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Question: Specialization refers to the degree of niche breadth of a species. Generalist species are able to persist in a broad range of habitats, whereas specialist species are adapted to a restricted range of environmental conditions. Cities host a great heterogeneity of habitats with variable degrees of human impact. This is generally reflected in the functional composition of the urban floras. The aim of our study is thus to explore whether the degree of functional specialization of urban plant assemblages varies among habitats subject to different degrees of human impact and disturbance regimes. Location: Thirty‐two cities in Central Europe with more than 100,000 inhabitants. Methods: We used a data set containing plots of urban floras sampled in seven habitat types within each city: historical city square, boulevard, residential area with a compact building pattern, residential area with an open building pattern, city park, early successional site, and mid‐successional site. These habitats differ in the level of human impact, ranging from moderately urbanized suburban habitats to the most urbanized habitats in the city center. For each plot, we calculated a recently introduced specialization index, which is based on the application of concentration measures to Grime's community‐level mean CSR strategies. Results: Along the urbanization gradient, from peripheral to central habitats, we observed a marked intensification in the degree of functional specialization of urban habitats, which is primarily attributable to an increase in the selection of ruderal species. Conclusions: Urban ecosystems are characterized by a wide variety of human impacts that affect the functioning of the resident species. Considering cities as heterogeneous systems is thus of paramount importance for understanding the mechanisms that drive the assembly of urban floras. [ABSTRACT FROM AUTHOR]

The Mediterranean Basin has historically been subject to alien plant invasions that threaten its unique biodiversity. This seasonally dry and densely populated region is undergoing severe climatic and socioeconomic changes, and it is unclear whether these changes will worsen or mitigate plant invasions. Predictions are often biased, as species may not be in equilibrium in the invaded environment, depending on their invasion stage and ecological characteristics. To address future predictions uncertainty, we identified invasion hotspots across multiple biased modelling scenarios and ecological characteristics of successful invaders. We selected 92 alien plant species widespread in Mediterranean Europe and compiled data on their distribution in the Mediterranean and worldwide. We combined these data with environmental and propagule pressure variables to model global and regional species niches, and map their current and future habitat suitability. We identified invasion hotspots, examined their potential future shifts, and compared the results of different modelling strategies. Finally, we generalised our findings by using linear models to determine the traits and biogeographic features of invaders most likely to benefit from global change. Currently, invasion hotspots are found near ports and coastlines throughout Mediterranean Europe. However, many species occupy only a small portion of the environmental conditions to which they are preadapted, suggesting that their invasion is still an ongoing process. Future conditions will lead to declines in many currently widespread aliens, which will tend to move to higher elevations and latitudes. Our trait models indicate that future climates will generally favour species with conservative ecological strategies that can cope with reduced water availability, such as those with short stature and low specific leaf area. Taken together, our results suggest that in future environments, these conservative aliens will move farther from the introduction areas and upslope, threatening mountain ecosystems that have been spared from invasions so far. [ABSTRACT FROM AUTHOR]

Trait‐based ecology has already revealed main independent axes of trait variation defining trait spaces that summarize plant adaptive strategies, but often ignoring intraspecific trait variability (ITV). By using empirical ITV‐level data for two independent dimensions of leaf form and function and 167 species across five habitat types (coastal dunes, forests, grasslands, heathlands, wetlands) in the Italian peninsula, we found that ITV: (i) rotated the axes of trait variation that define the trait space; (ii) increased the variance explained by these axes and (iii) affected the functional structure of the target trait space. However, the magnitude of these effects was rather small and depended on the trait and habitat type. Our results reinforce the idea that ITV is context‐dependent, calling for careful extrapolations of ITV patterns across traits and spatial scales. Importantly, our study provides a framework that can be used to start integrating ITV into trait space analyses. [ABSTRACT FROM AUTHOR]

