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Surveying multiple invasive pest species at the same time can help reduce the cost of detecting new pest invasions. In this paper, we describe a new method for mapping the relative likelihood of pest invasion via plant propagation material in a geographic setting. The method simulates the invasion of a range of pest species, including arrival in an uninvaded area, spread, and survival in a novel landscape, using information on the spatial and temporal distribution of the suitable host crop species and tentative knowledge of the spread and survival capacities of the target pests. The methodology is applied to a gridded map in which each map cell represents a site in a landscape. The method uses stochastic simulations to depict plausible realizations of the invasion outcomes and estimate the distribution of pest invasion likelihood for each cell in the area of concern. The method then prioritizes the cells based on the stochastic invasion outcomes using a pairwise stochastic dominance rule and a hypervolume indicator. We demonstrate the approach by assessing the relative likelihood of pest invasion for strawberry production in Finland. Our method helps to differentiate sites in a landscape using both the estimates of pest invasion risk and their uncertainty. It can be applied to prioritize sites for plant health surveys and allocate survey resources among large geographic regions. The approach is generalizable and can be used in situations where knowledge of the harmful pest species is poor or nonexistent. [ABSTRACT FROM AUTHOR]

Aims: Biological invasions are recognized to put native species in risk of extinction. In this study, I tested whether the invasion of Artocarpus heterophyllus Lam. (Moraceae; jackfruit) in the Neotropics was explained by its biotic stability, an intrinsic force, or by human occupation, an extrinsic force. Methods: I used an ensemble framework combining 12 ecological niche models (ENMs) and 4 atmosphere-ocean general circulation models. ENMs were constructed for the pre-industrial time period in the Indo-Malaya biogeographic region, the native habitat of A. heterophyllus, and were then projected to past (last glacial maximum, 21 000 years ago and mid-Holocene, 6000 years ago) and future (end of century, 2080) periods. The ENMs were used to establish the biotic stability of A. heterophyllus in areas where it was predicted to be present concomitantly within these four time periods. This biotic stability was projected onto the Neotropics, and then I used a null model and logistic regression to test what the main driver of A. heterophyllus invasion. Important Findings: In general, the presence of A. heterophyllus in the Neotropics was not explained by biotic stability, tested by the null model. However, human occupation explained much of its presence in the invaded habitat, once all standardized coefficients related to this driver was significant positive in the logistic regression. Based on these results, humans sustained the presence of A. heterophyllus in the Neotropics, probably because of the additive influences of propagule pressure and habitat disturbance. Thus, the recommendation is that the cultivation of A. heterophyllus in the Neotropics must be regulated and supervised, primarily near reserve areas. [ABSTRACT FROM AUTHOR]

Biological invasions are a major threat to biological diversity, agriculture, and human health. To predict and prevent new invasions, it is crucial to develop a better understanding of the drivers of the invasion process. The analysis of 4,533 border interception events revealed that at least 51 different alien ant species were intercepted at US ports over a period of 70 years (1914-1984), and 45 alien species were intercepted entering New Zealand over a period of 68 years (1955-2013). Most of the interceptions did not originate from species' native ranges but instead came from invaded areas. In the United States, 75.7% of the interceptions came from a country where the intercepted ant species had been previously introduced. In New Zealand, this value was even higher, at 87.8%. There was an overrepresentation of interceptions from nearby locations (Latin America for species intercepted in the United States and Oceania for species intercepted in New Zealand). The probability of a species' successful establishment in both the United States and New Zealand was positively related to the number of interceptions of the species in these countries. Moreover, species that have spread to more continents are also more likely to be intercepted and to make secondary introductions. This creates a positive feedback loop between the introduction and establishment stages of the invasion process, in which initial establishments promote secondary introductions. Overall, these results reveal that secondary introductions act as a critical driver of increasing global rates of invasions. [ABSTRACT FROM AUTHOR]

