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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.

Cold environments at high elevation and high latitude are often viewed as resistant to biological invasions. However, climate warming, land use change and associated increased connectivity all increase the risk of biological invasions in these environments. Here we present a summary of the key discussions of the workshop ‘Biosecurity in Mountains and Northern Ecosystems: Current Status and Future Challenges’ (Flen, Sweden, 1–3 June 2015). The aims of the workshop were to (1) increase awareness about the growing importance of species expansion—both non-native and native—at high elevation and high latitude with climate change, (2) review existing knowledge about invasion risks in these areas, and (3) encourage more research on how species will move and interact in cold environments, the consequences for biodiversity, and animal and human health and wellbeing. The diversity of potential and actual invaders reported at the workshop and the likely interactions between them create major challenges for managers of cold environments. However, since these cold environments have experienced fewer invasions when compared with many warmer, more populated environments, prevention has a real chance of success, especially if it is coupled with prioritisation schemes for targeting invaders likely to have greatest impact. Communication and co-operation between cold environment regions will facilitate rapid response, and maximise the use of limited research and management resources.

Antarctica is increasingly vulnerable to invasive species, some of which have already established on the Antarctic Peninsula. The East Antarctic environment is currently recorded to be free from established non-native invertebrates. Here we report the first record of a highly invasive springtail species, Hypogastrura viatica (Collembola: Hypogastruridae), in East Antarctica in 2020. The animals were detected live in the unpacking of imported fresh produce at an Antarctic research station. This is the first record of the transfer of H. viatica to Antarctica via fresh food. Fresh produce is an uncommon pathway for H. viatica , as the species is typically associated with coastal or wet inland environments . Extensive management and surveillance were undertaken following detection, however, taxonomic identification of specimens did not occur until May 2024. We highlight the importance of mandatory reporting and prompt identification of non-native species detections to ensure appropriate responses to future incidents. A lack of species identification may lead to more serious consequences for the environment and ecosystems of East Antarctica.

Global warming is affecting marine biodiversity in a multitude of ways, promoting several direct and indirect effects. Across the Mediterranean basin, rising temperatures are greatly favouring the northward expansion and invasion of thermophilic predator species, that may impact the populations of resident prey. As a model example of this phenomenon, two species are considered: the thermophilic annelid Hermodice carunculata , a generalist predator which is expanding northward; and its prey Parazoanthus axinellae, a boreal zoanthid which is particularly sensitive to the increasing temperature. With the hypothesis that the spreading of H. carunculata may affect the P. axinellae population, monitoring activities were conducted in the Capo Carbonara Marine Protected Area (NW Mediterranean) in 2020 and repeated in 2021. Moreover, the interaction between the two species was investigated under controlled conditions in the laboratory. A significant correlation between the increasing abundance of H. carunculata and the decreasing cover of P. axinellae was observed in the field. Laboratory experiments showed that the consumption of P. axinellae by H. carunculata increased significantly after exposing P. axinellae to a thermal stress and was concentrated on zoanthids showing signs of necrosis due to the heat shock. Considering the ongoing global temperature increase, the predation by H. carunculata could not constitute the only cause of the observed reduction of P. axinellae : it can be seen as an element of a cascading effect of global warming that could further affect the zoanthid populations, which are already suffering from rising temperatures.

The Functional Response (FR) has been identified as a powerful predictive tool to forecast the ecological impacts of existing, emerging and future invasive alien species. In particular, the parameters of attack rate a and handling time h may be predictive of the ecological impacts of invaders when utilised in comparison with trophically analogous natives. However, researchers in many cases face somewhat contradictory impact predictions based on the use of one parameter or the other. Here, we thus propose a new metric, the Functional Response Ratio (FRR), which is simply a divided by h: that is, FRR = a/h. Given that high values of a and low values of h should associate with high impact, and vice versa, the FRR metric balances the information from both parameters. This also resolves contradictions when one parameter gives opposite predictions to the other. Using multiple examples obtained from the literature, we find that the FRR indeed resolves such contradictions and that values of FRR of invaders are consistently higher than those of natives, irrespective of experimental or environmental context. Accordingly, the use of FRR provides a novel and reliable metric for scientists, stakeholders and practitioners to predict the ecological impacts of existing, emerging and future invasive alien species across taxa and trophic groups.

