Notorious Invaders Research Articles

Assessing impacts of a notorious invader (common carp Cyprinus carpio) on Australia's aquatic ecosystems: Coupling abundance-impact relationships with a spatial biomass model

Quantifying the ecological impacts of non-native species is essential for large scale conservation management. Estimating such impacts often require spatially explicit abundance(/biomass) models of the target non-native species and knowledge of abundance-impact relationships, both of which are rarely known. Common carp (Cyprinus carpio) is a major threat to aquatic systems globally and relatively well-studied but yet models quantifying landscape-scale impacts of carp invasions are lacking. Here, we undertake a nonlinear meta-analytic approach to describe biomass-impact relationships for eight impact metrics and then integrate these relationships with a recently published spatial carp biomass model for Australia in order to quantify the ecological impacts of the carp invasion on Australian aquatic ecosystems. For the meta-analysis we collated 286 abundance(biomass)-impact estimates from 41 studies. Our meta-analysis identified both linear and nonlinear biomass-impact relationships across the impact metrics. Using a small, out-of-sample validation from carp removal experiments, the model had high prediction accuracy (within <20 % of estimate) for four metrics, but one metric (macrophyte recovery) was consistently underestimated by 10 to 35 %. Finally, we estimated that the carp invasion in Australia has resulted in decreases in macrophytes (median of −36 %) and macroinvertebrates (−31 %) and increases in nitrogen (2 %), plankton biomass (7 %), phosphorus (8 %) and turbidity (63 %). The invasive spread of carp has fundamentally altered Australia's aquatic environments and this study provides the first quantitative assessment of this impact and a tool to guide carp management decisions.

Advantages of growth and competitive ability of the invasive plant Solanum rostratum over two co-occurring natives and the effects of nitrogen levels and forms.

Atmospheric nitrogen (N) deposition has often been considered as a driver of exotic plant invasions. However, most related studies focused on the effects of soil N levels, and few on those of N forms, and few related studies were conducted in the fields. In this study, we grew Solanum rostratum, a notorious invader in arid/semi-arid and barren habitats, and two coexisting native plants Leymus chinensis and Agropyron cristatum in mono- and mixed cultures in the fields in Baicheng, northeast China, and investigated the effects of N levels and forms on the invasiveness of S. rostratum. Compared with the two native plants, S. rostratum had higher aboveground and total biomass in both mono- and mixed monocultures under all N treatments, and higher competitive ability under almost all N treatments. N addition enhanced the growth and competitive advantage of the invader under most conditions, and facilitated invasion success of S. rostratum. The growth and competitive ability of the invader were higher under low nitrate relative to low ammonium treatment. The advantages of the invader were associated with its higher total leaf area and lower root to shoot ratio compared with the two native plants. The invader also had a higher light-saturated photosynthetic rate than the two native plants in mixed culture (not significant under high nitrate condition), but not in monoculture. Our results indicated that N (especially nitrate) deposition may also promote invasion of exotic plants in arid/semi-arid and barren habitats, and the effects of N forms and interspecific competition need to be taken into consideration when studying the effects of N deposition on invasion of exotic plants.

Multiple invasion trajectories induce niche dynamics inconsistency and increase risk uncertainty of a plant invader

AbstractOur knowledge of how niche dynamic patterns respond to invasion trajectories and influence invasion risk prediction is elusive for the majority of notorious invaders, hindering scientific understanding, biosecurity planning and practice, and management implementation of biological invasions. We used Mikania micrantha, one of the world's worst invasive alien species (IAS), to test the hypothesis that multiple invasion trajectories could induce niche dynamics inconsistency and increase risk uncertainty of IAS. We compiled a robust database of M. micrantha occurrence across its native range in Central and South America and invaded range in China. This database was used to clarify different invaded ranges and invasion trajectories of M. micrantha in China. Principal components analysis of climatic variables associated with the database was used to explore the niche dynamic patterns associated with multiple invasion trajectories of M. micrantha. Maximum entropy algorithm was used to predict the high‐risk area of M. micrantha invasion using occurrence datasets for invaded ranges where niches remained conservative, and to detect area changes with the inclusion of occurrence datasets for invaded ranges where niche shifts occurred. M. micrantha invasion occurred in three geographically distinct regions, with conservative climate niches in southern and southeastern China and climatic niche shifts in southwestern China. A high‐risk area for M. micrantha invasion spanned multiple provinces and cities and expanded considerably with the inclusion of the occurrence dataset for southwestern China. Our findings contribute to the theoretical understanding of invasion mechanisms and the practical optimization of biosecurity planning and implementation.