Abstract: The theory of island biogeography predicts that area and age explain species richness patterns (or alpha diversity) in insular habitats. Using a unique natural phenomenon, pumice rafting, we measured the influence of area, age, and oceanic climate on patterns of species richness. Pumice rafts are formed simultaneously when submarine volcanoes erupt, the pumice clasts breakup irregularly, forming irregularly shaped pumice stones which while floating through the ocean are colonized by marine biota. We analyze two eruption events and more than 5,000 pumice clasts collected from 29 sites and three climatic zones. Overall, the older and larger pumice clasts held more species. Pumice clasts arriving in tropical and subtropical climates showed this same trend, where in temperate locations species richness (alpha diversity) increased with area but decreased with age. Beta diversity analysis of the communities forming on pumice clasts that arrived in different climatic zones showed that tropical and subtropical clasts transported similar communities, while species composition on temperate clasts differed significantly from both tropical and subtropical arrivals. Using these thousands of insular habitats, we find strong evidence that area and age but also climatic conditions predict the fundamental dynamics of species richness colonizing pumice clasts. [ABSTRACT FROM AUTHOR]

Abstract: In response to the introduction and spread of the chestnut gall wasp Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae) in metropolitan France, including Corsica, the exotic parasitoid Torymus sinensis Kamijo (Hymenoptera: Torymidae) was deliberately introduced in more than 50 locations covering most of the areas of chestnut production. To test the impact of propagule pressure (i.e., the number and size of introductions) on establishment success and post‐release dynamics, the introductions were done according to three experimental modalities: (1) a single introduction of 100 females, (2) two sequential introductions of 50 females, or (3) a single introduction of 1 000 females. Post‐release surveys demonstrated a very high local establishment of T. sinensis, regardless of the introduction modality. Post‐introduction dynamics were found to follow a two‐phase process. First, early dynamics were characterized by an exponential growth of T. sinensis populations without a significant decrease in D. kuriphilus populations. Later, middle‐term dynamics indicated a global decrease in both D. kuriphilus and T. sinensis populations. Quite surprisingly, propagule pressure had a limited effect on post‐introduction dynamics, with a lasting demographic advantage for the largest introductions, but no influence of the number of introductions. Finally, site connectivity had a positive effect on T. sinensis population size, suggesting successful colonization and establishment at a wide spatial scale beyond the introduction sites. In addition, we observed that some T. sinensis exhibited a very short developmental time compared to the majority of the emerged individuals, which may be interpreted as a diversified bet hedging strategy against environmental stochasticity. These findings confirm the strong potential of T. sinensis for successful establishment and sustainable control of the chestnut gall wasp in Europe. [ABSTRACT FROM AUTHOR]

Abstract: Aim: We develop a novel modelling framework for analysing the spatio‐temporal spread of biological invasions. The framework integrates different invasion drivers and disentangles their roles in determining observed invasion patterns by fitting models to historical distribution data. As a case study application, we analyse the spread of common ragweed (Ambrosia artemisiifolia). Location: Central Europe. Methods: A lattice system represents actual landscapes with environmental heterogeneity. Modelling covers the spatio‐temporal invasion sequence in this grid and integrates the effects of environmental conditions on local invasion suitability, the role of invaded cells and spatially implicit “background” introductions as propagule sources, within‐cell invasion level bulk‐up and multiple dispersal means. A modular framework design facilitates flexible numerical representation of the modelled invasion processes and customization of the model complexity. We used the framework to build and contrast increasingly complex models, and fitted them using a Bayesian inference approach with parameters estimated by Markov chain Monte Carlo (MCMC). Results: All modelled invasion drivers codetermined the A. artemisiifolia invasion pattern. Inferences about individual drivers depended on which processes were modelled concurrently, and hence changed both quantitatively and qualitatively between models. Among others, the roles of environmental variables were assessed substantially differently subject to whether models included explicit source‐recipient cell relationships, spatio‐temporal variability in source cell strength and human‐mediated dispersal means. The largest fit improvements were found by integrating filtering effects of the environment and spatio‐temporal availability of propagule sources. Main conclusions: Our modelling framework provides a straightforward means to build integrated invasion models and address hypotheses about the roles and mutual relationships of different putative invasion drivers. Its statistical nature and generic design make it suitable for studying many observed invasions. For efficient invasion modelling, it is important to represent changes in spatio‐temporal propagule supply by explicitly tracking the species’ colonization sequence and establishment of new populations. [ABSTRACT FROM AUTHOR]

