Presence Of Non-native Species Research Articles

Pestrost in pojavljanje domačih in tujerodnih drevesnih in grmovnih vrst na ploskvah nacionalne gozdne inventure v Sloveniji

In Slovenia, the National Forest Inventory (NFI) is used to monitor the state and development of forests at the national level. In this paper, we analysed the diversity of tree and shrub species and assessed the presence of non-native tree species in Slovenian forests. According to the literature, Slovenia hosts 71 autochthonous tree species, of which 60 were found among the trees measured on the 2 x 2 km NFI density plot grid. The highest average number of trees and shrubs, as well as the Shannon-Wiener index of species diversity, were observed in sample plots located in the Pre-Alpine Ecological Region (H’ = 0.85), while the lowest values were found in the Alpine Ecological Region (H’ = 0.58). The total growing stock of trees and shrubs in Slovenia is 330.7 m3/ha ± 2.1%, with the growing stock of small trees and shrubs (less than 10 cm DBH for trees and shrubs) estimated at 9.7 m3/ha ± 5.9%. Common beech (Fagus sylvatica) (31.9%) and Norway spruce (Picea abies) (28.2%) dominate the growing stock of tree and shrub species, while common hazel (Corylus avellana) (85.0%) represents the highest proportion of shrub species. Ten different non-native tree species were identified across 138 NFI plots, with the highest distributions in the Sub-Mediterranean and Pre-Pannonian Ecological Regions. Black locust (Robinia pseudoacacia) dominates the growing stock of non-native tree species. Among small trees (those with a DBH of less than 10 cm), common beech represents 32.4%, with Norway spruce and manna ash (Fraxinus ornus) each contributing more than 10.0%. The growing stock of small shrub species (shrubs with a DBH of less than 10 cm) is dominated by common hazel (Corylus avellana) with 78.3%, while more than 2% is also represented by cornel (Cornus mas), old man’s beard (Clematis vitalba) and elderberry (Sambucus nigra). The results show that the combination of a panel system, a large number of sample plots (3027) and an improved coding system enabled the first comprehensive and objective assessment of tree and shrub species diversity, as well as the presence of non-native species in Slovenian forests.

Molecular identification of the ubiquitous green algae Ulva reveals high biodiversity, crypticity, and invasive species in the Atlantic-Baltic Sea region

Correct species identification is fundamental for assessment and understanding of biodiversity. Erroneous species identification may impede conservation management and may delay detection of invasive species. The ubiquitous green algal genus Ulva is known for its wide environmental tolerance, plastic morphology, occurrence of cryptic species and ambiguous species concepts that hinder clear identification. We used molecular monitoring to assess species diversity and distribution of Ulva along the full Atlantic-Baltic Sea salinity gradient (> 10,000 km). Ulva specimens were collected from Denmark, Finland, Germany, Norway, and Sweden. DNA barcoding analysis of the tufA gene revealed 20 genetic entities in total, of which 11 could be identified to species level (U. californica, U. flexuosa, U. torta, U. linza, U. prolifera, U. fenestrata, U. australis, U. intestinalis, U. compressa, U. gigantea, U. lacinulata). Nine entities (Ulva sp. 1–9; [Ulva capillata]) yielded novel sequence reads that belonged to either unidentified species, species complexes, or singletons. At least 3 of the discovered species (U. australis, U. californica, U. gigantea) are considered non-native and potentially invasive. Furthermore, considerable differences between the observed and the historically estimated species distributions were found. The highest diversity was recorded in the Atlantic and Skagerrak region whereas only two entities of taxonomically accepted species where found north-east the Blekinge coast. Our study shows that the species diversity of Ulva in the study area is diverging from previous reports, and that molecular methods are imperative for species identification in this morphologically plastic genus. Furthermore, the presence of non-native species indicates a necessity for further fine-scale monitoring in specific areas to e.g. mitigate formation of green tides.

