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Measuring impacts of non-native species is challenging, particularly for long-established invasions in poorly characterised native ecosystems. Recreating historical population dynamics using dendrochronological methods is a popular approach for addressing conservation and forest management questions. However, these tools are rarely applied for addressing questions of invasion. Classical dendrochronology is also not well suited to many tropical tree species as they do not produce growth rings. Here we test the validity of an alternative approach, based on the analysis of multiple morphological markers, that could allow for both the recreation of historical invasion dynamics as well as quantify the impacts of invasion on the recipient native ecosystem. We validate this method on the Cecropia peltata invasion in Cameroon and its potential impacts on a native tree, Musanga cecropioides. We were able to compare architectural development over time in a mixed secondary forest where the two species co-occur and revealed differences in performance (growth, branching and flower production) between the two tree species. Our results revealed more sustained growth during early establishment and an early sexual maturity for the non-native C. peltata, compared to its native counterpart. A lower density of M. cecropioides was observed in the region of co-occurrence, supporting a hypothesis of competitive exclusion of the native species at the juvenile stage. Our work provides a novel way to understand the impacts of plant invasions via retrospective analysis that could well be applied to other invasions globally, opening up more opportunities to prioritise management on an impact-focused basis. [ABSTRACT FROM AUTHOR]

Processes that drive plant invasions play out across multiple spatial and temporal scales. Understanding individual steps along the introduction-naturalization-invasion continuum and its drivers is crucial for management. This review, targeting the broad audience of invasion scientists, field ecologists and land managers, summarizes the state-of-the-art and potential of remote sensing (RS) in plant invasion science and management. It identifies challenges and research gaps, discusses the discrepancies between technology, science and practice, and suggests ways of addressing some of these issues. Mapping, modelling and predicting invasion processes across scales is a major challenge since they are dynamic and highly complex. Integration of RS data collected at different spatial and temporal scales ("rocking" across scales) has the potential to elucidate the dynamics of invasions and to reveal its drivers, thereby improving the efficiency of control measures. Increasing spatial/temporal resolution of imagery from satellites and drones has much potential to (i) precisely identify even less conspicuous invasive species; (ii) map invasion dynamics; and (iii) provide information on environmental variables and landscape structure at scales fine enough to capture underlying ecological processes. Until now, RS research has focussed primarily on spatio-temporal patterns of plant invasions. Other more challenging topics, such as early monitoring, and revealing the invasion mechanisms and impacts have received less attention. Despite the power of RS technology and recent developments, large discrepancies remain between possibilities and actual implications in research and practical management of invasions. Although recent technological advances, such as powerful algorithms, cloud solutions, and data streams from citizen science, might overcome some limitations, the mutual dialog among field ecologists, managers, invasion scientists and RS specialists remains crucial; our review contributes to such communication. [ABSTRACT FROM AUTHOR]

Biological invasions remain one of the greatest threats to biodiversity and livelihoods, and are predicted to increase due to climate change and globalization. In this study, we produced a comprehensive checklist of alien plants in Nigeria from online flora databases, herbarium records, published field surveys, and questionnaires administered to botanical gardens. The resulting alien flora was classified into naturalized, invasive, and cultivated plants. We then fitted a random forest model to identify the attributes which facilitate the naturalization of alien plants in Nigeria. We also used separate chi-squared tests to investigate if the frequency of these attributes is significantly different between the naturalized and invasive plants. The results include 1,381 alien plant taxa, comprising 238 naturalized, 190 invasive, and 953 cultivated species. The naturalized and invasive plants (428 species) are from 91 families, with Fabaceae and Poaceae having the highest representations. The random forest model showed that life forms and local economic uses were the most important drivers of alien plant naturalization in Nigeria. Chi-squared tests revealed a non-random distribution of life forms, higher frequencies of naturalized plants from the Indomalaya and the Neotropics, greater introductions during the British colonial rule, and that naturalized species are mostly used for medicinal, ornamental, food, or animal fodder purposes. Naturalized and invasive plants were recorded in all regions of Nigeria and are mostly found in urban and agricultural landscapes. This baseline information can support further ecological studies and conservation actions in Nigeria. [ABSTRACT FROM AUTHOR]

Correlative niche models are commonly used in the prevention and management of invasive species. The climatic similarity between non-native and native environments is a necessary assumption for the maintenance of species niches, influencing ecological processes in the persistence of non-native species in novel environments. Spatial patterns derived from distribution models provide a cost-effective method for predicting the occurrence of invasive species, but these models also allow the investigation of processes in the current patterns of non-native species occurrence. Here we used a literature review and niche modeling to investigate the introduction pathway and niche dynamics for non-native vertebrate species in Brazil. We found that environmental enhancement and commodity species are the primary pathways of introduction. Because our model indicated the coastal regions of Brazil as suitable for vertebrate introductions, and these pathways are associated with the animal trade, we highlight that port facilities are key points for species introductions. Non-native species at the early invasive stages showed a higher prevalence of niche unfilling, while those at the later invasive stages showed niche expansion. Also, recent introductions occurred in the margin of suitable climatic conditions, while later introductions generally occurred outside analog climatic conditions. This result emphasizes the significant role of niche shift and climatic conditions in the initial stages of the invasion process as a proximate factor in promoting species persistence. [ABSTRACT FROM AUTHOR]

The risk of invasion from exotic alien plants is enhanced by the increased global flow of humans and trade. Exploring the colonizing ability of invasive alien organisms in local areas is conducive to formulating prevention and control measures. At present, model prediction of potential distribution areas has been frequently used, while there are relatively few experimental tests. Yellow top [Flaveria bidentis (L.) Kuntze] is a globally problematic invasive plant that has become wide-spread throughout northern China. Model predictions were controversial as to whether Flaveria bidentis will spread to southern China. In 2018, seven fitness traits were measured, and seeds were collected from individual plants in 31 populations (899 individuals) of Flaveria bidentis in northern China (invaded area). In 2019, the collected were sown in a common garden in southern China (uninvaded area) under two treatments: manual weeding and no manual weeding. Annual monitoring of the occurrence of Flaveria bidentis seedlings in a common garden in southern China was conducted from 2020 to 2022. Our results showed that in southern China, the 31 populations of Flaveria bidentis could all complete their life history in the common garden with manual weeding. However, in the common garden without manual weeding, the life cycle could not be completed and no surviving seedlings were found in the three-year survey. Compared with the values observed in northern China, the plant height, 1000-grain weight, germination vigor, germination rate and germinable seed number per plant were significantly decreased in the manually weeded common garden in southern China, but the seed number per plant was significantly increased, so the germinable seed number per plant could still reach 4104 ± 1026. Comparison of the phenotypic differentiation coefficient and phenotypic plasticity index showed that the phenotypic difference in different populations was mainly influenced by environmental differences. The above results showed that once Flaveria bidentis is free from biotic resistance from local plants in southern China, it can complete its life cycle and produce abundant offspring, thus achieving colonization, and strong phenotypic plasticity is conducive to its adaptation and diffusion. Therefore, in southern China, monitoring of Flaveria bidentis should be strengthened to prevent it from producing seeds, and the native plant cover is conducive to inhibiting the germination of seeds that may be contained in the soil and seedling growth. [ABSTRACT FROM AUTHOR]

