Perceptions of impact: Invasive alien plants in the urban environment

Many alien plant species are introduced to urban areas to create, augment or restore ecosystem services (ES). However, many of these species spread beyond original plantings, sometimes causing negative effects on existing ES or creating novel ecosystem disservices (EDS). An understanding of the perceptions of urban residents regarding invasive alien plants (IAPs) and the ES and EDS they provide is needed for the effective prioritisation of IAP management efforts in cities. Using the city of Cape Town, South Africa as a case study, we conducted questionnaire-based surveys (online and face-to-face) to determine the perceptions of urban residents regarding IAPs and their capacity to provide ES and EDS. Most urban residents perceive IAPs negatively (i.e. agreeing that they create EDS), but many recognise their importance in providing ES. Although most residents are not opposed to the management of IAPs, such actions are not perceived as a high priority relative to other environmental problems. Socio-demographic variables such as age, education, environmental awareness, and ethnicity shape urban residents' perceptions of IAPs. Older, more educated respondents were more likely to perceive IAPs negatively, while respondents with greater environmental awareness were aware of the benefits provided by IAPs. This study highlights the need to integrate public perceptions into the planning and management of IAPs and emphasises the importance of including ES assessments into the decision-making process, particularly in urban areas.

The Functional Potential of the Rhizospheric Microbiome of an Invasive Tree Species, Acacia dealbata

Plant-microbe interactions mediate both the invasiveness of introduced plant species and the impacts that they have in invaded ecosystems. Although the phylogenetic composition of the rhizospheric microbiome of Acacia dealbata (an invasive Australian tree species) has been investigated, little is known about the functional potential of the constituents of these altered microbial communities. We used shotgun DNA sequencing to better understand the link between bacterial community composition and functional capacity in the rhizospheric microbiomes associated with invasive A. dealbata populations in South Africa. Our analysis showed that several genes associated with plant growth-promoting (PGP) traits were significantly overrepresented in the rhizospheric metagenomes compared to neighbouring bulk soils collected away from A. dealbata stands. The majority of these genes are involved in the metabolism of nitrogen, carbohydrates and vitamins, and in various membrane transport systems. Overrepresented genes were linked to a limited number of bacterial taxa, mostly Bradyrhizobium species, the preferred N-fixing rhizobial symbiont of Australian acacias. Overall, these findings suggest that A. dealbata enriches rhizosphere soils with potentially beneficial microbial taxa, and that members of the genus Bradyrhizobium may play an integral role in mediating PGP processes that may influence the success of this invader when colonizing novel environments.

Stakeholder engagement in the study and management of invasive alien species

Invasive alien species are a major driver of global environmental change and a range of management interventions are needed to manage their effects on biodiversity, ecosystem services, human well-being and local livelihoods. Stakeholder engagement is widely advocated to integrate diverse knowledge and perspectives in the management of invasive species and to deal with potential conflicts of interest. We reviewed the literature in the ISI Web of Science on stakeholder engagement (the process of involving stakeholders (actors) in decision making, management actions and knowledge creation) in invasion science to assess and understand what has been done (looking at approaches and methodologies used, stakeholders involved, and outcomes from engagement) and to make recommendations for future work. Research on stakeholder engagement in invasion science has increased over the last decade, helping to improve scientific knowledge and contributing towards policy formulation and co-implementation of management. However, many challenges remain and engagement could be made more effective. For example, most studies engage only one stakeholder group passively using questionnaires, primarily for assessing local knowledge and perceptions. Although useful for management and policy planning, these stakeholders are not active participants and there is no two-way flow of knowledge. To make stakeholder involvement more useful, we encourage more integrative and collaborative engagement to (1) improve co-design, co-creation and co-implementation of research and management actions; (2) promote social learning and provide feedback to stakeholders; (3) enhance collaboration and partnerships beyond the natural sciences and academia (interdisciplinary and transdisciplinary collaboration); and (4) discuss some practical and policy suggestions for improving stakeholder engagement in invasion science research and management. This will help facilitate different stakeholders to work better together, allowing problems associated with biological invasions to be tackled more holistically and successfully.

