An Assessment of Habitat Diversity and Transformation on La Réunion Island (Mascarene Islands,Indian Ocean) as a Basis for Identifying Broad-scale Conservation Priorities

Most natural habitat in the Mascarene Islands (Mauritius, La Réunion and Rodrigues) has been transformed. Although urbanisation, agriculture and alien plant invasions have transformed large areas in La Réunion, the island has by far the greatest area of intact habitats in the Mascarenes, but remaining natural areas are under threat. We propose a protocol for defining a system of habitat types and for using these to provide a preliminary assessment of conservation priorities for La Réunion. The protocol draws on existing data and expert knowledge to map habitat types, assesses the extent of habitat transformation, and quantifies heterogeneity between habitat types based on climate, topography and geology. The pattern of habitat transformation was uneven among the nineteen habitat types identified. While three habitats have lost > 95% of their original area, four still retain> 80% of their original extent. Habitat types could be grouped into the following categories: (i) transformed habitats with low levels of plant endemism, (ii) habitats confined to homogenous geology with high levels of plantendemism, and (iii) species-rich heterogeneous habitats on diverse geological types. Priority habitats were also identified using municipalities as a basis for implementation. Urgent action is required for several habitat types where a large part of the original extent has been transformed. Three municipalities which contain more than 10 habitat types should receive conservation priority. The analysis provides the basis for setting conservation priorities in La Réunion at the regional and local scale. Implications of the results are discussed with reference to requirements for finer-scale conservation planning.     

Consistent performance of invasive plant species within and among islands of the Mediterranean basin

Since the success of an invasive species depends not only upon its intrinsic traits but also on particular characteristics of the recipient habitat, assessing the performance of an invader across habitats provides a more realistic analysis of risk. Such an analysis will not only provide insights into the traits related to invasiveness, but also the habitat characteristics that underpin vulnerability to invasion that, taken together, will facilitate the selection of management strategies to mitigate the invader’s effect. In the present study, we considered the Mediterranean basin islands as an excellent study region to test how the same invasive species perform in different habitats within a single island, and to scale up differences among islands with similar climate. We tested how the performance of three widespread plant invaders with clonal growth but contrasting life-history traits, a deciduous tree Ailanthus altissima, a succulent subshrub Carpobrotus spp., and an annual geophyte Oxalis pes-caprae, varied depending upon the species identity, habitat, and invaded island. The environmental parameters considered were habitat type, elevation, species diversity in the invaded plot, and several soil traits (% C, % N, C/N, pH, and relative humidity). The study documents that the performance of these three important and widespread plant invaders is dependent mainly on species identity, and less upon the invaded island’s general features. Likewise, differences in performance among habitats were only significant in the case of Ailanthus, whereas Carpobrotus and Oxalis appear to perform equally well in different environments. Ailanthus thus appears to have a broader spectrum of invasiveness, being able to invade a larger number of habitat types. On the contrary, Carpobrotus spp. have not yet invaded habitats different from those where the species have been originally introduced and where they are still commonly spread by humans. Oxalis distribution is mainly related to agricultural activities and disturbed sites, and the total area infested by this geophyte may be more reflection of the extent of suitable habitats than of invasiveness or ecological impact. Our results confirm the potential for these species to significantly alter the functioning of ecosystems in the Mediterranean islands and highlight the risk to other islands not yet invaded.     

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.     

