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Most invasions start with the introduction of a few individuals and the majority fail to establish and become invasive populations. A possible explanation for this is that some species are subject to Allee effects—disadvantages of low densities—and fail to perform vital activities due to the low availability of conspecifics. We propose that ‘facilitation’ from native individuals to non-natives through heterospecific sociability could enhance chances of the latter establishing in novel environments by helping them avoid Allee effects and even reducing the minimum number of non-native individuals necessary to achieve the density for a viable population (the Allee effect threshold). There is evidence from experiments carried out with freshwater fish, snails, lizards, mussels and bird that supports the idea of heterospecific sociability between native and non-native species as a process to promote invasion success. We propose that to understand invasion success in social non-native species we need to investigate how they integrate into the recipient community. Furthermore, to manage them, it may be necessary to reduce population density not just below the Allee effect threshold but also to understand how natives could help them shift the conspecific Allee effect threshold to their benefit. This article is part of the theme issue ‘Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes’.

Crayfish represent important links in aquatic food webs because they have diverse, omnivorous diets and are an important source of energy for fishes and birds. Crayfish have the ability to increase sediment transport through bioturbation, some are considered ecosystem engineers due to their burrowing habits, and crayfish invasions have been linked to large declines in biodiversity and changes in ecosystem structure and function. Despite their ecological importance and the threats that invasive crayfishes pose, the distribution of crayfishes in the Laurentian Great Lakes is not well studied. Here, we report on four years of intensive crayfish surveys in the southwestern portion of the Lake Michigan Basin, a region with diverse freshwater ecosystems and few previous records of crayfish distribution. From 2015 to 2018, baited minnow traps and SCUBA were used to document the distribution and abundance of crayfish across streams, rivers, inland lakes, and Lake Michigan. Six species of crayfish were captured, including two invasive species. The invaders are the widely distributed and abundant Faxonius rusticus (rusty crayfish) and Procambarus clarkii (red Swamp crayfish), a species early in the invasion phase. Native species were found in fewer habitat types and were less abundant than invasive F. rusticus. Comparing our results to previous sampling showed that native crayfish distribution and diversity have declined at the same time that F. rusticus has spread over recent decades. There is potential for new and recently introduced invaders, such as the red swamp crayfish, to further alter ecosystems.

Freshwater ecosystems in North America have been greatly affected by invasive species, including invasive amphipods, which has motivated the development of predictive models to inform where...

Scenario analysis has emerged as a key tool to analyze complex and uncertain future socio-ecological developments. However, currently existing global scenarios (narratives of how the world may develop) have neglected biological invasions, a major threat to biodiversity and the economy. Here, we use a novel participatory process to develop a diverse set of global biological invasion scenarios spanning a wide range of plausible global futures through to 2050. We adapted the widely used “two axes” scenario analysis approach to develop four families of four scenarios each, resulting in 16 scenarios that were later clustered into four contrasting sets of futures. Our analysis highlights that socioeconomic developments and technological innovation have the potential to shape biological invasions, in addition to well-known drivers, such as climate and human land use change and global trade. Our scenarios partially align with the shared socioeconomic pathways created by the climate change research community. Several factors that drive differences in biological invasions were underrepresented in the shared socioeconomic pathways; in particular, the implementation of biosecurity policies. We argue that including factors related to public environmental awareness and technological and trade development in global scenarios and models is essential to adequately consider biological invasions in global environmental assessments and thereby obtain a more integrative picture of future social–ecological developments This research was funded through the COST Action “Alien Challenge” [Grant number TD1209]; the 2017–2018 Belmont Forum and BiodivERsA joint call for research proposals, under the BiodivScen ERA-Net COFUND programme, and with the funding organisations AEI, FWF and BMBF [grant numbers AEI PCI2018-092966 (NRP)/FWF project 4011-B32 (FE, SD, GL, BeL)/BMBF projects 01LC1807A (HS) and 01LC1807B (JMJ)]; Deutsche Forschungsgemeinschaft [grant numbers InDyNet, JE 288/8-1; JE 288/9-1, 9-2 (JMJ)/via iDiv FZT 118, 202548816 (MW)]; OP RDE grant EVA4.0 [grant number CZ.02.1.01/0.0/0.0/16_019/0000803] (AML); CONICYT [grant number AFB170008] (AP); UK-SCAPE programme, Natural Environment Research Council [grant number NE/R016429/1] (HER)

Non-native crayfishes can have large impacts on biodiversity and the provisioning of ecosystem services in freshwaters. In 2015 we discovered an established population of the globally widespread red swamp crayfish (Procambarus clarkii) in the North Shore Channel of the Chicago Area Waterway System. This population overlaps with a population of rusty crayfish (Faxonius rusticus), a previous invader that is widely distributed and usually the dominant crayfish species across the Great Lakes region. If P. clarkii continues to spread in the Great Lakes region it will frequently encounter F. rusticus. Factors such as water clarity, competition for food when limited, and susceptibility to predation may alter P. clarkii’s ability to become established and spread. We sampled the overlapping populations and found that P. clarkii are significantly larger than F. rusticus. Next, we conducted lab experiments to examine the outcomes of competition between these species for shelter and food. F. rusticus were significantly more likely to seek shelter when threatened, while P. clarkii were significantly more likely to respond aggressively. P. clarkii won more competitions for food. Finally, we conducted field experiments to investigate rates of predation on each species and found that P. clarkii are predated significantly more often. Our results suggest that P. clarkii is dominant in interactions with F. rusticus but that higher rates of predation, likely occurring because P. clarkii is less likely to flee from threats, mitigate these benefits. We suggest that P. clarkii will dominate crayfish communities in water with low clarity, but not in clear-water habitats where visual predators are more effective.

