water alien species from more hydrologically stable habitats.Main conclusions: Despite marked differences in the distribution patterns of native and alien species, evolutionary and introduction histories as well as seawater tolerance are central factors explaining the current distribution of inland fishes. Darlington's divisions proved useful for addressing ecological and biogeographical questions at broader spatial scales.

The enormous biodiversity of tropical freshwater combined with a considerable increase in the construction of reservoirs urges to understand the ecological effects caused by damming. Using rarely available data obtained before (one year) and after (four years) the filling of a hydroelectric plant on the Teles Pires River (Amazon River basin), the effects on abundance, biomass, and diversity of the fish assemblage were evaluated using two complementary approaches: a BACI (before-after-control-impact) design with mixed models and analyses of covariance. Significant Before-After × Control-Impact interactions in abundance, biomass, and species richness were observed, with decreases of abundance and species richness and more stable biomass after filling. Some abundant species, such as Jupiaba polylepis, Jupiaba acanthogaster, Knodus cf. heteresthes, and Moenkhausia lepidura among others, declined in abundance or disappeared from the impact sites. However, temporal and particularly spatial variation independent of damming explained more variation in all the response variables analyzed, including species composition, and analyses of covariance demonstrated general negative trends irrespective of damming. This study illustrates the usefulness of BACI designs to assess the effects of damming but also that other statistical approaches are complementary, given the difficulty of identifying control sites and the short length of most ecological time series. The results also suggest that preserving tributaries upstream of reservoirs and natural regimes of spatial and temporal environmental variation might help to mitigate the impacts of damming in tropical ecosystems.