The Ichthyofauna of the Bednja River, Ichthyological ‘Hot Spot’ in the Danube Basin—Exceptional Diversity under Strong Threats

The Bednja River is the longest river flowing with its full course exclusively through Croatia and one of the largest right tributaries of the Drava River, which belongs to the Danube River basin. Due to the variety of habitats present within the course of the Bednja River, as well as older literature reports, it can be expected that this river harbors a high number of freshwater fish species and would likely benefit from conservation and preservation efforts. We compiled and analyzed the existing literature data on the Bednja River fish communities and performed field investigations at various localities on this river in order to describe the current structure of its freshwater fish fauna and monitor changes induced by human activities. Our results corroborate the presence of a rich and diverse fish community. Moreover, with 36 native species, the Bednja River harbors one of the richest fish communities in Croatia as well as in the Danube basin. Unfortunately, modifications of the native fish community were evident in the form of local extinctions, reductions in the population abundance of several native species and the presence of non-native species. Habitat degradation and fragmentation were identified as the most serious threats provoking negative effects on the native fish populations, followed by predatory and competitive effects of invasive species.

Understanding the taxonomic homogenization of road-influenced plant assemblages in the Qionglai mountain range: A functional and phylogenetic perspective.

As an increasingly prevalent form of human activity, roads drive the taxonomic homogenization of mountain plant assemblages, threatening global biodiversity. However, little is known about how mountain roads impact functional and phylogenetic beta diversity and how these effects are related to taxonomic homogenization. To understand the mechanism of taxonomic homogenization triggered by mountain roads, we used species absence/presence data from 76 plots (2 m*50 m) and values for 12 traits measured on 978 species from the interior and roadside communities in the Qionglai mountain range, one of the temperate regions with the highest plant species richness in the world. We used a structural equation modeling approach (SEM) to consider several surrogates of road disturbance (changes in soil physicochemical properties and the presence or absence of roads) and the causal relationship between three facets of beta diversity (taxonomic beta diversity, TBD; functional beta diversity, FBD and phylogenetic beta diversity, PBD). The results suggest that TBD, FBD and PBD respond inconsistently to mountain roads, despite strong positive correlations between the three facets of plant beta diversity in the study area. Compared with the interior community, the βtotal.tax and βtotal.func of the roadside community decreased by 2.54% and 2.22%, respectively, which were related to the reduction of species and trait richness differences and replacements; however, we did not find the same results when assessing the changes in βtotal.phy, which represents tip-weighted PBD (twPBD). Furthermore, the largest effect of roads on beta diversity was reflected in basal-weighted PBD (bwPBD), which decreased by 9.97%, indicating that those species with fewer extant relatives and longer evolutionary histories are more sensitive to mountain roads. Therefore, it is necessary to take targeted protection measures for ancient species in roadside communities. In addition, we believe that it is still necessary to take measures to prevent the further dispersal of nonnative species, although the presence of non-native species in roadside plots has led to small changes in three facets of beta diversity. There were causal relationships between the three facets of beta diversity, but their intensity and sign different in the SEM of different components of beta diversity (i.e., richness difference and replacement). Our findings suggest that the homogenization of community species composition at the landscape scale arises by a combination of adaptive responses of the functional traits of organisms to environmental consistency (e.g., reduced the differences in soil variables) caused by roads and resorting or reassembly of community clades composition due to environmental filtering. These results contribute to our comprehensive understanding of the impact of mountain roads on plant diversity, which highlights the complex relationship between human pressure and biodiversity loss.

Assessing cumulative impacts of human-induced pressures on reef and sandbank habitats and associated biotopes in the northeastern Baltic Sea.