The invasive alien plant species Solidago gigantea alters ecosystem properties across habitats with differing fertility

Question: Invasive alien plants can affect biomass production and rates of biogeochemical cycling. Do the direction and intensity of such effects depend upon the functional traits of native and alien species and upon the properties of the invaded habitat, with the same alien species having differing impacts in different habitats? Location: Lowlands of Switzerland. Methods: Fourteen grassland and wetland sites invaded by Solidago gigantea and widely differing in biomass production and soil P availability were surveyed. To determine whether the impact of the species was related to site fertility, we compared the invaded and native vegetation in terms of biomass, species composition, plant traits and soil properties. Results: S. gigantea generally increased the above‐ground biomass production of the vegetation and soil C content, while reducing nutrient concentrations in biomass and N availability in the soil. However, it had no significant effect on plant species richness, soil respiration, soil pH and P availability. Leaves of S. gigantea had a greater C content than those of native species; other leaf traits and root phosphatase activity did not differ significantly. Conclusions: Our results suggest that a conservative nutrient‐use strategy allows S. gigantea to invade a broad range of habitats. The observed effects of invasion did not vary according to biomass production of the invaded sites, but some effects did depend on soil P availability, being more pronounced at more P‐rich sites. Thus, the full range of invaded habitats should be considered in studying the potential impact of plant invasions on ecosystem processes.     

Focal species diversity patterns can provide diagnostic information on plant invasions

In Europe, coastal sandy habitats are considered highly endangered among those included in the EC Directive 92/43/EEC (Habitats Directive). Among the different threats which affect coastal communities, the spread of alien plants has been claimed to induce changes in community diversity and structure. We therefore set out to analyse diversity patterns of native and focal species (diagnostic and characteristic of coastal dune habitats of European conservation interest) in sandy coastal habitats invaded by Carpobrotus aff. acinaciformis, a widespread alien plant. Focal species are a major conservation target for the Habitats Directive and their decline should be considered a serious threat for the whole habitat. The study was performed in the Central Western coast of Italy. We randomly sampled the vegetation of the holocenic dune by 2 m × 2 m plots. First we split the collected data in two sets: invaded and non-invaded. We compared overall native and focal species richness patterns of the two sets by rarefaction curves. Then, in order to describe the singular aspects of species diversity (e.g. richness, Shannon index, Simpson index, Berger–Parker index), we also compared Rènyi's diversity profiles and we tested the significance of the differences between invaded and non invaded sets using a bootstrap procedure. Rarefaction curves of the non-invaded set rise quickly and reach higher accumulation values than the invaded set, but differences between the two curves were not significant. With respect to Rènyi's profiles, the profile for the invaded dataset was always below the non-invaded one, but differences in diversity were significant only when specifically considering the focal species (Shannon, Simpson and Berger–Parker indices). In the analysed case, the invasion is significantly associated with changes in focal species diversity, instead those differences are not evident on the all native species pool. In the case of recent invasions, a consistent decline on focal species diversity may represent an early alarm sign of diversity loss and may help define specific conservation actions to prevent the decrease of overall diversity.     

Neophyte Invasion in Moldavia (Eastern Romania) in Different Habitat Types

The actual state of neophyte invasion in Moldavia (Eastern Romania) is described in this paper on the basis of 11,055 phytosociological relevés. We analyzed the i) proportion of relevés with neophytes, ii) mean proportion of neophytes per relevés, and iii) mean coverage of neophytes per relevé for 36 EUNIS habitat types to identify general plant invasion patterns. The level of invasion differed considerably between habitats. The invasion of neophytes especially affected habitats strongly determined or influenced by man, such as anthropogenic woodlands, ruderal habitats, arable lands or trampled areas. Most natural habitats are either slightly invaded or entirely free of neophytes. Only riverine willow stands and wet tall-herb stands are relatively highly invaded. However, the absence of neophytes in some natural habitats less represented in the phytosociological dataset could be of artifactual nature. No significant relationship between the number of neophytes and non-neophytes was found in the analysis across different habitats. When the analyses were made within-habitats, both negative and positive relationships were found, which confirm that the relationship between alien and native species richness depends on the habitats. A total number of 105 neophyte species were recorded in the phytosociological relevés used in this study. Among these, 13 species that are currently considered invasive in Moldavia occur in at least 10 types of habitats.     

