Comparing naturalized alien plants and recipient habitats across an east–west gradient in the Mediterranean Basin

Aim To investigate alien plant species invasion levels in different habitats and alien species traits by comparing the naturalized flora in different areas of the same biogeographical region. Location Spain, Italy, Greece and Cyprus. Methods Comparison of floristic composition, species traits and recipient habitats of naturalized alien neophytes across an east–west gradient comprising four countries in the European Mediterranean basin. Results A total of 782 naturalized neophytes were recorded; only 30 species were present in all four countries. Although floristic similarity is low, the four alien floras share the same patterns of growth form (mostly herbs), life cycle (mostly perennials) and life form (mostly therophytes, hemicryptophytes and phanerophytes). The majority of the recipient habitats were artificial. Wetlands were the natural habitats, with the highest numbers of naturalized species. Floristic similarity analyses revealed: (1) the highest floristic similarity between Italy and Spain, both of which were more similar to Greece than to Cyprus; (2) two groups of floristic similarity between habitat categories in each country (Greece–Cyprus and Italy–Spain); (3) a higher degree of homogenization in the plant assemblages in different habitats in Greece and Cyprus and a lower degree of homogenization in those in Italy and Spain; and (4) a higher degree of homogenization in artificial and natural fresh‐water habitats than in the other natural habitats. Main conclusions The floristic similarity of naturalized neophytes between the four countries is low, although the overall analysis indicates that the western group (Italy–Spain) is separated from the eastern group (Greece–Cyprus). Similar patterns emerged regarding the life‐history traits and recipient habitats. The artificial habitats and the natural wet habitats are those that are invaded most and display the greatest homogenization in all four countries. Coastal habitats display a lower degree of homogenization but a high frequency of aliens. Dry shrubs and rocky habitats display a lower degree of homogenization and a low frequency of aliens.     

Contrasting patterns in the invasions of European terrestrial and freshwater habitats by alien plants,insects and vertebrates

Aim To provide the first comparative overview on the current numbers of alien species that invade representative European terrestrial and freshwater habitats for a range of taxonomic groups. Location Europe. Methods Numbers of naturalized alien species of plants, insects, herptiles, birds and mammals occurring in 10 habitats defined according to the European Nature Information System (EUNIS) were obtained from 115 regional data sets. Only species introduced after ad 1500 were considered. Data were analysed by ANCOVA and regression trees to assess whether differences exist among taxonomic groups in terms of their habitat affinity, and whether the pattern of occurrence of alien species in European habitats interacts with macroecological factors such as insularity, latitude or area. Results The highest numbers of alien plant and insect species were found in human‐made, urban or cultivated habitats; if controlled for habitat area in the region, wetland and riparian habitats appeared to support relatively high numbers of alien plant species too. Invasions by vertebrates were more evenly distributed among habitats, with aquatic and riparian, woodland and cultivated land most invaded. Mires, bogs and fens, grassland, heathland and scrub were generally less invaded. Habitat and taxonomic group explained most variation in the proportions of alien species occurring in individual habitats related to the total number of alien species in a region, and the basic pattern determined by these factors was fine‐tuned by geographical variables, namely by the mainland–island contrast and latitude, and differed among taxonomic groups. Main conclusions There are two ecologically distinct groups of alien species (plants and insects versus vertebrates) with strikingly different habitat affinities. Invasions by these two contrasting groups are complementary in terms of habitat use, which makes an overall assessment of habitat invasions in Europe possible. Since numbers of naturalized species in habitats are correlated among taxa within these two groups, the data collected for one group of vertebrates, for example, could be used to estimate the habitat‐specific numbers of alien species for other vertebrate groups with reasonable precision, and the same holds true for insects and plants.     

Do climatically similar regions contain similar alien floras? A comparison between the mediterranean areas of central Chile and California