Abstract: Aim: Dispersal range is a key factor for understanding species' persistence in dynamic landscapes. However, dispersal, especially over long distances, is inherently difficult to study. Making use of a unique system of anthropogenically disturbed, geographically isolated mires, we assessed dispersal ranges for a group of plants restricted to wet calcareous conditions via empirical studies of colonization patterns. We hypothesized that more species would have colonized the less isolated mires and that colonization frequencies would be related to traits influencing propagule pressure. Location: Sweden. Taxon: Calcicolous vascular plants and bryophytes. Methods: The study system consisted of 52 acidic mires that had acquired a high pH through active liming by the Swedish government during the past two decades. These conditions killed off mat‐forming peat mosses, rendering the mires open to colonization by other species. In each mire, we recorded the presence of rich fen plant species typically found in high pH wet soils throughout the country. We used citizen science‐collected records of occurrences of obligate‐rich fen species surrounding each mire to examine the likely dispersal distances that were involved in creating the colonization patterns. Results: A lower proportion of vascular plants than bryophytes from their respective species pools colonized the limed mires (27% vs. 67%, p = .001). The number of colonized rich fen species per site was 0–6 for vascular plants and 10–31 for bryophytes, and was positively related to potential diaspore sources >20 km from the mires (p = .026 and p = .012, respectively). The proportion of colonized mires was positively related to the species' regional frequency, but not with their diaspores' terminal velocity. Main conclusions: Many bryophyte species can effectively disperse over long distances (tens of kilometres) and variation among species in total diaspore production seems to be an important regulator of colonization across landscapes, for both vascular plants and bryophytes, in communities that are open to colonization. [ABSTRACT FROM AUTHOR]

Abstract: Invasion success is regulated by multiple factors. While the roles of disturbance and propagule pressure in regulating the establishment of non‐native species are widely acknowledged, that of propagule morphology (a proxy for quality) is poorly known. By means of a multi‐factorial field experiment, we tested how the number (5 vs. 10) and quality (intact, without fronds or without rhizoids) of fragments of the clonal invasive seaweed, Caulerpa cylindracea, influenced its ability to establish in patches of the native seagrass, Posidonia oceanica, exposed to different intensities of disturbance (0, 50, or 100% reduction in canopy cover). We hypothesized that the ability of fragments to establish would be greater for intact fragments (high quality) and reduced more by frond removal (low quality) than rhizoid removal (intermediate quality). At low propagule pressure or quality, fragment establishment was predicted to increase with increasing disturbance, whereas, at high propagule pressure or quality, it was predicted to be high regardless of disturbance intensity. Disturbance intensity, fragment number and quality had independent effects on C. cylindracea establishment success. Disturbance always facilitated fragment establishment. However, fragments retaining fronds, either intact or deprived of rhizoids, had higher establishment success than fragments deprived of fronds. Increasing propagule number had weak effects on the cover of C. cylindracea. Our results demonstrate that propagule traits enabling the acquisition of resources made available by disturbance can be more important than propagule number in determining the establishment and spread of clonal non‐native plants. More generally, our study suggests that propagule quality is a key, yet underexplored, determinant of invasion success. [ABSTRACT FROM AUTHOR]