不同生境下空心莲子草响应模拟昆虫采食的生长和化学防御策略

外来植物往往可以入侵多种生境并受到多种昆虫的采食,而不同生境条件将可能会影响这些入侵植物对昆虫采食的防御策略。以入侵我国的克隆植物——空心莲子草为研究对象,分别选择生长在水生生境、水陆两栖生境和陆生生境中的无性个体(分株),通过50%去叶处理模拟昆虫采食,分析不同生境下空心莲子草对模拟昆虫采食处理的生长及化学防御响应的差异。模拟昆虫采食处理显著抑制了陆生生境、水陆两栖生境以及水生生境下空心莲子草的根、茎、叶和总生物量,但对3种生境下空心莲子草的生物量分配(根冠比、根生物量分配、茎生物量分配和叶生物量分配)均无显著影响。陆生生境下空心莲子草根、茎和总生物量显著高于水陆两栖生境和水生生境,根冠比显著低于水陆两栖生境和水生生境。模拟昆虫采食处理显著降低了空心莲子草的木质素含量,而对单宁和总酚含量影响不显著。生境对木质素含量无显著影响,但陆生生境下空心莲子草单宁含量显著高于水陆两栖生境和水生生境,且总酚含量显著高于水陆两栖生境,表明陆生生境中空心莲子草具有更强的防御能力。空心莲子草木质素含量与总生物量无显著相关性,但在模拟采食情况下,其总酚含量与总生物量呈显著负相关,而无论模拟昆虫采食处理存在与否,空心莲子草单宁含量与总生物量均呈显著正相关。因此,空心莲子草存在昆虫介导的生长和化学防御之间的权衡,在昆虫采食的情况下可通过减少生长来增加对化学防御物质的投入,但生境对空心莲子草这种生长-防御权衡的影响十分有限。     

重要外来入侵植物随南水北调工程传入京津冀受水区的风险评估

【目的】外来物种在入侵地的扩张蔓延是其造成危害的关键。南水北调工程可为已入侵外来物种的进一步扩张蔓延提供通道和驱动力。风险评估可为预防入侵植物通过该途径的扩散蔓延提供依据。【方法】以国家重点管理外来入侵物种名录中的入侵植物为研究对象,根据生物入侵的发生过程(传入、定殖、扩散、危害)构建了包括4个层次29个指标的外来物种入侵综合风险评估的指标体系,规范了风险指数的计算方法,系统评估了24种入侵植物沿南水北调输水通道向北扩散而入侵京津冀受水区的风险。【结果】紫茎泽兰和互花米草的入侵风险值(R)相对较低(R0.6),其余22种入侵植物的风险值均较高(R0.6),其中,喜旱莲子草、凤眼莲和大薸3种外来水生植物的入侵风险等级最高(R0.8)。【结论】南水北调工程可能会促进入侵植物向北扩张蔓延并最终入侵京津冀受水区。建议尽早开展监测预警工作,以控制入侵物种随南水北调工程的扩张蔓延,进而阻止或降低其对京津冀尤其是华北最大水源地——白洋淀和雄安新区生态环境的威胁。     

Habitat structure modified by an invasive grass enhances inundation withstanding in a salt-marsh wolf spider

Vegetation and underground structures are known to influence flood avoidance and flood resistance in invertebrates. In bimonthly-flooded European salt marshes, recent invasions by the nitrophilous grass Elymus athericus strongly modified usual habitat structure, notably by the production of a deep litter layer. Consequently, invaded habitats provide more interstitial spaces that may act as a refuge during flood events. By using both controlled and field designs, we tested whether invaded habitats may change the ability to resist flooding by the creation of new refuges during tides for a ground-living, predatory arthropod. The wolf spider Arctosa fulvolineata was employed as a model species since it occurs abundantly in both invaded and uninvaded salt-marsh habitats. In the field, its abundance strongly decreased (divided by three) after tidal flooding in uninvaded habitats by but did not change in invaded patches. Under controlled laboratory conditions, ten times more individuals withstood simulated flooding in the presence of litter and less decided to float. The presence of litter did not influence flood resistance, i.e. survival underwater. Our results show that habitat structure (i.e. the presence of litter) influences flood-avoiding behavior of A. fulvolineata, by providing more refuges. As the invasion of E. athericus alters salt-marsh habitat structure, it may enhance population size of a rare predatory spider by changing its behavior during flooding and resulting in less deleterious impacts of tides. Yet biological invasions are detrimental for biodiversity conservation, our study shows that an invasive species might indirectly benefit a few mobile rare species in a flood-disturbed habitat.     