Aim Taxonomic comparisons of alien floras across climatically similar regions have been proposed as a powerful approach for increasing our understanding of plant invasions across scales. However, detailed comparisons between the alien biotas of climatically similar regions are scarce. This study aims to compare the taxonomic patterns of alien species richness in mediterranean‐type climate areas of central Chile and California, in order to better understand how climatically similar regions converge or diverge in terms of their alien flora. Location Central Chile and California, United States. Methods We compared the alien floras of the state of California in the United States and central Chile, considering within‐region variation and taxonomic composition up to the species level. To test for within‐region variation, administrative units and counties were grouped within seven latitudinal bands for each region. We tested for differences in the relative contributions of the various origins of the naturalized species to each region. We used a family naturalization index to establish which families had relatively higher numbers of naturalized species in each region. We evaluated the similarity, using cluster analyses with Jaccard’s similarity index, of alien taxa between regions and latitudinal bands using presence–absence matrices at the species, genus and family levels. We used principal components analysis to determine the presence of a compositional gradient including all latitudinal bands. Results We recorded 1212 alien plant species in California and 593 in central Chile, of which 491 are shared between the two regions. These figures include 25 species that are native to California and 37 that are native to Chile. A comparison between the alien floras of central Chile and California reveals three major trends: (1) higher naturalized species diversity for California than for Chile, at all taxonomic levels; (2) differences in the proportion of species according to origin, with America, Africa, Asia and Australia providing a larger number of species in California than in Chile; (3) segregation between regions in terms of taxonomic composition of their alien flora, and a rather weak differentiation within regions; and (4) a trend towards higher similarity between the alien floras of latitudinal bands associated with higher levels of human disturbances. Main conclusions The alien floras of central Chile and California are significantly different, but this difference diminishes in highly disturbed areas. Thus, the current high levels of species movement caused by globalization, together with increasing levels of anthropogenic disturbances, should reduce the differentiation of the alien floras in these regions, increasing overall biotic homogenization.     

Do non‐native species invasions lead to biotic homogenization at small scales? The similarity and functional diversity of habitats compared for alien and native components of Mediterranean floras

Although a number of recent studies have demonstrated biotic homogenization, these have mainly focused on larger spatial scales. Homogenizing effects are equally important at finer resolutions, e.g. through increasing similarity between habitats, which may result in a simplification of ecosystem structure and function. One major cause of homogenization is the expanding ranges of alien species, although it is not clear whether they are inherently homogenizing at smaller scales. We therefore assessed whether the alien flora is less complex across habitats than the resident native flora of Mediterranean Islands. From a regional data base, we examined floristic lists for between‐habitat taxonomic and functional similarity, and within‐habitat functional diversity, using resampled data sets to control for sample size biases. Aliens and natives showed equivalent complexity in most respects. At the taxonomic level, between‐island and between‐habitat similarities were almost identical, and when ecosystem function was measured by a functional group classification system, this was also true of between‐habitat similarities and within‐habitat diversities. When ecosystem function was measured using Grime's CSR classification, aliens were found to be more functionally homogenous between‐habitats and less functionally diverse within habitats. However, since the CSR profiles of aliens and natives differed, simplification is not inevitable due to ecological segregation of the two floras (aliens tend to be recruited to disturbed habitats rather than displacing natives). One deficiency is a lack of large scale species abundance data. A simple simulation exercise indicated that this is likely to lead to substantial overestimation of true levels of similarity, although would only influence the comparison between aliens and natives if they have different abundance distribution curves. The results indicate that alien floras are not intrinsically more simple than natives, but a higher proportion of competitive strategists among aliens may still cause small‐scale homogenization as these include many strong competitors that are likely to dominate communities.     

Role of non-established plants in determining biotic homogenization patterns in Pacific Oceanic Islands

Numerous organisms have been relocated by human agency among remote regions of the world. One of the consequences of alien invasions (and associated native extinctions) is that the taxonomic similarity between areas trends to increase, a process called biotic homogenization. This process is studied in plants using naturalized species, while the role of non-established (but nevertheless present) plants is not investigated. Here we evaluate if adding the non-established component to the pool of alien plants modifies similarity patterns recorded in a preceding study of biotic homogenization in six Oceanic Islands of the South-eastern Pacific. Although our analyses confirm previous findings of floristic homogenization for these Islands, the effect of adding the non-established component results in several changes. By consideration of only naturalized plants we detected two cases of increased similarity (i.e. floristic homogenization), while the other 13 comparisons yielded non-significant changes. By adding non-established plants, four pairs of Islands show increased similarity, while in one case there is decreased similarity (i.e. floristic differentiation). These results support the hypothesis that non-established species can modify qualitative and quantitative trends of floristic change, revealing the complexity of biotic change. Although discrimination between only native and naturalized species appears reasonable for some groups, among plants it becomes a critical decision because of the importance of non-established species as ecological players and as purveyors of early information on future biotic change.     