The role of invasive alien species in shaping local livelihoods and human well-being: A review

Invasive alien species are a well-recognised driver of social-ecological change globally. Much research has focused on ecological impacts, but the role of invasive species for livelihoods and human well-being is less well known. Understanding the effects (benefits and costs) of invasive species on livelihoods and human well-being is important for guiding policy formulation and management. Here we review the literature on the role of invasive species in livelihoods to assess what is known, identify knowledge gaps and provide recommendations for future research. Literature was collected using key word searches and included both journal publications and grey literature. Slightly less than half (48%) of species studied had both substantial positive and negative impacts on local livelihoods (e.g. Australian Acacia spp. species; Camelus dromedaries; Lantana camara; Prosopis spp.), with 37% inducing mainly costs (Chromolaena odorata; Lissachatina fulica; Opuntia stricta) and 16% producing mainly benefits (Opuntia ficus-indica; Acacia spp.). Some species, such as Acacia dealbata, fell into different categories depending on the social-ecological context. Key benefits or services included the provision of fuelwood, fodder, timber and food products for local households communities and to a lesser extent supporting and regulating services such as soil improvement and shade. A number of species also provided cultural services such as recreation and spiritual values and provided many with an opportunity to earn a cash income. However, invasive species also harm livelihoods and increase vulnerability through encroaching on land and reducing mobility or access. They can also decrease the supply of natural resources used by households and reduce agricultural production (livestock and/or crops) which can result in losses of income and increased vulnerability. Furthermore, some invasive species were seen to have negative implications for human health and safety and reduce the cultural value of landscapes. Economic impacts on livelihoods as a result of invasive species were highly variable and very dependent on the social-ecological contexts. These negative implications can reduce resilience and adaptive capacity of households and communities thus increasing their vulnerability to change. Drawing on case studies we highlight that efforts for managing invasive species need to safeguard livelihood benefits while mitigating negative impacts. In concluding we highlight future research and policy needs on the topic of invasive species, livelihoods and human well-being.

Mine land rehabilitation in Brazil: Goals and techniques in the context of legal requirements

Environmental legislation in many countries demands the rehabilitation of degraded areas to minimize environmental impacts. Brazilian laws require the restitution of self-sustaining ecosystems to historical conditions but ignore the emergence of novel ecosystems due to large-scale changes, such as species invasions, extinctions, and land-use or climate changes, although these novel ecosystems might fulfill ecosystem services in similar ways as historic ecosystems. Thorough discussions of rehabilitation goals, target ecosystems, applied methods, and approaches to achieving mine land rehabilitation, as well as dialogues about the advantages and risks of chemical inputs or non-native, non-invasive species that include all political, economic, social, and academic stakeholders are necessary to achieve biological feasibility, sociocultural acceptance, economic viability, and institutional tractability during environmental rehabilitation. Scientific knowledge of natural and rehabilitating ecosystems is indispensable for advancing these discussions and achieving more sustainable mining. Both mining companies and public institutions are responsible for obtaining this knowledge.

The human and social dimensions of invasion science and management

Biological invasions are a leading cause of global environmental change given their effects on both humans and biodiversity. Humans introduce invasive alien species and may facilitate their establishment and spread, which can alter ecosystem services, livelihoods, and human well-being. People perceive the benefits and costs of these species through the lens of diverse value systems; these perspectives influence decisions about when and where to manage them. Despite the entanglement of humans with invasive alien species, most research on the topic has focused on their ecological aspects. Only relatively recently have the human and social dimensions of invasions started to receive sustained attention in light of their importance for understanding and governing biological invasions. This editorial draws on contributions to a special issue on the "Human and Social Dimensions of Invasion Science" and other literature to elucidate major trends and current contributions in this research area. We examine the relation between humans and biological invasions in terms of four crosscutting themes: (1) how people cause biological invasions; (2) how people conceptualise and perceive them; (3) how people are affected - both positively and negatively - by them; and (4) how people respond to them. We also highlight several ways in which research on the human and social dimensions of invasion science improves understanding, stakeholder engagement, and management.