Ambrosia artemisiifolia is an annual weed from North America that nowadays is invasive in many countries worldwide. In Austria, numerous populations of A. artemisiifolia are located along the Danube River, especially along the 'New Danube' (Vienna). This area is characterised by ruderal and riparian sites, which are regularly flooded. To better understand the spread of A. artemisiifolia and its colonising behaviour along the Danube River, we analysed genetic structure and diversity based on 23 populations linearly arranged along the Viennese Danube riverbed and upstream, utilising the Amplified Fragment Length Polymorphism (AFLP) fingerprint method. We generated 284 polymorphic AFLP markers across 446 A. artemisiifolia plants. The genetic diversity within populations was higher (HW = 0.091) than among populations (HB = 0.007). This result indicates A. artemisiifolia introductions from similar mixtures of sources or spread from a single already mixed introduction. Within our local setting, we were unable to identify neither source or sink populations nor an obvious linear genetic structuring. Genetic among-population differentiation was low to moderate (AMOVA-derived FST = 0.124). Lack of geographical structuring is indicative of highly dynamic gene flow, which is further supported by the absence of an isolation- by-distance pattern. Multiple introductions and non-directional gene flow are most likely promoted by anthropogenic disturbance and human-mediated dispersal. Our results demonstrate the ability and speed of A. artemisiifolia to settle in newly disturbed areas and the difficulties to predict invasion directions, as downstream river dispersal was negligible. [ABSTRACT FROM AUTHOR]

Abstract: Identifying the factors that determine the success of biological invasions has major consequences for both ecological theory and conservation decision‐making. Reliably inferring these factors depends on adequately accounting for the known effects of propagule pressure on establishment success, but detailed information on the size and number of introduced populations is often lacking. Here, we conduct simulations to explore the effects of incomplete knowledge of propagule pressure on inferences regarding the correlates of establishment success. We compare situations where we have complete information on propagule number and propagule size across species, allowing success to be modelled at the population scale (population‐level analysis), with those where data for propagule size (species‐level analysis) and both propagule size and number (location‐level analysis) are unavailable. We assess the ability to correctly infer the effects of a covariate on establishment success when this covariate exhibits varying degrees of correlation with propagule pressure. We show that when establishment success is modelled at the level of species, rather than populations, this leads to an elevated tendency to incorrectly infer the effects of species‐level traits on establishment success (higher type 1 error and lower power), particularly when traits in question are strongly associated with propagule pressure. These biases are magnified when using proxies for propagule pressure, such as the number of locations where species have been introduced, and are magnified further when these proxies are converted to binary variables. Our results validate the current best practice for the analysis of establishment success in alien species at the population level, when the effects of propagule size and a covariate predicting establishment probability can both be reliably inferred. However, given the growing interest in understanding correlates of biological invasions, they strongly urge caution in interpreting results based on incomplete knowledge of propagule pressure. [ABSTRACT FROM AUTHOR]

Better predictions of the success of species’ introductions require careful evaluation of the relative importance of at least three kinds of factors: species characteristics, characteristics of the site of introduction, and event-level factors such as the numbers of individuals released. (Henceforth, we call this propagule pressure.) The 1644 introductions of 17 Phasianid species released in various US states during the Foreign Game Investigation Program provides a particularly rich source of data to test these ideas. An examination of these records indicates that 13 of these 17 species always failed, despite generally numerous individual releases and large numbers of individuals in each release. Moreover, ten of these species have been successfully introduced elsewhere. Only four of the 17 species were successful in at least one state. Some 20 sets of releases of three of these four species always failed in some states, again given generally numerous individual releases of large numbers of individuals in each release. Simply, the combination of site and species factors explain the lack of successes. This leaves a combination of 18 states where one or more of the four species succeeded. For these, there are significant differences in the numbers of birds introduced from state to state. But only for two species Alectoris chukar and; Tetraogallus himalayensis are there significant differences that show a greater chance of success when more individuals are introduced. These results support the conclusion that the number of individuals released, meaning propagule pressure, is not as important as characteristics of the species and the location to where its introduction occurred. [ABSTRACT FROM AUTHOR]