Early detection of invasive alien species and the ability to track their spread are critical for undertaking appropriate management decisions. Citizen science surveys are potentially valuable tools for quickly obtaining information on biodiversity and species distributions. The Asian brown marmorated stink bug, Halyomorpha halys , is an invasive pest of agricultural crops and a dwelling nuisance. Halyomorpha halys was first recorded in Italy in 2012 in Emilia Romagna, one of the most important fruit producing regions of Europe. To rapidly obtain data on its distribution in the newly invaded area, a survey that combined citizen science and active search was set up using multimedia channels. Data concerning when, where and how the bugs were spotted were collected, together with photographs and specimens. The survey detected established breeding populations in different areas of Northern Italy and Southern Switzerland, indicating a potentially high risk for crop damage that extends beyond the territories of first detection. Furthermore, new data on H. halys phenology, host plants, voltinism and behaviour were obtained. The importance of citizen science in early detection of introduced pest species is highlighted. This paper also provides a picture-based key to recognize H. halys from similar pentatomids in the world.

Since the 1990s, there have appeared numerous articles in scholarly journals and the popular press that deny the risks posed by non-native species and claim that the field of invasion biology is biased, uninformative and pseudoscientific. Unlike normal scientific debates, which are evidence based, this discourse typically uses rhetorical arguments to disregard, misrepresent or reject evidence in attempt to cast doubt on the scientific consensus that species introductions pose significant risks to biodiversity and ecosystems; thus, it is similar to the denialism that has affected climate science and medical science. Invasive species denialism, like science denialism in general, is typically expressed in forums where it avoids expert peer review. Denialist articles have increased exponentially over the past three decades, most notably in the mainstream popular press. This burgeoning phenomenon could impede development and implementation of policies designed to safeguard against invasive species spread and impact.

Europe has adopted innovative legislation on invasive species that could signal a step-change in the global response to biological invasion threats. The discussion that took place within EU institutions—EU Parliament, European Commission, and the Member States—permitted significant improvement on the initial proposal presented by the European Commission, including removing the initial 50 species cap, explicitly allowing national authorities to take stringent measures on invasive species of national concern, and encouraging coordinated approaches to invasive species in boundary areas. An independent “Scientific Forum” to inform implementation has been introduced, and the EU Regulation will permit only limited licensing for specific activities using invasive alien species. However, the real strength of the legislation will largely depend on the decisions of a committee of representatives of the Member States, with the risk that the real enforcement will be limited by political and economic, rather than scientific, considerations. In this regard it will be crucial to set up a framework of roles and responsibilities among the different bodies that ensure transparent and objective decision processes. Also, it will be essential that adequate resources be secured for implementing the provisions of the legislation. Finally, the regulatory approach introduced by the Regulation will have only a limited impact unless European citizens raise their awareness of this threat and adopt more responsible behaviours.

Knowing which species will become invasive has been the holy grail of invasion biology. A survey of woody plants was conducted in 2001 on an island (Isla Victoria) where 135 non-native woody plant species had been introduced 80 years previously. The survey showed that nearly 10% of introduced species had spread further than 100 m from the original sites. For some introduced species on this island longer time lags between introduction and invasion (or further spread) could be at play. To test if new invasions have begun since the original survey or if ongoing invasions have spread further, we repeated the survey a decade later. The proportion of introduced species that became invasive did not increase between surveys, suggesting that longer time lags may not reveal major invasions from new species on this island. However, we found that the relative frequency of taller individuals (above 2 m) has increased, suggesting a change in age structure of these invasive populations. Further, we found that woody invader densities and maximum heights have increased since the original survey, suggesting that woody plant invasion is progressing, and for some species even accelerating. These results highlight the importance of research on how long invasions of long-lived woody plants can take, providing key data to guide long-term monitoring of sites with multiple non-native plant introductions.

The harlequin ladybird (Harmonia axyridis) was introduced in numerous countries around the world as a biological control agent but nowadays it is considered as a pest itself. It is a highly invasive species that has negative impacts on native biodiversity, may affect some crops, and causes a nuisance to humans. Despite its relevance worldwide, the invasion by H. axyridis in South America has received little attention. Here we used a citizen science approach to study the distribution of H. axyridis in Argentina where the species was intentionally introduced in 1986. We also informally tested and evaluated the preferences for different methods for reporting records: iNaturalist website, Google form, email, WhatsApp, and Facebook. Most records were reported through WhatsApp and iNaturalist. We found that H. axyridis is widely distributed in Argentina but there are large gaps, particularly in arid regions. The invasion seems to be recent in the south of the country. Citizen science is a valuable tool for mapping invasive alien species in a large country like Argentina, and will help to monitor the continuous expansion of H. axyridis.