Showing papers in "Biological Invasions in 2015"

‘Double trouble’: the expansion of the Suez Canal and marine bioinvasions in the Mediterranean Sea

Abstract: ‘‘Egypt to build new Suez canal... ‘This giant project will be the creation of a new Suez canal parallel to the current channel’ said Mohab Mamish, the chairman of the Suez Canal Authority, in a televised speech.’’ (http://www.theguardian.com/world/2014/aug/05/ egypt-build-new-suez-canal, viewed August 13, 2014). This is ominous news. Expected to double the capacity of the Suez Canal, the expansion is sure to have a diverse range of effects, at local and regional scales, on both the biological diversity and the ecosystem goods and services of the Mediterranean Sea. Of nearly 700 multicellular non-indigenous species (NIS) currently recognized from the Mediterranean Sea, fully half were introduced through the Suez Canal since 1869 (Galil et al. 2014). This is one of the most potent mechanisms and corridors for invasions by marine species known in the world. Further, molecular methods demonstrate high levels of gene flow between the Red Sea and the Mediterranean populations

EU adopts innovative legislation on invasive species: a step towards a global response to biological invasions?

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

DNA (meta)barcoding of biological invasions: a powerful tool to elucidate invasion processes and help managing aliens

Abstract: Biological invasions are a major threat to the world’s biodiversity with consequences on ecosystem structure and functioning, species evolution, and human well-being (through ecosystem services). Conservation of biological diversity and management of biological resources require multi-level management strategies on non-native species, in order to (1) prevent biological introductions, (2) detect non-native species at an early stage of the introduction, and (3) eradicate or maintain at a low level of population density non-native species that were successfully introduced. A pre-requisite to any control measures on non-native species is the ability to rapidly and accurately identify the putative threatening alien species. DNA barcoding, and its recent extension, DNA metabarcoding are complementary tools that have proved their value in the identification of living beings. Here we review their use in the identification of non-native species at several steps of the introduction processes, and how they can be applied in the control and management of biological introductions. Through examples covering various taxa and ecosystems (terrestrial, freshwater, marine), we highlight the strengths and weaknesses of approaches that we foresee as crucial in the implementation of early warning strategies.

Reconstructing the invasion and the demographic history of the yellow-legged hornet, Vespa velutina, in Europe

Abstract: The yellow-legged hornet, Vespa velutina, was accidentally introduced from Southeast Asia and then invaded France and Korea over the last 10 years. Since its introduction, its predation on honeybee colonies has rapidly become an economic problem in invaded countries. Using mitochondrial cytochrome C oxidase and 22 nuclear microsatellite loci, we showed that native hornet populations were well differentiated and highly diverse. In contrast, introduced populations from France and Korea suffered a genetic bottleneck, which did not prevent their rapid geographic expansion. Analysis of the genetic data indicates that French and Korean populations likely arose from two independent introduction events. The most probable source population is from an area between the Chinese provinces of Zhejiang and Jiangsu. This invasion route is in agreement with knowledge on trade and historical records. By studying colonies of V. velutina, we demonstrated its polyandry, which is very rare among Vespidae. This mating behavior could have favored the success of this Asian hornet in Europe and Korea. Combined, the population and colony results suggest that very few or possibly only one single multi-mated female gave rise to the invasion.

Distribution of Corbicula fluminea (Müller, 1774) in the invaded range: a geographic approach with notes on species traits variability

Abstract: Corbicula fluminea is considered one of the most important non-native invasive species (NIS) in aquatic systems mainly due to its widespread distribution and ecological and economic impacts. This species is known to negatively affect native bivalves, also with severe effects on biodiversity and ecosystem functioning. Throughout an exhaustive bibliographic survey and with the aid of Geographic Information Systems tools, this study tracks the species dispersion from its native range, including the description of important physical and environmental barriers. Additional analyses were conducted to examine possible influences of latitudinal/temperature gradients on important traits (e.g. life span, maximum and mean body length, growth at the end of first year). Altitude and winter minimum temperature appear to be delaying the invasion worldwide, but it seems inevitable that the species will spread across the globe. Latitude and summer temperature show a relationship with growth and life span. Overall, the information gathered in this review may be relevant to forecast future distribution patterns of this NIS, and to anticipate the possible implementation of effective management measures. Moreover, it may constitute a valuable tool in the prediction of population responses to an increasingly changing environment.