Global change pressures are highlighting the need to better understand the mechanisms driving the temporal stability of natural communities under different environmental conditions. There is ample evidence that species richness helps communities to withstand environmental fluctuations and stabilise over time. However, it is still debated whether richness promotes stability through the diversity of species functional traits, phylogenetic lineages and ecological strategies in the community or because of the likelihood of including stable species. Furthermore, it is unclear whether the positive effect of diversity on stability is maintained in conditions of strong environmental fluctuations (e.g. frequent disturbances and stress).To address these questions, we analysed long‐term monitoring data of 84 permanent plots in coastal dune plant communities distributed along a gradient of natural stress and disturbance, with communities closer to the sea subject to greater stress and more frequent disturbances. Specifically, we used structural equation models to disentangle the relative influence of the environmental gradient and the different diversity components (species richness, functional and phylogenetic diversity; SR, FD and PD), as well as of the dominant ecological strategy (captured by species lifespan) on community stability, through their effect on two key stability mechanisms (population stability and species asynchrony).We found that the sea–inland environmental gradient was the main driver of stability mechanisms. Stress and disturbance decreased both population stability and species asynchrony, but also reduced species richness, which thus exerted a stabilising effect only on the communities in more favourable environmental conditions.Surprisingly, we did not find an effect of FD and PD on community stability, neither directly nor via asynchrony. However, the dominance of perennial species mitigated the instability generated by stress and disturbance. Perennial species were on average more stable than annuals and displayed a wider range of species fluctuations, including compensatory dynamics among species (i.e. asynchrony).Synthesis: Overall, our results highlight the importance of accounting for the environmental context when examining mechanisms of community stability. Species richness remains a useful direct predictor of community stability. Species ecological strategies, like the acquisitive–conservative trade‐off connected to lifespan, however, should also be routinely considered as drivers of both population stability and compensatory dynamics. [ABSTRACT FROM AUTHOR]

The role of plant traits in shaping community assembly along environmental gradients is a topic of ongoing research. It is well accepted that plant traits of aboveground organs tend to be conservative in stressful conditions. However, there is limited understanding of how belowground traits respond. Plants may have similar strategies above and belowground, but an intriguing possibility is that there is a tradeoff between above and belowground traits of communities to both ensure efficient resource‐use and limit niche overlap along the gradient. To test this, we asked whether the response of above and belowground traits of communities is coordinated or not along a stress gradient in Mediterranean sand dune communities. We analyzed 80 vegetation plots in central Italy to test for coordinated vs independent patterns in above vs belowground plant traits using community weighted mean and standardized effect size of functional richness. Our results show that plant communities close to the sea, which experience higher stress, were characterized by higher convergence towards aboveground resource conservation and conservative water‐use strategies but belowground resource acquisition, consistent with a strong effect of habitat filtering and an above–belowground tradeoff favoring adaptation to harsh and dry conditions. At the opposite end of the gradient with lower stress, plants exhibited higher trait diversity for both above and belowground traits, but overall a dominance of aboveground fast resource acquisition and generally acquisitive water‐use strategies, combined with conservative belowground strategies. This suggests that fast growth rate aboveground was compensated by more conservative fine‐root strategies, but processes such as competition limited niche overlap overall. Our findings provide new insights into the relationship between functional traits and environmental gradients in plant communities, shedding light on the tradeoffs between the above and belowground dimensions. [ABSTRACT FROM AUTHOR]

Question: Vegetation around the alpine–treeline ecotone faces changes in both climate and land use (i.e. grazing abandonment). Broad‐scale shrub encroachment is considered an effect of these changes, but it remains unclear how this process is mediated by local‐scale environmental heterogeneity. Our goal is to determine which local‐scale environmental factors shape the spatial distribution and temporal trends of alpine dwarf shrub vegetation dominated by Juniperus communis in Mediterranean mountains. Location: Three sites in the Central Apennine Mountain Range (Italy): Mt. Terminillo, Mt. Duchessa and Mt. Ernici. Methods: Combining a set of environmental variables obtained at a fine scale (25‐m resolution) from multi‐year remote sensing imagery and field‐collected vegetation data, we modelled the occurrence and cover of Juniperus communis‐dominated dwarf shrubland, as well as its change over time, as a function of local climate, topography and land use, using linear and generalized mixed effects models. Results: Over a period of almost 60 years (1954–2012) shrubland occurrence increased by 12% and shrubland cover by 10% in our study sites. Its current distribution and change over time appear to be strongly shaped by the joint influences of fine‐scale topography, above‐ground biomass, land use and microclimate. Shrublands have been favoured locally in areas with harsher alpine environmental constraints and stronger resource limitations. Conclusions: Our study shows that in the Mediterranean high‐mountain environment J. communis dwarf shrubland acts as a stress‐tolerant pioneer vegetation, occurring in areas that are otherwise sparsely vegetated. Contrary to our expectations, at fine scales, warmer temperatures and the regional decline in grazing did not favour shrub encroachment. Despite increasing overall, J. communis shrubs have little competitive ability to successfully encroach grasslands, and remain restricted to less‐productive areas. Our results confirm that fine‐scale environmental heterogeneity can strongly influence shrub distribution and dynamics, thereby modulating future responses in evolving alpine ecosystems. [ABSTRACT FROM AUTHOR]