Human-mediated dispersal is a major contributor of biological invasions. To reduce impacts induced by the introduction and spread of exotic species, biosecurity interventions are put into place. These interventions often rely on risk-assessment procedures, whereby biosecurity practitioners (which includes researchers, stakeholders such as national park managers, and all other decision makers who determine when and how to protect biodiversity) attempt to preemptively identify and predict which exotic species could potentially become a threat to natural ecosystems. In theory, extensive field and experimental studies would be required to accurately and precisely determine the risks of biological invasion of a species or group of species. However, due to a lack of resources or knowledge, such critical studies are limited. As a result, biosecurity practitioners rarely have a full picture of the extent to which the exotic species has and will spread at the time of decision making. Hence, they instead opt for preventive measures such as identifying and managing potential target exotic species which are likely to be invasive or dispersal pathways through which exotic species are likely to be introduced and spread. As most of the uncertainties pertaining to biosecurity interventions lie in the resolution of data made available to practitioners at the time of decision making, we first present some of the different types of information which are readily available during the risk-assessment procedure. We then highlight how one could exploit these different resolutions of data during the risk-assessment procedure using network analysis to better understand human-mediated dispersal of exotic species. By doing so, our paper puts forward what network analysis has to offer practitioners in the context of biosecurity interventions. [ABSTRACT FROM AUTHOR]

Understory vegetation is a vital part of urban forests and provides a habitat for the sustainability of plant and animal biodiversity. Understory vegetation in urban forests is highly sensitive to anthropogenic stress and thus more prone to plant invasions. However, the influencing factors and invasion mechanisms of nonnative species (nonnatives) in the understory layers of urban forests remain poorly understood. Here, we studied the understory community structure and composition in 75 plots across 16 urban forests in Shanghai, China. We employed the random forest model, structural equation models and phylogenetic methods to explore the factors contributing to invasion success and impact of nonnatives, and also examined the phylogenetic distance and trait difference between native and nonnatives. We found that 19.4% of the species were nonnatives and Erigeron philadelphicus Willd. was the most frequent species, occurring in 33.5% of the plots. Socio-economic variables (gross domestic product, population, and distance from the city center), the understory cover of native species, and overstory canopy cover were the primary factors driving the invasion success and impact of nonnatives. The variation of the nearest phylogenetic distance between native and nonnative species indicated that both anthropogenic stress and light availability affect understory invasion success, but with different mechanisms. Specifically, an increase in light availability reduces the competition for light and provides invasion opportunities for nonnatives that are phylogenetically close to natives, while more habitat types created by human activities provide more invasion opportunities for species with distant phylogenetic relationships with the native species. We believe that these findings have important implications in the management and control of understory invasions in urban forests. [ABSTRACT FROM AUTHOR]

Introduced invasive plants are a major environmental problem, but public interest in invasive plants is generally considered low compared to climate change and threatened flagship species, hindering support for effective management and policy. To understand what does drive public interest in invasive plants in the US, we investigated Google Trends search data from 2010 to 2020 for 209 introduced plant species found in the continental US. Using a phylogenetically-controlled structural equation model, we investigated three hypothesized drivers of interest: (1) plant abundance as quantified by national and state-level occurrence records in the Global Biodiversity Information Facility, (2) four key plant traits that might influence plant conspicuousness to the general public: ornamental use, human health risks, monoculture formation, and plants with positive economic value, and (3) media coverage, in particular the volume and sentiment of news articles over the same 10-year period. Public search interest was highest for the most abundant introduced species and those with human health risks, but significantly lower for ornamentals. News coverage was mostly negatively toned and disproportionately focused on a relatively small group of widespread invasive species, with significantly lower and more positively-worded coverage of ornamentals. Ultimately, we suggest that a narrow emphasis on a few highly covered 'notorious' invasive plant species, with lower and more positive coverage of ornamental introduced species, could send mixed messages and weaken public awareness of the threats of biological invasions. However, the generally strong linkages between public search interest and media coverage of invasive plants suggests ample opportunity to improve messaging and increase public awareness. [ABSTRACT FROM AUTHOR]

Invasive plant management is a costly endeavor, with new areas constantly being invaded and new invaders perpetually appearing. Managers need to be efficient in how they use the limited resources they have for management activities, especially when managing large areas or extensive invasions. While a large body of developed mathematical models predicting plant invasion spread and impact can help determine optimal strategies to achieve the maximum return from management investment, we still lack adequate knowledge to generalize optimal strategies in the field since little empirical work has been done to validate existing conclusions from the modeling approaches. To address critical gaps between invasive plant management and modeling, we discuss how a variety of developed models can be used to inform on-the-ground management and identify major challenges that inhibit field application of modeling findings. We propose potential solutions to these challenges, including (1) developing models that share mutual objectives with field managers; (2) using model input parameters that are easily measured in the field to improve communication and understanding between modelers and managers; (3) moving away from models that rely on data- and time-intensive individual-based measurements and towards models that are more patch-based and/or hierarchical in nature; and (4) encouraging managers to better integrate model output/results into management activities by developing field-applicable models with output parameters that are familiar to land managers, e.g., socioeconomic or logistical factors. These solutions are expected to facilitate communication and create a culture in which long-term interactions and interdisciplinary teams between managers and modelers can be built, which will ultimately contribute to more efficient incorporation of relevant modeling results into management activities and improve our ability to manage invasive plant species. [ABSTRACT FROM AUTHOR]

Urena lobata, a pan-African weed has been described as a noxious invader which has spread across several countries in the world. Its ability to grow in a variety of habitats has enabled its success as an invader. However, there is a paucity of data on its invasion ecology in relation to land use in invaded ranges of Nigeria. In this study, the cover of U. lobata along roadsides and in relation to the land use of adjacent lands in five sites across major cities in Nasarawa State, Nigeria was assessed. Its abundance and impacts on native plant diversity and species richness were investigated. U. lobata was discovered in 74.6% of the sampled sites along the roadsides in Nasarawa State. Land use of the adjacent land had a significant effect on the roadside cover of U. lobata in the study area. The density of U. lobata ranged from 9533 to 17,166 mature individual ha−1 across the State. This plant exhibited a negative impact on native plant diversity by reducing the species richness and diversity indices of the invaded sites. From this study, it is evident that land use plays a significant role in the spread and establishment of U. lobata across the guinea savanna vegetation of Nigeria. [ABSTRACT FROM AUTHOR]

Cortaderia selloana (pampas grass), native to South America, is a widespread invasive plant in several regions of the World, including the south of the Atlantic Arc (Europe), where it has been used as an ornamental species. Citizens may help to spread it, e.g., planting it in their gardens, but on the other hand, when they are aware of its invasiveness, can contribute to control it and prevent its spread. An online survey was performed to better understand the perception and knowledge of Portuguese and Spanish citizens, regarding pampas grass. The influence of education and occupation, along with age, gender and country of residence, on the knowledge and perceptions of respondents was analysed. The questionnaire was answered by 486 and 839 citizens in Portugal (PT) and Spain (ES), respectively. Most respondents were between 41 and 64 years old, mostly women in Portugal and equally women and men in Spain, with higher education and working mostly in the services sector. The majority of respondents in both countries recognized the plant, knew it is invasive and were able to name it, alerting to a possible bias of the target audience toward citizens already aware of the invasiveness of the pampas grass. Fewer respondents were aware of the legislation that limits its use, and most were unable to identify particular characteristics of the species. The results showed that respondents' occupation in PT and education in ES influenced their knowledge and perception about pampas grass. This study confirms that education and raising awareness regarding invasive species is of utmost importance, as respondents identified academic training and projects with a strong focus on public awareness as the main sources of knowledge regarding pampas grass. Better informed citizens can be part of the solution rather than part of the problem, especially regarding invasive species with such ornamental interest as pampas grass. [ABSTRACT FROM AUTHOR]

Some invasive ants have worldwide distributions and impose substantial impacts on human society and native biodiversity. Yet we know little about how ants impact soil ecosystems in general, much less how soil ecosystems shift when invasive ants move in. We excavated the coarse roots of a monodominant savanna tree in invaded and uninvaded areas to test the hypothesis that the presence of invasive ants would be associated with changes in root distribution and biomass across the landscape. We found that in the presence of invasive ants, trees had a shifted distribution of lateral coarse roots, with proportionally less root biomass near the surface and far from tree stems. In addition, the density of lateral coarse-root biomass was ~ 20% lower for trees within invaded landscapes. Our results suggest that soil-nesting invasive ants can drive important changes in rooting strategy for a tree species that serves a foundational role in the biogeochemical cycles of vertisol savannas. [ABSTRACT FROM AUTHOR]