Consistency in the habitat degree of invasion for three invasive plant species across Mediterranean islands

Habitats are known to vary in their vulnerability to invasion by alien plants and different species often colonise distinct habitats. To assess the consistency in the degree of invasion of particular habitats, this study examined the frequency of occurrence and local abundance of three invasive plant taxa: Ailanthus altissima, Carpobrotus spp., and Oxalis pes-caprae across different habitat types on four representative Mediterranean islands. We conducted systematic field surveys recording the presence-absence and cover of these taxa on the islands of Mallorca, Corsica, Sardinia and Crete. Drawing on the results of 5,285 sample points, the frequency of occurrence of the three invaders tends to be higher than expected in urban, ruderal and roadside habitats. In contrast, scrub habitats rarely contain any of the three invaders, indicating that they may be more resistant to invasion. The degree of invasion, determined by the local abundance of an invasive plant in any one habitat, varies according to the identity of the invader and the island. However, based on average abundance, Oxalis pes-caprae exhibits the highest degree of invasion, and Carpobrotus spp. the least. There is no indication that any one of the four islands is more prone to either higher frequencies or abundances of the three invaders. These patterns suggest that anthropogenic changes in Mediterranean islands will increase the vulnerability of certain habitats to invasion and increase the distribution of these three invasive taxa at any of the four islands.     

Multi-scale assessment of macroinvertebrate richness and composition in Mediterranean-climate rivers

1. Similar constraints in distant, but climatically comparable, regions may be expected to yield biotic assemblages with similar attributes. Environmental factors that constrain communities at smaller scales, however, may be different between climatically similar regions. Thus, patterns observed at large scales may differ from those detected at small scales, and international comparisons should be focussed at multiple scales. 2. Mediterranean‐climate regions (MCRs) are characterized by remarkable seasonal variability in precipitation and temperature. Accordingly, rivers in these regions have seasonal and predictable floods and droughts, and temporary reaches are frequent. Present in six geographical regions of the world, MCRs have similar environmental constraints and are ideal for testing intercontinental similarities between macroinvertebrate communities. 3. We examined aquatic macroinvertebrate taxon richness and composition in MCRs at three scales: regional, reach and macrohabitat. At the regional scale, the Mediterranean Basin had the highest taxon richness at family level, and southwestern Australia the lowest. Taxonomic composition showed c. 85% similarity between the northern hemisphere MCRs of California and the Mediterranean Basin, which were followed in similarity by South Africa. The two Australian MCRs (South west and South) showed a similarity to each other of about 70% whereas the Chilean fauna was the most distinct. 4. At the reach scale, taxon richness was not significantly different between permanent and temporary reaches in any MCR, whereas taxonomic composition was significantly different among northern hemisphere MCRs. At the macrohabitat scale, taxon richness was not significantly different between lotic and lentic macrohabitats within any of the MCRs, but differences in macroinvertebrate communities were found between macrohabitats when considering regions. 5. Our results show that the strength of similarity between distant but climatically similar regions is scale‐dependent, being highest at the macrohabitat scale. Although the similarities in richness and composition at the macrohabitat scale are presumed to be universal, the seasonal predictability of drought in MCRs is expected to result in characteristic macroinvertebrate responses at the reach scale. We suggest, however, that regional evolutionary history and environmental characteristics may override this general pattern of a similar response of MCRs at different scales. The Mediterranean Basin and California, having similar historical and environmental condition, thus appeared as the most similar MCRs at all scales.     

塔里木盆地鱼类入侵及区系演变趋势

鱼类入侵是塔里木盆地土著鱼类濒危的关键性影响因素之一,结合历史文献数据及近年调查数据,系统综述了塔里木盆地鱼类入侵现状,并就鱼类入侵引起的鱼类区系均一化问题进行了分析。结果显示,该地区记录鱼类63种,其中土著种19种,入侵种44种。尽管入侵鱼类提升了塔里木盆地鱼类群落属级及科级的多样性水平,但相应的G-F多样性指数却明显下降,表明该区鱼类群落从物种组成简单、分化明显的特点演变为物种成分复杂、分化贫乏的特点。入侵种中源于长江和额尔齐斯河分别有30种(68.2%)和7种(15.9%),源于美欧和亚洲其他区域的有7种(15.9%)。入侵鱼类的进入引起塔里木盆地与其相关区域鱼类区系相似性显著上升(P0.01),并导致该区鱼类区系从单一的中亚高原山区复合体演变为多区系混合体。进一步利用鱼类个体生态矩阵分析方法研究显示,外来种在塔里木盆地适应性广泛,能够占据水域各种栖息生境,显著压缩了土著种的栖息空间,进而通过捕食、食物竞争及其他作用途径严重危及土著鱼类种群的续存,提示须采取有力措施限制入侵种的进一步扩散及对濒危土著物种迅速开展人工保育工作。     