Marine ecosystems are impacted by multiple individual and combined anthropogenic pressures. We used meta-analysis and data-driven PlanWise4Blue decision support tool to predict individual and combined impacts of wind park development, nutrient loading, and invasive species on vulnerable reef and sandbank habitats and associated species-specific biotopes in the northeastern Baltic Sea. Many impacts were not statistically significant due to large between-study variance in effect sizes. Wind park development is predicted to have less impact than nutrient loading and invasive species. Predicted impacts varied greatly among larger-scale habitats versus smaller-scale biotopes with impacts being generally stronger at small scale. Excessive nutrient loading damages algae-based biotopes, the presence of nonnative species has substantial negative impacts on larger-scale reef and sandbank habitats. The results showed that a 25 % reduction of nutrient loading improves all examined benthic habitats, whereas nonnative species, which cannot be removed from ecosystems, pose a significant threat to these habitats.

When and how much a non-native tree species changes the temporal patterns and biomass of litterfall input in subtropical streams

Context In headwater streams, allochthonous litterfall input is an essential process to maintain the ecosystem functioning. The presence of non-native species in the riparian vegetation, with phenological characteristics distinct from those of most native tree species, can alter this process. Aims We evaluated the effect of the phenology of a non-native species (Hovenia dulcis) on the temporal patterns and biomass of litterfall input into streams by comparing one stream with (Hovenia stream) and another without (Native stream) H. dulcis in their riparian vegetation. Methods We quantified the litterfall input from native tree species and H. dulcis for 1 year by using buckets suspended above the streambeds. Key results The temporal pattern of litterfall input changed between streams, with quantitative differences between them during autumn and winter. In the Native stream, litterfall input was slightly higher in spring (∼79 g m−2 month−1), followed by winter (∼68 g m−2 month−1) and autumn (∼54 g m−2 month−1), whereas in the Hovenia stream, it was concentrated in autumn (∼126 g m−2 month−1). Conclusions and implications Our results indicated that the presence of H. dulcis in the riparian vegetation, when in high density, changes the temporal pattern and biomass of litterfall input into subtropical streams.

Plant Community Structure within a Reclamation Field Trial and Forested Reference Sites in a Post-Mine Environment

Early successional plant community assemblage within a reclamation field trial at the Detour Lake Mine in northeastern Ontario is assessed, and compared with reference forested and historically reclaimed sites. The reclamation field trial examines eight amendment treatment combinations that include treatments with a winter kill cover crop of oats, fertilizer, biosolids, peat, and combinations thereof. The objectives of this study are to: (1) Investigate how soil amendments influence plant functional group establishment and growth in mine overburden; and (2) Explore the amendment properties that best support the establishment and growth of a plant community that resembles the baseline reference sites. Currently, the presence of non-native species and a dominant woody plant community explains the largest proportion of variance between the forested upland and lowland reference sites and all reclaimed sites. Similar to non-native species, graminoids were absent from the upland forested reference sites. The difference in the graminoid community explains much of the variance between the forested reference sites and all reclaimed sites. The cumulative additions of fertilizer and peat increased alpha diversity of non-native and graminoid plants within the amendment treatments, which had greater alpha diversity of these plant functional groups than the forested reference sites. Within the amendment treatments, non-native and graminoid alpha diversity was initially greater in the nutrient treatments, but by 2019 there was no significant difference in non-native or graminoid alpha diversity between amendment treatments. The results indicate that applications of nutrients through fertilizer or biosolids may increase graminoid alpha diversity and abundance within reclamation units in year 1. The results also confirm that the vascular plant community composition present within the historically reclaimed sites and amendment treatments does not resemble the forested reference sites. The plant community present within the amendment treatment sites is best described as early successional, with the presence of non-native herbaceous legumes dominating the historically reclaimed sites. Despite this, the results indicate that fertilizer and biosolids-based treatments have developed a vascular plant community, excluding woody species that is more similar to the forested reference sites than the peat-based treatments. Further research and long-term monitoring are needed to determine which amendment treatment will best support a plant community that resembles the forested reference sites. In addition, future studies of this nature might consider including wildfire affected and post-harvested forest stands as additional reference sites, to better capture possible plant community trajectories of a severely disturbed environment.