Author(s): Lockwood, JL; Welbourne, DJ; Romagosa, CM; Cassey, P; Mandrak, NE; Strecker, A; Leung, B; Stringham, OC; Udell, B; Episcopio-Sturgeon, DJ; Tlusty, MF; Sinclair, J; Springborn, MR; Pienaar, EF; Rhyne, AL; Keller, R | Abstract: The annual trade in exotic vertebrates as pets is a multi-billion-dollar global business. Thousands of species, and tens of millions of individual animals, are shipped both internationally and within countries to satisfy this demand. Most research on the exotic pet trade has focused on its contribution to native biodiversity loss and disease spread. Here, we synthesize information across taxa and research disciplines to document the exotic pet trade's contribution to vertebrate biological invasions. We show recent and substantial worldwide growth in the number of non-native animal populations introduced via this invasion pathway, which demonstrates a strong potential to increase the number of invasive animals in the future. Key to addressing the invasion threat of exotic pets is learning more about the socioeconomic forces that drive the massive growth in the exotic pet market and the socioecological factors that underlie pet release by owners. These factors likely vary according to cultural pet-keeping traditions across regions and whether purchases were legal or illegal. These gaps in our understanding of the exotic pet trade must be addressed in order to implement effective policy solutions.

The spread of non-native aquatic species among waterbodies has become a major social, environmental, and economic concern. An important mechanism of this spread is the inadvertent transport of organisms on recreational boats as they are moved among waterbodies. Organisms can survive on the exterior of the boat, the interior, attached to fishing tackle, and can be intentionally moved by boaters. In response, local, state, and federal U.S. agencies have invested in outreach campaigns to educate boaters about the impacts of invasive aquatic species and the ways that boaters can reduce the risk of spread. We surveyed boaters in the U.S. state of Illinois to determine their travel patterns and how frequently they clean different parts of their boats. A majority of boaters reported that they always take recommended actions to clean their boat exterior (72% of respondents), boat interior (78%), and fishing tackle (55%), and only 4% reported that they intentionally move organisms. We used network methods to analyze the movement of recreational boaters and found strong connections among 28 highly visited waterbodies. When we removed the 38% of respondents who Always take recommended actions to reduce risk of species spread by all four mechanisms this network was minimally altered and still contained all 28 waterbodies. This indicates that despite high adoption of conservation behaviors there is a continuing risk of non-native species transport among all waterbodies. This work shows that further action is necessary if the impacts of invasive aquatic species are to be reduced in the future.

Scenario analysis has emerged as a key tool to analyze complex and uncertain future socio-ecological developments. However, current global scenarios (narratives of how the world may develop) have neglected biological invasions, a major threat to biodiversity and the economy. We used a novel participatory process to develop a diverse set of global biological invasion scenarios spanning a wide breadth of plausible global futures through 2050. We adapted the widely used “two axes” scenario analysis approach to develop four families of four scenarios each, resulting in 16 scenarios that were later clustered into four contrasting sets of futures. Our analysis highlighted that socio-economic developments and changes in sustainability policies and lifestyle have the potential to shape biological invasions, in addition to well-known ecological drivers, such as climate and human land use change. Our scenarios align fairly well with the recently developed shared socio-economic pathways, but the factors that drive differences in biological invasions are underrepresented there. Including these factors in global scenarios and models is essential to adequately consider biological invasions in global environmental assessments, and obtain a more integrative picture of future socio-ecological developments.

Aim International trade in plants and animals generates significant economic benefits. It also leads to substantial unintended impacts when introduced species become invasive, causing environmental disturbance or transmitting diseases that affect people, livestock, other wildlife or the environment. Policy responses are usually only implemented after these species become established and damages are already incurred. International agreements to control trade are likewise usually based on selection of species with known impacts. We aim to further develop quantitative invasive species risk assessment for bird imports and extend the tool to explicitly address disease threats. Location United States of America. Methods We use a two-step approach for rapid risk assessment based on the expected biological risks due to both the environmental and health impact of a potentially invasive wildlife species in trade. We assess establishment probability based on a model informed by historical observations and then construct a model of emerging infectious disease threat based on economic and ecological characteristics of the exporting country. Results We illustrate how our rapid assessment tool can be used to identify high-priority species for regulation based on a combination of the threat they pose for becoming established and vectoring emerging infectious diseases. Main conclusions Our approach can be executed for a species in a matter of days and is nested in an economic decision-making framework for determining whether the biological risk is justified by trade benefits.

Alien invasive species cause significant impacts on ecosystems and economies, but the impacts on human well-being and livelihoods are less well known. Negative impacts can be particularly severe when caused by floating aquatic plants, which can reduce access to freshwater for extraction and navigation, reduce the harvest of fish and other resources, and change water cycling and chemistry. This paper reviews and discusses some of these impacts globally and then concentrates on the case study of Wular Lake, India. Wular is the largest freshwater lake in Jammu and Kashmir state and is highly important for local livelihoods through the provision of a range of services, including fish and edible aquatic plants, and water to local communities. The supply of these services has decreased due to a long history of environmental degradation, and recent invasions by the floating plants Azolla cristata and Alternanthera philoxerodies (alligator weed) have further impacted human well-being. Here, we review the published literature about these invasions, present information from interviews with locals living near Wular Lake, and review the global literature about invasive floating plant species to assess the present and predict the future impacts of these species. We find that the implications of these invasions for livelihoods reliant on lake resources and services provide good justification for management efforts. We discuss some options and challenges to such a management program.