Interactions between alien plant species traits and habitat characteristics in agricultural landscapes in Finland

The survival and success of alien plant species is determined by species traits (i.e., invasiveness) and the characteristics of the habitats in the region of introduction (i.e., invasibility). However, little is known about species traits as related to habitat characteristics. We assessed the characteristics of successful invaders and the interaction of environmental factors and life-history traits for alien plant species. The vascular plants were recorded from 52 agricultural landscapes in Finland. We compared the traits of native and alien plant species with Fisher’s exact test and used a three table ordination analysis, RLQ analysis, to relate species traits to environmental conditions. Species were clustered according to their position on the RLQ axes, and the clusters were tested for phylogenetic independence. The successful alien plant species were associated with life form and preferences for moisture and nitrogen, but the trait composition varied according to the habitat type. Two RLQ axes explained 80.5% of the variation, and the species traits were significantly associated with environmental variables. The clustering showed that the occurrence of alien plant species in agricultural habitats was driven by invasion history, traits related to dispersal (dispersal type, seed mass) and habitat preferences, as well as environmental features, such as geographical location, temperature and the quality and disturbance regime of the habitats. All clusters were phylogenetically non-independent. Thus, the clusters of alien species comprised species of diverse taxonomic affinities, although, they shared the traits explaining their occurrence in particular habitats. This information is useful for understanding the link between species traits and the environmental conditions of the habitats, and complexity of the invasion process.     

Macroecology of global bryophyte invasions at different invasion stages

In this study we provide the first comprehensive assessment of the environmental and anthropogenic factors driving bryophyte invasions worldwide. We compiled data of alien bryophyte distributions from 82 regions on five continents and oceanic islands and region specific variables. For each species, we collected data on its region‐specific invasion stage, i.e. casual (ephemeral) vs naturalized (persistent) occurrences, and we differentiated between known aliens and those which are likely to be alien (cryptogenic). We used these data to test how species attributes, environmental and socio‐economic conditions of the study areas as well as introduction effort affect invasion probabilities at different invasion stages and of known alien vs cryptogenic species. We collected information on species’ attributes (native range size and location, niche breadth, habitat affiliation), and calculated variables characterising the environmental, biogeographic and socio‐economic features of the native and recepient regions. Subsequently, we related the probability of alien occurrence across different invasion stages with these species‐ and region‐wise predictor variables using generalized linear mixed effects models. Greater native range size raised the likelihood that a species becomes alien or cryptogenic. Islands are more invaded by alien (and cryptogenic) bryophytes than continental regions. Native range size and socio‐economic activity increase the likelihood that a species becomes alien or cryptogenic elsewhere. Interestingly, among alien bryophytes naturalizations occur more frequently in regions of the complementary hemisphere than in regions of their native hemisphere. In general, regions in the Southern Hemisphere have higher numbers of naturalized bryophytes. We conclude that there is a conspicuous change in factors determining bryophyte invasions at different invasion stages. Whereas alien and cryptogenic bryophyte species occurrences are more frequent on islands and depend on native range size, and hence probably propagule pressure, naturalized bryophytes are more frequent in areas which are biogeographically separated but climatically similar to the native ranges.     

European map of alien plant invasions based on the quantitative assessment across habitats