Status of Endemic Freshwater Fish Fauna Inhabiting Major Lakes of Turkey under the Threats of Climate Change and Anthropogenic Disturbances: A Review

Due to its peculiar geographical position and its environmental heterogeneity, Turkey represents an important biodiversity hotspot for freshwater fish fauna. Unfortunately, native fish communities of Turkey, mainly from lentic ecosystems, have been massively altered in the past decades. Furthermore, these species, especially the endemic species, are now threatened by several human activities in addition to the global issue of climatic changes. The aim of this paper is to provide an updated review on the current status of endemic fish species from main lakes of Turkey including major threats affecting fish assemblages. By gathering data from the literature and authors’ personal observations, 62 endemic fish species were reported to occur in the considered 37 Turkish Lakes. The presence of non-native species, agriculture activities, climatic drought, and decreasing water level were found to be the threats that most affect the fish communities of the considered Turkish Lakes.

Do Weeds Hinder the Establishment of Native Plants on a Reclaimed North American Boreal Mine Site?

The majority of plant diversity in the boreal forest of northern Alberta, Canada is comprised of native understory plant species that are continuously facing competition from other species, including both undesirable native and weedy species. In oil sands mine reclamation, cover soils rich in organic matter are used to cap overburden materials. The aim of this study is to understand the role of weeds on different reclamation cover soils (forest floor-mineral mix and peat-mineral mix) and determine if they hinder the establishment of the native plant community. This study was conducted four growing seasons after site establishment in June 2019. At that time, both soil types had approximately 45% total cover, had 21 species per plot, and were composed of mainly native vegetation. Competition from non-native forbs (11% average cover, mainly Sonchus arvensis and Melilotus alba) did not seem to impact the development of the native vegetation community on either soil type given the high cover and richness of native forbs. However, native graminoids (predominantly Calamagrostis canadensis) were associated with reduced native forb cover and richness at graminoid cover greater than 17%. Overall, non-native forbs appeared to have little impact on the native forb community on either soil type while native graminoids had a negative influence. We suggest that the classification of what is considered an undesirable weedy species should be evaluated in the context of ecosystem management goals rather than simply the presence of non-native species.

Current status and future prospects of Lhalu wetland on the Tibetan Plateau

Lhalu wetland, located in the northwest of Lhasa city, Tibet, is the highest and largest urban natural wetland in the world. Due to its specific climate and the unique plateau ecosystem, it is a hotspot of endemic and endangered species. Lhalu wetland is an important wetland for Lhasa city for its biodiversity and for enhancing human well-being. However, due to global warming, over-exploitation and the presence of non-native species, it has suffered serious ecosystem damage and biodiversity loss. To protect biodiversity and the functioning of the ecosystem, new measures are needed, and current measures should be better enforced. This study is important for biodiversity conservation and the management of Lhalu wetland in the Qinghai- Tibet plateau.

Current status and future prospects of Lhalu wetland on the Tibetan Plateau

Lhalu wetland, located in the northwest of Lhasa city, Tibet, is the highest and largest urban natural wetland in the world. Due to its specific climate and the unique plateau ecosystem, it is a hotspot of endemic and endangered species. Lhalu wetland is an important wetland for Lhasa city for its biodiversity and for enhancing human well-being. However, due to global warming, over-exploitation and the presence of non-native species, it has suffered serious ecosystem damage and biodiversity loss. To protect biodiversity and the functioning of the ecosystem, new measures are needed, and current measures should be better enforced. This study is important for biodiversity conservation and the management of Lhalu wetland in the Qinghai- Tibet plateau.