Marine invasion genetics: from spatio-temporal patterns to evolutionary outcomes

Abstract: Over the last 15 years studies on invasion genetics have provided important insights to unravel cryptic diversity, track the origin of colonizers and reveal pathways of introductions. Despite all these advances, to date little is known about how evolutionary processes influence the observed genetic patterns in marine biological invasions. Here, firstly we review the literature on invasion genetics that include samples from European seas. These seas constitute a wide array of unique water masses with diverse degrees of connectivity, and have a long history of species introductions. We found that only a small fraction of the recorded introduced species has been genetically analysed. Furthermore, most studies restrict their approach to describe patterns of cryptic diversity and genetic structure, with the underlying mechanisms involved in the invasion process being largely understudied. Secondly, we analyse how genetic, reproductive and anthropogenic traits shape genetic patterns of marine introduced species. We found that most studies reveal similar genetic diversity values in both native and introduced ranges, report evidence of multiple introductions, and show that genetic patterns in the introduced range are not explained by taxonomic group or reproductive strategy. Finally, we discuss the evolutionary implications derived from genetic patterns observed in non-indigenous species. We identify different scenarios that are determined by propagule pressure, phenotypic plasticity and pre-adaptation, and the effects of selection and genetic admixture. We conclude that there is a need for further investigations of evolutionary mechanisms that affect individual fitness and adaptation to rapid environmental change.

Harmonia + and Pandora +: risk screening tools for potentially invasive plants, animals and their pathogens

Abstract: Given the large number of alien species that may potentially develop into invasives, there is a clear need for robust schemes that allow to screen species for such risks. The Harmonia+ framework presented here brings together 30 questions that refer to distinct components of invasion. Together, they cover the stages of introduction, establishment, spread, and multiple kinds of impacts, viz. referring to the health of the environment (including wild species), cultivated plants, domesticated animals and man. In a complete assessment, input is provided by choosing among predefined ordinal answers and by supplementing these with textual clarification. Uncertainty is covered by indicating levels of confidence. By converting answers into scores, which are then condensed into summary statistics, Harmonia+ allows for quantitative output on stage-specific and general risks. Test assessments on five species emerging in Belgium showed the perceived environmental risks of Procambarus clarkii to be highest (0.72), and that of Threskiornis aethiopicus to be lowest (0.13). Given the considerable parallels that exist between invasive alien species and emerging infectious diseases, we additionally created Pandora, which is a risk analysis scheme for pathogens and parasites. It consists of 13 key questions and has the same structure as Harmonia+. Since diseases play a paramount role in biological invasions, results of Pandora assessments may feed into Harmonia+ through a slightly adapted, host-specific version named Pandora+. Harmonia+, Pandora and Pandora+ may be used both for prioritization purposes and for underpinning detailed risk analyses, and can be consulted online through http://ias.biodiversity.be.

Naturalization and invasion of alien plants in Puerto Rico and the Virgin Islands

Abstract: A fundamental goal in invasion ecology is to identify and understand the factors explaining why some alien species become invasive when others fail. In this study we gathered data on taxonomy, invasive status, invasion history, geographic distribution, and biological and ecological traits of 1,032 alien plant species occurring on different habitats in Puerto Rico and the Virgin Islands. These data were used to evaluate the relative importance of habitat and species attributes in influencing the likelihood of alien plants to become naturalized and subsequently invasive on these islands. Our results showed that alien species were more likely to become naturalized if they grow in semi-natural habitats, have large native distribution ranges, long residence time, were introduced for horticulture and have mixed breeding systems. On the other hand, naturalized species were more likely to become invasive if they were introduced for horticul- ture, behave as weeds, have tolerance to different climatic life-zones, thrive in ruderal habitats, have mixed breeding systems with hermaphroditic flowers, reproduce vegetatively and produce small seeds. Whereas some of these parameters were important for both transitions, others were important for either naturalization or invasion. Overall, our results empha- size the importance of studying different stages of the invasion process in order to understand the mecha- nisms explaining successful invasions rather than baseline approaches of simply comparing invasive with natives or noninvasive alien species. Understand- ing the process by which alien species become naturalized or invasive could provide a more objective and accurate approach for managing and predicting biological invasions.

Priority effects can lead to underestimation of dispersal and invasion potential

Abstract: Molecular analyses are frequently used to assess biological gene flow and dispersal, yet recent data suggest that the operation of density-dependent priority effects often leads to underestimation of species movement patterns and associated invasive potential. Although individual movement is broadly considered to promote connectivity among populations, emerging genetic evidence on a range of scales indicates that it often fails to do so; instead, it can be a strategy that allows first colonizers to wedge a ‘foot in the door’ when new space becomes available. Founding lineages can then rapidly dominate, blocking colonization by later arrivals; subsequent invasion opportunities may be contingent on the extirpation of locals. Many contemporary studies, however, ignore the role of such density-dependent priority effects, and thus fail to assess major differences between movement and establishment. Understanding the role of these processes in the successful establishment of dispersing organisms is critical if we are to predict distributional range shifts and deal with invasive pest species.