Does plastic type matter? Insights into non-indigenous marine larvae recruitment under controlled conditions.

Marine plastic debris (MPD) are a global threat to marine ecosystems. Among countless ecosystem impacts, MPD can serve as a vector for marine 'hitchhikers' by facilitating transport and subsequent spread of unwanted pests and pathogens. The transport and spread of these non-indigenous species (NIS) can have substantial impacts on native biodiversity, ecosystem services/functions and hence, important economic consequences. Over the past decade, increasing research interest has been directed towards the characterization of biological communities colonizing plastic debris, the so called Plastisphere. Despite remarkable advances in this field, little is known regarding the recruitment patterns of NIS larvae and propagules on MPD, and the factors influencing these patterns. To address this knowledge gap, we used custom-made bioassay chambers and ran four consecutive bioassays to compare the settlement patterns of four distinct model biofouling organisms' larvae, including the three notorious invaders Crassostrea gigas, Ciona savignyi and Mytilus galloprovincialis, along with one sessile macro-invertebrate Spirobranchus cariniferus, on three different types of polymers, namely Low-Linear Density Polyethylene (LLDPE), Polylactic Acid (PLA), Nylon-6, and a glass control. Control bioassay chambers were included to investigate the microbial community composition colonizing the different substrates using 16S rRNA metabarcoding. We observed species-specific settlement patterns, with larvae aggregating on different locations on the substrates. Furthermore, our results revealed that C. savignyi and S. cariniferus generally favoured Nylon and PLA, whereas no specific preferences were observed for C. gigas and M. galloprovincialis. We did not detect significant differences in bacterial community composition between the tested substrates. Taken together, our results highlight the complexity of interactions between NIS larvae and plastic polymers. We conclude that several factors and their potential interactions influenced the results of this investigation, including: (i) species-specific larval biological traits and ecology; (ii) physical and chemical composition of the substrates; and (iii) biological cues emitted by bacterial biofilm and the level of chemosensitivity of the different NIS larvae. To mitigate the biosecurity risks associated with drifting plastic debris, additional research effort is critical to effectively decipher the mechanisms involved in the recruitment of NIS on MPD.

Substantial genetic mixing among sexual and androgenetic lineages within the clam genus Corbicula

“Occasional” sexuality occurs when a species combines clonal reproduction and genetic mixing. This strategy is predicted to combine the advantages of both asexuality and sexuality, but its actual consequences on the genetic diversity and species longevity are poorly understood. Androgenesis, a reproductive mode in which the offspring inherits its entire nuclear genome from the father, is often reported as a strictly clonal reproductive mode. Androgenesis is the predominant reproductive mode within the hermaphroditic, invasive lineages of the mollusk genus Corbicula. Their ability to reproduce clonally through androgenesis has been determinant in their invasive success, having colonized during the 20th century American and European freshwater systems, where they became notorious invaders with a widespread, global distribution. However, in androgenetic Corbicula clams, occasional genetic mixing between distinct lineages has also been observed when the sperm of one lineage fertilizes the oocyte of another one. Because of these occasional introgressions, the genetic relationships between Corbicula species remained unclear, and the biogeographic origins of the invasive androgenetic lineages have been challenging to identify. To address these issues, we analyzed the patterns of allele sharing for several nuclear and mitochondrial molecular markers among Corbicula individuals collected across both the native and invasive range. Our results show the occurrence of an allelic pool encompassing all Corbicula freshwater species worldwide, including sexual and androgenetic ones, which highlights the substantial genetic mixing within this genus. However, the differences in allele sharing patterns between invasive lineages, and the low diversity within each lineage, suggest recent, distinct biogeographic origins of invasive Corbicula androgenetic lineages. Finally, the polyploidy, high heterozygosity, and hybrid phenotypes and genotypes found in our study probably originated from hybridization events following egg parasitism between distinct Corbicula lineages. This extensive cross-lineage mixing found in Corbicula may generate nuclear diversity in an otherwise asexually reproducing species.

