International audienceStudy of the impacts of biological invasions, a pervasive component of global change, has generated remarkable understanding of the mechanisms and consequences of the spread of introduced populations. The growing field of invasion science, poised at a crossroads where ecology, social sciences, resource management, and public perception meet, is increasingly exposed to critical scrutiny from several perspectives. Although the rate of biological invasions, elucidation of their consequences, and knowledge about mitigation are growing rapidly, the very need for invasion science is disputed. Here, we highlight recent progress in understanding invasion impacts and management, and discuss the challenges that the discipline faces in its science and interactions with society

In a recent Opinion article in TREE [1], Gurevitch and Padilla concluded that the importance of invasive species in causing declines and extinctions of species is unproven. They analyzed the IUCN Red List database [2] and stated that only 6% of the taxa are threatened with extinction as a result of invasion by alien species and !2% (ten terrestrial plants and no animal species) of the 762 extinctions were the result of the introduction of alien species. We believe that these figures and the message of the article are misleading.The IUCN database includes a searchable hierarchical classification of threats to wildlife (e.g. habitat loss, invasive alien species, harvesting, and so on), which was used by Gurevitch and Padilla in their article [1]. However, this classification system is used in only 5.1% (39 out of 762) of the extinct species (e.g. there are 129 extinct species of birds, but none of them has been assigned a extinction cause, despite the fact that many are among the best documented cases of extinction) and detailed information about the causes of extinction is provided in other fields of the database (e.g. the robust white-eye Zosterops strenuus, endemic to Lord Howe Island, Australia, 'was common before 1918, but plummeted to extinction following the arrival of black rat'). We reanalyzed the extinctions included in the IUCN Red List database on a species-by-species basis and reassessed the role of invasive species in those extinctions.The conclusion is radically different from that reached by Gurevitch and Padilla. Of the 680 extinct animal species, causes could be compiled for 170 (25%), of which 91 (54%) included the effects of invasive species. For 34 cases (20%), invasive species were the only cited cause of extinction. Habitat destruction and harvesting (hunting and/or gathering) were cited for 82 and 77 species, respectively.Our results agree with those of recent statistical analyses [3,4], modelling of future scenarios [5], and several reviews of particular taxa by expert groups that have concluded that invasive species are the leading cause of extinction of birds (65 out of 129 spp.) [6] and the second cause of the extinction of North American fish (27 out of 40 spp. [7]), world fish (11 out of 23 spp. [8]) and mammals (12 out of 25 spp. [9]). Although extinction is often the end result of invasions, there are other ecological and evolutionary impacts of biotic homogenization that are less understood [10,11], thus prevention and the precautionary principle are of particular relevance to invasive species.