Invasion of alien macroalgae in different Mediterranean habitats

The study evaluated different macroalgal invasions in the main Mediterranean coastal habitats on hard bottom. Biodiversity, species composition and structure of macroalgal assemblages were compared among non-invaded areas and areas invaded by the Chlorophyta Caulerpa racemosa var. cylindracea and by the turf-forming Rhodophyta Womersleyella setacea in three different habitats: shallow rocky bottom, deep rocky bottom and dead matte of the seagrass Posidonia oceanica. Results showed that alien macroalgae constituted a relevant component of benthic assemblages in invaded areas of the Mediterranean Sea. Assemblages invaded by Womersleyella setacea and Caulerpa racemosa showed lower values of diversity and large differences in the structure and species composition related to non-nvaded assemblages. The species that mostly suffered from invasion were erect species reproducing sexually; moreover, the dominance of W. setacea led to low abundance of native filamentous algae, while C. racemosa colonization seemed particularly threatening for encrusting algae. All the studied habitats appeared highly invasible by alien macroalgae, even if W. setacea appeared more invasive in deeper habitats, while colonization of C. racemosa seemed more serious in shallower habitats; the dead matte of P. oceanica represented a suitable substrate for the spread of both species. Differences among assemblages in different habitats were reduced in invaded areas.     

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.     

Habitat invasion risk assessment based on Landsat 5 data,exemplified by the shrub Rosa rubiginosa in southern Argentina

Prediction of invasive species spread helps to plan management actions. We performed a risk assessment by quantifying habitat invasibility, predicted the potential distribution of an invasive species using the Maxent modelling program and confirmed patterns using detailed field studies. Our study was conducted in southern Argentina, Patagonia, where large areas are already invaded by the European shrub Rosa rubiginosa. A total of 163 R. rubiginosa locations served as ground truth data, and predictors were obtained from the spaceborne sensor Landsat 5. Based on the Maxent Method (area under the receiver operating characteristic curve 0.8), the habitat invasibility map covered about 5000 km². Our model revealed that R. rubiginosa has the potential to invade 36% of the area along a steep precipitation gradient (target region 600–1400 mm per year). The Tasseled Cap brightness index and the normalized vegetation index explained most of the variance in our model, followed by the Tasseled Cap greenness and wetness indices, which can be interpreted as indicators of disturbance. Highest levels of invasibility were predicted for urban areas, along roads and rivers, on pastures, in Austrocedrus chilensis forests and inside Nothofagus dombeyi forest gaps. Detailed field assessments of rose cover performed in seven habitat types supported these results: rose cover significantly decreased with increasing tree cover (P < 0.01). Our data revealed that the occurrence of R. rubiginosa is not connected to a certain habitat type, but that it thrives in open patches following habitat disturbance. Our approach is a widely applicable, cost‐free remote sensing method that can serve as a risk assessment tool for alien plant species invasion of habitats.     

Commercially Important Trees as Invasive Aliens – Towards Spatially Explicit Risk Assessment at a National Scale