Abstract: Emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is the most significant invasive forest pest in North America. Laboratory research on this species requires sources of adult and larval insects that are of the same fitness as those present in the wild. Production of adult EAB relies on flushing adults from logs which are subject to cold storage for some period prior to use. The effect of this storage on the number of insects emerging or the fitness of those that emerge has not been investigated. We subjected logs of EAB‐infested white ash, Fraxinus americana L. (Oleaceae), to 7–14 months of cold storage and quantified the number of insects that emerged, the time to emergence, and the body condition of adults as a measure of fitness. Body condition was evaluated using Soxhlet fat extraction and water weight. No published methods for Soxhlet fat extraction were available for this species so we developed extraction protocols. The number of insects emerging decreased with time, but fitness (i.e., fat and water content) did not decrease. Time to emergence did increase but only in the longest storage treatment, whereas a comparison of male vs. female emergence provides evidence for protandry in EAB. Rearing programs for EAB using wood from cold storage should adjust the amount used to produce a given number of insects but the quality of those individuals emerging will not be affected. We suggest that those insects that perished during storage were of lower quality when entering diapause and thus would serve as poor‐quality host in rearing programs for natural enemies of EAB. These data also provide evidence for one pathway of introduction for EAB, suggesting that refrigeration in transit was required for EAB to remain viable and establish its beachhead in North America. [ABSTRACT FROM AUTHOR]

High disturbance frequency, low water availability, and advantageous growth mechanisms of invasive annual compared to native perennial grasses reduce native grass establishment throughout arid rangelands. Modifying seeding dispersal processes, including seeding rate and time, may increase native grass recruitment by influencing safe site occupation. A better understanding of seedling development through life history stages and the ecological processes occurring during these stages may be necessary to comprehend modified dispersal dynamics on plant community assembly. We tested the effects of spring vs. fall annual grass seeding times, adding water, and varying annual and perennial grass propagule pressure on perennial and annual grass recruitment in an eastern Oregon shrub-steppe ecosystem. Across species, survival rates were lowest between germination and emergence stages. However, perennial grass germination rates were highest when perennials were seeded with annual grasses in autumn. Perennial grass recruitment was generally low, especially when annual grass propagule pressure was higher than 150 seeds m −2 . Although, by the second growing season, perennial grasses had the highest density when perennials were seeded with annuals in autumn and water was added. Consequently, modifying native perennial grass dispersal, like priority autumn seeding and increasing propagule pressure, should produce higher perennial grass recruitment across arid lands. [ABSTRACT FROM AUTHOR]

Abstract: Aim: Information about the importance of propagule pressure and habitat invasibility in invasion success of dispersal‐limited species is scarce. We aimed to assess invasiveness of Quercus rubra within stands of 14 tree species, and the effects of distance from propagule source on invasion success, to highlight limiting factors for further application in nature conservation. Location: Siemianice Experimental Forest—a common garden forest experiment with 14 tree species, western Poland. Methods: We investigated aboveground biomass, leaf area index and density of Q. rubra natural regeneration within 53 experimental plots, as well as distance from the seed source. We also analysed light availability changes between 2005 and 2015 on plots of each tree species. We used multiple linear regression and variable importance to quantify the effect of each factor. Results: All factors tested influenced ecological success of Q. rubra. Invasion success decreased with increasing distance from the seed source and decreasing light availability and was higher within stands of pioneer tree species. Leaf area index depended mostly on tree stand species, density depended on distance from the propagule source and biomass depended on both. Light availability explained 7.2%–30.2% of the variance; tree species—from 36.1% to 57.4%; and distance from the propagule source—from 12.4% to 56.7%. Main conclusions: Tree stand species, light availability and distance from the propagule source influence ecological success of invasive Q. rubra, displaying their importance for spread of this species. These factors are controllable in forest/conservation management and may be used to prevent Q. rubra invasion. Planting late‐successional tree species that cast dense shade, maintaining canopy closure and removing fruiting trees from surrounding more invasible stands may prevent Q. rubra invasion. [ABSTRACT FROM AUTHOR]