Identification of Mangrove Invasive Plant Derris Trifoliate Using UAV Images and Deep Learning Algorithms

<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Derris trifoliate</i> , one of the most notorious invaders of Mangroves in South China, seriously threatens the growth of Mangroves and the stability of local ecosystem. In order to effectively control the spread of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Derris trifoliate</i> and stabilize the Mangrove ecosystem, it is necessary to identify the distribution and simulate the occurrence of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Derris trifoliate</i> in Mangrove forests. While previous methods for invasive plant mapping based on satellite images were limited by low temporal and spatial resolution, the newly born Unmanned Aerial Vehicles (UAV) images have provided a fast, fine-grained, and low-cost alternative for rapid invasive plant monitoring. However, extracting <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Derris trifoliate</i> in mangrove forests based on UAV images is still a challenge. For one thing, it is difficult to collect enough data for model training, since the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Derris trifoliate</i> is hard to be distinguished in Mangroves. For another thing, few existing methods can meet the requirements of high computing efficiency and low memory consumption of UAVs. Therefore, we proposed two lightweight deep learning networks based on DenseNet and VGG, namely, the lightweight DenseNet (LDN) and the lightweight VGG (LVG), and investigated the capability of LDN and LVG in identifying <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Derris trifoliate</i> from Mangrove forests with small amounts of data. This study have verified the effect of the lightweight deep learning algorithms for the accurate detection of Mangrove invasive plants <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Derris trifoliate</i> from UAV images.

Plankton diversity in Anthropocene: Shipping vs. aquaculture along the eastern Adriatic coast assessed through DNA metabarcoding

Coastal ecosystems globally are exposed to the most pervasive anthropogenic activities, caused by a suite of human infrastructure and enterprises such as shipping ports, aquaculture facilities, fishing, and tourism. These anthropogenic activities may lead to changes in ecosystem biodiversity, followed by loss of ecosystem functioning and services. Shipping industry and aquaculture have also been recognized as the main vectors for introduction of marine non-indigenous species (NIS) worldwide. In this study, we used DNA metabarcoding-based methods to investigate plankton biodiversity under varying anthropogenic pressures (shipping and bivalve aquaculture) along the eastern Adriatic coast (the northernmost part of the Mediterranean Sea). Our comparative assessment revealed similar community structures among investigated coastal locations (Northern, Central and Southern Adriatic). When the whole plankton communities were considered, they did not differ significantly between port and aquaculture sites. However, the proportion of the unique zOTUs in the port samples was remarkably higher than that in aquaculture sites (40.5% vs 8.2%), indicating that port areas may receive higher abundance and species richness of NIS than aquaculture sites. Further important difference between the two types of anthropogenically impacted habitats was a high abundance of three notorious invaders – M. leidyi, M. gigas, and H. elegans in late summer at the aquaculture site in Northern Adriatic. Therefore, the plankton community of the area is under pressure not only from aquaculture activities, but also establishment of NIS. Port areas are probably under greater introduction pressure from NIS, but aquaculture sites may experience greater community changes due to their establishment.