Spatial distribution of native fish species in tributaries is altered by the dispersal of non-native species from reservoirs

Reservoirs are known to alter temperature and flow regimes, shift nutrient cycles, reduce downstream species diversity and enable a predominantly upstream spread of non-native species. However, information about the seasonal dynamics of the spread of non-natives from a reservoir to its tributaries and the further consequences regarding the spatial distribution of native species is rare. We observed the occurrence of fish in the Vltava River and its tributaries (Elbe catchment area, central Europe) upstream of the Lipno Reservoir for five consecutive years. We radio-tagged two non-native and four native species. To detect assemblage spatial variability, we sampled sites in the study area by electrofishing twice per year (spring and autumn). We expected seasonal trends in non-native species appearance in upstream reservoir tributaries and, conversely, low motivation of native fishes to descend to the reservoir. By analysing nearly 3000 individuals of 21 species from the longitudinal profile of the study area, we observed an effect of reservoir distance on the native species ratio in the upper Vltava catchment area, i.e., an increase in distance increased the native species proportion, and the opposite was observed for non-native species. Analyses of 3798 tracking positions of 193 tagged individuals showed massive spring dispersal of non-native species from the reservoir to the main tributary, the Vltava River, and their return to the reservoir for wintering. Their upstream movement positively correlated with an increase in flow rate. Native Salmo trutta showed a specific shift from the Vltava River to smaller streams during the summer, when the presence of non-native species in the Vltava River was most significant. These findings indicate that non-native species repeatedly spread from the reservoir to the upstream river stretch and its tributaries and potentially compete with native species for resources.

Climate gradients, and patterns of biodiversity and biotic homogenization in urban residential yards.

Residential yards constitute a substantive biodiverse greenspace within urban areas. This biodiversity results from a combination of native and non-native species and can contribute to biotic homogenization. Geographical climatic patterns affect the distribution of native species and may differently affect non-native species. In this study, we examined biodiversity and biotic homogenization patterns of yard-dwelling land snails across 12 towns in Oklahoma and Kansas (USA). The 3 x 4 array of towns incorporated a N-S winter temperature gradient (mean low January temperature range = -8.4 to 0.1°C) and an E-W annual rainfall gradient (annual rainfall range = 113.8 to 61.3 cm/yr). Ten yards per town were surveyed. We hypothesized that mild winter temperatures and greater annual rainfall would be associated with greater snail abundance and richness, and that the presence of non-native species would contribute to biotic homogenization. Non-native snails were present and often abundant in all towns. Snail communities varied with both rainfall and cold temperature. Contrary to our prediction, snail abundance was inversely related to annual rainfall-likely because drier conditions resulted in greater yard watering that both augmented rainfall and maintained moist conditions. Sørensen similarity between towns for the entire land snail community and for only non-native species both showed distance-decay patterns, with snail composition becoming less similar with increasing distance-patterns resulting from species turnover. The biotic homogenization index also showed a distance-related pattern, such that closer towns were more likely to have biotic homogenization whereas more distant towns tended to have biotic differentiation. These results support the concept that biotic homogenization is more likely regionally and that climatic changes over distance result in species turnover and can reduce spatially broad biotic homogenization.

Contrasting continental patterns and drivers of taxonomic and functional turnover among fish assemblages across Brazilian reservoirs

In this paper, we investigated composition and trait turnover among fish assemblages in reservoirs distributed across major Brazilian basins, in order to contrast taxonomic and functional turnover and to investigate their respective drivers. We investigated the hypothesis that reservoir assemblages present, on a continental scale, divergent species compositions but with a similar set of traits. Species lists and functional traits were compiled from 79 reservoirs located in the Amazon, Sao Francisco, Parana and Atlantic basins. We observed considerable variation in species and trait composition among reservoirs, with higher intra-basin similarity. Taxonomic turnover ranged between 0 and 1 (0.44 ± 0.22 SD), and functional turnover between 0 and 0.91 (0.37 ± 0.19); functional turnover correlated positively with taxonomic turnover, but showed lower values. Observed functional turnover values did not differ from null expectations, indicating lack of functional convergence. We detected significant effects of basin, longitude, latitude and elevation on turnover values, and the presence of non-native species was associated with either homogenization or differentiation patterns. Our results indicated that fish composition is heterogeneous among impoundments, providing little support to the hypothesis that reservoir assemblages are homogenized on a continental scale. Species and trait composition probably respond to multiple spatial, environmental and biogeographic factors.