A multi-criterion approach for prioritizing areas in urban ecosystems for active restoration following invasive plant control

Resources for biodiversity conservation and invasive plant management are limited, and restoring invaded vegetation is labour-intensive and expensive. Managers must prioritize their actions to achieve their goals efficiently and effectively. They must distinguish between areas that require only the removal of invasive alien plants ("passive restoration") from those that require additional restoration measures ("active restoration"). This study used a multi-criterion approach (Analytical Hierarchical Process) to develop a framework for identifying areas that require active restoration, and then to prioritize these areas for active restoration. The South African city of Cape Town is used as a test case to illustrate the utility of the framework. Framework criteria selected in determining the need for active restoration included: dominant alien species invading the area, density of invasion, duration of invasion, indigenous vegetation cover, adjacent land use, level of disturbance, size of the area, aspect, soil texture, soil depth and erodibility, slope and vegetation type. In deciding which areas to prioritize for active restoration, factors such as vegetation conservation status, selection in a regional conservation plan and connectivity function were assessed. Importance in ecosystem functioning (by providing a diversity of habitats and soil conservation) and the delivery of ecosystem service benefits were also considered. The resulting framework provides an objective tool for prioritizing sites for active restoration.

Managing Urban Plant Invasions: a Multi-Criteria Prioritization Approach

Alien plant invasions in urban areas can have considerable impact on biodiversity and ecosystem services (ES). Managing urban plant invasions is particularly challenging given the complex interactions between ecological, economic and social elements that exist in the urban milieu. Strategic landscape-scale insights are crucial for guiding management, as are tactical site-scale perspectives to plan and coordinate control efforts on the ground. Integrating these requirements to enhance management efficiency is a major challenge. Decision-support models have considerable potential for guiding and informing management strategies when problems are complex. This study uses multi-criteria decision tools to develop a prioritization framework for managing invasive alien plants (IAPs) in urban areas at landscape and local scales. We used the Analytic Hierarchy Process (AHP; a multi-criteria decision support model) to develop and rank criteria for prioritising IAP management in the City of Cape Town (CoCT), South Africa. Located within a global biodiversity hotspot, Cape Town has a long history of alien plant introductions and a complex socio-political make-up, creating a useful system to explore the challenges associated with managing urban plant invasions. To guide the prioritization of areas for IAP management across the CoCT, a stakeholder workshop was held to identify a goal and criteria for consideration, and to assess the relative importance given to each criterion in IAP management. Workshop attendees were drawn from multiple disciplines involved with different aspects of IAP research and management: government departments, scientists and researchers, and managers with a diverse set of skills and interests. We selected spatial datasets and applied our multi-criteria decision analysis in a Geographic Information System (GIS) to develop a landscape-scale prioritization map. To address issues relevant in an urban setting, we also modified an existing IAP management framework to develop a tactical (site-level) prioritization scheme for guiding on-the-ground control operations. High-priority sites for IAP management were identified at landscape- and local scales across the study area. Factors related to safety and security emerged as pivotal features for setting spatially-explicit priorities for management. The approach applied in this study can be useful for managers in all urban settings to guide the selection and prioritization of areas for IAP management.

Invasive plants differentially affect soil biota through litter and rhizosphere pathways: a meta-analysis

Invasive plants affect soil biota through litter and rhizosphere inputs, but the direction and magnitude of these effects are variable. We conducted a meta-analysis to examine the different effects of litter and rhizosphere of invasive plants on soil communities and nutrient cycling. Our results showed that invasive plants increased bacterial biomass by 16%, detritivore abundance by 119% and microbivore abundance by 89% through litter pathway. In the rhizosphere, invasive plants reduced bacterial biomass by 12%, herbivore abundance by 55% and predator abundance by 52%, but increased AM fungal biomass by 36%. Moreover, CO₂ efflux, N mineralisation rate and enzyme activities were all higher in invasive than native rhizosphere soils. These findings indicate that invasive plants may support more decomposers that in turn stimulate nutrient release via litter effect, and enhance nutrient uptake by reducing root grazing but forming more symbioses in the rhizosphere. Thus, we hypothesise that litter- and root-based loops are probably linked to generate positive feedback of invaders on soil systems through stimulating nutrient cycling, consequently facilitating plant invasion. Our findings from limited cases with diverse contexts suggest that more studies are needed to differentiate litter and rhizosphere effects within single systems to better understand invasive plant-soil interactions.