Aim Recent studies using vegetation plots have demonstrated that habitat type is a good predictor of the level of plant invasion, expressed as the proportion of alien to all species. At local scale, habitat types explain the level of invasion much better than alien propagule pressure. Moreover, it has been shown that patterns of habitat invasion are consistent among European regions with contrasting climates, biogeography, history and socioeconomic background. Here we use these findings as a basis for mapping the level of plant invasion in Europe. Location European Union and some adjacent countries. Methods We used 52,480 vegetation plots from Catalonia (NE Spain), Czech Republic and Great Britain to quantify the levels of invasion by neophytes (alien plant species introduced after ad 1500) in 33 habitat types. Then we estimated the proportion of each of these habitat types in CORINE land‐cover classes and calculated the level of invasion for each class. We projected the levels of invasion on the CORINE land‐cover map of Europe, extrapolating Catalonian data to the Mediterranean bioregion, Czech data to the Continental bioregion, British data to the British Isles and combined Czech–British data to the Atlantic and Boreal bioregions. Results The highest levels of invasion were predicted for agricultural, urban and industrial land‐cover classes, low levels for natural and semi‐natural grasslands and most woodlands, and the lowest levels for sclerophyllous vegetation, heathlands and peatlands. The resulting map of the level of invasion reflected the distribution of these land‐cover classes across Europe. Main conclusions High level of invasion is predicted in lowland areas of the temperate zone of western and central Europe and low level in the boreal zone and mountain regions across the continent. Low level of invasion is also predicted in the Mediterranean region except its coastline, river corridors and areas with irrigated agricultural land.     

Regional assessment of plant invasions across different habitat types

Questions: 1. Which habitats have the highest degree of invasion? 2. Do native species-rich communities have also a high degree of invasion? 3. Do the patterns of association between native and alien species richness vary between habitats. Location: Catalonia region (NE Spain). Methods: We conducted a large regional analysis of 15655 phytosociological relevés to detect differences in the degree of invasion between European Nature Information System (EUNIS) habitats representative of temperate and Mediterranean European areas. Results: Alien species were present in less than 17 % of the relevés and represented less than 2% of the total number of species per habitat. The EUNIS habitats with the highest alien species richness were arable land and gardens followed by anthropogenic forb-rich habitats, riverine and lakeshore scrubs, southern riparian galleries and thickets and trampled areas. In contrast, the following habitats had never any alien species: surface running waters, raised and blanket bogs, valley mires, poor fens and transition mires, base-rich fens, alpine and sub-alpine grasslands, sub-alpine moist or wet tall-herb and fern habitats, alpine and sub-alpine scrub habitats and spiny Mediterranean heaths. There was a unimodal relationship between the mean native and mean alien species richness per EUNIS habitat with a high number of aliens in habitats with intermediate number of native species and a low number of aliens at both extremes of the native species gradient. Within EUNIS habitats, the relationship was positive, negative or non-significant depending on the habitat type without any clear pattern related to the number of native species. Alien species richness was not related to plot size, neither between habitats nor within habitats. Conclusions: The analysis emphasised that the habitats with a higher degree of invasion were the most disturbed ones and that in general habitats rich in native species did not harbour less invaders than habitats poor in native species.     

华南地区外来入侵和归化植物分析

为了解华南地区外来植物现状,通过野外调查和查阅文献等,确定华南地区有外来入侵和归化植物45科141属223种,以菊科(Asteraceae,38种)、豆科(Fabaceae,36种)、禾本科(Poaceae,19种)植物为主,其中草本植物和原产美洲的植物占优势,分别有204种(占总数的91.5%)和163种(占73.1%)。广东外来入侵植物有159种,归化植物23种;广西有入侵植物135种,归化植物16种;海南有入侵植物111种,归化种15种;香港有入侵植物105种,归化植物9种;澳门有入侵植物89种,归化种4种;华南5省区共有的外来入侵和归化植物为57种(55种为入侵植物,2种为归化植物)。广东是外来植物种类最多的地区,与其他4省区共有的外来入侵和归化植物种类也最多,说明广东同时是外来植物输入和输出大省。由于气候和生态生境的相似性,各省区都面临着其他植物从周边地区入侵的风险,因此在治理入侵植物时,应建立联合防控机制对外来入侵植物的联合监测和防控,以提升外来入侵植物的治理成效和降低其对人类健康和生态安全的威胁。     

Impacts of Myriophyllum aquaticum invasion in a Mediterranean wetland on plant and macro-arthropod communities

The invasion by alien macrophytes in aquatic ecosystems may produce a strong alteration of the native aquatic vegetation leading to heavy impacts for both plant and faunal native diversity. Myriophyllum aquaticum is an aquatic plant native of Southern America, invasive in several part of the world. We studied the effects of M. aquaticum invasion on plant and macro-arthropod communities in the canals around a protected wetland in the Mediterranean basin. We sampled plant and macro-arthropod communities in 10 transects in invaded and non-invaded tracts of the canals. We assessed the differences in plant and macro-arthropod species richness, diversity, taxonomic diversity and species composition between invaded and non-invaded habitats by means of univariate and multivariate analyses. Our study shows a significant loss of plant diversity between non-invaded to invaded sites, leading to communities numerically and taxonomically impoverished and highly divergent in the species composition. We also detected significant differences in arthropod species composition between invaded and non-invaded transects. Some taxa such as mosquitoes and malacostraca were more frequent in the M. aquaticum-dominated stands. Furthermore, the study shows a positive relation between invaded habitats and juvenile individuals of the invasive alien crayfish Procambarus clarkii.     