Anthropogenic habitat loss accelerates the range expansion of a global invader

AbstractAimUnderstanding the patterns and correlates of the range expansion of established alien species is crucial for predicting invasion impacts and developing effective control strategies. With accelerating globalization, it is key to identify the interactions of different global change processes, such as how land‐use change may influence range expansion, yet empirical studies remain limited.LocationLiuji Town, Jiangsu Province, China.MethodsWe first divided the study area into 128 grids with a resolution of 1 × 1 km and conducted visual encounter surveys over two years for a total of 492 water bodies to explore the establishment and range expansions of a global notorious invader, the American bullfrog Lithobates catesbeianus (Shaw, 1802) (= Rana catesbeiana (Shaw, 1802)) using generalized linear mixed models. Then, we investigated the residence time of the established bullfrogs in each water body based on a questionnaire survey. We quantified the habitat loss and range expansion of the past 30 years via GIS‐based spatial analysis and explored their temporal dynamics using the breakpoint regression technique.ResultsWe found that the area of suitable habitats was the most important variable positively related to the bullfrog establishment. There was a similar temporal trend of the range expansion and habitat loss, although the optimal time of habitat loss was slightly earlier than that of the great increase in bullfrog range expansion. Overall, the bullfrogs tended to expand faster with greater habitat loss after controlling for temporal non‐independence.Main conclusionsOur results demonstrated that loss of suitable habitats may facilitate invaders with faster range expansion to occupy the remaining limited resources. Alien species might thus accelerate invasions under human‐induced land‐use modifications in the era of global change. The time lag between range expansion and habitat loss is the golden window for preventing the spread of established alien species in disturbed habitats.

Combined allelopathy of Canada goldenrod and horseweed on the seed germination and seedling growth performance of lettuce

The allelopathy on the seed germination and seedling growth performance (SgeSgrPe) of indigenous plant species (IPS) are considered as the main fact of the successful colonization of multiple invaders. The co-invasion of two invaders is common in some natural ecosystems. Thus, it is essential to assess the combined allelopathy of two invaders on SgeSgrPe of IPS to address the mechanisms driving the successful colonization. This study objects to assess the independent and combined allelopathy of two notorious invaders Canada goldenrod (Solidago canadensis L.) and horseweed [Conyza canadensis (L.) Cronq.] (using leaf extracts) on SgeSgrPe of the IPS lettuce (Lactuca sativa L.) via the incubation experiment in Petri dishes. Specifically, the independent and combined allelopathy of Canada goldenrod and horseweed leaf extracts on most of the seedling growth parameters of lettuce enhanced with the growing concentration of leaf extracts. The independent Canada goldenrod leaf extracts motivate greater allelopathy on most of SgeSgrPe parameters of lettuce compared to the independent horseweed leaf extracts at the same concentration. Consequently, the allelopathy on IPS may act a more prominent role in the successful colonization posed by Canada goldenrod than horseweed supposedly. The combined Canada goldenrod and horseweed leaf extracts trigger significantly higher allelopathy on most of seedling growth parameters of lettuce than the independent horseweed leaf extracts but pose significantly lower allelopathy than the independent Canada goldenrod leaf extracts at the same concentration. Thus, an antagonistic effect of allelopathy could occur after the co-invasions of the two invaders in some ecosystems, especially on the seedling growth of IPS. This implies that the allelopathy of Canada goldenrod and horseweed on the seedling growth of IPS may play a more prominent role in their single invasion process (particularly for Canada goldenrod) than in their co-invasion.

Confirmation of the shell-boring oyster parasite Polydora websteri (Polychaeta: Spionidae) in Washington State, USA