The role of exotic ladybeetles in the decline of native ladybeetle populations: evidence from long-term monitoring

Abstract: Ladybeetles (Coleoptera: Coccinellidae) are ubiquitous predators which play an important role in suppressing pest insects. In North America, the coccinellid community is increasingly dominated by exotic species, and the abundance of some native species has declined dramatically since the 1980s. Several hypotheses have been proposed to describe the mechanism of invasion coupled with native species declines, e.g. vacant niche exploitation, intraguild predation, competitive exploitation and habitat compression. We analyze a 24-year dataset of coccinellid community structure in southwestern Michigan to elucidate the most likely mechanism(s) of native coccinellid decline and implications for their conservation. Correlation analyses indicated that impact of exotic species on native coccinellids varies with their degree of interaction. Although several native species were observed to be in numerical decline, only Adalia bipunctata and Coleomegilla maculata had declines that were statistically significant. The magnitude of decline in these two species varied with the degree of dietary overlap with invaders, thus their decline is most likely driven by competitive exploitation. Habitat use patterns by some native species (A. bipunctata and Coccinella trifasciata) changed during years when the exotic Harmonia axyridis reached high numbers, lending support to the habitat compression hypothesis, where native species survive in ancestral (i.e. natural or semi-natural) habitats when invaders dominate cultivated habitats. Coccinellid communities occurring in semi-natural forested habitats were unique in both composition and variability from those occurring in cultivated habitats. Such semi-natural habitats can act as refuges for native coccinellids and may play a role in maintaining the functional resilience of coccinellid communities.

Citizen science contributes to our knowledge of invasive plant species distributions.

Abstract: Citizen science is commonly cited as an effective approach to expand the scale of invasive species data collection and monitoring. However, researchers often hesitate to use these data due to concerns over data quality. In light of recent research on the quality of data collected by volunteers, we aimed to demonstrate the extent to which citizen science data can increase sampling coverage, fill gaps in species distributions, and improve habitat suitability models compared to professionally generated data sets used in isolation. We combined data sets from professionals and volunteers for five invasive plant species (Alliaria petiolata, Berberis thunbergii, Cirsium palustre, Pastinaca sativa, Polygonum cuspidatum) in portions of Wisconsin. Volunteers sampled counties not sampled by professionals for three of the five species. Volunteers also added presence locations within counties not included in professional data sets, especially in southern portions of the state where professional monitoring activities had been minimal. Volunteers made a significant contribution to the known distribution, environmental gradients sampled, and the habitat suitability of P. cuspidatum. Models generated with professional data sets for the other four species performed reasonably well according to AUC values (>0.76). The addition of volunteer data did not greatly change model performance (AUC > 0.79) but did change the suitability surface generated by the models, making them more realistic. Our findings underscore the need to merge data from multiple sources to improve knowledge of current species distributions, and to predict their movement under present and future environmental conditions. The efficiency and success of these approaches require that monitoring efforts involve multiple stakeholders in continuous collaboration via established monitoring networks.

Acoustical deterrence of Silver Carp ( Hypophthalmichthys molitrix )

Abstract: The invasive Silver Carp (Hypophthalmichthys molitrix) dominate large regions of the Mississippi River drainage and continue to expand their range northward threatening the Laurentian Great Lakes. This study found that complex broadband sound (0–10 kHz) is effective in altering the behavior of Silver Carp with implications for deterrent barriers or potential control measures (e.g., herding fish into nets). The phonotaxic response of Silver Carp was investigated using controlled experiments in outdoor concrete ponds (10 × 4.9 × 1.2 m). Pure tones (500–2000 Hz) and complex sound (underwater field recordings of outboard motors) were broadcast using underwater speakers. Silver Carp always reacted to the complex sounds by exhibiting negative phonotaxis to the sound source and by alternating speaker location, Silver Carp could be directed consistently, up to 37 consecutive times, to opposite ends of the large outdoor pond. However, fish habituated quickly to pure tones, reacting to only approximately 5 % of these presentations and never showed more than two consecutive responses. Previous studies have demonstrated the success of sound barriers in preventing Silver Carp movement using pure tones and this research suggests that a complex sound stimulus would be an even more effective deterrent.