The vulnerability of habitats to plant invasion: disentangling the roles of propagule pressure,time and sampling effort

Aim To quantify the vulnerability of habitats to invasion by alien plants having accounted for the effects of propagule pressure, time and sampling effort. Location New Zealand. Methods We used spatial, temporal and habitat information taken from 9297 herbarium records of 301 alien plant species to examine the vulnerability of 11 terrestrial habitats to plant invasions. A null model that randomized species records across habitats was used to account for variation in sampling effort and to derive a relative measure of invasion based either on all records for a species or only its first record. The relative level of invasion was related to the average distance of each habitat from the nearest conurbation, which was used as a proxy for propagule pressure. The habitat in which a species was first recorded was compared to the habitats encountered for all records of that species to determine whether the initial habitat could predict subsequent habitat occupancy. Results Variation in sampling effort in space and time significantly masked the underlying vulnerability of habitats to plant invasions. Distance from the nearest conurbation had little effect on the relative level of invasion in each habitat, but the number of first records of each species significantly declined with increasing distance. While Urban, Streamside and Coastal habitats were over‐represented as sites of initial invasion, there was no evidence of major invasion hotspots from which alien plants might subsequently spread. Rather, the data suggest that certain habitats (especially Roadsides) readily accumulate alien plants from other habitats. Main conclusions Herbarium records combined with a suitable null model provide a powerful tool for assessing the relative vulnerability of habitats to plant invasion. The first records of alien plants tend to be found near conurbations, but this pattern disappears with subsequent spread. Regardless of the habitat where a species was first recorded, ultimately most alien plants spread to Roadside and Sparse habitats. This information suggests that such habitats may be useful targets for weed surveillance and monitoring.     

不受欢迎的生物多样性：香港的外来植物物种

香港早在19世纪中叶开始就有外来植物入侵的记录,迄今为止,已发现多达238种已归化的外来或怀疑为外来的植物,其中又以薇甘菊（Mikania micrantha)、五爪金龙（Ipomoea cairica)、假臭草（Eupatorium catarium)、大黍（Panicum maximum)等最常见,外来植物最常见于受人为干扰的生境,例如荒废农田及路旁等,而较少在天然林地生境及贫瘠的灌草丛中发现,外来植物的对本地生态系统的影响主要局限于低地生境,它们常形成单优种群,减少了生境及贫瘠的灌草丛中发现,外来植物对本地生态系统的影响主要局限于低地生境,它们常形成单优种群,减少少了生境及动植物的多样性,外来动物对香港原生植物影响最大的是于20世纪70年代入侵的松树线虫（Bur-saphelenchus xylophilus)。外来的脊椎动物也有可能对香港的植物被演替产生影响,目前香港的外来植物当中,有些在大陆较少分布或没有记录,作为华南最大的港口,香港对外来物种的引入扮演着重要的角色,因此制定控制外来种在香港及华南地区的引入及传播的政策及措施非常重要。     

The cobblers stick to their lasts: pollinators prefer native over alien plant species in a multi-species experiment

The majority of plant species rely, at least partly, on animals for pollination. Our knowledge on whether pollinator visitation differs between native and alien plant species, and between invasive and non-invasive alien species is still limited. Additionally, because numerous invasive plant species are escapees from horticulture, the transition from human-assisted occurrence in urbanized habitats to unassisted persistence and spread in (semi-)natural habitats requires study. To address whether pollinator visitation differs between native, invasive alien and non-invasive alien species, we did pollinator observations for a total of 17 plant species representing five plant families. To test whether pollinator visitation to the three groups of species during the initial stage of invasion depends on habitat type, we did the study in three urbanized habitats and three semi-natural grasslands, using single potted plants. Native plants had more but smaller flower units than alien plants, and invasive alien plants had more but smaller flowers than non-invasive alien plants. After accounting for these differences in floral display, pollinator visitation was higher for native than for alien plant species, but did not differ between invasive and non-invasive alien plant species. Pollinator visitation was on average higher in semi-natural than in urbanized habitats, irrespective of origin or status of the plant species. This might suggest that once an alien species has managed to escape from urbanized into more natural habitats, pollinator limitation will not be a major barrier to establishment and invasion.     