Aim: Understanding the variation in community composition and species abundances (i.e., β‐diversity) is at the heart of community ecology. A common approach to examine β‐diversity is to evaluate directional variation in community composition by measuring the decay in the similarity among pairs of communities along spatial or environmental distance. We provide the first global synthesis of taxonomic and functional distance decay along spatial and environmental distance by analysing 148 datasets comprising different types of organisms and environments. Location: Global. Time period: 1990 to present. Major taxa studied: From diatoms to mammals. Method: We measured the strength of the decay using ranked Mantel tests (Mantel r) and the rate of distance decay as the slope of an exponential fit using generalized linear models. We used null models to test whether functional similarity decays faster or slower than expected given the taxonomic decay along the spatial and environmental distance. We also unveiled the factors driving the rate of decay across the datasets, including latitude, spatial extent, realm and organismal features. Results: Taxonomic distance decay was stronger than functional distance decay along both spatial and environmental distance. Functional distance decay was random given the taxonomic distance decay. The rate of taxonomic and functional spatial distance decay was fastest in the datasets from mid‐latitudes. Overall, datasets covering larger spatial extents showed a lower rate of decay along spatial distance but a higher rate of decay along environmental distance. Marine ecosystems had the slowest rate of decay along environmental distances. Main conclusions: In general, taxonomic distance decay is a useful tool for biogeographical research because it reflects dispersal‐related factors in addition to species responses to climatic and environmental variables. Moreover, functional distance decay might be a cost‐effective option for investigating community changes in heterogeneous environments. [ABSTRACT FROM AUTHOR]

Aim: Non‐native species threaten ecosystems worldwide, but we poorly know why some species invade more. Functional traits, residence time and native range size have been often used as invasion predictors. Here, we advance in the field by linking invasion success to native range parameters derived from dark diversity – a set of species present in the surrounding region that are absent in a study location even if ecological conditions are suitable. We tested whether those parameters improve the description of species success outside their native range. Location: North America; Europe and Mediterranean Basin. Methods: For 170 tree species native in one and non‐native in another region, we defined their invasion success as the number of locations occupied at the non‐native range. The probabilistic dark diversity was estimated based on the species co‐occurrences in their native ranges. It specifies how suitable is a species for a location, even if the species is absent. We calculated two parameters: sum of native location suitabilities (niche breadth proxy) and dark diversity probability (how often a species is absent from suitable locations, indicating niche realization limitations). We explored whether models including the dark diversity parameters performed better than one with a common species range measure, the number of locations occupied. We accomplished our models by adding functional traits, residence time and invasion direction. Results: Invasion success increased with the sum of native location suitabilities and decreased with dark diversity probability. This model with dark diversity parameters outperformed an alternative using the number of native locations occupied. Our best model included invasion direction, functional traits (including mycorrhizal status) and residence time, but dark diversity parameters remained important predictors. Main conclusions: The dark diversity parameters can contribute to invasion ecology by linking the species performance in the non‐native range to its niches parameters, derived from the native range. [ABSTRACT FROM AUTHOR]