Non-linear effects of invasive lionfish density on native coral-reef fish communities

Abstract: One of the major goals of invasion biology is predicting the effects of invaders on native species, which is often accomplished by linearly scaling-up per- capita effects with invader abundance. However, the relationship between invader density and their ecolog- ical impact is poorly understood, and it is likely that the effects of invasive species scale non-linearly with increasing invader density. The Pacific red lionfish (Pterois volitans) is an invasive predator that has reached high abundances throughout the tropical and sub-tropical western Atlantic, Caribbean, and Gulf of Mexico. A single lionfish can have extremely large effects on native reef-fish communities, yet the rela- tionship between lionfish density and their ecological effects is not well known. I manipulated juvenile lionfish densities on small patch reefs in the Bahamas and monitored the subsequent effects on native coral- reef fish abundance, biomass, richness, evenness, composite diversity, and community structure over 7 weeks. Native fish abundance and biomass decreased non-linearly with increasing lionfish density, with the largest drops in abundance and biomass at low lionfish densities and their effects leveling off at high densities. Lionfish density also significantly affected richness and community structure, but these effects could not be clearly classified as either linear or non-linear. Even- ness and composite diversity were not significantly affected by lionfish density. Given that the effects of lionfish on native fish abundance and biomass level-off at high lionfish densities, it appears important to remove all lionfish from small patch reefs to have the biggest influence on conserving the native community.

Harbor networks as introduction gateways: contrasting distribution patterns of native and introduced ascidians

Abstract: Harbors and marinas are well known gateways for species introductions in marine environments but little work has been done to ascertain relationships between species diversity, harbor type, and geographic distance to uncover patterns of secondary spread. Here, we sampled ascidians from 32 harbors along ca. 300 km of the NW Mediterranean coast and investigated patterns of distribution and spread related to harbor type (marina, fishing, commercial) and geographic location using multivariate techniques. In total, 28 ascidians were identified at the species level and another 9 at the genus level based on morphology and genetic barcoding. Eight species were assigned to introduced forms, 15 were given native status and 5 were classified as cryptogenic. Aplidium accarense was reported for the first time in the Mediterranean Sea and was especially abundant in 23 of the harbors. Introduced and cryptogenic species were abundant in most of the surveyed harbors, while native forms were rare and restricted to a few harbors. Significant differences in the distribution of ascidians according to harbor type and latitudinal position were observed. These differences were due to the distribution of introduced species. We obtained a significant correlation between geographic distance and ascidian composition, indicating that closely located harbors shared more ascidian species among them. This study showed that harbors act as dispersal strongholds for introduced species, with native species only appearing sporadically, and that harbor type and geographic location should also be considered when developing management plans to constrain the spread of non-indigenous species in highly urbanized coastlines.

Linking above- and belowground resource use strategies for native and invasive species of temperate deciduous forests

Abstract: Non-native invasive species are often more productive aboveground than co-occurring natives. Because aboveground productivity is closely tied to plant nitrogen (N) uptake and use, high invader leaf productivity should be associated with root growth and plant N use strategies. However, little is known about the above- and belowground carbon (C) and N use strategies of native and invasive plants. We measured shoot and root attributes and soil properties associated with 10 native and 14 non-native invasive forest shrubs and lianas of the Eastern U.S. in a common garden in Syracuse, New York (USA), including leaf growth and chemistry (C, N), root growth, specific root length (SRL), root tissue density, and associated soil C and N concentration, each determined at 2-month intervals (July–November). Non-native species had greater leaf and root production, leaf N concentration, and SRL, but lower leaf N resorption rates and root N concentration than natives. Soil N concentration associated with non-natives was significantly lower than that of native species. Our results suggest that greater aboveground productivity of invasive forest species is linked to greater production of fine roots that may increase the capacity of invaders to take up soil resources. In addition, our findings suggest that invaders beget more rapid plant-soil N feedbacks by promoting N cycling compared to the strategy of slow growing native species that emphasizes recycled plant N. Such differences in N use strategy between native and non-native species would significantly impact forest soil nutrient cycling.

Trade of ornamental crayfish in Europe as a possible introduction pathway for important crustacean diseases: crayfish plague and white spot syndrome