This first inventory of casual, naturalized, and invasive alien plants in Iran provides a knowledge base for managing the threats associated with plant invasions in this country. Based on a wide range of data sources, including published work, reports, online databases, botanical records, and field observations, we identified 311 alien vascular plants, of which 131 are classified as casual, 167 naturalized, and 13 invasive. Therophytes are most represented among naturalized plants (50.9%), while phanerophytes (49.6%) are most represented among casuals. Poaceae, Fabaceae and Asteraceae are the families with the highest richness of alien species (35, 28, and 24, respectively). The largest fractions of naturalized taxa originated from South America and Central America (22.2% and 20.4% of all naturalized aliens, respectively). Horticulture and agriculture are the main pathways of new introductions of alien plants to Iran; this is reflected in naturalized species playing a major role in the weed flora of Iran, with about a half of them growing in agricultural habitats. Naturalized plants are also common in ruderal habitats, while casual plants commonly occur not only in these two types of human-disturbed habitats but also in open forest. We suggest that exploring the effect of bioclimatic conditions along with human population density in this large and diverse country could provide further information about alien species invasions; for that, future research should focus on mapping alien species spatial distribution in Iran and continue monitoring new arrivals in order to develop robust quarantine system at the national level. [ABSTRACT FROM AUTHOR]

Controlling invasive alien species invasion and maintaining the survival of native species have attracted increasing attention, and habitat destruction can be used to achieve these aims. However, whether and how to promote the long-term survival of native species facing invaders through the use of habitat destruction remain unclear. In this study, we developed a spatially explicit simulation model in which invaders and natives were exposed to habitat destruction with different properties, including the spatial structure and the introduction time of habitat destruction, the interval between two destruction events, and the proportion of destroyed habitat. The results showed the following: (1) introducing habitat destruction could promote the long-term survival of native species, especially for a clustered initial spatial distribution of species or long-distance dispersal; (2) the positive effect of habitat destruction on the survival of native species occurred only for a period of time after introduction, such that the destroyed habitats gradually encompassed natives and separated them from invaders, prior to which habitat destruction substantially decreased the abundance of native species; (3) intermediate to high levels of habitat destruction were the most beneficial to the protection of native species for the clustered spatial distribution of species at the initial time or the short dispersal distance; (4) and even when ignoring the proportion of destroyed habitats, introducing spatially dispersed habitat destruction at an earlier time and shortening the interval between two habitat destruction events were very beneficial to the protection of natives. These insights can help facilitate the protection of natives under invasion by adjusting the implementation method of habitat destruction. [ABSTRACT FROM AUTHOR]

Invasive plants can alter fuels and fire regimes in ways that facilitate their spread and dominance through a process known as the invasion-fire cycle. This phenomenon can result in considerable fire and ecosystem impacts, but mechanisms, habitat susceptibility, and prevalence of invasion-fire cycles are poorly understood. Here, we reviewed literature on invasion-fire cycles and describe how mechanisms by which and habitats in which invasion-fire cycles occur are influenced by invader growth form, including woody versus herbaceous and perennial versus annual species, among other factors, and highlight research needs to better understand invasion-fire cycles. We found evidence that annual herbaceous species facilitated more continuous and frequent fires in shrublands and deserts by increasing fine fuel continuity, while perennial grasses and woody invaders more often facilitated intense and vertically continuous fires in forest habitats by increasing fuel loads. There was some evidence woody invaders can suppress fires by decreasing fine fuels, and both woody invaders and perennial grasses and forbs can inhibit fires due to high fuel moisture and low flammability, but effects of fire suppression by invaders on native communities were ambiguous. Fire suppression and climate change may complicate effects of invasions on fire regimes directly, or indirectly through shifting abundances of fire prone or fire adapted native plant species. More research is needed to understand how propagule pressure, ignitions, climate, and resource availability affect invasion-fire cycles, and to determine relative importance of invasion-fire cycles in driving plant invasions and effects of invader driven changes to fire regimes on native communities. [ABSTRACT FROM AUTHOR]

Over the last few decades, rainfall has become more variable, with a worldwide increase in the frequency of extreme precipitation events. While increases in rainfall variability are expected to significantly affect plant species, the effects of precipitation dynamics on plant invasions remains understudied. We examined the growth response of Alternanthera philoxeroides to varying water availability at the community level when grown in a monoculture and mixed community with four commonly co-occurring native species. The native species were also grown together as a control to compare to the invasive species communities. Seven water treatments were applied to each community, including a 'normal' treatment (based on the average rainfall for the area), drought (water was one third of the normal treatment), flood (water was double the normal treatment), and other simulated extreme events (where water availability was more variable than the normal treatment). All plants were measured for growth (e.g., biomass and stolon length) and competitive traits (i.e., relative competitive dominance and relative interaction indices). Most growth traits in A. philoxeroides were enhanced with increased and/or more variable water availability in both the monoculture and mixed community. In contrast, differences in growth traits in the native plants were mostly non-significant across treatments in each plant community. Compared to the normal treatment, A. philoxeroides had higher relative competitive dominance (RDI) and interaction (RII) indices in response to flooding. Conversely, RII in the native species was not significantly different among treatments. Overall, our results suggest that A. philoxeroides is more responsive to flooding compared to the natives. Our study provides useful insights into growth response and competitiveness of A. philoxeroides to precipitation variability across different plant communities. [ABSTRACT FROM AUTHOR]

Natural infections of Verticillium spp. (Fungi, Ascomycota) on Ailanthus altissima have suggested to consider the biological control as a promising strategy to counteract this invasive plant, which is otherwise difficult to control by traditional mechanical and chemical treatments. Verticillium wilt is able to lead plants to death, throughout a pathogenic mechanism including vessel occlusions and production of degrading enzymes and phytotoxins. In this study, a 10 weeks open air pot experiment was set to investigate the ecophysiological and biochemical responses of Ailanthus trees artificially inoculated in the trunk with the V. dahliae strain VdGL16, previously isolated in Central Italy from the same host. Inoculated plants showed visible injuries starting from 2 weeks post inoculation (wpi), that progressively developed until a final severe defoliation. The fungal infection rapidly compromised the plant water status, and photosynthesis was impaired due to both stomatal and mesophyll limitations from 4 wpi, with subsequent detrimental effects also on PSII activity. Moreover, the disease altered the translocations of nutrients, as confirmed by cation and carbohydrate contents, probably due to a consumption of simple sugars and starch reserves without replacement of new photosynthesized. An accumulation of osmolytes (abscisic acid and proline) and phenylalanine (a precursor of phenylpropanoids) was also reported at 8 wpi, this being a response mechanism that needs to be further elucidated. However, the activation delay of such defence strategy inevitably did not avoid the premature defoliation of plants and the decline of physiochemical parameters, confirming the key role of Verticillium in Ailanthus decay. [ABSTRACT FROM AUTHOR]

Regulations provide the legal basis for managing biological invasions, but assessments of their effectiveness are rare. To assess the influence of national and local regulations on alien plant species richness and composition in a large protected area (Kruger National Park [KNP], South Africa) we surveyed tourist camps and staff villages for alien ornamental plants. We compared our survey results in 2020 with a previous survey carried out between 1999 and 2003, in the context of national regulations on alien plants promulgated in 2001 and 2014. The number of alien plant species recorded in KNP has almost doubled since the first survey (from 231 to 438), although there has been significant species turnover (93% average replacement across all camps). Importantly, however, both the number of listed and regulated alien plant species found in KNP, and their species richness per camp, have declined (by 38% overall and by 56% per camp). This suggests that regulations are effective. In contrast, the number of unregulated ornamental alien species recorded has increased (by 157% overall). This is likely partly due to an increase in survey effort. Alien species regulations provide clear guidance for conservation managers, and there are promising signs of their effectiveness in directing management in KNP. However, converting alien species lists into priorities for control or regulation will continue to require risk analyses sensitive to park user needs. We advocate for better monitoring of the effectiveness of the regulations, and for the results of such monitoring to be interpreted based on local management needs and concerns. [ABSTRACT FROM AUTHOR]