Invasions by shell-boring polychaetes such as Polydora websteri Hartman have resulted in the collapse of oyster aquaculture industries in Australia, New Zealand, and Hawaii. These worms burrow into bivalve shells, creating unsightly mud blisters that are unappealing to consumers and, when nicked during shucking, release mud and detritus that can foul oyster meats. Recent findings of mud blisters on the shells of Pacific oysters (Crassostrea gigas Thunberg) in Washington State suggest a new spionid polychaete outbreak. To determine the identity of the polychaete causing these blisters, we obtained Pacific oysters from two locations in Puget Sound and examined them for blisters and burrows caused by polychaete worms. Specimens were also obtained from eastern oysters (Crassostrea virginica Gmelin) collected in New York for morphological and molecular comparison. We compared polychaete morphology to original descriptions, extracted DNA and sequenced mitochondrial (cytochrome c oxidase I [mtCOI]) and nuclear (small subunit 18S rRNA [18S rRNA]) genes to determine a species-level molecular identification for these worms. Our data show that Polydora websteri are present in the mud blisters from oysters grown in Puget Sound, constituting the first confirmed record of this species in Washington State. The presence of this notorious invader could threaten the sustainability of oyster aquaculture in Washington, which currently produces more farmed bivalves than any other US state.

Allelopathic effects of Canada goldenrod leaf extracts on the seed germination and seedling growth of lettuce reinforced under salt stress.

Allelopathic effects on the seed germination and seedling growth of the natives play a crucial role in the successful invasion of numerous invaders. Meanwhile, soil salinity is an emerging driver of the spread of many invaders, especially in the colonization of saline habitats. Thus, the allelopathic effects of the invaders on the seed germination and seedling growth of the natives may be altered or even reinforced under salt stress. This study aims to address the allelopathic effects of the notorious invader Canada goldenrod (Solidago canadensis L.; goldenrod hereafter) on the seed germination and seedling growth of the native lettuce (Lactuca sativa L.; lettuce hereafter) under a gradient of salt stress. Goldenrod leaf extracts with high concentration significantly decreased root length, leaf shape index, germination percentage, germination potential, germination index, germination vigor index, and germination rate index of lettuce. However, goldenrod leaf extracts with low concentration significantly increased root length and leaf width of lettuce. Goldenrod leaf extracts with high concentration display more serious allelopathic effects on the seed germination and seedling growth of lettuce than those with low concentration. Salt stress regardless of concentration significantly decreased seedling height, root length, leaf shape index, and seedling biomass (fresh weight) of lettuce. The combined goldenrod leaf extracts and salt stress have a synergistic effect on seedling height, root length, leaf shape index, germination percentage, germination potential, germination index, and germination rate index of lettuce. Thus, the allelopathic effects of the invaders on the seed germination and seedling growth of the natives may be reinforced under salt stress. Accordingly, salt stress may be beneficial to the further invasion of the invaders mainly via the reduced growth performance of the natives.

Environmental tolerance of three gammarid species with and without invasion record under current and future global warming scenarios

AbstractAimNumerous regions worldwide are highly impacted by anthropogenic activities and globalization, with climate change and species introductions being among the greatest stressors to biodiversity and ecosystems. A main donor region of non‐indigenous species (NIS) for numerous European water bodies, as well as in the North American Great Lakes is the Ponto‐Caspian region (i.e., Black, Azov and Caspian Seas), with some of those species having significant impact on local communities and ecosystem functioning.LocationNorthern European, Ponto‐Caspian and North American regions.MethodsTo determine environmental tolerance of native species and related NIS under current and future global warming scenarios of the Baltic Sea, we conducted common garden experiments to test temperature tolerance of three euryhaline gammarid species: one Baltic (Gammarus oceanicus), one Ponto‐Caspian (Pontogammarus maeoticus) and one North American species (Gammarus tigrinus) in two different salinities.ResultsOur results determined that mortality of P. maeoticus in all temperature treatments (i.e., increased, control, and decreased) at the end of both experiments (i.e., conducted in salinities of 10 and 16 g/kg) was lower when compared to mortality of G. oceanicus and (c) G. tigrinus. The highest mortality was observed for G. oceanicus, reaching 100% in both experiments in the increased temperature treatment.Main conclusionsDue to the high environmental tolerance of the Ponto‐Caspian species tested in this study, as well as the fact that Ponto‐Caspian species evolved in environmentally variable habitats and currently inhabit warmer waters than species from North America and Northern Europe, we suggest that species from the Ponto‐Caspian region may benefit from global warming when invading new areas. Those new invasions may, in the best case scenario, increase biodiversity of the Baltic Sea. However, if notorious invaders arrive, they may have a significant impact on local communities and ecosystem functioning.