Abstract: Rapidly growing trade of ornamental animals may represent an entry pathway for emerging pathogens; this may concern freshwater crayfish that are increasingly popular pets. Infected crayfish and contaminated water from aquaria may be released to open waters, thus endangering native crustacean fauna. We tested whether various non-European crayfish species available in the pet trade in Germany and the Czech Republic are carriers of two significant crustacean pathogens, the crayfish plague agent Aphanomyces astaci and the white spot syndrome virus (WSSV). The former infects primarily freshwa- ter crayfish (causing substantial losses in native European species), the latter is particularly known for economic losses in shrimp aquacultures. We screened 242 individuals of 19 North American and Australasian crayfish taxa (the identity of which was validated by DNA barcoding) for these pathogens, using molecular methods recommended by the World Organisation for Animal Health. A. astaci DNA was detected in eight American and one Australian cray- fish species, comprising in total 27 % of screened batches. Furthermore, viability of A. astaci was confirmed by its isolation to axenic cultures from three host taxa, including the parthenogenetic invader Marmorkrebs (Procambarus fallax f. virginalis). In contrast, WSSV was only confirmed in three individ- uals of Australian Cherax quadricarinatus. Despite modest prevalence of detected infections, our results demonstrate the potential of disease entry and spread through this pathway, and should be considered if any trade regulations are imposed. Our study highlights the need for screening for pathogens in the ornamental trade as one of the steps to prevent the transmission of emerging diseases to wildlife.

Bamboo invasion of native broadleaf forest modified soil microbial communities and diversity.

Abstract: The effect of plant invasion on soil microbial communities in various ecosystems has increasingly become the focus of research over the last decade. Moso bamboo (Phyllostachys edulis) invasion of native forests in Tianmushan National Nature Reserve located in southeastern China has resulted in greatly decreased biodiversity of plants and birds. We combined three different microbial community techniques (Biolog, cellular fatty acids, and 16S-PCR–DGGE) to examine whether changes in the overstory of plant taxa, or any associated environmental changes, modified soil microbial communities. Three types of forests were examined: mono-bamboo forest, mixed forest of bamboo and broadleaf, and native broadleaf forest. The fatty acid and DGGE results showed that bamboo invasion of the native forest influenced soil community structure and increased microbial biomass and taxonomic diversity despite decreased plant diversity. The Biolog results indicated no change in microbial functional diversity as a result of bamboo invasion. Evidence from bacterial PCR–DGGE suggested that bamboo stimulated the growth of otherwise undetected soil bacterial species. Overall, the results indicate that bamboo invasion may significantly affect associated soil microbial communities.

Adaptive invasive species distribution models: a framework for modeling incipient invasions

Abstract: The utilization of species distribution model(s) (SDM) for approximating, explaining, and predicting changes in species’ geographic locations is increasingly promoted for proactive ecological management. Although frameworks for modeling non-invasive species distributions are relatively well developed, their counterparts for invasive species—which may not be at equilibrium within recipient environments and often exhibit rapid transformations—are lacking. Additionally, adaptive ecological management strategies address the causes and effects of biological invasions and other complex issues in social-ecological systems. We conducted a review of biological invasions, species distribution models, and adaptive practices in ecological management, and developed a framework for adaptive, niche-based, invasive species distribution model (iSDM) development and utilization. This iterative, 10-step framework promotes consistency and transparency in iSDM development, allows for changes in invasive drivers and filters, integrates mechanistic and correlative modeling techniques, balances the avoidance of type 1 and type 2 errors in predictions, encourages the linking of monitoring and management actions, and facilitates incremental improvements in models and management across space, time, and institutional boundaries. These improvements are useful for advancing coordinated invasive species modeling, management and monitoring from local scales to the regional, continental and global scales at which biological invasions occur and harm native ecosystems and economies, as well as for anticipating and responding to biological invasions under continuing global change.

How do native species respond to invaders? Mechanistic and trait-based perspectives

Abstract: Adaptive responses of native species are important in enabling their persistence in the face of unprecedented biotic exchange. In the present paper I discuss how native species respond to invasive species both from a mechanistic and trait-based perspective. An earlier review by Strauss et al. (Ecol Lett 9:357–374, 2006) discussed a conceptual model of native species evolution in which the likelihood of an evolutionary response to an invader is dependent upon the strength of the selective pressure imposed (degree of variation in fitness between genotypes) and the adaptive capacity of the native (extent of pre-adaptation or genetic diversity). I aim to update and build upon this framework in light of new information on the interaction of phenotypic plasticity and evolutionary processes in adaptive responses of native species. Phenotypic plasticity can be a precursor to or an inhibitor of evolutionary responses and, under conditions of strong selection, phenotypic plasticity may enable adaptation where natives have a low evolutionary capacity. Based on current evidence, it is likely that phenotypic plasticity is the first front in native species adaptation, after which genetic changes occur via a genetic accommodation mechanism. Lastly, I review the literature on behavioural, morphological, physiological and life history trait changes of responding native species in light of this framework. Knowledge of the genetic and physiological underpinnings of adaptive responses in native species is limited and would aid in distinguishing the contributions of phenotypic plasticity and evolutionary change in future studies.