The little fire ant, Wasmannia auropunctata, is an invasive species known to negatively affect many native species in its introduced range. Here, we studied the effect of little fire ant presence on the biomass of soil fauna in rainforest of New Caledonia to assess if little fire ants have an impact on an endangered endemic flightless bird, the kagu, Rhynochetos jubatus. The average biomass of soil fauna (except for millipedes) was lower in 53 sample plots with little fire ants than in 597 sample plots without little fire ants and the biomass decreased with increasing density of little fire ant nests. Millipedes on the contrary seemed to be positively impacted as their average biomass was higher in areas with fire ants than in areas without, but even millipede biomass decreased with increasing nest density of fire ants. Kagu density decreased with increasing area of rainforest invaded by little fire ants, suggesting, given their observed negative impact on soil fauna biomass, that they may limit food resources for kagu. Little fire ants might therefore transform rainforest into a less suitable habitat for the kagu by reducing the biomass of their prey and thus have a negative impact for kagu conservation. [ABSTRACT FROM AUTHOR]

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Humans are facilitating the introduction and range expansion of invasive alien species (IAS), which have negatively impacted ecological and socio-economic systems worldwide. Understanding the global diffusion of IAS is important for developing environmental policies and management strategies. We estimate the rate of increase and the doubling times of the number of new records of 178 IAS using a global dataset with c. 3.4 million records obtained over c. 100 years. Here, we show that the number of records of IAS have exponentially increased with a mean double time of c. 14 years across the Earth. For the most analysed species, the number of records increased faster in the non-native than native continents, suggesting that such IAS might be exponentially expanding their range size. We also found that each continent has a taxonomic group with a particular increase in IAS records. Governments and scientists should pay attention to these taxonomic groups to implement appropriate control or management actions. Our study provides an indication that the current local, regional and continental efforts to control invasions may be not sufficient at the global scale. This is a concerning situation given the great number of areas available for invasion worldwide. [ABSTRACT FROM AUTHOR]

Cities and towns can be conceptualized as invasion hotspots. The connections created by roads or highways facilitate the mobility of these species, expanding their range of distribution and contributing to their expansion through the landscape to other urban areas or nearby natural and semi-natural ecosystems. Here we describe the actual distribution of invasive plants in a region of Colombia and determine the role that urban centers, road edges, and rivers have in shaping their distribution. We mapped—at high resolution—the distribution of exotic species in the Alto Ricaurte region (Boyacá, Colombia), specifically in the towns of Villa de Leyva, Sáchica, Sutamarchán, and Arcabuco and connecting roads. Initially, a list of 40 exotic plant species with invasive potential was assembled: 26 of which were mapped in the region. Then, we used Poisson models to test whether invasive species appear more frequently near cities, roads, and riverbanks. We found that roadside and riverbank areas host more exotic species than more distant zones. Our findings suggest that roads and rivers are efficient dispersal corridors connecting different invasive hotspots with other landscape elements. Urban centers act as islands of invasion and roads and rivers as corridors for species dispersal. This invasion scenario is already causing economic and ecological damage: roads are heavily deteriorated byR. communis, K. densiflora, and C. jubata, while P. aquilinum and M. minutiflora may increase the occurrence of fires in the region. [ABSTRACT FROM AUTHOR]

Biological invasions are one of the top drivers of the ongoing biodiversity crisis. An underestimated consequence of invasions is the enormity of their economic impacts. Knowledge gaps regarding economic costs produced by invasive alien species (IAS) are pervasive, particularly for emerging economies such as India—the fastest growing economy worldwide. To investigate, highlight and bridge this gap, we synthesised data on the economic costs of IAS in India. Specifically, we examine how IAS costs are distributed spatially, environmentally, sectorally, taxonomically, temporally, and across introduction pathways; and discuss how Indian IAS costs vary with socioeconomic indicators. We found that IAS have cost the Indian economy between at least US$ 127.3 billion to 182.6 billion (Indian Rupees ₹ 8.3 trillion to 11.9 trillion) over 1960–2020, and these costs have increased with time. Despite these massive recorded costs, most were not assigned to specific regions, environments, sectors, cost types and causal IAS, and these knowledge gaps are more pronounced in India than in the rest of the world. When costs were specifically assigned, maximum costs were incurred in West, South and North India, by invasive alien insects in semi-aquatic ecosystems; they were incurred mainly by the public and social welfare sector, and were associated with damages and losses rather than management expenses. Our findings indicate that the reported economic costs grossly underestimate the actual costs, especially considering the expected costs given India's population size, gross domestic product and high numbers of IAS without reported costs. This cost analysis improves our knowledge of the negative economic impacts of biological invasions in India and the burden they can represent for its development. We hope this study motivates policymakers to address socio-ecological issues in India and launch a national biological invasion research programme, especially since economic growth will be accompanied by greater impacts of global change. [ABSTRACT FROM AUTHOR]

Ecological and socioeconomic impacts from biological invasions are rapidly escalating worldwide. While effective management underpins impact mitigation, such actions are often delayed, insufficient or entirely absent. Presently, management delays emanate from a lack of monetary rationale to invest at early invasion stages, which precludes effective prevention and eradication. Here, we provide such rationale by developing a conceptual model to quantify the cost of inaction, i.e., the additional expenditure due to delayed management, under varying time delays and management efficiencies. Further, we apply the model to management and damage cost data from a relatively data-rich genus (Aedes mosquitoes). Our model demonstrates that rapid management interventions following invasion drastically minimise costs. We also identify key points in time that differentiate among scenarios of timely, delayed and severely delayed management intervention. Any management action during the severely delayed phase results in substantial losses (> 50 % of the potential maximum loss). For Aedes spp., we estimate that the existing management delay of 55 years led to an additional total cost of approximately $ 4.57 billion (14% of the maximum cost), compared to a scenario with management action only seven years prior (< 1% of the maximum cost). Moreover, we estimate that in the absence of management action, long-term losses would have accumulated to US$ 32.31 billion, or more than seven times the observed inaction cost. These results highlight the need for more timely management of invasive alien species—either pre-invasion, or as soon as possible after detection—by demonstrating how early investments rapidly reduce long-term economic impacts. [ABSTRACT FROM AUTHOR]

Biological invasions are one of the main threats to biodiversity within protected areas (PAs) worldwide. Meanwhile, the resilience of PAs to invasions remains largely unknown. Consequently, providing a better understanding of how they are impacted by invasions is critical for informing policy responses and optimally allocating resources to prevention and control strategies. Here we use the InvaCost database to address this gap from three perspectives: (i) characterizing the total reported costs of invasive alien species (IAS) in PAs; (ii) comparing mean observed costs of IAS in PAs and non-PAs; and (iii) evaluating factors affecting mean observed costs of IAS in PAs. Our results first show that, overall, the reported economic costs of IAS in PAs amounted to US$ 22.24 billion between 1975 and 2020, of which US$ 930.61 million were observed costs (already incurred) and US$ 21.31 billion were potential costs (extrapolated or predicted). Expectedly, most of the observed costs were reported for management (73%) but damages were still much higher than expected for PAs (24%); in addition, the vast majority of management costs were reported for reactive, post-invasion actions (84% of management costs, focused on eradication and control). Second, differences between costs in PAs and non-PAs varied among continents and environments. We found significantly higher IAS costs in terrestrial PA environments compared to non-PAs, while regionally, Europe incurred higher costs in PAs and Africa and Temperate Asia incurred higher costs in non-PAs. Third, characterization of drivers of IAS costs within PAs showed an effect of environments (higher costs in terrestrial environments), continents (higher in Africa and South America), taxa (higher in invertebrates and vertebrates than plants) and Human Development Index (higher in more developed countries). Globally, our findings indicate that, counterintuitively, PAs are subject to very high costs from biological invasions. This highlights the need for more resources to be invested in the management of IAS to achieve the role of PAs in ensuring the long term conservation of nature. Accordingly, more spatially-balanced and integrative studies involving both scientists and stakeholders are required. [ABSTRACT FROM AUTHOR]