Effective engagement among scientists, government agency staff, and policymakers is necessary for solving fisheries challenges, but remains challenging for a variety of reasons. We present seven practices learned from a collaborative project focused on invasive species in the Great Lakes region (USA-CAN). These practices were based on a researcher-manager model composed of a research team, a management advisory board, and a bridging organization. We suggest this type of system functions well when (1) the management advisory board is provided compelling rationale for engagement; (2) the process uses key individuals as communicators; (3) the research team thoughtfully selects organizations and individuals involved; (4) the funding entity provides logistical support and allows for (5) a flexible structure that prioritizes management needs; (6) a bridging organization sustains communication between in-person meetings; and (7) the project team determines and enacts a project endpoint. We predict these approaches apply equally effectively to other challenges at the research-management-policy interface, including reductions of water pollution, transitions to renewable energy, increasing food security, and addressing climate change.

The Laurentian Great Lakes and the Mississippi River are two of the largest freshwater ecosystems in North America, and each contains large numbers of non-native species. In 1900 the Great Lakes and Mississippi were permanently connected with the opening of the Chicago Sanitary and Ship Canal in the US state of Illinois. More recently, movement of trailered boats, bait, and other overland vectors have increased and further enabled movement of non-native aquatic species. To investigate the role of Illinois in continent-wide species spread we assembled a comprehensive database of recorded occurrences of aquatic non-native species in Illinois inland waters. For each species we determined vector, location, current stage in the invasion sequence (introduced or established), and ecological impacts. The arrival of non-native species has accelerated over time. Sixty species are now established, and a further 39 have been recorded. The Great Lakes have been a stronger source of species to Illinois and the Mississippi River basin than the reverse. Over the last two decades the most important vectors delivering non-native aquatic species have been unintentional release and shipping. Through a survey of Illinois aquatic ecologists we found that established species exhibit a continuous range of ecological impacts and that almost a third have high or very high ecological impacts. Local, national, and continental approaches will be required to mitigate the threat of further invasive species spreading into Illinois and between the Great Lakes and Mississippi basins.

Risk analysis of species invasions links biology and economics, is increasingly mandated by international and national policies, and enables improved management of invasive species. Biological invasions proceed through a series of transition probabilities (i.e., introduction, establishment, spread, and impact), and each of these presents opportunities for management. Recent research advances have improved estimates of probability and associated uncertainty. Improvements have come from species-specific trait-based risk assessments (of estimates of introduction, establishment, spread, and impact probabilities, especially from pathways of commerce in living organisms), spatially explicit dispersal models (introduction and spread, especially from transportation pathways), and species distribution models (establishment, spread, and impact). Results of these forecasting models combined with improved and cheaper surveillance technologies and practices [e.g., environmental DNA (eDNA), drones, citizen science] enable more efficient management by focusing surveillance, prevention, eradication, and control efforts on the highest-risk species and locations. Bioeconomic models account for the interacting dynamics within and between ecological and economic systems, and allow decision makers to better understand the financial consequences of alternative management strategies. In general, recent research advances demonstrate that prevention is the policy with the greatest long-term net benefit.

Aim Impacts of non-native species have motivated development of risk assessment tools for identifying introduced species likely to become invasive. Here, we develop trait-based models for the establishment and impact stages of freshwater fish invasion, and use them to screen non-native species common in international trade. We also determine which species in the aquarium, biological supply, live bait, live food and water garden trades are likely to become invasive. Results are compared to historical patterns of non-native fish establishment to assess the relative importance over time of pathways in causing invasions. Location Laurentian Great Lakes region. Methods Trait-based classification trees for the establishment and impact stages of invasion were developed from data on freshwater fish species that established or failed to establish in the Great Lakes. Fishes in trade were determined from import data from Canadian and United States regulatory agencies, assigned to specific trades and screened through the developed models. Results Climate match between a species’ native range and the Great Lakes region predicted establishment success with 75–81% accuracy. Trophic guild and fecundity predicted potential harmful impacts of established non-native fishes with 75–83% accuracy. Screening outcomes suggest the water garden trade poses the greatest risk of introducing new invasive species, followed by the live food and aquarium trades. Analysis of historical patterns of introduction pathways demonstrates the increasing importance of these trades relative to other pathways. Comparisons among trades reveal that model predictions parallel historical patterns; all fishes previously introduced from the water garden trade have established. The live bait, biological supply, aquarium and live food trades have also contributed established non-native fishes. Main conclusions Our models predict invasion risk of potential fish invaders to the Great Lakes region and could help managers prioritize efforts among species and pathways to minimize such risk. Similar approaches could be applied to other taxonomic groups and geographic regions.

Risk assessment tools for non-native species can avert ecological and economic harm when they inform regulatory or voluntary management actions that seek to reduce the probability of introducing high-risk species. The Laurentian Great Lakes region contains many aquatic invasive plants, non-native species whose introduction causes economic or environmental harm or harm to human health. Additionally, new species continue to arrive, including through trade (e.g., aquarium, water garden). Currently, each Great Lakes jurisdiction manages a separate risk assessment program, leading to a regional situation with diverse assessment methods and large discrepancies in assessed and regulated species. Because the Great Lakes ecosystem crosses state and national borders, each jurisdiction will be best protected when all jurisdictions prevent the import of potentially harmful species. We have modified an existing risk assessment tool for use across the Great Lakes Basin to assess the invasion risks posed by aquatic plants. The tool comprises 38 questions, with points associated with each response that are summed to give a total score. We assessed all known established aquatic plant species in the Great Lakes (n=40) and found this score to be positively correlated with invasiveness, allowing thresholds to be identified that distinguish between invasive and non-invasive species with 84% to 90% accuracy. Assessing species proposed for introduction with this tool, and using these thresholds to determine acceptable risk, could reduce the number of future invasions. If widely adopted, this risk assessment tool would enable a common suite of species to be regulated and thus a more effective approach to reducing the risk of future invasions. Regional risk assessment approaches should reduce the threat of invasive species where environmental and climate conditions are relatively consistent across jurisdictional boundaries.