Alien species that are desirable and commercially important in parts of the landscape, but damaging invaders in other parts, present a special challenge for managers, planners, and policy-makers. Objective methods are needed for identifying areas where control measures should be focussed. We analysed the distribution of forestry plantations and invasive (self-sown) stands of Acacia mearnsii and Pinus spp. in South Africa; these two taxa account for 60% of the area under commercial plantations and 54% of the area invaded by alien trees and shrubs. The distribution of commercial forestry plantations and invasive stands of these taxa were mapped and the data was digitised and stored as Geographic Information System (GIS) (Arc/Info) layers. A series of environmental parameters were derived from GIS layers of climate, topography, geology, land use, and natural vegetation. The current distribution of the two taxa was subdivided into three groups according to the degree of invasion, planting history and the precision of the data collection. We used regression-tree analysis to relate, for each taxon, the distribution of invasive stands with environmental variables, and to derive habitat suitability maps for future invasion. The current distribution of invasive stands in South Africa was largely influenced by climatic factors. At a national scale, the distribution of large commercial plantations was a poor predictor of areas invaded by both taxa. Using environmental factors identified by the regression trees, we found that 6.6% and 9.8% of natural habitats currently not invaded and untransformed by urbanisation or agriculture are suitable for invasion by Pinus spp. and A. mearnsii, respectively. We then derived guidelines for policy on alien plant management based on vegetation type, degree of transformation, extent of invasion, and the risk of future alien spread. These factors were used to identify demarcated areas where these alien species can be grown with little risk of invasions, and areas where special measures are needed to manage spread from plantations.     

Relative abundance of an invasive alien plant affects native pollination processes

One major characteristic of invasive alien species is their occurrence at high abundances in their new habitat. Flowering invasive plant species that are visited by native insects and overlap with native plant species in their pollinators may facilitate or disrupt native flower visitation and fertilisation by forming large, dense populations with high numbers of flowers and copious rewards. We investigated the direction of such a proposed effect for the alien invasive Rhododendron ponticum in Irish habitats. Flower visitation, conspecific and alien pollen deposition, fruit and seed set were measured in a self-compatible native focal plant, Digitalis purpurea, and compared between field sites that contained different relative abundances of R. ponticum. Flower visitation was significantly lower at higher alien relative plant abundances than at lower abundances or in the absence of the alien. Native flowers experienced a significant decrease in conspecific pollen deposition with increasing alien abundance. Heterospecific pollen transfer was very low in all field sites but increased significantly with increasing relative R. ponticum abundance. However, lower flower visitation and lower conspecific pollen transfer did not alter reproductive success of D. purpurea. Our study shows that indirect interactions between alien and native plants for pollination can be modified by population characteristics (such as relative abundance) in a similar way as interactions among native plant species. In D. purpurea, only certain aspects of pollination and reproduction were affected by high alien abundances which is probably a result of high resilience due to a self-compatible breeding system. Native species that are more susceptible to pollen limitation are more likely to experience fitness disadvantages in habitats with high relative alien plant abundances.     

Invasion success of alien plants: do habitat affinities in the native distribution range matter?

Aim To assess how habitat affinities in the native distribution range influence the invasion success of 282 central European neophytes (alien plants introduced after ad 1500). Location Czech Republic. Methods Classification trees were used to determine which native habitats donate the most alien species, the correspondence between habitats occupied by species in their native and invaded distribution ranges, and invasion success of species originating from different habitats. Results The species most likely to naturalize in Central Europe are those associated with thermophile woodland fringes in their native range (81%), cultivated areas of gardens and parks (75%) and broad‐leaved deciduous woodlands (72%). The largest proportions of invasive species recruit from those that occur on riverine terraces and eroded slopes, or grow in both deciduous woodland and riverine scrub. When the relative role of habitats in the native range is assessed as a determinant of the probability that a species will become invasive in concert with other factors (the species’ residence time, life history, region of origin), the direct effect of habitat is negligible. However, the effect of native habitats on patterns of invasions observed in central Europe is manifested by large differences in the numbers of species they supply to the invaded region. More than 50 neophytes were recruited from each of the following habitats: dry grasslands, ruderal habitats, deciduous woodland, inland cliffs, rock pavements and outcrops, and tall‐herb fringes and meadows. Main conclusions Casual species recruit from a wider range of habitats in their native range than they occupy in the invaded range; naturalized but not invasive species inhabit a comparable spectrum of habitats in both ranges, and successful invaders occupy a wider range of habitats in the invaded than in the native range. This supports the idea that the invasive phase of the process is associated with changes in biological features that allow for extension of the spectrum of habitats invaded.     