Abstract: Aim: To evaluate how the establishment risk of freshwater fish species from the aquarium trade will change under a climate change scenario forecast for the year 2050. Location: North America. Methods: In order to estimate changes in the magnitude of risk across geography and across different species in the aquarium pathway, we considered an integrated approach to modelling the probability of establishment, which simultaneously included proxies of propagule pressure, environmental variables, species traits and interactions between environment and traits. We then used the parameters of our model to predict how the risk of establishment will change under a scenario of climate change forecast for the year 2050. Results: Our joint model performed better than submodels, suggesting that combining all components is worthwhile. The most predictive factors were precipitation, maximum temperature tolerance, maximum fish length and minimum temperature. Our joint model forecasted a 40% increase in the average risk of establishment by 2050 in the United States. In contrast to our expectations, the absolute establishment risk associated with this pathway remained very low for the entire suite of species in the aquarium trade in northern regions, such as Quebec, Canada. Instead, Florida, which has one of the highest current risks of establishment, was also forecasted to have the greatest absolute risk increase. Main conclusions: Our methodology for risk assessment allows invasive species management strategies to consider entire suites of species at a time and to forecast establishment risk for each species and location. While the aquarium pathway is likely to become more important for the United States, the Quebec government should prioritize other pathways of introduction in its exotic invasive species strategy. Our approach can be extended to be applied to different sets of species pertaining to the same or different pathways. [ABSTRACT FROM AUTHOR]

Habitat modification and biological invasions are key drivers of global environmental change. However, the extent and impact of exotic plant invasions in modified tropical landscapes remain poorly understood. We examined whether logging drives exotic plant invasions and whether their combined influences alter understory plant community composition in lowland rain forests in Borneo. We tested the relationship between understory communities and local- and landscape-scale logging intensity, using leaf area index (LAI) and above-ground biomass (AGB) data from 192 plots across a logging-intensity gradient from primary to repeatedly logged forests. Overall, we found relatively low levels of exotic plant invasions, despite an intensive logging history. Exotic species were more speciose, had greater cover, and more biomass in sites with more local-scale canopy loss. Surprisingly, though, exotic species invasion was not related to either landscape-scale canopy loss or road configuration. Moreover, logging and invasion did not seem to be acting synergistically on native plant composition, except that seedlings of the canopy-dominant Dipterocarpaceae family were less abundant in areas with higher exotic plant biomass. Current low levels of invasion, and limited association with native understory community change, suggest there is a window of opportunity to manage invasive impacts. We caution about potential lag effects and the possibly severe negative impacts of exotic plant invasions on the long-term quality of tropical forest, particularly where agricultural plantations function as permanent seed sources for recurrent dispersal along logging roads. We therefore urge prioritization of strategic management plans to counter the growing threat of exotic plant invasions in modified tropical landscapes. [ABSTRACT FROM AUTHOR]

Abstract: Aquaculture is the main vector for introduction of non‐native species in Brazil and around the world. Despite the potentially serious and irreversible ecological impacts caused by non‐native species, they continue to be in many cases the preferred option in aquaculture farms, of which the recent plans of aquaculture expansion promoted by the Brazilian Government are an emblematic example. In this study, we present a survey of publicly available information on aquaculture parks to be installed across the Brazilian territory, with emphasis on species status as native or non‐native, and discuss the implications for the conservation of aquatic biodiversity. One hundred and thirty‐nine aquaculture parks (APs), with a total of 1556 sites covering 941.38 hectares, have been called for bids. Among these, 122 APs will contain at least one non‐native species, and 68 APs will be based exclusively on their cultivation. A predictable consequence is the enhancement of propagule pressure in surrounding aquatic ecosystems, increasing the risk of non‐native species establishment or persistence, which will likely intensify the environmental impacts already in course in four major river basins and along the Brazilian coast. These impacts will add up to more direct effects of aquaculture farming – for example elevated input of nutrients and organic matter – and include changes in habitat and water quality, spread of diseases, biotic homogenization, loss of population viability resulting from hybridization and outbreeding depression, and the local extirpation of native species. [ABSTRACT FROM AUTHOR]