Landscape context modulates alien plant invasion in Mediterranean forest edges

Natural habitats in human-altered landscapes are especially vulnerable to biological invasions, especially in their edges. We aim to understand the influence of landscape and local characteristics on biological invasions by exploring the level of plant invasion and alien species traits in forest edges in highly urbanized landscapes. We identified all plant species in 73 paired plots in the edge and 50 m towards the interior of the forest. We explored the association between alien species richness and similarity in species composition between edge and interior plots with landscape and local variables, using generalized linear models and variance partitioning techniques. Then, we performed Fourth-corner analyses to explore the association between alien plant traits and local and landscape variables. In contrast to native species richness, alien species richness was more affected by the surrounding landscape than by the local characteristics of the edge. Road proximity was positively associated with alien species richness and proportion and was its most important correlate, whereas disturbance was negatively associated with native species richness and was its most influential factor. Alien plant traits were also primarily associated with landscape characteristics. For instance, species of Mediterranean origin and introduced for agriculture were associated with higher agriculture use in the landscape. Our findings suggest that risk analyses of habitat vulnerability to invasion must consider the landscape context in order to successfully predict highly invaded areas and identify potentially successful invaders.     

Invasibility of a coastal strip in NE Spain by alien plants

Abstract. The alien plant species and the ecological factors that facilitate their invasion to a coastal strip in the Baix Camp region (Tarragona, NE Spain) were studied. A detailed inventory of the area showed that 20% of the plant species, most of them from the American Continent, were aliens, many of which were strongly invasive. At the habitat level, the relationships between the invasive behaviour and a number of autecological, ecological and habitat variables were analysed by means of logistic analyses. In the best model five variables were related to alien plant invasions: climatic affinity, disturbance of the invaded habitat, route of introduction, soil moisture during summer, and life form. To elucidate the environmental factors that could be responsible for alien plant invasions at a regional scale, the number of alien taxa and the environmental features at 13 localities of the western Mediterranean area were analysed. The warm lowlands, subjected to low annual rainfall and high population density, exhibited the greatest reception capacity for alien plants. It is concluded that various specific environmental features – high mean temperatures, the abundance of riparian systems, the existence of biotopes with favourable water balance which harbour a great richness of alien species and the high human pressure to which the enclave is subjected, combined with the ecological requirements of the alien species and certain species attributes (biotype) can interact at different scales and have caused the over‐representation of alien plants.     

Telling a different story: a global assessment of bryophyte invasions

We assess and review spatio-temporal patterns, habitat affiliations, pathways, impacts, and management experience of bryophyte invasions in extra-tropical countries and regions (n = 82) from five continents and maritime islands spanning both hemispheres. Distribution data were extracted and critically checked from a wide range of sources and supplemented with data on biology and introduction history. We identified 139 bryophytes species which we consider to be alien in at least one of our study regions (106 mosses, 28 hepatics and 5 hornworts). Numbers of average alien bryophyte species are significantly higher on islands than in continental regions of similar size, and peak on maritime islands. Cumulative numbers of first records have grown slowly until 1950 and have strongly increased since then. Accidental import as hitch-hiker (34 species) or with ornamental plants (27 species) constitute the most important introduction pathways. We found a remarkably high contribution from distant donor regions to alien bryophyte floras, especially from the complementary hemisphere. Most alien bryophytes prefer strongly modified habitats (e.g. ruderal vegetation, roadsides, lawns), and only few natural ecosystems (forests, rocks) are regularly invaded. Evidence for an ecological impact of bryophyte invasions is scarce and competitive replacement of native moss species, or vascular plant seedlings, by alien bryophytes has only been documented in a few cases. We conclude that bryophytes differ profoundly in many respects from vascular plants, and so do their invasion patterns at large scale. Our global bryophyte invasion state assessment provides the basis for future, more explicit considerations of this largely neglected taxonomic group in invasion ecology, a step we suggest to be urgently needed as studying them might provide novel insights into patterns and processes of plant invasions in general.