Aim: Invasive species provide an opportunity to study biogeography in action, allowing us to observe how species adapt and fill their environmental niche when introduced to new ecological settings. Here we use sea spurge—a foredune specialist plant species native to Europe which has recently spread across Australia's southern coasts—as a model system to explore species' environmental niches adaptations and potential for future spread following introduction outside their native range. Location: Europe and Australia. Taxon: Sea spurge, Euphorbiaparalias, Euphorbiaceae. Methods: We compiled presence‐absence data of E.paralias from >190,000 vegetation surveys in the native and invaded range. We combined presence‐absence data with information on climate, soil, coastal morphology and human pressure, to test whether E.paralias' environmental niche has shifted following invasion and used species distributions models (SDMs) to map its invasion potential under current and future climatic conditions. Results: The environmental niche of E.paralias has shifted since reaching Australia, expanding into areas further away from people, closer to the shoreline and with higher temperatures. SDMs revealed that alongside broad‐scale gradients in temperature and rainfall, the distribution of E.paralias is also constrained by soil substrate and dune morphology—highlighting the importance of these fine‐scale drivers in shaping invasion dynamics in coastal environments. Moreover, SDMs suggest that future expansion in Australia will result from continued niche filling, not changes in climatic suitability. Main conclusions: Despite its impressive dispersal ability, E.paralias has not yet reached equilibrium in its invaded range and is likely to continue to expand its distribution in Australia regardless of climate change. E.paralias' key to success has been its ability to suit novel environments. We provide one of the first examples of how to leverage distribution data and SDMs to test hypotheses about niche conservatism and expansion in coastal dune invasive plant species. [ABSTRACT FROM AUTHOR]

Aim: An increasing number of exotic plants and their biological control agents are being introduced into new regions. Therefore, it is necessary to study their interactions and to manage the future directions of plant invasions under different scenarios of temperature rise. Location: China. Method: We investigated the distribution patterns of the two most prevalent invasive aquatic plants in the world, Alternanthera philoxeroides and Eichhornia crassipes, at a large scale and studied the interactions of both invasive plants with their respective biological control agents, Agasicles hygrophila and Neochetina eichhorniae, in response to different scenarios of temperature rise. Results: Both plants performed better in warmer climates in common garden experiments. However, large populations of A. philoxeroides occurred only in the temperate zone because this species experienced competitive exclusion from E. crassipes and suppression due to A. hygrophila herbivory in tropical and subtropical areas. Moreover, in both subtropical zones, where the two plants and A. hygrophila co‐occur, and the temperate zone, where only A. philoxeroides occurs at present, A. hygrophila herbivory and the competition from E. crassipes hindered the performance of A. philoxeroides. Moreover, in the extreme high‐temperature environment, A. philoxeroides performance improved, while E. crassipes performance worsened. In addition, the combination of N. eichhorniae herbivory and competition from A. philoxeroides also reduced the performance of E. crassipes, but E. crassipes still dominated when in competition with A. philoxeroides. Main conclusions: Our results indicate that climate warming and the introduction of herbivores do not alter the interspecific relationship between E. crassipes and A. philoxeroides. Moreover, our study suggests that under climate warming, E. crassipes will replace A. philoxeroides as the dominant species in some communities in warm temperate zones, though extremely high‐temperature events will slow this replacement process. [ABSTRACT FROM AUTHOR]

Although invasive plants increasingly contribute to the current biodiversity crisis, the mechanisms through which they impact native communities are still poorly understood. Community ecology theory has emphasized direct competitive displacement over common resources, but invasion‐driven ecosystem modifications, such as altered soil pH, might also have consequences for plant diversity. However, the relative importance of ecosystem modification compared to direct resource competition has rarely been tested.Here we studied the invasive vine Vincetoxicum rossicum across invaded meadows in southern Ontario, Canada. In each meadow site, we quantified: (a) the strength of impact on the resident plant community, (b) the potential for competition with resident species (as the degree of niche dissimilarity and competitive superiority to the residents based on their functional traits) and (c) the amount of ecosystem modification related to invasion.We found that impacts on plant biodiversity were more negative where the invader had greater potential to competitively displace species (because it had a similar niche as the residents or was competitively superior), but also where it strongly altered soil N pools, moisture and pH.Synthesis. Our case study suggests that while competition is undoubtedly an important driver of invasion impact, ecosystem modifications can have cascading effects on plant communities, thereby magnifying the impacts of biological invasions. [ABSTRACT FROM AUTHOR]