Human-mediated transport beyond biogeographic barriers has led to the introduction and 73The transport of species across biogeographic barriers by humans is a key component of 74 global environmental change [1][2][3] . Some of the species introduced to new regions will establish 75 self-sustaining populations and, thus, become a persistent part of the local biota 95We expect regions with higher gross domestic product per capita (GDPpc) or with higher 96 population densities to receive more alien species introductions across taxa (i.e., to experience 97 higher colonisation pressure through trade and transport), resulting in higher EAS richness 7,8,10,21 . 98We also test whether EAS richness patterns follow the latitudinal gradients often observed for 99 native biota, with higher richness in regions with higher mean annual temperature and 100 precipitation 22,23 . We expect island regions to have higher EAS richness than mainland regions, 101as islands are thought to be more prone to the establishment of alien species 12,24,25 . In addition, 102we expect more isolated oceanic islands to have greater EAS richness, as they have been shown 103 to receive more introductions, at least for birds 9 . We also expect coastal regions (as points of human population density, with a weak trend of higher alien richness in wetter regions (Table 1). 125While we only have potential proxy data (GDPpc, population density) for colonisation pressure 126 here (i.e., the total numbers of species introduced) 26 , our results suggest that cumulative numbers 127 7 of EAS are driven to a greater extent by differences in area and the pressure of introductions 128 from human history and activity 1,3,5,12,21 than by climate. 129Island regions have on average higher cross-taxon EAS richness (mean ± 1 S.D. 130proportional cross-taxon richness = 0.17 ± 0.11) than mainland regions (mean ± 1 S.D. = 0.11 ± 131 0.07; Table 1). In addition, models explaining alien richness of island and mainland regions 132 separately reveal that EAS richness is more strongly related to area, GDPpc and population 133 density on islands than in mainland regions (Table 1) (Table 1). Among mainland regions, EAS richness is greater for coastal (mean ± 1 S.D. 139proportional cross-taxon richness = 0.13 ± 0.09) than for landlocked regions (mean ± 1 S.D. = 140 0.10 ± 0.04). Cross-taxon EAS richness on islands tends to be higher for those further from 141 continental landmasses (Table 1). 143 Taxonomic congruence 144The strongest correlations in alien richness between taxonomic groups exist for ants and 145 reptiles (r s = 0.62), followed by birds and mammals, and vascular plants and spiders (both r s = 146 0.55) ( Table 2). For ants and reptiles, EAS richness is high in the Hawaiian Islands, southern 147United States (especially Florida) and Madagascar and the Mascarene Islands (Fig. 1b, 1g). (Fig. 1f, 1h). In Europe, the United Kingdom has the highest established alien 154 plant richness, while Germany has the highest spider richness (Fig. 1h, 1h). Overa...

Summary1. An analysis of variance (  ) or other linear models of the residuals of a simple linear regression is being increasingly used in ecology to compare two or more groups. Such a procedure (hereafter, 'residual index') was used in 8% and 2% of the papers published during 1999 in the Journal of Animal Ecology and in Ecology , respectively, and has been recently recommended for studying condition. 2. Although the residual index is similar to an analysis of covariance (  ), it is not identical and is incorrect for at least four reasons: (i) the regression coefficient used by the residual index differs from the one used in  and is not the least-squares estimator of the model.(ii) in contrast to the  , the error d.f. in the residual index are overestimated because of the estimation of the regression coefficient. (iii) the residual index also assumes the homogeneity of regression coefficients (parallelism assumption), which should be tested with a special  design. (iv) even if the assumptions of the linear model hold for the original variables, they will not hold for the residuals. 3. More importantly, the residual index is an ad hoc sequential procedure with no statistical justification, unlike the well-known  . For these reasons, I suggest that a t -test or an  of the residuals should never be used in place of an  to study condition or any other variable.

A popular species for food and sport, the European catfish (Silurus glanis) is well-studied in its native range, but little studied in its introduced range. Silurus glanis is the largestbodied freshwater fish of Europe and is historically known to take a wide range of food items including human remains. As a result of its piscivorous diet, S. glanis is assumed to be an invasive fish species presenting a risk to native species and ecosystems. To assess the potential risks of S. glanis introductions, published and 'grey' literature on the species' environmental biology (but not aquaculture) was extensively reviewed. Silurus glanis appears well adapted to, and sufficiently robust for, translocation and introduction outside its native range. A nest-guarding species, S. glanis is long-lived, rather sedentary and produces relatively fewer eggs per body mass than many fish species. It appears to establish relatively easily, although more so in warmer (i.e. Mediterranean) than in northern countries (e.g. Belgium, UK). Telemetry data suggest that dispersal is linked to flooding/spates and human translation of the species. Potential impacts in its introduced European range include disease transmission, hybridization (in Greece with native endemic Aristotle's catfish [Silurus aristotelis]), predation on native species and possibly the modification of food web structure in some regions. However, S. glanis has also been reported (France, Spain, Turkmenistan) to prey intensively on other non-native species and in its native Germany to be a poor biomanipulation tool for top-down predation of zooplanktivorous fishes. As such, S. glanis is unlikely to exert trophic pressure on native fishes except in circumstances where other human impacts are already in force. In summary, virtually all aspects of the environmental biology of introduced S. glanis require further study to determine the potential risks of its introduction to novel environments.

