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.

The introduction of invasive species, which often differ functionally from the components of the recipient community, generates ecological impacts that propagate along the food web. This review aims to determine how consistent the impacts of aquatic invasions are across taxa and habitats. To that end, we present a global meta-analysis from 151 publications (733 cases), covering a wide range of invaders (primary producers, filter collectors, omnivores and predators), resident aquatic community components (macrophytes, phytoplankton, zooplankton, benthic invertebrates and fish) and habitats (rivers, lakes and estuaries). Our synthesis suggests a strong negative influence of invasive species on the abundance of aquatic communities, particularly macrophytes, zooplankton and fish. In contrast, there was no general evidence for a decrease in species diversity in invaded habitats, suggesting a time lag between rapid abundance changes and local extinctions. Invaded habitats showed increased water turbidity, nitrogen and organic matter concentration, which are related to the capacity of invaders to transform habitats and increase eutrophication. The expansion of invasive macrophytes caused the largest decrease in fish abundance, the filtering activity of filter collectors depleted planktonic communities, omnivores (including both facultative and obligate herbivores) were responsible for the greatest decline in macrophyte abundance, and benthic invertebrates were most negatively affected by the introduction of new predators. These impacts were relatively consistent across habitats and experimental approaches. Based on our results, we propose a framework of positive and negative links between invasive species at four trophic positions and the five different components of recipient communities. This framework incorporates both direct biotic interactions (predation, competition, grazing) and indirect changes to the water physicochemical conditions mediated by invaders (habitat alteration). Considering the strong trophic links that characterize aquatic ecosystems, this framework is relevant to anticipate the far-reaching consequences of biological invasions on the structure and functionality of aquatic ecosystems.

Principal Component Analysis (PCA) was performed to extract the main gradients of diet composition. Pearson's correlation and T-tests were used to assess the relation between diet characteristics (composition, diversity, taxonomic richness) and geographic and climatic variables. Results:A clear latitudinal gradient in trophic diversity and diet composition is observed. Otter diet is more diverse and features more prey classes in southern localities, while the species is more piscivorous towards the north, where it predates upon a higher number of fish families. This pattern is contrasting when temperate and Mediterranean localities of Europe are compared. Mediterranean otters behave as more generalist predators than temperate ones, relying less on fish, and more on crayfish, aquatic invertebrates and reptiles.Main conclusions: Geographical differences in otters feeding ecology in Europe seem to be related with the two contrasted climatic conditions affecting prey populations. The otter can act as a highly specialised piscivorous predator in temperate freshwater ecosystems, which do not suffer a dry season and are 3 comparatively more stable than Mediterranean ones. However, the unpredictable prey availability in Mediterranean areas, affected by strong spatial and temporal water shortages, would favour a diversification of otter diet. 4

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecological Applications. Abstract. Nonnative invasive species are one of the main global threats to biodiversity. The understanding of the traits characterizing successful invaders and invasion-prone ecosystems is increasing, but our predictive ability is still limited. Quantitative information on biotic homogenization and particularly its temporal dynamics is even scarcer. We used freshwater fish distribution data in the Iberian Peninsula in four periods (before human intervention, 1991, 1995, and 2001) to assess the temporal dynamics of biotic homogenization among river basins. The percentage of introduced species among fish faunas has increased in recent times (from 41.8% in 1991 to 52.5% in 2001), leading to a clear increase in the similarity of community composition among basins. The mean Jaccard's index increase (a measure of biotic homogenization) from the pristine situation to the present (17.1%) was similar to that for Californian fish but higher than for other studies. However, biotic homogenization was found to be a temporally dynamic process, with finer temporal grain analyses detecting transient stages of biotic differentiation. Introduced species assemblages were spatially structured along a latitudinal gradient in the Iberian Peninsula, with species related to sport fishing being characteristic of northern basins. Although the comparison of fish distributions in the Iberian Peninsula and France showed significant and generalized biotic homogeniza-tion, nonnative assemblages of northeastern Iberian basins were more similar to those of France than to those of the rest of the Iberian Peninsula, indicating a main introduction route. Species introduced to the Iberian Peninsula tended to be mainly piscivores or widely introduced species that previously had been introduced to France. Our results indicate that the simultaneous analysis of the spatial distribution of introduced assemblages (excluding native species that reflect other biogeographical patterns) and their specific traits can be an effective tool to detect introduction and invasion routes and to predict future invaders from donor regions.

1.We used a basin approximation to analyse distribution patterns of different components of biodiversity (taxonomic richness, endemicity, taxonomic singularity, rarity) and conservation status of freshwater fish fauna in 27 Mediterranean Iberian rivers. 2.Basin area alone explained more than 80% of variation in native species richness. Larger basins featured not only a higher number of native species, but also more endemic and rare species and less diversified genera than smaller ones. 3.In contrast, smaller basins scored higher community conservation values, due to their lower degree of invasion by introduced species. 4.The presence of dams was the most important factor determining the conservation status of fish communities, and it was also positively associated with the number of introduced species. 5.While the most important components of Iberian freshwater fish biodiversity are located in large basins, small unregulated ones feature better conserved fish communities.2

Co‐extinctions are increasingly recognized as one of the major processes leading to the global biodiversity crisis, but there is still limited scientific evidence on the magnitude of potential impacts and causal mechanisms responsible for the decline of affiliate (dependent) species. Freshwater mussels (Bivalvia, Unionida), one of the most threatened faunal groups on Earth, need to pass through a parasitic larval (glochidia) phase using fishes as hosts to complete their life cycle. Here, we provide a synthesis of published evidence on the fish–mussel relationship to explore possible patterns in co‐extinction risk and discuss the main threats affecting this interaction. We retrieved 205 publications until December 2015, most of which were performed in North America, completed under laboratory conditions and were aimed at characterizing the life cycle and/or determining the suitable fish hosts for freshwater mussels. Mussel species were reported to infest between one and 53 fish species, with some fish families (e.g., Cyprinidae and Percidae) being used more often as hosts than others. No relationship was found between the breadth of host use and the extinction risk of freshwater mussels. Very few studies focused on threats affecting the fish–mussel relationship, a knowledge gap that may impair the application of future conservation measures. Here, we identify a variety of threats that may negatively affect fish species, document and discuss the concomitant impacts on freshwater mussels, and suggest directions for future studies.

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Different components of global change can have interacting effects on biodiversity and this may influence our ability to detect the specific consequences of climate change through biodiversity indicators. Here, we analyze whether climate change indicators can be affected by land use dynamics that are not directly determined by climate change. To this aim, we analyzed three community-level indicators of climate change impacts that are based on the optimal thermal environment and average latitude of the distribution of bird species present at local communities. We used multiple regression models to relate the variation in climate change indicators to: i) environmental temperature; and ii) three landscape gradients reflecting important current land use change processes (land abandonment, fire impacts and urbanization), all of them having forest areas at their positive extremes. We found that, with few exceptions, landscape gradients determined the figures of climate change indicators as strongly as temperature. Bird communities in forest habitats had colder-dwelling bird species with more northern distributions than farmland, burnt or urban areas. Our results show that land use changes can reverse, hide or exacerbate our perception of climate change impacts when measured through community-level climate change indicators. We stress the need of an explicit incorporation of the interactions between climate change and land use dynamics to understand what are current climate change indicators indicating and be able to isolate real climate change impacts.