Canada goldenrod invasion cause significant shifts in the taxonomic diversity and community stability of plant communities in heterogeneous landscapes in urban ecosystems in East China

Invasive plant species (invaders hereafter) have led to larger shifts in the structure and functions of native ecosystems. Landscape heterogeneity in urban ecosystems can alter the invasion process mediated by the invaders. Thus, it is important to evaluate the effects of the invaders on the taxonomic diversity and stability of plant communities to better understand the mechanisms underlying successful plant invasion, especially in heterogeneous landscapes in urban ecosystems. This study aims to address the effects of the notorious invader Canada goldenrod (Solidago canadensis L.; goldenrod hereafter) on the taxonomic diversity and stability of plant communities by using a comparative study in heterogeneous landscapes in urban ecosystems in East China. Heterogeneous landscapes played a more obvious role in driving changed taxonomic diversity and stability of plant communities as compared to goldenrod invasion. The phenomenon may be most probably caused by the differences in environmental selection pressures in different types of landscape types. The taxonomic diversity (especially diversity and evenness) of plant communities were strongly correlated with the stability both in the uninvaded and invaded plant communities as well as the most types of urban ecosystems. Accordingly, the results of this study support the diversity hypothesis. There was a significantly negative correlation between the relative abundance of the most dominant species and the stability both in the uninvaded and invaded plant communities as well as in the all types of urban ecosystems. Thus, the results of this study did not support the mass ratio hypothesis. The relative abundance of goldenrod was not a primary driver in the stability of plant communities mainly due the fact that goldenrod invasion did not trigger noticeable impacts on the taxonomic diversity and stability of plant communities.

Behavioral differences in an over‐invasion scenario: marbled vs. spiny‐cheek crayfish

AbstractNew species often invade ecosystems already dominated by previous invaders. Ornamental freshwater crayfish, particularly parthenogenetic marbled crayfish (Procambarus virginalis), increasingly establish in European water bodies where they interact with resident native and non‐native species. Behavioral traits and behavioral syndromes can influence the outcome of these species interactions. The behavior of non‐native crayfish is often studied in notorious invaders but rarely in new and emerging species, although those provide the best opportunity for management. Activity, aggressiveness, and boldness have repeatedly been associated with invasion success and species displacement. Further, crayfish can adapt their behavior after they have established in the new range. We investigated whether marbled crayfish can displace the widely established spiny‐cheek crayfish (Orconectes limosus). Specifically, we compared their behavioral traits and evaluated whether these traits differ, using marbled crayfish populations from aquaria and the field and spiny‐cheek crayfish from the field. We staged agonistic encounters, measured activity levels, and recorded the response to a simulated threat of both species and both origins (field and aquarium) in laboratory trials. We found that in agonistic encounters, marbled crayfish were on average more aggressive than spiny‐cheek crayfish, even against larger opponents. Aggressiveness and activity were positively correlated, which is indicative for an aggression syndrome. Marbled crayfish from the field were less active than those from aquaria, but there was no difference in aggressiveness. Marbled crayfish often froze in response to a simulated threat, whereas spiny‐cheek crayfish reacted either offensively or defensively. These results from the laboratory illustrate potentially important behavioral mechanisms behind crayfish over‐invasions and show behavioral plasticity in a species where all known individuals are genetically identical. To better understand the invasion process in nature, the species’ reproductive biology and interactions with other members of the community should be considered. We conclude that the recent success of marbled crayfish in establishing new populations could be influenced by their behavioral flexibility and their potential to competitively persist in the presence of established invasive crayfish.

Contrasting ecological roles of non-native ungulates in a novel ecosystem.