Doria R. Gordon, S. Luke Flory, Deah Lieurance, Philip E. Hulme, Chris Buddenhagen, Barney Caton, Paul D. Champion, Theresa M. Culley, Curt Daehler, Franz Essl, Jeffrey E. Hill, Reuben P. Keller, Lisa Kohl, Anthony L. Koop, Sabrina Kumschick, David M. Lodge, Richard N. Mack, Laura A. Meyerson, Godshen R. Pallipparambil, F. Dane Panetta, Read Porter, Petr Pysek, Lauren D. Quinn, David M. Richardson, Daniel Simberloff, and Montserrat Vila*

Large-scale invasive species control initiatives are motivated by laudable desires for native species recovery and economic benefits, but they are not without risk. Management interventions and policies should include evidence-based risk–benefit assessment and mitigation planning.

Biological invasions cause many impacts that differ widely in how they are perceived. We argue that many conflicts in the valuation of the impacts of alien species are attributable to differences in the framing of the issue and implicit assumptions—such conflicts are often not acknowledged. We present 13 principles that can help guide valuation and therefore inform the management of alien species. Seven of these relate to the science domain, representing aspects of change caused by alien species that can be measured or otherwise assessed using scientific methods. The remaining six principles invoke values, risk perception, and environmental ethics, but also cognitive and motivational decision biases. We illustrate the consequences of insufficient appreciation of these principles. Finally, we provide guidance rooted in political agreements and environmental ethics for improving the consideration of the consequences of these principles and present appropriate tools for management decisions relating to alien species., Bioscience, 67 (2), ISSN:0006-3568, ISSN:1525-3244

1. Many alien taxa are known to cause socio-economic impacts by affecting the differ-ent constituents of human well-being (security; material and non-material assets; health; social, spiritual and cultural relations; freedom of choice and action). Attempts to quantify socio-economic impacts in monetary terms are unlikely to provide a useful basis for evaluating and comparing impacts of alien taxa because they are notoriously difficult to measure and important aspects of human well- being are ignored. 2. Here, we propose a novel standardised method for classifying alien taxa in terms of the magnitude of their impacts on human well-being, based on the capability ap-proach from welfare economics. The core characteristic of this approach is that it uses changes in peoples’ activities as a common metric for evaluating impacts on well-being. 3. Impacts are assigned to one of five levels, from Minimal Concern to Massive, ac-cording to semi-quantitative scenarios that describe the severity of the impacts. Taxa are then classified according to the highest level of deleterious impact that they have been recorded to cause on any constituent of human well-being. The scheme also includes categories for taxa that are not evaluated, have no alien popu-lation, or are data deficient, and a method for assigning uncertainty to all the classi-fications. To demonstrate the utility of the system, we classified impacts of amphibians globally. These showed a variety of impacts on human well-being, with the cane toad (Rhinella marina) scoring Major impacts. For most species, however, no studies reporting impacts on human well-being were found, i.e. these species were data deficient. 4. The classification provides a consistent procedure for translating the broad range of measures and types of impact into ranked levels of socio-economic impact, assigns alien taxa on the basis of the best available evidence of their documented deleteri-ous impacts, and is applicable across taxa and at a range of spatial scales. The sys-tem was designed to align closely with the Environmental Impact Classification for Alien Taxa (EICAT) and the Red List, both of which have been adopted by the International Union of Nature Conservation (IUCN), and could therefore be readily integrated into international practices and policies.

Intentional introductions of nonindigenous fishes are increasing globally. While benefits of these introductions are easily quantified, assessments to understand the negative impacts to ecosystems are often difficult, incomplete, or absent. Grass carp (Ctenopharyngodon idella) was originally introduced to the United States as a biocontrol agent, and recent observations of wild, diploid individuals in the Great Lakes basin have spurred interest in re-evaluating its ecological risk. Here, we evaluate the ecological impact of grass carp using expert opinion and a suite of the most up-to-date analytical tools and data (ploidy assessment, eDNA surveillance, species distribution models (SDMs), and meta-analysis). The perceived ecological impact of grass carp by fisheries experts was variable, ranging from unknown to very high. Wild-caught triploid and diploid individuals occurred in multiple Great Lakes waterways, and eDNA surveillance suggests that grass carp are abundant in a major tributary of Lake Michigan. SDMs predicted suitable grass carp climate occurs in all Great Lakes. Meta-analysis showed that grass carp introductions impact both water quality and biota. Novel findings based on updated ecological impact assessment tools indicate that iterative risk assessment of introduced fishes may be warranted.

International trade in nonnative species generates economic benefits but also introduces many harmful invasive species. Recent advances in nonnative species screening tools enable useful predictions of invasiveness which can be combined with estimates of impacts to effectively manage the trade-off between the benefits and costs of this trade. Despite this, most countries maintain an essentially “open door” policy where almost all nonnative species are allowed for introduction until they prove problematic. This approach implicitly favors minimizing one particular type of assessment error—mistakenly excluding safe species, or “false positives.” However, a comprehensive approach to management of species trade should involve balancing the trade-off between false positives and “false negatives” (mistakenly accepting invasive species). Barriers to implementing risk assessment tools include the perception that because assessment tools are imperfect they are not suitable for decision-making. However, recent economic research shows that, relative to an open door approach, “shutting the screen door” with imperfect but informative screening tools, to allow flow of only those species of acceptable invasion risk, increases the net benefits of trade. Given that these tools are relatively straightforward to apply, we argue that policy-makers should no longer allow the perfect to be the enemy of the good.