Invasive alien species (IAS) constitute a major threat to global biological diversity. In order to control their spread, a detailed understanding of the factors influencing their distribution is essential. Although international trade is regarded as a major force structuring spatial patterns of IAS, the role of other social factors remains unclear. Despite studies highlighting the importance of strong governance in slowing drivers of biodiversity loss such as logging, deforestation, and agricultural intensification, no study has yet analyzed its contribution to the issue of IAS. Using estimates of governance quality and comprehensive spatiotemporal IAS data, we performed multiple linear regressions to investigate the effect of governance quality upon the distribution of species listed under "100 of the worst" IAS in 38 Eurasian countries as defined by DASIE. Our model suggested that for countries with higher GDP, stronger governance was associated with a greater number of the worst IAS; in contrast, for the lowest GDP countries under analysis, stronger governance was associated with fewer of these IAS. We elucidate how the quality of governance within a country has implications for trade, tourism, transport, legislation, and economic development, all of which influence the spread of IAS. While our findings support the common assumption that strengthening governance benefits conservation interventions in countries of smaller economy, we find that this effect is not universal. Stronger governance alone cannot adequately address the problem of IAS, and targeted action is required in relatively high-GDP countries in order to stem the influx of IAS associated with high volumes of trade. [ABSTRACT FROM AUTHOR]

PREMISE OF THE STUDY: Invasions by non-native species are known to be related to present propagule pressure (e.g., the number of non-native seeds arriving in a site each year). However, previous studies have mostly ignored the potential effects of the length of time that a site has experienced propagule pressure. This study is novel in studying past as well as present propagule pressure and in demonstrating the importance of past propagule pressure. METHODS: We tested the importance of past and present propagule pressure in three plant communities in central Texas to quantify relationships between variables representing past and present propagule pressure, other environmental variables and the abundance of non-native and native woody plant species. KEY RESULTS: Duration of propagule pressure predicted non-native species richness. Sites had greater non-native species richness if they were nearer to development (houses, roads) and if nearby development was older. While mesic woodlands had the most native species, streamside woodlands had the most non-native species. CONCLUSIONS: First, future studies of non-native invasions would benefit from including past as well as present propagule pressure. If past propagule pressure is not considered, its effects may be wrongly ascribed to present propagule pressure. Second, the non-native species in this study are widely used in landscaping, and development age reflects the years that landscaping has been present nearby. As xeriscaping becomes more common, streamside woodlands may someday not have the highest non-native species richness: the new drought-tolerant landscaping plants may be better invaders of drier sites than their predecessors. [ABSTRACT FROM AUTHOR]

The spread of non-native species into natural communities is a noticeable phenomenon linked to global change. Drivers of such invasions, however, may differ according to specific regional environments. Here, we aim at disentangling the role of selected climate and non-climate drivers on the spread of native (Hedera helix and Ilex aquifolium) and non-native (Prunus laurocerasus and Trachycarpus fortunei) evergreen species in mature deciduous forests in southern Switzerland. Covers of target evergreens were determined using 200 quadratic plots of 100 m2, distributed on a regular grid of 100 × 100 m and spanning a steep climatic gradient ranging from −0.4 to 3.0 °C in the average temperature of the coldest month. Species covers were used as response variables to be related to climate, stand structure, disturbances, propagule pressure and geomorphology proxies by performing tobit regressions. Propagule pressure resulted to be the main driver of occurrence for three considered species, while meso-climate and stand structure played only a secondary role. In contrast, the presence of native I. aquifolium was mostly correlated with the temperature of the coldest month, though with an overall low impact on cover. Our study demonstrates different drivers of invasion for native and non-native species with similar life history traits. In particular, differences emerge from ecological requirements (niche) and propagule pressure. The ongoing spread of evergreen broadleaved species at the regional scale demonstrates how evergreens invade a largely empty ecological niche, mainly issued by land-use change rather than climate warming. [ABSTRACT FROM AUTHOR]