In addition to being a major threat to biodiversity and ecosystem functioning, biological invasions also have profound impacts on economies and human wellbeing. However, the threats posed by invasive species often do not receive adequate attention and lack targeted management. In part, this may result from different or even ambivalent perceptions of invasive species which have a dual effect for stakeholders—being simultaneously a benefit and a burden. For these species, literature that synthesizes best practice is very limited, and analyses providing a comprehensive understanding of their economics are generally lacking. This has resulted in a critical gap in our understanding of the underlying trade-offs surrounding management efforts and approaches. Here, we explore qualitative trends in the literature for invasive species with dual effects, drawing from both the recently compiled InvaCost database and international case studies. The few invasive species with dual roles in InvaCost provide evidence for a temporal increase in reporting of costs, but with benefits relatively sporadically reported alongside costs. We discuss methods, management, assessment and policy frameworks dedicated to these species, along with lessons learned, complexities and persisting knowledge gaps. Our analysis points at the need to enhance scientific understanding of those species through inter- and cross-disciplinary efforts that can help advance their management. [ABSTRACT FROM AUTHOR]

Regulation of alien invasive species by indigenous generalist herbivores is a strong component of ecosystem biotic resistance. Globally, Australian Acacia species are highly invasive trees that are regulated by specialist invertebrate herbivores, granivorous birds and consumption by indigenous and exotic vertebrates in their native ranges. Australian Acacias have become highly invasive in the Cape Floristic Region (CFR) of South Africa where seeds are consumed by generalist bird, ant, and rodent species, but there is as yet no evidence that generalist herbivores consume the seedlings. Despite this, indigenous mice are common in the CFR and we consequently hypothesised that seedling herbivory by indigenous herbivores may limit survival of Acacia cyclops in relatively undisturbed indigenous ecosystems. Acacia cyclops seedlings were transplanted into indigenous CFR coastal "strandveld" vegetation at two distinct study sites and monitored for eight days in one of three caged treatments (i) no cage, (ii) partially caged excluding large mammalian herbivores or (iii) fully caged excluding all mammalian herbivores. Herbivory-induced seedling mortality without a cage and for partially caged plants was significantly greater than for fully caged plants (all contrasts P < 0.001). Rapid herbivory of A. cyclops seedlings in the uncaged and partially caged treatments was largely attributable to highly abundant striped mice, Rhabodmys pumilio. Seedling herbivory was not dependent on rodent density, which was consistently high (200–300 mice ha−1). However, seedling herbivory was higher in areas with dense vegetation and lower in open-canopy areas, probably because R. pumilio is known to avoid foraging in open areas. These generalist herbivores reduced A. cyclops recruitment in relatively undisturbed indigenous ecosystems, contributing to a degree of ecosystem resistance. [ABSTRACT FROM AUTHOR]

Biological invasions are a major threat to natural systems, as well as to human wellbeing and livelihoods. An association of alien plant species with dump sites has received limited research attention in South Africa, and this creates a loophole for effective monitoring and management. We surveyed dump sites from 79 towns/localities in the Free State, Gauteng, and the Northern Cape and North West provinces of South Africa for presence of alien plant species. We recorded 206 alien plant species classified into 50 families, and the dominant families included Cactaceae (18.5%; N = 767), Asteraceae (12.1%), Solanaceae (10.5%), and Fabaceae (8.2%). Significant numbers of herbaceous species (33.0%; N = 206), and succulents (13.6%) had been introduced from North and South America and Europe, while woody species (39.8%) came from different regions of the world. We detected significantly fewer (i.e., 3.9% N = 206) emerging alien plant species in national regulations' category 1a suggesting they may be restricted to their introduction locations, while 8.8% were species not listed in the national regulations, thus suggesting that they should be listed. The species' richness was significantly and inversely correlated with environmental temperatures of each town/locality. In support of the study prediction, the dump sites in Free State Province had the highest number of alien plant species that are unknown in the main provincial species pool (i.e., 71); Northern Cape, 42 species, while the North West and Gauteng Provinces were equal in having 10 unknown species. We conclude that a context-specific management policy is urgently required for biological invasions in dump sites as a way of reducing further invasions and their impact, and that dump sites should be considered as monitoring points in South Africa. [ABSTRACT FROM AUTHOR]

Established non-native species can have significant impacts on native biodiversity without any possibility of complete eradication. In such cases, one management approach is functional eradication, the reduction of introduced species density below levels that cause unacceptable effects on the native community. Functional eradication may be particularly effective for species with reduced dispersal ability, which may limit rates of reinvasion from distant populations. Here, we evaluate the potential for functional eradication of introduced predatory oyster drills (Urosalpinx cinerea) using a community science approach in San Francisco Bay. We combined observational surveys, targeted removals, and a caging experiment to evaluate the effectiveness of this approach in mitigating the mortality of prey Olympia oysters (Ostrea lurida), a conservation and restoration priority species. Despite the efforts of over 300 volunteers that removed over 30,000 oyster drills, we report limited success. We also found a strong negative relationship between oyster drills and oysters, showing virtually no coexistence across eight sites. At experimental sites, there was no effect of oyster drill removal on oyster survival in a caging experiment, but strong effects of caging treatment on oyster survival (0 and 1.6% survival in open and partial cage treatments, as compared to 89.1% in predator exclusion treatments). We conclude that functional eradication of this species requires significantly greater effort and may not be a viable management strategy in this system. We discuss several possible mechanisms for this result with relevance to management for this and other introduced species. Oyster restoration efforts should not be undertaken where Urosalpinx is established or is likely to invade. [ABSTRACT FROM AUTHOR]

Elton's classic diversity-invasibility hypothesis posits that diversity of resident communities increases resistance against invaders. We tested whether the diversity-invasibility relationsip might be mediated by allelopathic effects of the resident species. In a large germination experiment, we exposed seeds of six alien and six native test species to leachates of one, three, six or twelve species. The leachates tended to slightly delay germination, and almost all single-species leachates reduced the proportion of germinated seeds. Nevertheless, the overall effect of the plant leachate mixtures on the proportion of germinated seeds was not significant. This was because a higher diversity of the leachates increased the proportion of germinated seeds, particularly for native test species. Among the six alien test species, it was only the most invasive one that benefited from increased diversity of the leachates, just like the natives did. Overall, our findings suggest that allelopathy of diverse communities does not provide resistance but could actually facilitate the germination of invaders. [ABSTRACT FROM AUTHOR]

The ecological impacts of invasive species may change or accumulate with time since local invasion, potentially inducing further changes in communities and the abiotic environment. Yet, time since invasion is rarely considered when investigating the ecological impacts of invasive non-native species. To examine the effect of time since invasion on the ecological impacts of Lupinus polyphyllus, a perennial nitrogen-fixing herb, we surveyed vascular plant communities in the presence and absence of L. polyphyllus in young, intermediate, and old semi-natural grassland sites (ca. 5, 10, 15 years representing both time since lupine invasion and plant community age). We analyzed vascular plant community composition, vascular plant species richness, and the cover of various ecological plant groups and L. polyphyllus. In contrast to our hypotheses, we found no change in the mean cover of L. polyphyllus (about 35%) with time since local invasion, and an ordination did not suggest marked changes in plant community composition. L. polyphyllus was associated with lower species richness in invaded plant communities but this effect did not change with time since invasion. Invaded plant communities were also associated with lower occurrence of generalist, oligotrophic (low-nutrient-adapted) and copiotrophic (nutrient-demanding) species but no temporal dynamics were detected. We conclude that even the intermediate cover of L. polyphyllus can reduce plant species richness, but the ecological impact caused by this invader might not dramatically change or accumulate with time since invasion. [ABSTRACT FROM AUTHOR]