Aquatic invasive species (AIS) pose major conservation challenges in freshwater ecosystems. In response, conservation organizations invest considerable resources in outreach to encourage AIS prevention behaviors among recreational boaters. Despite this, remarkably little is known about whether these efforts catalyze significant changes in boaters' perceptions, or whether they cause changes in behaviors that reduce AIS risk. We interviewed managers at the 14 Illinois organizations active in AIS outreach to determine regional priorities for, and investment in, AIS outreach. The results show a network of collaboration that reinforces a limited set of conservation messages. Next, we surveyed 515 recreational boaters to evaluate access to outreach, knowledge of AIS, and consistency of prevention behavior. Boater recognition of prevention slogans and knowledge of AIS and AIS prevention behavior was similar across Illinois regions despite large regional differences in investment in outreach. Most boaters (94%) report never intentionally moving organisms among waterbodies. Fewer reported that they Always perform recommended actions to reduce risk of AIS spread on their boat interior (68%), boat exterior (63%), or fishing tackle (47%). Recognition of prevention slogans and the number of AIS recognized were significantly, positively, associated with Always performing AIS prevention behavior on the vectors of the boat exterior, and fishing tackle, respectively. Our results suggest that increasing knowledge may be a necessary condition for higher adoption of AIS prevention behaviors, but that this alone may not be sufficient. Instead, efforts targeted at boaters who do not currently practice the recommended actions are likely to be necessary.

Aim Trait-based risk assessment for invasive species is becoming an important tool for identifying non-indigenous species that are likely to cause harm. Despite this, concerns remain that the invasion process is too complex for accurate predictions to be made. Our goal was to test risk assessment performance across a range of taxonomic and geographical scales, at different points in the invasion process, with a range of statistical and machine learning algorithms. Location Regional to global data sets. Methods We selected six data sets differing in size, geography and taxonomic scope. For each data set, we created seven risk assessment tools using a range of statistical and machine learning algorithms. Performance of tools was compared to determine the effects of data set size and scale, the algorithm used, and to determine overall performance of the trait-based risk assessment approach. Results Risk assessment tools with good performance were generated for all data sets. Random forests (RF) and logistic regression (LR) consistently produced tools with high performance. Other algorithms had varied performance. Despite their greater power and flexibility, machine learning algorithms did not systematically outperform statistical algorithms. Geographic scope of the data set, and size of the data set, did not systematically affect risk assessment performance. Main conclusions Across six representative data sets, we were able to create risk assessment tools with high performance. Additional data sets could be generated for other taxonomic groups and regions, and these could support efforts to prevent the arrival of new invaders. Random forests and LR approaches performed well for all data sets and could be used as a standard approach to risk assessment development.

Aim Some nations, and the International Maritime Organization, are moving towards requirements for managing ballast water to reduce the number of alien species transported and released. These and other measures will be most efficient when targeted at ships posing the greatest risks. Here, we analyse world-wide ship movements and port environmental conditions to explore how these risk components differ across arriving ships. Location Global, with a case study of the Laurentian Great Lakes. Methods We gathered salinity and temperature data for all global shipping ports, and data for all global ship movements during a 12 -month period. We applied these data to the Laurentian Great Lakes to determine which global ports may donate new species to the Great Lakes via ship traffic, and which are most environmentally similar to the Great Lakes. Results We show that ships regularly travel to the Great Lakes from all major coastal, and many inland, regions of the world. Most global ports, and thus the species in them, are separated from the Great Lakes by no more than two ship voyages. Combined with a measure of environmental similarity among global ports, we identify ship routes likely to transport species adapted for survival in the Great Lakes and global regions that may be the source of increasing future invasions. Main conclusions The Great Lakes account for a small fraction of global shipping yet are closely connected to all other ports, and the species in them, by the shipping network. Our methods and data allow risks from individual ships to be ranked so that management activities can be targeted at ships most likely to introduce new invaders. Because our data sets are global, they could be applied to ship arrivals at any global port.

Nonindigenous freshwater species cause large ecological and economic impacts in Great Britain. In response the government is in the process of implementing a broad, new nonindigenous species strategy. We assembled a list of all nonindigenous freshwater species that are or were established in Great Britain, their date of first record, and their vector of introduction. This list provides a baseline against which the success of new policies can be assessed. Because the biota of Great Britain has been well recorded, our results provide a highly resolved case study of the vectors and drivers of species transport and establishment. A total of 117 nonindigenous freshwater species are currently established in Great Britain; a further 17 species were once established but are now extirpated. Between 1800 and 2000 the number of established species increased at an accelerating rate, and this increase correlated with the growth in human population and gross domestic product. The construction of large reservoirs in Great Britain occurred over a short period and overlapped high rates of new species establishment, indicating that habitat modification may have been an important driver of establishment. Nonindigenous species now account for 24% of fish, 12% of plant, 54% of amphibian, and 88% of decapod crustacean freshwater species richness in Great Britain. The ornamental trades have been responsible for the greatest percentages of intentionally (73%) and unintentionally (34%) introduced species that have become established. Shipping and aquaculture have also been strong vectors. These vectors should be prioritized for management within the new nonindigenous species strategy.

