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In central Chile, many exotic species associated with cereal culture and livestock activities were introduced during Spanish colonization. Nowadays, Chilean semi-natural grasslands are a mixture of native species and exotics that mainly originated in the Mediterranean Basin. The establishment and persistence of exotics (i.e. naturalization) can be due to abiotic (climate and soil properties) and biotic (interaction between plants) factors. We assess the importance of these environmental factors as filters that have promoted/ limited the successful naturalization of Spanish species in Chile. Fifteen sites distributed throughout a wide range of Mediterranean climatic conditions, with similar geomorphology and land-use, were selected in both Chile and Spain. At each site we recorded a broad set of soil and climate variables as well as plant species richness during two consecutive years. In Chile, species were classified as natives or exotics whereas in Spain species were classified as colonizers (species that have been naturalized in Chile) or exclusives (only present in Spain). Species richness was higher in Spain (229 species) than in Chile (152), the latter with a high proportion (almost 50 %) of exotics. Different environmental factors affected species richness in each Mediterranean region. In Spain, species classified as colonizers were weakly related to a combination of soil and climate properties, while in Chile the number of exotic species was highly related with climate conditions (especially water availability). Lack of association between native and exotic species richness indicated that biotic filters (i.e. species competition) are less important than abiotic ones in transcontinental naturalization in Chile.

Weeds are commonly considered a threat to biodiversity, yet interactions between native and exotic species in grasslands are poorly understood and reported results vary depending on the spatial scale of study, the factors controlled for and the response variables analysed. We tested whether weed presence and abundance is related to declines in biodiversity in Australian grasslands. We employed existing field data from 241 plots along a disturbance gradient and correlated species richness, cover and Shannon diversity for natives and exotics, controlling for seasonal rainfall, climatic gradients and nutrient status. We found no negative relationships in terms of emergent diversity metrics and occupation of space, indeed, many positive relationships were revealed. When split by land-use, differences were found along the disturbance gradient. In high-moderately disturbed grasslands associated with land-uses such as cropping and modified pastures, positive associations were enhanced. Tolerance and facilitation mechanisms may be involved, such as complementary roles through different life history strategies: the exotic flora was dominated mainly by annual grasses and herbs whereas the native flora represented more diverse growth-forms with a higher proportion of perennials. The positive relationships existing between native and exotic plant species in high-moderately disturbed grasslands of South Australia are most likely due to facilitation through different strategies in occupation of space given that the effect of habitat suitability was controlled for by including environmental and disturbance factors. Consequently, although particular weeds may negatively impact biodiversity, this cannot be generalised and management focusing on general weed eradication in grasslands might be ineffectual.

Dispersal and reproductive traits of successful plant invaders are expected to undergo strong selection during biological invasions. Numerous Asteraceae are invasive and display dimorphic fruits within a single flower head, resulting in differential dispersal pathways -wind-dispersed fruits vs. nondispersing fruits. We explored ecotypic differentiation and phenotypic plasticity of seed output and fruit dimorphisms in exotic Chilean and native Spanish populations of Leontodon saxatilis subsp. rothii. We collected flower heads from populations in Spain and Chile along a rainfall gradient. Seeds from all populations were planted in reciprocal transplant trials in Spain and Chile to explore their performance in the native and invasive range. We scored plant biomass, reproductive investment and fruit dimorphism. We observed strong plasticity, where plants grown in the invasive range had much greater biomass, flower head size and seed output, with a higher proportion of wind-dispersed fruits, than those grown in the native range. We also observed a significant ecotype effect, where the exotic populations displayed higher proportions of wind-dispersed fruits than native populations. Together, these patterns reflect a combination of phenotypic plasticity and ecotypic differentiation, indicating that Leontodon saxatilis has probably increased propagule pressure and dispersal distances in its invasive range to enhance its invasiveness.The impacts of invasive plant species on resident communities and ecosystem functions are a global concern, which has led to considerable resources being invested into studying invasiveness. Of particular importance is predicting which plants will become invasive. The invasiveness of alien plants depends on the habitat characteristics of the recipient area (e.g. the fluctuating resource availability theory 1 ), as well as on species traits 2 . The characteristics of recipient habitats have received considerable attention 3, 4 , highlighting that the habitats more prone to be invaded are those that are more productive or more disturbed 5,6 . However, despite some recent attention, understanding the role played by species traits in the invasion process still remains a key knowledge gap in invasion biology 7,8 .These knowledge gaps exist because invasion success is primarily studied species-by-species 9, 10 , but these gaps also exist because most studies do not compare species traits in native and invasive ranges 11 . Nevertheless, some plant traits related to reproductive and dispersal characteristics have been suggested to be of key importance to invasiveness, such as plant growth rate, seed size, and distance of seed dispersal 7, 12-14 . For example, previous studies have shown that greater plant growth accounts for the invasiveness of many alien plant species 15 . Likewise,

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Understanding the mechanisms that support the arrival, establishment and spread of species over an introduced range is crucial in invasion ecology. We analysed the unintentionally introduced herbaceous species that are naturalised in the five Mediterranean-climate regions. There is an asymmetry in the species flows among regions, being the Iberian Peninsula the main donor to the other regions. At interregional scale, the species’ capacity to spread among regions is related to the ecological versatility of the species in the donor area (Iberian Peninsula). At intraregional scale, the species’ capacity to successfully occupy a complete region first depends on the time elapsed from its introduction and afterwards on the degree of occurrence in the region of origin, which is commonly related to its chance of coming into contact with humans. Information on exotic species in their origin region provides insights into invasion process and decision-making to reduce the risks of future invasions.

Aim Most studies on invasibility consider the characteristics of the habitats colonized. However, the success of the establishment of exotic species can be conditioned by the characteristics of the donor communities. In this study, we analyse the extent to which the distribution of exotic herbaceous species in Chile is conditioned either by the climatic characteristics of the recipient area or by the environmental features of the source areas on the Iberian Peninsula. Location Chile and the Iberian Peninsula (Portugal and Spain).Methods For Chile, we characterized the exotic species according to their current Chilean distribution and their region of origin. For the Iberian Peninsula, we compiled the floristic composition of 11,702 relev es. We classified each relev e according to key habitat characteristics (bioclimate, soil nutrient status and type of community associated with human activities) and calculated the percentage of species in common with Chile in different climatic regions therein. ResultsOver half of Chile's exotic species exhibited a geographic distribution related to the climate of the recipient area. The main donor communities were those associated with ruderal and arable land habitats, although their importance depended upon the climate in the recipient area. Correspondence was observed between the climatic characteristics of the communities in the source area and those of the recipient areas.Main conclusions The results highlight the influence of the characteristics of habitats in the source area on the successful establishment of exotic species in Chile. The relationships between source and recipient area are scale dependent, climate constituting the main driver at broad scale. Within each climatic region, the communities associated with habitats presenting greater anthropic influence act as the main donors. Both features indicate the existence of filters that select species pre-adapted to the climatic and habitat conditions in the recipient area.