Invasions by non-native plant species are widely recognized as a major driver of biodiversity loss. Globally, (sub-)tropical islands form important components of biodiversity hotspots, while being particularly susceptible to invasions by plants in general and vines in particular. We studied the impact of the invasive vine A. leptopus on the diversity and structure of recipient plant communities on the northern Caribbean island St. Eustatius. We used a paired-plot design to study differences in species richness, evenness and community structure under A. leptopus-invaded and uninvaded conditions. Community structure was studied through species co-occurrence patterns. We found that in plots invaded by A. leptopus, species richness was 40–50% lower, and these plots also exhibited lower evenness. The magnitude of these negative impacts increased with increasing cover of A. leptopus. Invaded plots also showed higher degrees of homogeneity in species composition. Species co-occurrence patterns indicated that plant communities in uninvaded plots were characterized by segregation, whereas recipient plant communities in invaded plots exhibited random co-occurrence patterns. These observations suggest that invasion of A. leptopus is not only associated with reduced species richness and evenness of recipient communities in invaded sites, but also with a community disassembly process that may reduce diversity between sites. Given that A. leptopus is a successful invader of (sub-)tropical islands around the globe, these impacts on plant community structure highlight that this invasive species could be a particular conservation concern for these systems. [ABSTRACT FROM AUTHOR]

Species of the genus Acacia have been introduced worldwide and have negative environmental and socio-economic impacts in many introduced regions. This study makes use of environmental and socio-economic impact classification schemes for alien taxa (EICAT and SEICAT) to assess the impacts that 33 acacias introduced to South Africa have at a global scale. The aims of this study were: (1) to compare the EICAT impact categories which are based on literature with expert assessments; (2) to determine which environmental and socio-economic mechanisms underlie acacia impacts; and (3) to test if certain habitats experience higher impact magnitudes than others. Most acacias had a massive impact when evaluated by experts, while the impact was mostly major for EICAT. This could be due to the use of different definitions for the impact categories. It might also show that the data available is insufficient or inadequate in showing that such high impacts exist. Competition was found to be the most often recorded mechanism underlying acacia environmental impacts and was one of the mechanisms with the largest impact magnitude. Grassland, shrubland, marine-coastal and forest habitats were found to be impacted by acacias equally as much. Using impact scoring schemes as an evidence-based and transparent approach to determine the impact status of alien species provides a more robust method to aid management prioritisation and risk assessment than expert opinion alone. However, data quality and availability could limit their effectiveness, especially for less well studied species. [ABSTRACT FROM AUTHOR]

Geographical variation in the likelihood of biological invasions can be affected by propagule pressure and habitat suitability, which are driven by ecological and social processes. Past studies have empirically quantified the role of drivers by comparing geographical variation in numbers of invading species with variation in candidate factors; however, lack of data has limited empirical studies for individual species. Lymantria dispar (L.), a nonnative forest pest formerly known as gypsy moth, is an exemplar species for exploring invasion drivers because of extensive records on its spread. Since its establishment in eastern United States in 1869, it has been repeatedly introduced into outlying areas, prompting 325 eradication programs from 1972 to 2014. We used these eradication programs as proxies for new establishment events, with the assumption that populations would have established in the absence of eradication treatments. These proxy events were used to quantify the effects of socio-environmental factors on the probability of L. dispar arrival and establishment. Establishment probability was significantly affected by propagule pressure (distance to the previously invaded area, human population size, and the area of source outbreaks) and habitat suitability (climate and availability of host trees). The statistical model developed here can be used to predict invasions and inform surveillance strategies to more efficiently manage these invasions. [ABSTRACT FROM AUTHOR]

Compared to other facets of invasion science, the impacts of biological invasions have been understudied, but many studies have been published in the last decade. This paper reviews the growing body of evidence of impacts of invasions in South Africa. We classified information for individual species into ten ecological and four social categories of impact. We also reviewed studies that upscaled this information to larger spatial scales, as well as progress with assigning invasive species to impact severity categories. We identified 123 studies that documented the impacts of 71 invasive alien species, about 5 of the country's naturalized alien biota. The most frequently reported impact category was species interactions (changes to habitat suitability, pollination networks or seed dispersal mechanisms), followed by direct competition, changes to ecosystem functioning (hydrology or nutrient dynamics), hybridization and predation. Trees and shrubs accounted for more than half of the species studied, but there were examples from most other groups of plants and animals. The social consequences of invasions have been less well studied at the level of individual species. Most studies (72%) considered the impacts of a single species, based on data collected on < 1 ha, and were completed in less than a year. Space-for-time substitution was widely used, but widespread collection of data from numerous small plots allowed for reporting impact over larger spatial scales. We also identified seven studies that either monitored impacts over longer periods (up to 40 years), or repeated surveys in the same area to assess change over time. Prominent landscape-scale impacts included reductions in water resources, the attrition of native biodiversity, reductions in rangeland productivity, predation of marine birds and freshwater fishes, and disease organisms affecting native mammals and trees. Nineteen studies at broader scales estimated substantial impacts on landscape-scale water yield, habitats and biodiversity, rangeland productivity, and the economic value of ecosystem services. Despite considerable progress, our understanding remains fragmentary. Impacts are expected to grow as invasions enter exponential phases of spread and densification and as the duration of invasions increases. A robust understanding needs to be developed to provide justification for management costs. [ABSTRACT FROM AUTHOR]

Wildlife trade imposes direct and indirect negative impacts on the environment but particularly through the continual introduction of species beyond their native range. The high demand for various ornamental plant species at global scale, combined with modern and more efficient modes of trade (i.e., e-commerce) highlight the horticultural trade industry as a point of major conservation concern. Historically, ferns are well documented as being a popular ornamental plant group and recent studies have highlighted their high propensity towards invasion. Despite this, no studies have considered the role of trade as a driver of invasiveness in this large plant group. In this study we developed an inventory of traded terrestrial true ferns (Polypodiophyta) using catalogues from on-ground (i.e., brick and mortar) and e-commerce (i.e., online) nurseries across 6 major trading countries: Australia, Canada, New Zealand, South Africa, the United Kingdom, and the United States of America. A total of 382 traded ferns including alien and native species were identified. Generalised linear models were used to determine which market and species traits influenced the probability of establishment success in the country of trade. The final model highlighted that various market traits positively affected the likelihood of establishment success in alien ferns, i.e., the number of varieties and cultivars available for a species (a proxy for the effects of horticultural manipulation and ecotypic variation), a high market presence, and trade via e-commerce. Species traits such as a broad native range and successful establishment elsewhere were also important predictors. Three families (Dryopteridaceae, Pteridaceae, and Polypodiaceae) were identified as the most popular fern families in trade. These families have also contributed a significant portion of alien and invasive ferns in this and previous studies and are commonly promoted by horticulturalists. Twenty-nine out of 261 traded alien fern species were identified as having successfully invaded regions other than the country of trade as well as having a high market presence, with Dryopteris erythrosora, Dryopteris cycadina, Polystichum polyblepharum, and Cyrtomium falcatum being of particular concern. This study emphasised the role of horticultural trade in invasion success in alien ferns and highlighted the value of early detection through screening horticultural catalogues to identify introduced and potentially invasive species that should be monitored in trade. [ABSTRACT FROM AUTHOR]