Conservation has long focused on preserving or restoring pristine ecosystems. However, understanding and managing novel ecosystems has grown in importance as they outnumber pristine ecosystems worldwide. While non-native species may be neutral or detrimental in pristine ecosystems, it is possible that even notorious invaders could play beneficial or mixed roles in novel ecosystems. We examined the effects of two long-established non-native species—Philippine deer (Rusa marianna) and feral pigs (Sus scrofa)—in Guam, Micronesia, where native vertebrate frugivores are functionally absent leaving forests devoid of seed dispersers. We compared the roles of deer and pigs on seedling survival, seed dispersal and plant community structure in limestone karst forests. Deer, even at low abundances, had pronounced negative impacts on forest communities by decreasing seedling and vine abundance. By contrast, pigs showed no such relationship. Also, many viable seeds were found in pig scats, whereas few were found in deer scats, suggesting that pigs, but not deer, provide an ecosystem function—seed dispersal—that has been lost from Guam. Our study presents a discrepancy between the roles of two non-native species that are traditionally managed as a single entity, suggesting that ecological function, rather than identity as a non-native, may be more important to consider in managing novel systems.

The combined treatments of Canada goldenrod leaf extracts and cadmium pollution confer an inhibitory effect on seed germination and seedling development of lettuce

Increasing levels of heavy metals are released into ecosystems. The influence of heavy metal pollution on successful invasive species has raised considerable interest, particularly regarding potential allelopathic effects on seed germination and seedling development of native species. Adding heavy metals may alter or even enhance such allelopathic effects of invasive species. The aim of the present study was to address the combined treatments of the invasive species Canada goldenrod (Solidago canadensis L.) leaf extracts and cadmium (Cd) pollution on seed germination and seedling development of the homologous native species lettuce (Lactuca sativa L.). Results showed that the combined treatments of Canada goldenrod leaf extracts and Cd pollution significantly decreased seed germination and seedling development of lettuce compared with the control. In addition, the indices of allelopathic effects for all seed germination and seedling development indices of lettuce were less than zero under the combined treatments of high concentration of Canada goldenrod leaf extracts and Cd pollution (regardless of concentration). Thus, the combined treatments of high concentration of Canada goldenrod leaf extracts and Cd pollution pose an inhibitory effect on seed germination and seedling development of lettuce. Further, the combined treatments of high concentration of Canada goldenrod leaf extracts and Cd pollution (regardless of concentration) cause more toxic effects than the combined treatments of low concentration of Canada goldenrod leaf extracts and Cd pollution (regardless of concentration) on all seed germination and seedling development indices of lettuce. Thus, the inhibitory effects of Canada goldenrod on the seed germination and seedling development of co-occurring native species may be intensified at heavy invasion degrees under increased heavy metal pollution. Subsequently, the competitiveness and fitness of native species may be notably decreased via the reduced seed germination and seedling development and then the notorious invader can establish progressively-growing populations in the colonised ecosystems.

Diversity and distribution of genetic variation in gammarids: Comparing patterns between invasive and non-invasive species.

Biological invasions are worldwide phenomena that have reached alarming levels among aquatic species. There are key challenges to understand the factors behind invasion propensity of non‐native populations in invasion biology. Interestingly, interpretations cannot be expanded to higher taxonomic levels due to the fact that in the same genus, there are species that are notorious invaders and those that never spread outside their native range. Such variation in invasion propensity offers the possibility to explore, at fine‐scale taxonomic level, the existence of specific characteristics that might predict the variability in invasion success. In this work, we explored this possibility from a molecular perspective. The objective was to provide a better understanding of the genetic diversity distribution in the native range of species that exhibit contrasting invasive propensities. For this purpose, we used a total of 784 sequences of the cytochrome c oxidase subunit I of mitochondrial DNA (mtDNA‐COI) collected from seven Gammaroidea, a superfamily of Amphipoda that includes species that are both successful invaders (Gammarus tigrinus, Pontogammarus maeoticus, and Obesogammarus crassus) and strictly restricted to their native regions (Gammarus locusta, Gammarus salinus, Gammarus zaddachi, and Gammarus oceanicus). Despite that genetic diversity did not differ between invasive and non‐invasive species, we observed that populations of non‐invasive species showed a higher degree of genetic differentiation. Furthermore, we found that both geographic and evolutionary distances might explain genetic differentiation in both non‐native and native ranges. This suggests that the lack of population genetic structure may facilitate the distribution of mutations that despite arising in the native range may be beneficial in invasive ranges. The fact that evolutionary distances explained genetic differentiation more often than geographic distances points toward that deep lineage divergence holds an important role in the distribution of neutral genetic diversity.