An important focus of community ecology, including invasion biology, is to investigate functional trait diversity patterns to disentangle the effects of environmental and biotic interactions. However, a notable limitation is that studies usually rely on a small and easy‐to‐measure set of functional traits, which might not immediately reflect ongoing ecological responses to changing abiotic or biotic conditions, including those that occur at a molecular or physiological level. We explored the potential of using the diversity of expressed genes—functional genomic diversity (FGD)—to understand ecological dynamics of a recent and ongoing alpine invasion. We quantified FGD based on transcriptomic data measured for 26 plant species occurring along adjacent invaded and pristine streambeds. We used an RNA‐seq approach to summarize the overall number of expressed transcripts and their annotations to functional categories, and contrasted this with functional trait diversity (FTD) measured from a suite of characters that have been traditionally considered in plant ecology. We found greater FGD and FTD in the invaded community, independent of differences in species richness. However, the magnitude of functional dispersion was greater from the perspective of FGD than from FTD. Comparing FGD between congeneric alien–native species pairs, we did not find many significant differences in the proportion of genes whose annotations matched functional categories. Still, native species with a greater relative abundance in the invaded community compared with the pristine tended to express a greater fraction of genes at significant levels in the invaded community, suggesting that changes in FGD may relate to shifts in community composition. Comparisons of diversity patterns from the community to the species level offer complementary insights into processes and mechanisms driving invasion dynamics. FGD has the potential to illuminate cryptic changes in ecological diversity, and we foresee promising avenues for future extensions across taxonomic levels and macro‐ecosystems. [ABSTRACT FROM AUTHOR]

Aim: Here, we aim to: (a) investigate the local effect of environmental and anthropogenic factors on alien plant invasion in sub-Antarctic islands; and (b) explore whether and how functional traits affect alien species dependence on anthropogenic factors in these environments. Location: Possession Island, Crozet archipelago (French sub-Antarctic islands). Methods: Single-species distribution models were used to explore the effect of high-resolution topoclimatic and human-related variables on the occurrence of six alien plants colonizing French sub-Antarctic islands. Furthermore, plant responses to human-related variables and the effect of those variables in interaction with plant traits were analysed by means of a multi-species distribution model. This allowed identifying functional features mediating the influence of human activities on the occurrence probability of alien plant species. Results: We observed two main invasion patterns: (a) species predicted to occur close to the introduction sites, whose occurrence probability appeared to be strongly affected by anthropogenic factors; and (b) species predicted to occur nearly everywhere on Possession Island, except in areas featuring particularly harsh climatic conditions. Differences in the influence of human-related variables on the occurrence of the alien species were mostly related to their life history, plant height and residence time, with perennial and low-statured species introduced earlier appearing less dependent on human-induced dispersal and disturbance. Conclusions: We conclude that both topoclimatic and anthropogenic factors affect plant invasion on sub-Antarctic islands. Specifically, species predicted to occur close to their introduction sites appear much more dependent on human presence and activity, potentially due to the lack of key functional traits allowing them to spread successfully across Possession Island under the harsh sub-Antarctic climate. Yet, particularly severe abiotic conditions are a major constraint which equally limits the occurrence of all alien plants, irrespective of their dependence on anthropogenic factors. [ABSTRACT FROM AUTHOR]