Aim  To identify key research questions and challenges that will, if addressed in a timely manner, significantly advance the field of freshwater fish biogeography and conservation. Location  Globe. Methods  By drawing on expertise from different regions of the world, we integrate an illustrative conspectus of recent scientific advancements in fish biogeography with a prospectus of needed areas of scientific inquiry to identify information gaps and priority research needs to advance the science. Results  We identified the following core challenges: (1) Testing current and forging new theories in biogeography; (2) Advancing a trait‐based biogeography of freshwater fishes; (3) Quantifying extinction risk and loss of fish species in a changing environment; (4) Evaluating the magnitude and geography of extinction debt for freshwater fishes; (5) Elucidating the patterns and drivers of freshwater fish invasions; (6) Forecasting the future geography of freshwater fishes; (7) Understanding the interactive effects of multiple stressors in freshwater ecosystems; (8) Quantifying new features of the biodiversity crisis: fish faunal homogenization and the emergence of novel assemblages; (9) Promoting scientific rigour in emerging freshwater fish conservation strategies and (10) Improving conservation planning strategies for freshwater fish species. Main conclusions  By reflecting on recent scientific progress in fish conservation biogeography, we have identified a set of core challenges and priorities requiring future research investment.

Invasive species are increasingly recognized as one of the main threats to biodiversity and both an urgent need and a unique tool for ecological research. Although attempts to identify future invasive species are not new to ecology, rigorous quantitative analyses emanate mostly from the last decade. In 2001, quantitative studies dealing with the distinguishing ecological features of invasive species were reviewed but no papers on fish species were identified. Subsequently, several quantitative studies have addressed this issue for freshwater fishes, including those that have focused on California, Colorado, the Great Lakes of North America and the Iberian Peninsula. In the present paper, 12 such studies are reviewed and compared with regard to their conclusions and methodology. The issues of different invasion stages and comparison strategies, propagule pressure, information-theoretic analyses v. sequential techniques, use of phylogenetic comparative methods and spatial scale are discussed. Non-native fish transport and release are the least investigated although taxonomy and human interests seem key in these first initial stages. Establishment success, which has received more study, seems more multi-factorial, context-dependent and more mediated by species-specific life-history traits. The dispersal and impact phases are less understood, although the comparison of traits (and taxonomy) between native and invasive species and particularly its variability holds promise. The lack of data on propagule pressure and the use of sequential techniques for observational data sets with many intercorrelated variables could affect the conclusions of previous studies. Research on the dispersal, impact and particularly transport and introduction phases should be prioritized rather than establishment. All the studies identified were at temperate latitudes in the northern hemisphere; studies in other regions and comparison of different regions and multiple scales are lackingFinancial support for my research was provided by the Spanish Ministry of Education (REN2003–00477 and CGL2006-11652-C02-01/BOS), the Government of Catalonia (Catalan Government Distinction Award for university research 2004), and the European Commission (FP6 Integrated Project ‘ALARM’, GOCE-CT-2003-506675

Substantial progress has been made in understanding how pathways underlie and mediate biological invasions. However, key features of their role in invasions remain poorly understood, available knowledge is widely scattered, and major frontiers in research and management are insufficiently characterized. We review the state of the art, highlight recent advances, identify pitfalls and constraints, and discuss major challenges in four broad fields of pathway research and management: pathway classification, application of pathway information, management response, and management impact. We present approaches to describe and quantify pathway attributes (e.g., spatiotemporal changes, proxies of introduction effort, environmental and socioeconomic contexts) and how they interact with species traits and regional characteristics. We also provide recommendations for a research agenda with particular focus on emerging (or neglected) research questions and present new analytical tools in the context of pathway research and management.