INVASÃO BIOLÓGICA NO PARQUE NACIONAL SERRA DE ITABAIANA, SERGIPE, BRASIL

O Parque Nacional Serra de Itabaiana é uma Unidade de Conservação que foi criada em 15 de junho de 2005. Apesar de sua elevada riqueza de espécies, está ameaçado devido a uma série de fatores, dentre eles a presença de espécies não nativas. Diante dessa realidade, o presente trabalho buscou responder as seguintes perguntas: (i) quantas são e quem são as espécies naturalizadas e exóticas invasoras que ocorrem no Parque Nacional Serra de Itabaiana? (ii) como essas espécies estão distribuídas no local? As espécies não nativas (naturalizadas e exóticas invasoras) foram coletadas, herborizadas e depositadas no herbário ASE. Com os dados de georreferenciamento foi confeccionado um mapa de manchas de invasão utilizando-se o programa Google Fusion Tables. Ao todo foram amostradas 49 espécies distribuídas em 45 gêneros e 19 famílias. Dentre elas, 16 espécies foram consideradas naturalizadas e 33 exóticas invasoras. Também se observou que os sítios com maiores manchas de espécies estão associados especialmente a ambientes antropizados. Os resultados do presente estudo são alarmantes devido à grande quantidade de espécies não nativas e especialmente pela presença de táxons que causam distintos impactos ambientais.

Occurrence of non-native species and their potential impact on plant communities in protected areas in the Brazilian Amazon region

Abstract. Introduction: There is a large information gap on the occurrence of non-native species and their impacts on native biodiversity in the Amazon region in Brazil. Objective: The objective of this study was to characterize the floristic composition of a protected area in Manaus, Amazonas, and assess the potential impact of non-native invasive species. Methods: A floristic survey was carried out in 30 plots measuring 20 x 20 m with 1 x 1 m subplots. The estimated parameters were density, frequency, dominance, Importance Value Index (IVI), and Environmental Impact of Non-Native Species (IIAE). Results: In total, 8 out of 264 species registered in the tree-shrub layer were not native. A total of 61 species were identified in the herbaceous layer, five of which were non-native. The impact is estimated based on the highest abundance of species of non-native species. Conclusions: The presence of non-native species in the study area is an indication of a potential impact on biodiversity and ecosystem functions.

Greenhouses – urban biodiversity hotspot of alien Oribatida (Acari) species

Palm houses and other greenhouses, due to maintaining constant temperature and humidity, allow the cultivation in Europe of plants from different parts of the world, even from tropical regions. However, sometimes they are also a habitat for alien species of spiders, mites, insect, etc. These animals have been introduced accidentally with contaminated plants, seeds, seedlings, soil and thanks to stable conditions maintained in greenhouses, they may colonize these places. Example of arthropods, of which even tropical species occur in several greenhouses, are oribatid mites – minute saprophagous arachnids that mostly inhabit soil. In Europe they are represented by about 2,000 species, while worldwide – over 10,000 taxa were described. The aim of this research was to investigate the selected greenhouses for the biodiversity of oribatid mites and the presence of non-native species. In total, 49 taxa were recorded, including 23 alien species (for example, a Neotropical taxon Galumna hamifer, or Oriental Suctobelbella parallelodentata). These results confirm that greenhouses are the places of occurrence of many alien oribatid species. The obtained results may be used in future research on the biology of poorly known tropical mites.