Questions: Which environmental factors influence fine‐grain beta diversity of vegetation and do they vary among taxonomic groups? Location: Palaearctic biogeographic realm. Methods: We extracted 4,654 nested‐plot series with at least four different grain sizes between 0.0001 m² and 1,024 m² from the GrassPlot database, covering a wide range of different grassland and other open habitat types. We derived extensive environmental and structural information for these series. For each series and four taxonomic groups (vascular plants, bryophytes, lichens, all), we calculated the slope parameter (z‐value) of the power law species–area relationship (SAR), as a beta diversity measure. We tested whether z‐values differed among taxonomic groups and with respect to biogeographic gradients (latitude, elevation, macroclimate), ecological (site) characteristics (several stress–productivity, disturbance and heterogeneity measures, including land use) and alpha diversity (c‐value of the power law SAR). Results: Mean z‐values were highest for lichens, intermediate for vascular plants and lowest for bryophytes. Bivariate regressions of z‐values against environmental variables had rather low predictive power (mean R² = 0.07 for vascular plants, less for other taxa). For vascular plants, the strongest predictors of z‐values were herb layer cover (negative), elevation (positive), rock and stone cover (positive) and the c‐value (U‐shaped). All tested metrics related to land use (fertilization, livestock grazing, mowing, burning, decrease in naturalness) led to a decrease in z‐values. Other predictors had little or no impact on z‐values. The patterns for bryophytes, lichens and all taxa combined were similar but weaker than those for vascular plants. Conclusions: We conclude that productivity has negative and heterogeneity positive effects on z‐values, while the effect of disturbance varies depending on type and intensity. These patterns and the differences among taxonomic groups can be explained via the effects of these drivers on the mean occupancy of species, which is mathematically linked to beta diversity.We analysed fine‐grain beta diversity of grasslands and other open habitats in the Palaearctic using 4,654 nested‐plot series and the z‐values of power‐law species–area relationships. Mean z‐values were highest for lichens, intermediate for vascular plants and lowest for bryophytes. The strongest environmental predictors of z‐values were herb layer cover (negative), elevation (positive), rock and stone cover (positive) and the c‐value (U‐shaped). In a conceptual figure, we summarize the resulting hypotheses how different predictors could influence z‐values via mean occupancy. [ABSTRACT FROM AUTHOR]

Aim: Mutualistic interactions between alien plants and native pollinators are needed to enable plant invasions. Although the increasing abundance of invasive plants in a habitat causes a dramatic decline of native pollinators, pollination services received by invaders are often sustained. This invader–pollinator paradox might be attributed to differences in pollination effectiveness and varying vulnerability to invasion among pollinators with different life history traits. In an experimental study, we explored the relationships between pollinator body size, pollination effectiveness and abundance of invasive species. Location: Kraków area, Poland. Methods: We placed a pair of potted invasive goldenrods (Solidago gigantea) at 25 sites differing in goldenrod abundance (cover: 0%–100%). Floral visitation rate of the potted goldenrods, as well as seed set and viability, was noted. Results: Species richness of pollinators visiting inflorescences decreased with the increase of the goldenrod cover, whereas the floral visitation rate remained unchanged. However, the seed set was positively related to the goldenrod cover. Body size of floral visitors was structured along with the goldenrod cover so that pollinators' size increased with the cover. Also, the seed set of the potted plants, as well as goldenrod seed viability, depended positively on the body size of visiting pollinators. Main conclusions: Invasive goldenrods did not suffer from pollinator shortage and ineffective pollination, especially in habitats densely covered by the invader, due to the presence of large‐bodied pollinators. Our study highlights that pollination and reproduction of invasive plants might be sustained through ecological filtering, affecting the composition of pollinators with traits increasing pollination effectiveness. [ABSTRACT FROM AUTHOR]

Aims: Humans have deeply eroded biogeographic barriers, causing a rapid spread of alien species across biomes. The Mediterranean Basin is a biodiversity hotspot but is also known as a hub of alien plant invasions, particularly in its European part. Yet, a comprehensive inventory of alien species in the area is missing and understanding of the drivers of Mediterranean invasions is poor. Here, we aim to identify the main alien plant species in the European part of the Mediterranean Basin and quantify their invasion success in order to understand the plant species flows from other biomes of the world. Location: The Mediterranean region of Europe, Anatolia and Cyprus. Methods: We analyzed 130,000 georeferenced vegetation plots from the European Vegetation Archive (EVA) and identified 299 extra-European alien plant species. We identified their biomes of origin and quantified the mean geographic distance, trade exchange and climatic similarity from each biome to the study area. After estimating the invasion success of each species in the study area, we tested which biomes have donated more alien species than expected by chance and which drivers best explain these non-random patterns. Results: We found that other Mediterranean climatic regions, as well as temperate and xeric biomes of the world, are the main donors of successful alien species to Mediterranean Europe, beyond what would be expected by chance. Our results suggest that climatic matching, rather than geographic proximity or trade, has been the most important driver of invasion. However, climatic pre-adaptation alone also does not appear to predict the invasion success of established species in the study area. Conclusions: Our results highlight the need to pay special attention to alien plant species from the same or climatically similar biomes, but also suggest that further research is needed for early screening of the most problematic alien species. [ABSTRACT FROM AUTHOR]