Nonindigenous earthworms are causing large and undesirable changes to forests across the U.S. Upper Midwest. Because earthworms have slow rates of natural spread, and because their distribution remains patchy in many areas, it would be possible to slow the rate of invasion if vectors of introduction can be identified and controlled. Earthworm populations are often found near lakes, and it has been suggested that anglers discarding unwanted bait are a vector for the establishment of new populations. Here, we have surveyed the bait trade and anglers to determine whether bait stores sell known invasive species and whether angler behavior is likely to lead to these species becoming introduced near lakes. All bait stores surveyed sold known invasive species and 44% of anglers who purchase bait dispose of unwanted bait on land or in trash. We conclude that the bait trade and subsequent disposal of worms by anglers constitute a major vector for earthworm introductions. Thus, slowing the spread of invasi...

In the Laurentian Great Lakes region, commercial activities involving live fish bait, horticultural and water-garden plants, biological supplies, pets, and live food are the principal pathways for intentional introductions of live aquatic organisms. We sampled species for sale in these trades and found that the risks of new invasions and of spreading known invaders are high. Moreover, most animals were identified by common name only, and even though scientific names were more often applied to plants, consumers cannot be certain what species they are receiving because misidentification is common. Finally, 90 percent of plant orders arrived contaminated with unordered live organisms. The policy goal of US and Canadian national and state or provincial agencies is to reduce the risk of harmful introductions. Our results demonstrate that meeting this goal will require accurate identification of species by vendors, the removal of known and likely invasive species from trade, and reductions in the numbe...

The most efficient way to reduce future damages from nonindigenous species is to prevent the introduction of harmful species. Although ecologists have long sought to predict the identity of such species, recent methodological advances promise success where previous attempts failed. We applied recently developed risk assessment approaches to nonindigenous freshwater molluscs at two geographic scales: the Laurentian Great Lakes basin and the 48 contiguous states of the United States. We used data on natural history and biogeography to discriminate between established freshwater molluscs that are benign and those that constitute nuisances (i.e., cause environmental and/or economic damage). Two statistical techniques, logistic regression and categorical tree analysis, showed that nuisance status was positively associated with fecundity. Other aspects of natural history and biogeography did not significantly affect likelihood of becoming a nuisance. We then used the derived statistical models to predict the chance that 15 mollusc species not yet in natural ecosystems would cause damage if they become established. We also tested whether time since establishment is related to the likelihood that nonindigenous mollusc species in the Great Lakes and United States would cause negative impacts. No significant relationship was evident at the U.S. scale, but recently established molluscs within the Great Lakes were more likely to cause negative impacts. This may reflect changing environmental conditions, changing patterns of trade, or may be an indication of “invasional meltdown.” Our quantitative analyses could be extended to other taxa and ecosystems and offer a number of improvements over the qualitative risk assessments currently used by U.S. (and other) government agencies. Resumen: La prevencion de la introduccion de especies perjudiciales es la manera mas eficiente de reducir los danos futuros ocasionados por especies no nativas. Aunque los ecologos han buscado predecir la identidad de tales especies durante mucho tiempo, avances metodologicos actuales prometen exito en donde han fallado intentos anteriores. Aplicamos metodos de evaluacion de riesgo, desarrollados recientemente, en moluscos dulceacuicolas en dos escalas regionales: la cuenca Laurentian de Grandes Lagos y los 48 estados contiguos de los Estados Unidos. Utilizamos datos de historia natural y biogeografia para discriminar moluscos dulceacuicolas establecidos que son beneficos de los que son perjudiciales (i.e., causan dano ambiental y/o economico). Dos tecnicas estadisticas, regresion logistica y analisis de arbol categorico, mostraron que el estatus perjudicial estaba asociado positivamente con la fecundidad. Otros aspectos de la historia natural y biogeografia no alteraron la probabilidad de convertirse en perjudicial. Posteriormente utilizamos los modelos estadisticos derivados para predecir la probabilidad de que 15 especies de moluscos que aun no estan en ecosistemas naturales pudieran causar danos en caso de establecerse. Tambien probamos si el tiempo transcurrido desde el establecimiento esta relacionado con la probabilidad de que especies de moluscos no nativos en los Grandes Lagos y en Estados Unidos pudieran causar impactos negativos. No hubo relacion significativa evidente en la escala de E. U. A., pero los moluscos recientemente establecidos en los Grandes Lagos tuvieron mayor probabilidad de provocar impactos negativos. Esto puede ser reflejo de condiciones ambientales cambiantes, de patrones de comercio cambiantes o puede ser un indicador de una “fundicion invasiva.” Nuestros analisis cuantitativos podrian ser extendidos a otros taxa y ecosistemas y ofrecen numerosas mejorias de las evaluaciones de riesgo cualitativas que actualmente son utilizadas por agencias gubernamentales de E.U.A (y otros paises).

Aquatic invasive species cause deleterious environmental and economic impacts, and are rapidly spreading through ecosystems worldwide. Despite this, very few data sets exist that describe both the presence and the absence of invaders over long time periods. We have used Geographical Information Systems (GIS) to analyse timeseries data describing the spread of the freshwater invasive New Zealand mudsnail, Potamopyrgus antipodarum, in Victoria, Australia, over 110 years. We have mapped the snail’s spread, estimated the percentage of stream length invaded through time, calculated the functional form of the spread rate, and investigated the role that the two proposed vectors — fish stocking and angling — have had in this invasion. Since it was first found in 1895, P. antipodarum has expanded its range in Victoria and now occurs throughout much of the southern and central areas of the state. The north of the state is relatively less invaded than the south, with the division corresponding approximately to the presence of the Great Dividing Range. We show that the snail’s range has been increasing at an approximately exponential rate and estimate that 20% of total Victorian stream length is currently invaded. We also show that using long-term data can change the outcome of analyses of the relationship between vectors of spread and invasion status of separate catchments. When our time-series data were aggregated through time, the total numbers of fish stocking events and angling activity were both correlated with invasion. However, when the time-series data were used and the number of fish stocking events calculated up until the date of invasion, no relationships with stocking were found. These results underline the role that time-series data, based on both presences and absences, have to play when investigating the spread of invasive species.