A tale of two invaders: divergent spreading kinetics of the alien green algae Caulerpa taxifolia and Caulerpa cylindracea

Abstract: The two alien green algae Caulerpa taxifolia and Caulerpa cylindracea (formerly Caulerpa racemosa var. cylindracea) are among the most notorious and threatening invasive species in the Mediterranean Sea. From the beginning of their introduction, C. taxifolia aroused a great concern due to its initial exponential spread and impacts on native ecosystems, whilst C. cylindracea received lower attention. In this paper, the distribution of the two aliens over the last 30 years in the Italian side of the Ligurian Sea (NW Mediterranean Sea) is reviewed and the kinetics of their spreading is compared. We combined available data on habitat occupancy with data on substratum cover obtained during underwater surveys to compute the average annual spreading rates for both aliens. C. taxifolia had an impressive expansion phase from 1984 to 2000 but then, its dispersal rate showed lower than that predicted and the species did not persist in areas formerly colonized. Today, abundance of this species is strongly declined as it disappeared from most of the attained areas. On the contrary, C. cylindracea exhibited an impressive and constant expansion from the beginning of its first appearance in the Ligurian Sea and, today, it is still increasing its range and habitat occupancy. Its abundance results 1.5-times greater than that reached by C. taxifolia during the period of its maximum expansion. The divergent kinetics of spreading of the two aliens prevents any possibility of generalization of the future behaviour of invasive species in the Mediterranean Sea: continuous and periodic surveys are thus mandatory to understand the kinetics of expansion and to define species-specific models.

Insights from community ecology into the role of enemy release in causing invasion success: the importance of native enemy effects

Abstract: The enemy release hypothesis (ERH) predicts that the success of invasive species is caused by reduced enemy pressure in species’ introduced ranges. The ERH is a highly-cited explanation for invasion success, yet rigorous evidence is lacking for most species and ecosystems. Most evidence comes from observations of enemies in native and introduced ranges. These studies assess one aspect of the ERH—“enemy loss.” They do not provide a direct test of the ERH and overlook the assumption of “native enemy effects.” This is a critical limitation as enemy release will not occur if enemies do not affect species in their native ranges, even if enemy loss occurs. Biogeographical experiments, providing a direct test of the ERH, are largely restricted to terrestrial plants. We present a synthesis of community ecology and invasion biology studies, including a novel meta-analysis of native enemy effects, to assess the potential for release for species in different taxonomic groups and ecosystems. We suggest that species that are subject to strong enemy effects in their native range will have a high potential for enemy release. We found that native enemy effects were stronger in aquatic systems than in terrestrial systems. They were particularly weak for terrestrial plants; and strong for marine organisms, and freshwater plants. Studies are needed for species that have strong potential for release, such as for aquatic invasive species. Alternative explanations should be explored for invasive species that are not affected by enemies in their native range, and future studies should emphasize native enemy effects rather than only enemy loss.

Non-native species litter reduces germination and growth of resident forbs and grasses: allelopathic, osmotic or mechanical effects?

Abstract: Non-native plant species may contain allelopathic substances that might help to out-compete native vegetation. These allelochemicals may be released from live or dead plant tissues and be accumulated in the soil. We tested whether non-native species leaf litter and their leachates reduced seedling establishment and growth of native species. We subjected seeds of six native species to the effect of litter leachates of three of the most important invasive plants in Europe and to mannitol solutions with similar osmotic potential in germination chamber experiments. Additionally, we measured the effect of the same litter on emergence and growth of the native species in an outdoor pot experiment. Litter leachates delayed and reduced germination and affected initial root growth of all native species. The effects of leachates were significantly higher than those of mannitol, indicating the action of toxic, most probably allelochemical substances. Emergence of seedlings in pots was also reduced, but total biomass per pot was not affected and biomass per seedling increased. Allelochemicals may affect germination and early stages of seedling recruitment. However, these negative effects seem to cease shortly after germination, when other mechanisms such as competition may be more important. Consequently, litter-borne allelochemicals are unlikely to drive the invasion of the studied non-native species, but they may contribute to maintain mono-dominant stands reinforcing invasion success.

Part of the solution? Stakeholder awareness, information and engagement in tree health issues.

Abstract: The dangers posed to wooded environments from tree pests introduced by the expansion of international trade in live plants and the continued use of wood packaging in transporting materials have been widely accepted. A lack of awareness of the issues amongst key stakeholders involved in the movement of these materials can hamper an effective response as their unaltered behaviours continue to have unintended consequences. Better communication and engagement is needed to enrol this wider range of actors, such as plant buyers, traders and woodland owners, in preventative action or mitigation of tree pest impacts. However, as this review paper shows, current published evidence on awareness levels and effective engagement methods is limited, and lessons must be sought from research into other closely related issues such as invasive plants. We provide a summary of this available evidence, related to key stakeholder groupings, their levels of awareness and current modes of information provision and reception. It show what can at best be described as mediocre levels of awareness, and highlights the role of traditional media, such as television and newspapers, as sources of information. It further notes the urgent need for research to more fully map the tree health stakeholder landscape and to further our understanding of how to increase awareness and effect changes in behaviour.