Restoration of Arthropod Assemblages in a Spartina Salt Marsh following Removal of the Invasive Plant Phragmites australis

Invasive plants are one of the most serious threats to native species assemblages and have been responsible for the degradation of natural habitats worldwide. As a result, removal of invasive species and reestablishment of natural vegetation have been attempted in order to restore biodiversity and ecosystem function. This study examined how native arthropod assemblages, an abundant and functionally important group of organisms in many ecosystems, are affected by the incursion of the invasive wetland plant Phragmites australis and if the restoration of the native vegetation in brackish Spartina alterniflora marshes results in the reestablishment of the arthropod community. The invasion of Phragmites into a coastal Spartina marsh in southern New Jersey seriously altered arthropod assemblages and trophic structure by changing the abundance of trophic groups (detritivores, herbivores, carnivores) and their taxonomic composition. Herbivore assemblages shifted from the dominance of external free‐living specialists (e.g., planthoppers) in Spartina to concealed feeders in Phragmites (stem‐feeding cecidomyiids). Moreover, free‐living arthropods in Phragmites became dominated by detritivores such as Collembola and chironomids. The dominant marsh spiders, web‐building linyphiids, were significantly reduced in Phragmites habitats, likely caused by differences in the physical environment of the invaded habitats (e.g., lower stem densities). Thus, trophic structure of arthropod assemblages in Phragmites, as seen in the large shifts in feeding guilds, was significantly different from that in Spartina. Removal of Phragmites with the herbicide glyphosate resulted in the rapid return of Spartina (≤5 yrs). Moreover, return of the dominant vegetation was accompanied by the recovery of most original habitat characteristics (e.g., live and dead plant biomass, water flow rate). The arthropod assemblage associated with Spartina also quickly returned to its preinvasion state and was not distinguishable from that in uninvaded Spartina reference sites. This study provides evidence that the reestablishment of native vegetation in areas previously altered by an invasive plant can result in the rapid recovery of the native arthropod assemblage associated with the restored habitat.     

Altitudinal variation in fertility and vegetative growth in the invasive plant Rubus alceifolius Poiret (Rosaceae), on Réunion island.

Rubus alceifolius Poiret (Rosaceae) was introduced to the island of Réunion in the southeastern Indian Ocean about 1850 and is now highly invasive. This bramble, native from southeastern Asia and Malaysia, has invaded a wide variety of habitats (lowland rainforest, mountain and submountain rainforest, Acacia heterophylla rainforest) from sea level to 1700 m. It is suspected to be monoclonal so, its remarkable success may be due in part to great phenotypic plasticity. On Réunion, bud, flower, fruit and seed production, the duration of the flowering period and the importance of the seed bank were found to be negatively correlated with elevation (50-1500 m a.s.l.). At a lowland site, fruit production in mature stands averaged between 30 and 80 fruits/m² during 1999 and 2000. No fruit set occurred above 1100 m. This fruit production pattern was similar over two years. Although the number of leaves per unit area is similar along the whole gradient studied, decrease of fruit set in upland areas might be compensated for by an increase in vegetative growth. Temperature variation is very sharp along the elevation gradient and may control the fruit and the seed production. Fruit production allows establishment of new populations all around the island via bird dissemination. Once established, R. alceifolius maintains dense patches that can grow vegetatively. Our results may be relevant for eradication programs that should take into account variation in reproductive strategy in lowland vs. highland habitats.     