The unintentional transport of invasive species (i.e., non-native and harmful species that adversely affect habitats and native species) through the Global Shipping Network (GSN) causes substantial losses to social and economic welfare (e.g., annual losses due to ship-borne invasions in the Laurentian Great Lakes is estimated to be as high as USD 800 million). Despite the huge negative impacts, management of such invasions remains challenging because of the complex processes that lead to species transport and establishment. Numerous difficulties associated with quantitative risk assessments (e.g., inadequate characterizations of invasion processes, lack of crucial data, large uncertainties associated with available data, etc.) have hampered the usefulness of such estimates in the task of supporting the authorities who are battling to manage invasions with limited resources. We present here an approach for addressing the problem at hand via creative use of computational techniques and multiple data sources, thus illustrating how data mining can be used for solving crucial, yet very complex problems towards social good. By modeling implicit species exchanges as a network that we refer to as the Species Flow Network (SFN), large-scale species flow dynamics are studied via a graph clustering approach that decomposes the SFN into clusters of ports and inter-cluster connections. We then exploit this decomposition to discover crucial knowledge on how patterns in GSN affect aquatic invasions, and then illustrate how such knowledge can be used to devise effective and economical invasive species management strategies. By experimenting on actual GSN traffic data for years 1997-2006, we have discovered crucial knowledge that can significantly aid the management authorities.

Over the past several decades, the field of invasion biology has rapidly expanded as global trade and the spread of human populations have increasingly carried animal and plant species across natural barriers that have kept them ecologically separated for millions of years. Because some of these nonnative species thrive in their new homes and harm environments, economies, and human health, the prevention and management of invasive species has become a major policy goal from local to international levels. Yet even though ecological research has led to public conversation and policy recommendations, those recommendations have frequently been ignored, and the efforts to counter invasive species have been largely unsuccessful. Recognizing the need to engage experts across the life, social, and legal sciences as well as the humanities, the editors of this volume have drawn together a wide variety of ecologists, historians, economists, legal scholars, policy makers, and communications scholars, to facilitate a dialogue among these disciplines and understand fully the invasive species phenomenon. Aided by case studies of well-known invasives such as the cane toad of Australia and the emerald ash borer, Asian carp, and sea lampreys that threaten US ecosystems, Invasive Species in a Globalized World offers strategies for developing and implementing anti-invasive policies designed to stop their introduction and spread, and to limit their effects.

Ecologists predict that invasive species and global climate change will be two of the leading drivers of global biodiversity loss over the next century (Sala et al., 2000). Society, however, has responded to these two threats in a very uneven way; global climate change has become a major focus of public policy, while problems from invasive species remain poorly addressed. This discrepancy is emphasized by the Kyoto Protocol, which brought 160 nations together in 1997 to create a program for worldwide reductions in greenhouse gas emissions. Despite the fact that ecologists have recognized invasive species as a serious problem since the 1950s (Elton, 1958), there has been no international effort comparable to the Kyoto Protocol to reduce their impacts. This discrepancy is also reflected at the national scale—this fiscal year the United States will spend close to $2 billion on climate change research (CCSP, 2004), while only $227 million is budgeted for invasive species research (NISC, 2005). In this editorial, we ask why ecologists have had so little success communicating the problems of invasive species to society, and offer some suggestions for how ecologists can be more effective at this in the future. Communicating the risks from invasive species is complicated. Each invasive species has different impacts, and there are many diverse vectors of introduction. In our experience, members of the general public are aware of a few specific examples of invasive species, but few people understand the global scale of vectors and impacts. In contrast, ecologists are

Harmful non-indigenous species (NIS) impose great economic and environmental impacts globally, but little is known about their impacts in Southeast Asia. Lack of knowledge of the magnitude of the problem hinders the allocation of appropriate resources for NIS prevention and management. We used benefit-cost analysis embedded in a Monte-Carlo simulation model and analysed economic and environmental impacts of NIS in the region to estimate the total burden of NIS in Southeast Asia. The total annual loss caused by NIS to agriculture, human health and the environment in Southeast Asia is estimated to be US$33.5 billion (5(th) and 95(th) percentile US$25.8-39.8 billion). Losses and costs to the agricultural sector are estimated to be nearly 90% of the total (US$23.4-33.9 billion), while the annual costs associated with human health and the environment are US$1.85 billion (US$1.4-2.5 billion) and US$2.1 billion (US$0.9-3.3 billion), respectively, although these estimates are based on conservative assumptions. We demonstrate that the economic and environmental impacts of NIS in low and middle-income regions can be considerable and that further measures, such as the adoption of regional risk assessment protocols to inform decisions on prevention and control of NIS in Southeast Asia, could be beneficial.