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Invasive alien species threaten tropical grasslands and native biodiversity across the globe, including in the natural mosaic of native grasslands and forests in the Shola Sky Islands of the Western Ghats. Here, grasslands have been lost to exotic tree invasion (Acacias, Eucalyptus, and Pines) since the 1950s, but differing invasion intensities between these species and intermixing with native species constitutes a major challenge for remotely sensed assessments. In this study, we assess the accuracy of three satellite and airborne remote sensing sensors (Sentinel-1 radar data, Sentinel-2 multispectral data and AVIRIS-NG hyperspectral data) and three machine learning classification algorithms to identify the spatial extent of native habitats and invasive tree species. We used the support vector machine (SVM), classification and regression trees (CART), and random forest (RF) algorithms implemented on the Google Earth Engine platform. Results indicate that AVIRIS-NG data in combination with SVM produced the highest classification accuracy (98.7%). Fused Sentinel-1 and Sentinel-2 produce 91% accuracy, while Sentinel-2 alone yielded 91% accuracy; but only with higher coverage of ground control points. The hyperspectral data (AVIRIS-NG) was the only sensor that permitted distinguishing recent invasions (young trees) with high precision. We suspect that large areas will have to be mapped and assessed in the coming years by conservation managers, NGOs to plan restoration or to assess the success of restoration activities, for which a choice of sensors may have to be made based on the age of invasion being mapped, and the quantum of ground control data available. [ABSTRACT FROM AUTHOR]

Assessing the impacts of alien plant species is scientifically important and critical for supporting invasion-related policies. Generic Impact Scoring System (GISS) and Environmental Impact Classification for Alien Taxa (EICAT) are standardized schemes to evaluate, compare, and eventually predict the magnitudes of the variety of impacts invasive species can have. Here, we apply these two systems to classify alien plants of Iran according to the magnitude of their environmental and socioeconomic impacts. A review of published literature and online resources was undertaken to collate information on the reported environmental and socioeconomics impacts of 27 alien plants in Iran. The resulting data ranked species by their total sum of impact scores and by their highest scores. According to total impact scores from GISS Eichhornia crassipes, Ailanthus altissima, Imperata cylindrica, Amsinckia menziesii, and Paulownia sp. had the highest impacts. About 60% of alien plants assessed had higher environmental impacts than socioeconomic impacts, 18% had higher scores for socioeconomic impacts, and 22% scored the same in both categories. According to EICAT, Ulex europaeus, Ambrosia psilostachya, E. crassipes, A. altissima, and A. menziesii were the five species with major impacts; other 16 species (59%) were classified as with moderate impacts, five with minor and two of minimal concern. Seven species had similar rankings by both GISS and EICAT. The deficit of scientific literature to quantify impacts on complex ecosystem services in Iran or emphasis on the reversibility of impacts in the EICAT protocol could explain differences in ranking of species by the two schemes. GISS and EICAT could be used to link impact magnitudes and type (environmental or socioeconomic) to biological traits to understand and forecast species with different types of impact. [ABSTRACT FROM AUTHOR]

Alien species in urban areas have a large effect on overall species diversity. A suitable metric of flora's response to environmental change is functional diversity (FD) that refers to the multivariate space of species' trait compositions, reflecting their ecological niches. We studied how FD changed over 320 years of urbanization in the city of Halle (Saale), Germany. Selected functional traits (related to stress-tolerance, reproduction, competitiveness and phenology) were examined for the difference in FD between native and alien plant species, the latter specifically for archaeophytes, neophytes and invasive species. Functional diversity for each trait was calculated using Rao's Q index followed by a linear model to test for changes in Rao's Q over time between the groups. Over the 320 years, overall FD remained constant despite species turnover, but FD significantly increased for neophytes and invasive species compared to native species. Plant height was the only trait showing increase in FD as main effect, while for the other traits examined FD decreased over time. Considering invasive species separately, the majority of traits exhibit a significant increase in FD except for seed mass where it decreased. Finally, FD of multiple functional traits combined decreased over time. This can be due to homogenization of functional trait between native and alien species, as a consequence of habitats becoming more similar and subsequent habitat filtering. Our results demonstrate that during the last three centuries, urbanization influenced plant FD in various ways and may contribute to future uniformity of urban floras and greater invasiveness. [ABSTRACT FROM AUTHOR]

Biological invasion is globally pervasive and an increasing threat to biodiversity. We need to be able to predict the ecological impacts of alien species, in order to prioritize management of those expected to be most damaging. Comparisons of functional response (FR) between invaders and trophically similar natives has been proposed as useful for predicting invader impacts, as interaction intensity tends to be reflected in higher FRs. We undertook feeding trials comparing FRs of four invasive poeciliids (mosquitofish [Gambusia affinis], guppy [Poecilia reticulata], liberty molly [P. salvatoris] and swordtail [Xiphophorus hellerii]) in Hong Kong with three similar-sized native fishes (ricefish [Oryzias curvinotus: Adrianichthyidae]; predaceous chub [Parazacco spilurus] and half-banded barb [Puntius semifasciolatus: Cyprinidae]). We tested whether FRs correctly reflected known impacts of the mosquitofish and guppy locally, and used FRs to forecast potential impacts of the molly and swordtail. Overall, the swordtail and molly consumed more prey and had higher FRs than the other five fishes, owing to their shorter prey handling time and/or higher attack rate. Mosquitofish and guppy had similar FRs to native fishes. All fishes showed type-II FRs, and had some potential to destabilize prey populations. Such results predict that the molly and swordtail could have strong ecological effects in Hong Kong freshwaters. However, FR alone was not highly predictive of known impacts of mosquitofish and guppy. It is suggested a more holistic approach incorporating estimates of field abundance and parameterization of other niche dimensions of the invader will be needed. [ABSTRACT FROM AUTHOR]

Assessing the effects of landscape composition on invasive and native wildlife abundance patterns is necessary to reach effective biodiversity management planning, especially on the margins of cities. However, we still have a limited understanding on the relationships between the landscape components and bird abundance. Given this knowledge gap, an urban–rural gradient approach was performed (1) to evaluate relationships between abundances of three sympatric dove species, namely invasive Eurasian collared dove (Streptopelia decaocto), expanding laughing dove (Spilopelia senegalensis), and native European turtle dove (Streptopelia turtur), and landscape composition, and (2) to identify the elements of the landscape that are determining in explaining the abundance patterns for these three species. Our results showed (1) the presence of a substantial segregation in the abundances of the three species along urban–rural gradient depending on the cover of built-up areas, (2) that the abundance of Eurasian collared dove increased with high cover (%) of built-up areas and low cover of cereals, (3) that laughing dove abundance increased with a high cover of permanent crops and low road lengths, but decreased when there are more than three fruit trees species, and (4) that of European turtle dove increased with a high cover of permanent crops, vegetable crops, and a high richness of fruit trees, but decreased with high built-up areas cover and when roads lengths exceed 1 km. Considering these responses to urban–rural gradient, these species can be classified into three distinct spatial categories: (1) "urban dweller" for the invasive Eurasian collared dove, (2) "urban utilizer" for expanding laughing dove, and (3) "urban avoider" for the native European turtle dove. The possible expansion of the urban areas at the detriment of permanent crops could be unfavourable for the native European turtle dove. Further monitoring, by a fixed time step, to detect environmental factors behind the changes in the composition of landscape and distribution of wildlife (both invasive and native) would be of great importance. The synergy among farmers, urban managers and researchers is recommended for the conservation of biodiversity in this region. [ABSTRACT FROM AUTHOR]