A taxonomically and geographically constrained information base limits non-native reptile and amphibian risk assessment: a systematic review

For many taxa, new records of non-native introductions globally occur at a near exponential rate. We undertook a systematic review of peer-reviewed publications on non-native herpetofauna, to assess the information base available for assessing risks of future invasions, resulting in 836 relevant papers. The taxonomic and geographic scope of the literature was also compared to a published database of all known invasions globally. We found 1,116 species of herpetofauna, 95% of which were present in fewer than 12 studies. Nearly all literature on the invasion ecology of herpetofauna has appeared since 2000, with a strong focus on frogs (58%), particularly cane toads (Rhinella marina) and their impacts in Australia. While fewer papers have been published on turtles and snakes, proportionately more species from both these groups have been studied than for frogs. Within each herpetofaunal group, there are a handful of well-studied species: R. marina, Lithobates catesbeianus, Xenopus laevis, Trachemys scripta, Boiga irregularis and Anolis sagrei. Most research (416 papers; 50%) has addressed impacts, with far fewer studies on aspects like trade (2%). Besides Australia (213 studies), most countries have little location-specific peer-reviewed literature on non-native herpetofauna (on average 1.1 papers per established species). Other exceptions were Guam, the UK, China, California and France, but even their publication coverage across established species was not even. New methods for assessing and prioritizing invasive species such as the Environmental Impact Classification for Alien Taxa provide useful frameworks for risk assessment, but require robust species-level studies. Global initiatives, similar to the Global Amphibian Assessment, using the species and taxonomic groups identified here, are needed to derive the level of information across broad geographic ranges required to apply these frameworks. Expansive studies on model species can be used to indicate productive research foci for understudied taxa.

From the cage to the wild: introductions of Psittaciformes to Puerto Rico

Introduced psittacine birds can become highly invasive. In this study, we assessed invasions of Psittaciformes in Puerto Rico. We reviewed the literature, public databases, citizen science records, and performed in situ population surveys across the island to determine the historical and current status and distribution of psittacine species. We used count data from Ebird to determine population trends. For species whose populations were increasing, we modelled their potential distribution using niche modeling techniques. We found 46 Psittaciformes in Puerto Rico, of which 26% are only present as pets, at least 29 species have been reported in the wild, and of those, there is evidence that at least 12 species are breeding. Our results indicate that most introduced species which have been detected as established still persist, although mostly in localized areas and small populations. Clear evidence of invasiveness was found for Brotogeris versicolurus and Myiopsitta monachus, which have greatly expanded their range in recent years. Psittacara erythrogenys and Eupsittacula canicularis also showed population increases, although to a lesser degree. The niche models predicted suitable areas for the four species, and also indicate the potential for range expansion. We discuss the factors leading to invasion success, assess the potential impacts, and we discuss possible management strategies and research prospects.

Pollination networks from natural and anthropogenic-novel communities show high structural similarity

The Anthropocene is marked by an unprecedented homogenisation of the world's biota, confronting species that never co-occurred during their evolutionary histories. Interactions established in these novel communities may affect ecosystem functioning; however, most research has focused on the impacts of a minority of aggressive invasive species, while changes inflicted by a less conspicuous majority of non-invasive alien species on community structure are still poorly understood. This information is critical to guide conservation strategies, and instrumental to advance ecological theory, particularly to understand how non-native species integrate in recipient communities and affect the interactions of native species. We evaluated how the structure of 50 published pollination networks changes with the proportion of alien plant species and found that network structure is largely unaffected. Although some communities were heavily invaded, the proportion of alien plant species was relatively low (mean = 10%; max. = 38%). We further characterized the pollination network in a botanic garden with a plant community dominated by non-invasive alien species (85%). We show that the structure of this novel community is also not markedly different from native-dominated communities. Plant-pollinator interactions revealed no obvious differences regarding plant origin (native vs. alien) or the native bioregion of the introduced plants. This overall similarity between native and alien plants is likely driven by the contrasting patterns of invasive plants (promoting generalism), and non-invasive aliens, suggested here to promote specialization.