We tested the accuracy of an invasive aquatic plant risk assessment system in the United States that we modified from a system originally developed by New Zealand's Biosecurity Program. The US system is comprised of 38 questions that address biological, historical, and environmental tolerance traits. Values associated with each response are summed to produce a total score for each species that indicates its risk of invasion. To calibrate and test this risk assessment, we identified 39 aquatic plant species that are major invaders in the continental US, 31 species that have naturalized but have no documented impacts (minor invaders), and 60 that have been introduced but have not established. These species represent 55 families and span all aquatic plant growth forms. We found sufficient information to assess all but three of these species. When the results are compared to the known invasiveness of the species, major invaders are distinguished from minor and non-invaders with 91% accuracy. Using this approach, the US aquatic weed risk assessment correctly identifies major invaders 85%, and non-invaders 98%, of the time. Model validation using an additional 10 non-invaders and 10 invaders resulted in 100% accuracy for the former, and 80% accuracy for the latter group. Accuracy was further improved to an average of 91% for all groups when the 17% of species with scores of 31-39 required further evaluation prior to risk classification. The high accuracy with which we can distinguish non-invaders from harmful invaders suggests that this tool provides a feasible, pro-active system for pre-import screening of aquatic plants in the US, and may have additional utility for prioritizing management efforts of established species.

Globalization of trade and travel has facilitated the spread of non-native species across the earth. A proportion of these species become established and cause serious environmental, economic, and human health impacts. These species are referred to as invasive, and are now recognized as one of the major drivers of biodiversity change across the globe. As a long-time centre for trade, Europe has seen the introduction and subsequent establishment of at least several thousand non-native species. These range in taxonomy from viruses and bacteria to fungi, plants, and animals. Although invasive species cause major negative impacts across all regions of Europe, they also offer scientists the opportunity to develop and test theory about how species enter and leave communities, how non-native and native species interact with each other, and how different types of species affect ecosystem functions. For these reasons, there has been recent growth in the field of invasion biology as scientists work to understand the process of invasion, the changes that invasive species cause to their recipient ecosystems, and the ways that the problems of invasive species can be reduced. This review covers the process and drivers of species invasions in Europe, the socio-economic factors that make some regions particularly strongly invaded, and the ecological factors that make some species particularly invasive. We describe the impacts of invasive species in Europe, the difficulties involved in reducing these impacts, and explain the policy options currently being considered. We outline the reasons that invasive species create unique policy challenges, and suggest some rules of thumb for designing and implementing management programs. If new management programs are not enacted in Europe, it is inevitable that more invasive species will arrive, and that the total economic, environmental, and human health impacts from these species will continue to grow.

Essl et al. (1) tested whether historical socioeconomic conditions have created an invasion debt in Europe (i.e., a suite of nonnative species that have not yet been discovered but whose establishment has been determined by previous socioeconomic conditions). Essl et al. (1) tested this theory by asking whether the cumulative numbers of nonnative species presently established in 28 European countries were more closely correlated to socioeconomic conditions in the year 1900 or 2000. In this letter, we describe a flaw in their logic that biases the analysis to concluding that an invasion debt does occur.

This chapter describes and critically evaluates the ‘state-of-the-art’ for national policy and management efforts designed to prevent the arrival of invasive species. Preventing the introduction of invasive species will almost always be less costly than managing and adapting to species once they arrive. Although this is widely recognized by biologists and economists, only a handful of countries have embraced this approach in their policies for environmental invaders. As nations work to meet their obligations under the Convention on Biological Diversity (CBD), it is likely that the number of countries with programs for preventing invasive species will grow.

Preventing the invasion of freshwater aquatic species is the surest way to reduce their impacts, but it is also often expensive. Hence, the most efficient prevention programs will rely on accurate predictions of sites most at risk of becoming invaded and concentrate resources at those sites. Using data from Vilas County, Wisconsin (U.S.A.), collected in the 1970s, we constructed a predictive occurrence model for rusty crayfish (Orconectes rusticus) and applied it to an independent data set of 48 Vilas County lakes to predict which of these were most likely to become invaded between 1975 and 2005. We nested this invasion model within an economic framework to determine whether targeted management, derived from our quantitative predictions of likely invasion sites, would increase the economic value of lakes in the independent data set. Although the optimum expenditure on lake protection was high, protecting lakes at this level would have produced net economic benefits of at least $6 million over the last 30 years. We did not attempt to determine the value of nonmarket benefits of protection; thus, our results are likely to underestimate the total benefits from preventing invasions. Our results demonstrate that although few data are available early in an invasion, these data may be sufficient to support targeted, effective, and economically rational management. In addition, our results show that ecological predictions are becoming sufficiently accurate that their application in management can produce net economic benefits.

International commerce in live organisms presents a policy challenge for trade globalization; sales of live organisms create wealth, but some nonindigenous species cause harm. To reduce damage, some countries have implemented species screening to limit the introduction of damaging species. Adoption of new risk assessment (RA) technologies has been slowed, however, by concerns that RA accuracy remains insufficient to produce positive net economic benefits. This concern arises because only a small proportion of all introduced species escape, spread, and cause harm (i.e., become invasive), so a RA will exclude many noninvasive species (which provide a net economic benefit) for every invasive species correctly identified. Here, we develop a simple cost:benefit bioeconomic framework to quantify the net benefits from applying species prescreening. Because invasive species are rarely eradicated, and their damages must therefore be borne for long periods, we have projected the value of RA over a suitable range of policy time horizons (10–500 years). We apply the model to the Australian plant quarantine program and show that this RA program produces positive net economic benefits over the range of reasonable assumptions. Because we use low estimates of the financial damage caused by invasive species and high estimates of the value of species in the ornamental trade, our results underestimate the net benefit of the Australian plant quarantine program. In addition, because plants have relatively low rates of invasion, applying screening protocols to animals would likely demonstrate even greater benefits.