Biodiversity is declining on a global scale and the spread of invasive alien species (IAS) is a major driver, particularly through predatory impacts. Thus, effective means of assessing and predicting the consequences of IAS predation on native prey population stability remains a vital goal for conservation. Here, we applied two classic ecological concepts, consumer functional response (FR) and prey switching, to predict and understand the ecological impacts of juveniles of the lionfish (Pterois volitans), a notorious and widespread marine invader. Functional responses and prey switching propensities were quantified towards three representative prey species: Artemia salina, Palaemonetes varians, and Gammarus oceanicus. Lionfish exhibited potentially destabilising Type II FRs towards individual prey species, owing to high consumption rates at low prey densities, whilst FR magnitudes differed among prey species. Functional response attack rates (a) were highest, and handling times (h) lowest, towards A. salina, followed by P. varians and then G. oceanicus. Maximum feeding rates (1/h) and functional response ratios (FRR; a/h) also followed this impact gradient for the three prey species. Lionfish, however, displayed a potentially population stabilising prey switching propensity (i.e. frequency-dependent predation) when multiple prey species were presented simultaneously, where disproportionately less of rare prey, and more of abundant prey, were consumed. Whilst FR and FRR magnitudes indicate marked per capita lionfish predatory impacts towards prey species, a strong prey switching propensity may reduce in-field impacts by offering low density prey refuge in biodiverse communities. Our results thus corroborate field patterns documenting variable impacts of lionfish, with prey extirpations less likely in diverse communities owing to frequency-dependent predation. [ABSTRACT FROM AUTHOR]

Research into the human dimensions of invasive alien species (IAS) management has received great attention to date. However, little is known about how public education influences stakeholders knowledge and management of IAS. Using key informant interviews and household questionnaires, we explored the role of public education in farmers knowledge and management of invasive Mikania micrantha in the China-Myanmar Border Region (China). We found ten common educational approaches that farmers were familiar with and/or adopted, and a high level of knowledge and management among farmers. We also found that public educational approaches helped to improve farmers knowledge and management, with some differences due to socio-demographic factors. We conclude that promotional materials and training workshops work better than personal experience, and that training workshops perform best. These results suggest that improving the design and implementation of public education could contribute to effective communication among stakeholders and long-term management of IAS. Our findings provide important insights for adopting public education programs in IAS management. [ABSTRACT FROM AUTHOR]

When colonizing new areas, alien plant species success can depend strongly on local environmental conditions. Microclimatic barriers might be the reason why some alien plant species thrive in urban areas, while others prefer rural environments. We tested the hypothesis that the climate in the native range is a good predictor of the urbanity of alien species in the invaded range. The relationship between climate in the native range and the percentage of artificially sealed surfaces (urbanity) at the occurrences of 24 emerging alien plant species, in European areas with a temperate climate (termed oceanic Europe) was evaluated. We found that alien species growing in more urban environments originated from warmer or drier native ranges than found in oceanic Europe. These results have strong conservation implications as climate-warming will likely lift climatic barriers that currently constrain numerous alien plant species to cities, boosting the role of cities as points of entry for invasive plants. [ABSTRACT FROM AUTHOR]

There is little understanding of the role of exotic bees in the observed pollinator decline. Recent models of species invasions predict that aggressive species have more impact; applying this theory to pollinators suggests that aggressive territorial Anthidium (Megachilidae) bees, whose range is expanding globally, could have high impacts on native bees. We examined exploitation and interference competition for floral resources between Anthidium and native bees in unmanaged urban meadows in Montreal, Canada. First, we conducted a survey of floral visits by Anthidium and native bee genera. We found high niche overlap with Megachile (Megachilidae), one of the most common genera of native pollinators in the area, suggesting high potential for exploitation competition. Second, we tested for interference competition between Anthidium and Megachile with behavioural observations of foraging on a common introduced host plant (Lotus corniculatus, Fabaceae). This presence of Anthidium decreased patch residence and number of floral visits by Megachile bees, suggesting that Anthidium has a significant per capita effect on foraging behavior of Megachile. [ABSTRACT FROM AUTHOR]

Millions of individuals of two species of non-native galliform birds, the Common Pheasant (Phasianus colchicus) and Red-legged Partridge (Alectoris rufa) are released into the British countryside annually in late summer, supplementing established breeding populations of these two species. The biomass of birds involved in these releases has been compared to the British breeding bird biomass. However, the validity of this comparison is compromised because the biomass of wild birds varies across the year due to reproduction, mortality and migration. How the biomass of Common Pheasants and Red-legged Partridges compares to that of other British bird species in late summer, or across the whole year, is currently unknown. Here, we produce estimates of how British bird biomass varies across the year, to assess the contribution of the two non-native galliforms to this variation. We show that overall British bird biomass is probably lowest around the start of the breeding season in April, and peaks in late summer and autumn. We estimate that around a quarter of British bird biomass annually is contributed by Common Pheasants and Red-legged Partridges, and that at their peak in August these two species represent about half of all wild bird biomass in Britain. [ABSTRACT FROM AUTHOR]

Cultural heritage sites such as historical or sacred areas provide suitable habitats for plants and play an important role in nature conservation, particularly in human-modified contexts such as urban environments. However, such sites also provide opportunities for the spread of invasive species, whose impact on monuments has been raising growing concerns. The aim of this study was to investigate the patterns of distribution and spread of invasive plants in heritage areas, taking the city of Rome as an example. We focused on woody species as they pose the greatest threat to the conservation of monuments, owing to the detrimental effects of their root system. We analysed changes in the diversity and traits of native and non-native flora growing on the walls of 26 ancient sites that have been surveyed repeatedly since the 1940s. We found that the diversity of the native flora has steadily decreased, while there has been an increase in non-native, larger and more damaging species. The introduced species that have expanded most are ornamental wind- or bird-dispersed trees, which represent a major management problem as their propagules can reach the upper sections of the monuments, where they become more difficult to control. The most widespread and damaging of such species is Ailanthus altissima, which has recently been included among the invasive species of European Union concern (EU Regulation 2019/1262). Our findings show that plant invasion is an emerging challenge for the conservation of heritage sites and needs to be prioritized for management to prevent future expansion. [ABSTRACT FROM AUTHOR]

Invasive species utilize a wide array of trait strategies to establish in novel ecosystems. Among these traits is the capacity to produce allelopathic compounds that can directly inhibit neighboring native plants or indirectly suppress native plants via disruption of beneficial belowground microbial mutualisms, or altered soil resources. Despite the well-known prevalence of allelopathy among plant taxa, the pervasiveness of allelopathy among invasive plants is unknown. Here we demonstrate that the majority of the 524 invasive plant species in our database produce allelochemicals with the potential to negatively affect native plant performance. Moreover, allelopathy is widespread across the plant phylogeny, suggesting that allelopathy could have a large impact on native species across the globe. Allelopathic impacts of invasive species are often thought to be present in only a few plant clades (e.g., Brassicaceae). Yet our analysis shows that allelopathy is present in 72% of the 113 plant families surveyed, suggesting that this ubiquitous mechanism of invasion deserves more attention as invasion rates increase across the globe. [ABSTRACT FROM AUTHOR]

Invasion by exotic species is recognized as one of the major threats to biodiversity. The effects of invasion by Opuntia ficus-indica (Cactaceae) on the species diversity, richness and composition of invaded communities were studied at three sites in the highlands of Eritrea, East Africa. This paper investigates whether the presence of O. ficus-indica causes a negative effect on the native biodiversity in a region rarely studied so far. The vegetation in invaded and uninvaded plots with similar habitat conditions was sampled and differences in the species composition, diversity and richness were compared between the plots. The overall plant species composition differed significantly with invasion by O. ficus-indica. The invasion by O. ficus-indica also led to a significant homogenization of community compositions. The species richness and Shannon diversity index did not differ significantly between the invaded and uninvaded plots. Nevertheless, we still detected species with significantly lower occurrence in the invaded plots (Psiadia punctulata), but also species which preferred invaded plots (Plectranthus hadiensis). We conclude that O. ficus-indica exerts a negligible effect on the species diversity and richness but that it affects species composition and that there are species which suffer due to its presence. Due to the continuous pressure of the invasion by O. ficus-indica on the species composition and dry climates, further homogenization in the native species diversity is to be expected in the future for the highlands of Eritrea. [ABSTRACT FROM AUTHOR]