Managing invasive species

Invasive species pose considerable harm to native ecosystems and biodiversity and frustrate and at times fascinate the invasive species management and scientific communities. Of the numerous non-native species established around the world, only a minority of them are invasive and noxious, whereas the majority are either benign or in fact beneficial. Agriculture in North America, for example, would look dramatically different if only native plants were grown as food crops and without the services of the European honey bee as a pollinator. Yet the minority of species that are invasive negatively alter ecosystems and reduce the services they provide, costing governments, industries, and private citizens billions of dollars annually. In this review, I briefly review the consequences of invasive species and the importance of remaining vigilant in the battle against them. I then focus on their management in an increasingly connected global community.

Assessment of the kidney and lung as immune barriers and hematopoietic sites in the invasive apple snail Pomacea canaliculata

Knowledge on the immune system of Pomacea canaliculata is becoming increasingly important, because of this gastropod's role as intermediate host and vector of Angiostrongylus cantonensis, the etiologic agent of eosinophilic meningitis in humans and domestic animals. Immune defenses of this gastropod comprise both humoral and cellular components, but they may also involve organs that act as immune barriers to prevent the spread of alien molecules and organisms. Both the kidney and lung are here shown to serve this function, because of (1) their positions in blood circulation, (2) the intricate architecture of their blood spaces, and (3) the proliferative and nodulation reactions of hemocytes to an immune challenge. However, these organs differ in that only the kidney shows permanent hemocyte aggregations. Microcirculation in the kidney was found to flow through an intricate vascular bed containing the permanent aggregations, which occurred either as hemocyte islets anchored by cytoplasmic projections of the renal epithelium or as perivascular accretions. Within 96 h of the injection of yeast cells, hemocyte nodules were formed both in the kidney and lung. Moreover, cell proliferation in renal hemocyte islets was measured by bromodeoxyuridine (BrdU) incorporation. The proportion of BrdU positive nuclei increased 48 h after injection. Signs of nodule regression (apoptotic bodies, lipofuscin-like deposits) and a decrease in the proportion of BrdU positive nuclei were found at 96 h. In addition, the area of renal hemocyte islets was significantly increased 96 h after injection. Nevertheless, the high complexity of the small vascular chambers that constitute the lung's respiratory lamina would also facilitate hemocyte-antigen contacts, required to elicit cellular aggregation, and hence, nodulation. To our knowledge, this paper includes the first quantitative indication of hemocyte proliferation after an immune challenge among Caenogastropoda.

Impoverished mobile epifaunal assemblages associated with the invasive macroalga Asparagopsis taxiformis in the Mediterranean Sea

There is an increasing concern about the ecosystem consequences of altering macroalgal assemblages. Many macrophytes are foundation species in coastal habitats, supporting much of the biodiversity of these ecosystems by providing essential resources such as food and habitat. The addition of invasive species strongly contributes to habitat modification, but the bottom-up impacts of non-native macroalgae on higher trophic levels remains difficult to predict. The main aim of this study was to evaluate the effects of the invasive macroalga Asparagopsis taxiformis on biodiversity by comparing the mobile macrofauna inhabiting this species to the dominant native species Halopteris scoparia. This is the first comprehensive study of the possible effects of this widespread invasive species on higher trophic levels. A hierarchical sampling design with two different spatial scales was conducted to explore the consistency of the patterns observed. Fifty-nine species belonging to superorder Peracarida were found, accounting 90% of all organisms. A. taxiformis hosted an impoverished epifaunal assemblage in comparison to that associated with the native seaweed, showing significantly lower values of diversity, abundance and number of epifaunal species across study locations. The structure of the associated macrofauna (both in terms of species composition, variability among samples and relative abundance of the species) was also different. Our results highlighted the strong influence of A. taxiformis in the resident community, with differences among the two macroalgae in all the parameters considered. Finally, our results also reflect a biotic homogenization of the epifaunal assemblages associated to A. taxiformis, a scarcely explored consequence of invasive processes in marine environments. Future studies exploring the cascading effects of the observed changes in the epifaunal assemblages would be necessary in order to estimate system responses to macroalgal invasions.