The influence of invasive jellyfish blooms on the aquatic microbiome in a coastal lagoon (Varano, SE Italy) detected by an Illumina-based deep sequencing strategy

Abstract: The rapid expansion of multicellular native and alien species outbreaks in aquatic and terrestrial ecosystems (bioinvasions) may produce significant impacts on bacterial community dynamics and nutrient pathways with major ecological implications. In aquatic ecosystems, bioinvasions may cause adverse effects on the water quality resulting from changes in biological, chemical and physical properties linked to significant transformations of the microbial taxonomic and functional diversity. Here we used an effective and highly sensitive experimental strategy, bypassing the efficiency bottleneck of the traditional bacterial isolation and culturing method, to identify changes of the planktonic microbial community inhabiting a marine coastal lagoon (Varano, Adriatic Sea) under the influence of an outbreak-forming alien jellyfish species. Water samples were collected from two areas that differed in their level of confinement inside in the lagoon and jellyfish densities (W, up to 12.4 medusae m−3; E, up to 0.03 medusae m−3) to conduct a snapshot microbiome analysis by a metagenomic approach. After extraction of the genetic material in the environmental water samples, we deep-sequenced metagenomic amplicons of the V5–V6 region of the 16S rRNA bacterial gene by an Illumina MiSeq platform. Experiments were carried out in triplicates, so six libraries of dual indexed amplicons of 420 bp were successfully sequenced on the MiSeq platform using a 2 × 250 bp paired-end sequencing strategy. Approximately 7.5 million paired-end reads (i.e. 15 million total reads) were generated, with an average of 2.5 million reads (1.25 M pairs) per sample replicate. The sequence data, analyzed through a novel bioinformatics pipeline (BioMaS), showed that the structure of the resident bacterial community was significantly affected by the occurrence of jellyfish outbreaks. Clear qualitative and quantitative differences were found between the western and eastern areas (characterized by many or few jellyfish), with 84 families, 153 genera and 324 species in the W samples, and 104 families, 199 genera and 331 species in the E samples. Significant differences between the two sampling areas were particularly detected in the occurrence of 16 families, 22 genera and 61 species of microbial taxa. This is the first time that a NGS platform has been used to screen the impact of jellyfish bioinvasions on the aquatic microbiome, providing a preliminary assessment of jellyfish-driven changes of the functional and structural microbial biodiversity.

Commercial Bombus impatiens as reservoirs of emerging infectious diseases in central México

Abstract: The rapid decline in range and relative abundance of some wild North American bumble bee species, combined with the commercialization of bumble bee colonies as agricultural pollinators, and recent evidence that bumble bees can be infected by honey bee viruses, suggest the possibility that invasive and emerging infectious diseases (EIDs) may play a substantial current and future role in the decline of wild bumble bee populations. Pollination in North American greenhouses is primarily mediated by industrially produced Bombus impatiens colonies. The use of B. impatiens is preferred in greenhouses because it is a native species of East North America and they are very efficient pollinators. However, B. impatiens is also host of various viruses that have been associated with colony collapse disorder in honey bees, as well as hosts to a number of bumble bee-specific pathogens and parasites. In this study, we used qPCR to screen adult worker bumble bees collected from 120 different greenhouses in central Mexico. Fifty-four locations were positive for one or more pathogens (45 %). The most frequently detected pathogen was Apicystis bombi, which was present in 32 colonies. Of these 32 A. bombi positive colonies, 15 were co-infected with at least one other pathogen or parasite, such as Locustacarus buchneri, Nosema bombi, or the viral pathogens ABPV, CBPV, DWV, IAPV and KBV. Routine use of this type of screening technology together with policy changes to restrict pathogen infested commercial bumble bees should help improve the selection of healthy commercial colonies of B. impatiens and could lead to a higher efficiency in greenhouse pollination thus providing better environmental conservation of natural Bombus spp. by preventing spillover of EIDs.