Factors regulating the invasive success of an alien frog: a comparison of the ecology of the native and alien populations

We examined niche occupancy of Discoglossus pictus, an anuran recently established in Europe, comparing the niches of native (North Africa) and alien populations (south-western Europe) at two spatial scales to determine whether adaptive divergence had occurred between these two populations. Additionally, we determine whether the alien species showed a wider larvae niche and higher phenotypic variability compared with co-occurring anurans. We characterized the breeding habitats and the climatic space occupied by native and alien groups of populations of D. pictus and examined morphological traits of D. pictus and sympatric anuran larvae. Our results revealed no divergence in breeding habitat use between native and alien populations. A shift was observed between the realized niches occupied by the native and alien populations, but this shift might only reflect cryptic niche conservatism. The range of reproductive habitats selected by D. pictus was not wider than those of most native species. In the invaded range, D. pictus showed morphological overlap with some native species and broader phenotypic variability, but the adaptive advantages of this latter attribute were uncertain. Our results suggest that the invasive capacity of this species depends on favourable abiotic conditions rather than on its adaptive advantages over native anurans.     

The alien flora of Greece: taxonomy,life traits and habitat preferences

The aim of the paper is the state-of-the-art assessment of the alien flora of Greece and its traits. The dataset consists of a total of 343 alien taxa, including 49 archaeophytes. The taxonomy, life traits and habitat of the 294 neophytes are analysed vs their naturalisation status. Out of the 122 (41%) naturalised neophytes, 50 are identified as exhibiting invasive behaviour. Poaceae, Asteraceae, Amaranthaceae, Solanaceae, Fabaceae, and Polygonaceae are the plant families richest in alien taxa. The majority of them are of American origin, followed by those of Asiatic and Mediterranean origin. The neophytes are predominantly herbs, most of them annuals. Yet, the perennial life cycle is equally frequent with the annual one and the proportion of phanerophytes in the alien flora is increased compared to the one of the native flora. Regarding flowering traits, most of the aliens have a long flowering period (over 1 month) and flower in late spring, summer and autumn, when few of the native plants are in bloom. Vertebrate zoochory and anemochory are the two dispersal modes mostly utilised by the alien plants (43 and 28%, respectively), while more than one dispersal mechanisms are functional for 56% of them. Artificial habitats have the highest frequencies of alien plants. The natural habitats with the highest numbers of aliens are the coastal ones and inland surface waters. Opuntia ficus-barbarica, Ailanthus altissima, Oxalis pes-caprae, Erigeron bonariensis, Amaranthus albus and Symphyotrichum squamatum are typical cases of plants characterised as invasive, having established in almost all the habitat groups identified. The diversity of the ecological characteristics of the plants suggests a potential of impacts that needs to be further assessed.     

New insights into the distribution of alien cyanobacterium Chrysosporum bergii (Nostocales,Cyanobacteria)

Invasive and alien cyanobacteria are considered as a serious threat to aquatic ecosystems due to their ability to produce cyanotoxins and outcompeting native species. Among cyanobacteria, Nostocales is a group with strong competitive advantages including the production of resting cells, ability to fix nitrogen or high affinity to phosphorus. A species Chrysosporum bergii has broadened its original distribution from brackish and seawater habitats of Caspian and Aral Seas to northern regions of Europe. The aim of our study was to expand the knowledge on the distribution of C. bergii, its preferred habitats in the invaded areas and examine whether the biomass of C. bergii is related with biomass of other alien or native cyanobacteria. We examined the phytoplankton community composition and the abiotic factors in randomly selected lakes of western Poland. For the first time, we showed that it occurs widely in lakes of this region. However, it occurred in one third of the investigated lakes and its contribution to total phytoplankton biomass was low. It occurred more frequently in shallow lakes with low conductivity and dissolved phosphorus, yet with higher total phosphorus concentration. The most remarkable finding was a negative relationship of C. bergii biomass with the biomass of native A. gracile, but a positive relationship with an invasive cyanobacterium C. raciborskii. This result suggests that these alien species occur under similar environmental conditions in Polish lakes. Moreover, the morphological features of C. bergii in Poland were similar to those of Anabaena bergii var. limnetica Couté et Preisig from Lithuania and Anabaena bergii from Czech Republic.