Factors influencing exotic species richness in Argentina's national parks

Exotic species introductions are a global phenomenon and protected areas are susceptible to them. Understanding the drivers of exotic species richness is vital for prioritizing natural resource management, particularly in developing countries with limited resources. We analyzed the influence of coarse resolution factors on exotic species richness (plants, mammals, and birds) in Argentina’s National Parks System. We collected data on native species richness, year of park formation, park area, region, elevation range, number of rivers crossing area boundaries, roads entering area, mean annual rainfall, mean annual temperature, mean annual number of visitors, and Human Influence Index within and surrounding each park. We compiled 1,688 exotic records in 36 protected areas: 83% plants and 17% animals (9.5% mammals, 5.5% birds, 1.5% fishes, 0% amphibians, 0% reptiles). The five parks with the most exotic species (all taxa combined) were in north Patagonia. Exotic grasses were the most common exotic plants, and within animals, lagomorphs and feral ungulates were remarkably widespread. Exotic plant richness was mostly influenced by temperature and native plant richness, while exotic mammal and bird richness was driven mostly by anthropogenic variables, with models explaining 36–45% of data deviance. Most variables that positively influenced exotic taxa were indirectly related to an increase in spatial heterogeneity (natural or anthropogenic), suggesting greater niche space variability as facilitators of exotic richness increase. Additional data are needed to further investigate the patterns and mechanisms of exotic species richness in protected areas, which will help to prioritize the greatest needs of monitoring and management.

Synergy between roads and disturbance favour Bromus tectorum L. invasion

Background

Global change produces pervasive negative impacts on biodiversity worldwide. Land use change and biological invasions are two of the major drivers of global change that often coexist; however, the effects of their interaction on natural habitats have been little investigated. In particular, we aimed to analyse whether the invasion of an introduced grass (Bromus tectorum; cheatgrass) along roads verges and the disturbance level in the natural surrounding habitat interact to influence the degree of B. tectorum invasion in the latter habitats in north-western Patagonia.

Methods

Along six different roads, totalling approximately 370 km, we set two 50 m × 2 m sampling plots every 5 km (73 plots in total). One plot was placed parallel to the road (on the roadside) and the other one perpendicular to it, towards the interior of the natural surrounding habitat. In each plot, we estimated the B. tectorum plant density in 1 m² subplots placed every 5 m. In the natural habitat, we registered the vegetation type (grassy steppe, shrub-steppe, shrubland, and wet-meadow) and the disturbance level (low, intermediate, and high). Disturbance level was visually categorized according to different signs of habitat degradation by anthropogenic use.

Results

B. tectorum density showed an exponential decay from roadsides towards the interior of natural habitats. The degree of B. tectorum invasion inside natural habitats was positively related to B. tectorum density on roadsides only when the disturbance level was low. Shrub-steppes, grassy steppes and shrublands showed similar mean density of B. tectorum. Wet-meadows had the lowest densities of B. tectorum. Intermediate and highly disturbed environments presented higher B. tectorum density than those areas with low disturbance.

Discussion

Our study highlights the importance of the interaction between road verges and disturbance levels on B. tectorum invasion in natural habitats surrounding roads of north-western Patagonia, particularly evidencing its significance in the invasion onset. The importance of invasion in road verges depends on disturbance level, with better conserved environments being more resistant to invasion at low levels of B. tectorum density along road verges, but more susceptible to road verges invasion at higher levels of disturbance. All the habitats except wet-meadows were invaded at a similar degree by B. tectorum, which reflects its adaptability to multiple habitat conditions. Overall, our work showed that synergies among global change drivers impact native environments favouring the invasion of B. tectorum.

Invasion waves and pinning in the Kirkpatrick-Barton model of evolutionary range dynamics

The Kirkpatrick-Barton model, well known to invasion biologists, is a pair of reaction-diffusion equations for the joint evolution of population density and the mean of a quantitative trait as functions of space and time. Here we prove the existence of two classes of coherent structures, namely "bounded trait mean differential" traveling waves and localized stationary solutions, using geometric singular perturbation theory. We also give numerical examples of these (when they appear to be stable) and of "unbounded trait mean differential" solutions. Further, we provide numerical evidence of bistability and hysteresis for this system, modeling an initially confined population that colonizes new territory when some biotic or abiotic conditions change, and remains in its enlarged range even when conditions change back. Our analytical and numerical results indicate that the dynamics of this system are more complicated than previously recognized, and help make sense of evolutionary range dynamics predicted by other models that build upon it and sometimes challenge its predictions.