Different pathways of propagation and dispersal of non-native species into new environments may have contrasting demographic and genetic impacts on established populations. Repeated introductions of rainbow trout ( Oncorhynchus mykiss) to Chile in South America, initially through stocking and later through aquaculture escapes, provide a unique setting to contrast these two pathways. Using a panel of single nucleotide polymorphisms, we found contrasting genetic metrics and patterns among naturalized trout in Lake Llanquihue, Chile's largest producer of salmonid smolts for nearly 50 years, and Lake Todos Los Santos ( TLS), a reference lake where aquaculture has been prohibited by law. Trout from Lake Llanquihue showed higher genetic diversity, weaker genetic structure, and larger estimates for the effective number of breeders ( Nb) than trout from Lake TLS. Trout from Lake TLS were divergent from Lake Llanquihue and showed marked genetic structure and a significant isolation-by-distance pattern consistent with secondary contact between documented and undocumented stocking events in opposite shores of the lake. Multiple factors, including differences in propagule pressure, origin of donor populations, lake geomorphology, habitat quality or quantity, and life history, may help explain contrasting genetic metrics and patterns for trout between lakes. We contend that high propagule pressure from aquaculture may not only increase genetic diversity and Nb via demographic effects and admixture, but also may impact the evolution of genetic structure and increase gene flow, consistent with findings from artificially propagated salmonid populations in their native and naturalized ranges. [ABSTRACT FROM AUTHOR]

Across the globe, invasive alien species cause severe environmental changes, altering species composition and ecosystem functions. So far, mountain areas have mostly been spared from large-scale invasions. However, climate change, land-use abandonment, the development of tourism and the increasing ornamental trade will weaken the barriers to invasions in these systems. Understanding how alien species will react and how native communities will influence their success is thus of prime importance in a management perspective. Here, we used a spatially and temporally explicit simulation model to forecast invasion risks in a protected mountain area in the French Alps under future conditions. We combined scenarios of climate change, land-use abandonment and tourism-linked increases in propagule pressure to test if the spread of alien species in the region will increase in the future. We modelled already naturalized alien species and new ornamental plants, accounting for interactions among global change components, and also competition with the native vegetation. Our results show that propagule pressure and climate change will interact to increase overall species richness of both naturalized aliens and new ornamentals, as well as their upper elevational limits and regional range-sizes. Under climate change, woody aliens are predicted to more than double in range-size and herbaceous species to occupy up to 20% of the park area. In contrast, land-use abandonment will open new invasion opportunities for woody aliens, but decrease invasion probability for naturalized and ornamental alien herbs as a consequence of colonization by native trees. This emphasizes the importance of interactions with the native vegetation either for facilitating or potentially for curbing invasions. Overall, our work highlights an additional and previously underestimated threat for the fragile mountain flora of the Alps already facing climate changes, land-use transformations and overexploitation by tourism. [ABSTRACT FROM AUTHOR]

Non-native species are a major driver of biodiversity loss. Aquaculture activities play a key role in introductions, including the escape of fishes from fish farm facilities. Here, the impact of flooding due to El Niño rains in 2015/2016 in the Lower and Middle Paranapanema River basin, southern Brazil, was investigated by evaluating fish escapes from 12 fish farms. The flooding resulted in the escape of approximately 1.14 million fishes into the river, encompassing 21 species and three hybrids. Non-native species were the most abundant escapees, especially Oreochromis niloticus (Linnaeus, 1758) and Coptodon rendalli (Boulenger, 1897) (96% of all fish). Only seven native fishes were in the escapee fauna, comprising 1% of all fish. Large floods, coupled with inadequate biosecurity, thus resulted in considerable inputs of non-native fish into this already invaded system. [ABSTRACT FROM AUTHOR]

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