Fish fauna in forested and rural streams from an ecoregion of high endemism, lower Iguaçu River basin, Brazil

Abstract The fish fauna of eight streams with different land uses of their watersheds (forested and rural areas) in the lower Iguaçu River basin was inventoried, in order to evaluate the composition and species richness. The fishes were sampled quarterly from May 2015 to February 2016, using the electrofishing technique. In total, 4,239 individuals were captured, belonging to six orders, 11 families and 26 species. The orders Siluriformes and Characiformes, and the families Characidae and Trichomycteridae were the most specious. Of the total species sampled, 65% were endemic to the Iguaçu River basin, four are not described and four are non-native. As expected to the Iguaçu River basin, the inventoried fauna revealed low richness and high endemism, however was highly nested within the species composition reported for main channel of Iguaçu River and their larger tributaries. The species recorded here corresponded to a subset of 24.5% of the 106 species documented for the basin. The streams presented different faunas, with only two species (Astyanax bifasciatus and Trichomycterus stawiarski) common to both forested and rural streams. In addition, higher species richness was recorded in streams inserted in conservation units. The presence of non-native species was more frequent in rural streams. These results highlight the importance of the preservation of forested areas in the watersheds of lower Iguaçu, which presents a peculiar fish fauna, along with several threats to biodiversity such as habitat loss by intensive agriculture use.

Growth and competition among understory plants varies with reclamation soil and fertilization

IntroductionFollowing oil sands mining in Alberta, Canada, the main land management goal is to establish a functioning boreal forest ecosystem, including the understory plant community. One of the challenges with restoring the understory is the presence of non-native species that compete with desirable native species for resources. In a greenhouse experiment, we studied the growth of two native understory species (Galium boreale and Vicia americana) and a non-native invasive species (Matricaria perforata) grown with either intra- or interspecific neighbors across three common land reclamation soils and a nitrogen fertilizer treatment.ResultsWhen grown by itself, V. americana aboveground biomass did not differ among soil or fertilizer treatments, likely due to its ability to fix nitrogen. Growth of M. perforata was directly related to soil nitrogen, and it had the greatest increase in biomass with fertilization. Growth and biomass of G. boreale was less than the other species, and it had the highest mortality in the nitrogen-poor soil. When grown together, the proportional biomass of M. perforata and V. americana varied with soil treatment such that M. perforata was dominant in the high-nitrogen forest floor-mineral mix treatment while V. americana was dominant in the low-nitrogen peat-mineral mix.ConclusionsOperationally, care should be taken when applying fertilizer to reclamation areas, as it may have an unwanted positive effect on growth for undesirable non-native plants at the expense of native species. In terms of seed mixtures, V. americana may be a good option for low inorganic nitrogen resource soils and G. boreale for high nitrogen resource soils.

The presence of non-native species is not associated with native fish sensitivity to water pollution in greatly hydrologically altered rivers

There is a risk of ‘ecological surprises’ if multiple potentially interacting stressors are managed individually, which is a question attracting significant current interest. Habitat degradation and species introductions are major threats to global biodiversity, and riverine fish are among the most threatened taxa in the world. Our interest was whether the presence of non-native species can affect native fish sensitivity to water quality deterioration in a large region in northeastern Spain (99,700km2, 15 catchments, 530 sites). We used a ‘base model’ with geographical and hydro-morphological variables, which are the major shaping factors in rivers. We tested whether water pollution, non-native species, or their interaction provided an improved understanding of patterns of distributions and health measurements of the twelve most common native species. There was little evidence that variation in native species abundance, where they occurred, the presence of diseases and changes in mean fish length or body condition was affected by water deterioration, the presence of non-native species, or their interaction. The disease rate and occurrence of native species might be affected, to a minor degree, by water quality changes and the presence of non-native species. Environmental conditions between sites with and without non-native fish differed in the condition of riparian areas and in water quality. Based on presence-absence data and changes in abundances through weighted average equations we also derived potential safe levels of salinization, nutrient pollution, and pH for the native fish. Overall, additive effects of stressors prevail over interactions, and the restoration of natural hydro-morphology in rivers is likely to be the most effective management approach to improving the prospects for the native fish fauna.