Sampling alien species inside and outside protected areas: Does it matter?

Data of alien species presences are generally more readily available in protected than non-protected areas due to higher sampling efforts inside protected areas. Are the results and conclusions based on analyses of data collected in protected areas representative of wider non-protected regions? We address this question by analysing some recently published data of alien plants in Greece. Mixed effects models were used with alien species presences in 8.25×8.25km cells as dependent variable and the percentage of protected area, as well as the agricultural and artificial land cover types richness (as indicators of human presence) as independent variables. In addition, the spatial cross-correlation between the percentage of protected area and alien species richness was examined across scales. Results indicated that the percentage of protected area per cell is a poor predictor of alien species richness. Spatial analysis indicated that cells with higher percentage of protected areas have slightly less alien species than cells with lower percentage of protected areas. This result is likely to be driven by the overall negative correlation between habitat protection and anthropogenic activities. Thus, the conclusions deduced by data deriving from protected areas are likely to hold true for patterns of alien species in non-protected areas when the human pressures are accounted for.

Impacts of Pathogen Introduction Risk on Importer Behavior and Gains from Trade in the Livestock Industry

Trade eliminates geographic barriers, allowing for novel exchange of goods and services, but also creates pathways for the unintentional spread of infectious pathogens such as foot and mouth disease. In the absence of trade regulation, a producer's choice of import origin depends on relative prices and costs associated with trading partners. This paper develops a framework for exploring importer behavior in a non-regulated economy, allowing for price and risk heterogeneity among potential import sources. In the model, importers determine the risk of introducing foot and mouth disease to home soil and choose import volumes using risk and market data. When importers consider the possibility of unreported or undetected outbreaks, they choose to import from multiple sources to minimize risk and simultaneously create gains from trade over the regulated outcome. Our results have implications for the development of import and inspection policies that could be specifically designed to target highest risk imports of livestock.

Effects of admixture in native and invasive populations of Lythrum salicaria

Intraspecific hybridization between diverged populations can enhance fitness via various genetic mechanisms. The benefits of such admixture have been proposed to be particularly relevant in biological invasions, when invasive populations originating from different source populations are found sympatrically. However, it remains poorly understood if admixture is an important contributor to plant invasive success and how admixture effects compare between invasive and native ranges. Here, we used experimental crosses in Lythrum salicaria, a species with well-established history of multiple introductions to Eastern North America, to quantify and compare admixture effects in native European and invasive North American populations. We observed heterosis in between-population crosses both in native and invasive ranges. However, invasive-range heterosis was restricted to crosses between two different Eastern and Western invasion fronts, whereas heterosis was absent in geographically distant crosses within a single large invasion front. Our results suggest that multiple introductions have led to already-admixed invasion fronts, such that experimental crosses do not further increase performance, but that contact between different invasion fronts further enhances fitness after admixture. Thus, intra-continental movement of invasive plants in their introduced range has the potential to boost invasiveness even in well-established and successfully spreading invasive species.

ALEX index enables detection of alien macroalgae invasions across habitats within a marine protected area

A modified version of the ALien Biotic IndEX (ALEX) has been recently proposed to evaluate biological invasions in macroalgal assemblages. ALEX was applied in a Marine Protected Area where a recreational-fishing port is present testing the following hypotheses: ALEX increases with the distance from the port, it changes between the two directions off the port and it changes among three different habitats: Cystoseira beds, algal turf and dead matte of the seagrass Posidonia oceanica. A total of 78 native macroalgal taxa and 4 introduced species were found, the Chlorophyta Caulerpa cylindracea and the Rhodophyta Apoglossum gregarium, Acrothamnion preissii and Womersleyella setacea. All study sites were in high quality status highlighting that the assemblages investigated were at an early stage of NIS invasion. However, ALEX detected different values among conditions and habitats within the MPA, suggesting a local dynamics of NIS spread and different resistance to invasion of the investigated habitats.