The progressive invasion of Bactrocera dorsalis (Diptera: Tephritidae) in South Africa

Abstract: The discovery of the exotic fruit fly pest Bactrocera dorsalis (Diptera: Tephritidae), previously recognized as Bactrocera invadens, on the African continent in 2003 raised biosecurity concerns in South Africa where agriculture is of major socio-economic importance This prompted the development of a nationally coordinated system to prevent introduction of this pest into the country A steering committee was constituted to provide a platform for multi-stakeholder cooperation A national action plan on B dorsalis was developed A surveillance network was initiated to provide for early detection of B dorsalis The first B dorsalis eradication campaign was launched in 2010 following the detection of the pest in the northern border region of South Africa Multiple point incursions were detected thereafter in the northern parts of the country and for the first 2 years all of these were considered successfully eradicated However, the rate and geographic spread of incursions increased over time In March 2013 the pest was declared present in the Vhembe district, Limpopo Province All areas affected by B dorsalis were placed under quarantine and eradication actions are still ongoing in areas other than the Vhembe district The national control strategy on B dorsalis continues to be focussed on preventing further incursions, slowing the spread of the pest and monitoring the extent of its distribution within South Africa

Invasive avian malaria as an emerging parasitic disease in native birds of Peru

Abstract: Some species of avian malaria parasites are invaders and responsible for diversity losses worldwide. Here we analyze the prevalence and genetic characterization of avian malaria and related haemosporidian parasites in Neotropical birds from two different regions of Peru. We detected an overall prevalence of 32.4 % comprising 12 infected bird species. The pathogen Plasmodium relictum SGS1 was widespread and the most prevalent parasite found in our study (39 % of the total infections), infecting 8 host species in both localities. To the best of our knowledge, this is the first report of this invasive pathogen in the mainland Americas, thus representing a possible menace to over one-third of all bird species in the world.

Introduction, establishment rate, pathways and impact of spiders alien to Europe

Abstract: A comprehensive analysis of spiders reported as alien for Europe over the last 200 years has yielded information for 184 spider species, which had been introduced at least once. The most common spider families are Theridiidae (27 species), Pholcidae (15), Salticidae (14), Sparassidae (14), Ctenidae (14), and Theraphosidae (13) but overall establishment rate was only 28 %. No ctenids or theraphosids established, and only one sparassid species, but many theridiids and pholcids. Most introduced species originated from South (34 %), Central (10 %) or North (12 %), America, Asia (19 %) and Africa (15 %). Only few of the South and Central American species could establish, while species from North America (36 %) and Asia (63 %) had much higher establishment rates. Over the last 200 years, introduction and establishment rates have been strongly increasing. Three pathways are responsible for the majority of introductions: fruit shipments (67 % of all cases), potted plants (16 %) and containers or packaging material (12 %). In contrast to fruit shipments, spiders introduced on plants or with containers have high establishment rates (65 and 47 %). Environmental impact of alien spiders can be expected on both insects (through predation) and spiders (through predation and competition), potentially leading to change of species composition and guild structure. Socio-economic impact includes reduction of marketability of horticultural products through excessive spinning activity which also may cause increased cleaning costs at facades and windows. Impact on human health may be caused by bites and subsequent need for medical treatments. For all these impact categories, however, only anecdotal evidence is given for alien spiders in Europe. This may change when spiders of medical importance such as the frequently introduced Latrodectus species will establish. Considering the current trends it is concluded that introduction and establishment rates of alien spiders will strongly increase in the next years unless preventive methods become more efficient.

Niche plasticity in invasive fishes in the Great Lakes

Abstract: The geographic range of an invasive species is a key determinant of relative impact in the invaded region. Comparison of invasive species that are widespread or rare in invaded ranges can highlight mechanistic traits that determine the risk of impact from invasion. Round Goby (Neogobius melanostomus) is more geographically widespread and abundant than Tubenose Goby (Proterorhinus semilunaris) across invaded ranges of the Laurentian Great Lakes. We used stable isotopes of carbon (δ13C) and nitrogen (δ15N) in liver and muscle to contrast the isotopic niche breadth and niche plasticity of Round Goby and Tubenose Goby near the inflow and outflow of Lake St. Clair and in western Lake Superior. At all sites, Round Goby and Tubenose Goby that matched in size (21–53 mm standard length) had distinct isotopic niches with no overlap, driven by higher δ15N in Round Goby. The variation in isotopic niche, and the mean difference in δ13C and δ15N between muscle and liver, was greater for Round Goby, suggesting both greater seasonal shifts in diet and niche plasticity in this more widely established invader. Round Goby that were significantly larger than Tubenose Goby had broader isotopic niches and greater niche plasticity in the majority of cases and this was associated with isotopic niche overlap with smaller Round Goby and Tubenose Goby. Our findings suggest that a broad and plastic isotopic niche provides scope for wider establishment range in invasive fish species.