A regional assessment of white-tailed deer effects on plant invasion

Herbivores can profoundly influence plant species assembly, including plant invasion, and resulting community composition. Population increases of native herbivores, e.g. white-tailed deer (Odocoileus virginianus), combined with burgeoning plant invasions raise concerns for native plant diversity and forest regeneration. While individual researchers typically test for the impact of deer on plant invasion at a few sites, the overarching influence of deer on plant invasion across regional scales is unclear. We tested the effects of deer on the abundance and diversity of introduced and native herbaceous and woody plants across 23 white-tailed deer research sites distributed across the east-central and north-eastern USA and representing a wide range of deer densities and invasive plant abundance and identity. Deer access/exclusion or deer population density did not affect introduced plant richness or community-level abundance. Native and total plant species richness, abundance (cover and stem density) and Shannon diversity were lower in deer-access vs. deer-exclusion plots. Among deer-access plots, native species richness, native and total cover, and Shannon diversity (cover) declined as deer density increased. Deer access increased the proportion of introduced species cover (but not of species richness or stem density). As deer density increased, the proportion of introduced species richness, cover and stem density all increased. Because absolute abundance of introduced plants was unaffected by deer, the increase in proportion of introduced plant abundance is likely an indirect effect of deer reducing native cover. Indicator species analysis revealed that deer access favoured three introduced plant species, including Alliaria petiolata and Microstegium vimineum, as well as four native plant species. In contrast, deer exclusion favoured three introduced plant species, including Lonicera japonica and Rosa multiflora, and 15 native plant species. Overall, native deer reduced community diversity, lowering native plant richness and abundance, and benefited certain invasive plants, suggesting pervasive impacts of this keystone herbivore on plant community composition and ecosystem services in native forests across broad swathes of the eastern USA.

A framework for engaging stakeholders on the management of alien species

Alien species can have major ecological and socioeconomic impacts in their novel ranges and so effective management actions are needed. However, management can be contentious and create conflicts, especially when stakeholders who benefit from alien species are different from those who incur costs. Such conflicts of interests mean that management strategies can often not be implemented. There is, therefore, increasing interest in engaging stakeholders affected by alien species or by their management. Through a facilitated workshop and consultation process including academics and managers working on a variety of organisms and in different areas (urban and rural) and ecosystems (terrestrial and aquatic), we developed a framework for engaging stakeholders in the management of alien species. The proposed framework for stakeholder engagement consists of 12 steps: (1) identify stakeholders; (2) select key stakeholders for engagement; (3) explore key stakeholders' perceptions and develop initial aims for management; (4) engage key stakeholders in the development of a draft management strategy; (5) re-explore key stakeholders' perceptions and revise the aims of the strategy; (6) co-design general aims, management objectives and time frames with key stakeholders; (7) co-design a management strategy; (8) facilitate stakeholders' ownership of the strategy and adapt as required; and (9) implement the strategy and monitor management actions to evaluate the need for additional or future actions. In case additional management is needed after these actions take place, some extra steps should be taken: (10) identify any new stakeholders, benefits, and costs; (11) monitor engagement; and (12) revise management strategy. Overall, we believe that our framework provides an effective approach to minimize the impact of conflicts created by alien species management.

Invasion ecology meets parasitology: Advances and challenges

Biological invasions threaten the diversity and functioning of native ecosystems, and the rate at which species are being introduced to new areas shows no sign of slowing down. Parasites play roles in biological invasions, for instance when native parasites interact with exotic hosts, or when parasites themselves are introduced to new areas. However, publication trends show clearly that research on parasitism in the context of biological invasions is lagging far behind research on biological invasions in general. The different articles in this special issue of International Journal for Parasitology-Parasites and Wildlife on 'Invasions' address various aspects of the interface between parasitology and invasion biology, including how invasive free-living species lose or gain parasites on the invasion front as they move away from their site of introduction, how these invasive species affect the dynamics of native parasites, and how exotic parasites become established and impact native hosts. Together, they highlight the challenges facing researchers in this area, and set the agenda for the next few years of research.