The impact of transportation and translocation on dispersal behaviour in the invasive cane toad.

Biological invasions transport organisms to novel environments; but how does the translocation process influence movement patterns of the invader? Plausibly, the stress of encountering a novel environment, or of the transport process, might induce rapid dispersal from the release site-potentially enhancing (or reducing) invader success and spread. We investigated the effect of transportation and release to novel environments on dispersal-relevant traits of one of the world's most notorious invaders, the cane toad (Rhinella marina). We collected toads in northern New South Wales from heath and woodland habitats, manipulated the level of transport stress and either returned toads to their exact collection point (residents) or reciprocally translocated them to a novel site. Both translocation and the level of transport stress drastically altered toad dispersal rates for at least 5days post-release. Translocated toads (depending on their level of transport stress and release habitat) moved on average two to five times further per day (mean range 67-148m) than did residents (mean range 22-34m). Translocated toads also moved on more days, and moved further from their release point than did resident toads, but did not move in straighter lines. A higher level of transport stress (simulating long-distance translocation) had no significant effect on movements of resident toads but amplified the dispersal of translocated toads only when released into woodland habitat. These behavioural shifts induced by translocation and transportation may affect an invader's ability to colonise novel sites, and need to be incorporated into plans for invader control.

Florida Inlets and Intertidal Biofouling Communities

AbstractThis study reports on the identity and coverage of rocky intertidal species in the major inlets of Florida’s Atlantic coast. From north to south, these inlets are Fort George, St. Augustine, Ponce De Leon, Port Canaveral, Sebastian, Fort Pierce, Jupiter, Lake Worth, Boca Raton, Port Everglades, Baker’s Haulover, and Port of Miami. Dominant coverage in the southerly inlets included star corals (Siderastrea radians,62% Port of Miami), ribbed barnacles (Tetraclita stalactifera, 18% Port Everglades), and zoanthid corals (Palythoasp., 40% Baker’s Haulover). In the north, the community shifted and species absent in the south became common (e.g., eastern oystersCrassostrea virginica, 9% Fort George, 15% St. Augustine; the macroalgaEnteromorpha lactuca, 10% Fort George, 17% Sebastian Inlet). The invasive bryozoanBugula neritinawas always present north of the Port of Miami and was a major community component north of Port Everglades (e.g., 27% Fort Pierce Inlet and 22% Ponce de Leon Inlet). Correlations between intertidal populations and environmental indicators included the oysterC. virginicawith various sea surface temperature (SST) parameters (e.g., inverse correlations with max SST,R2= 0.81,p= .038). Likewise, the coralline algaPneophyllum fragilewas correlated with various SST parameters (e.g., min SST,R2= 0.51,p= .020). Bare rock andB. neritinaboth showed inverse correlations with the human population of inlet drainage basins (R2= 0.28,p= .040 andR2= 0.33,p= .026, respectively), the latter relationship an unexpected pattern for a notorious invader. These data show latitudinal patterns and provide baselines for future comparisons in the wake of projected climate change.

The influence of hypo‐osmotic stress on the regenerative capacity of the invasive polychaete Marenzelleria viridis from its native range

AbstractThe euryhaline polychaete Marenzelleria viridis is a notorious invader of the Baltic region and while many studies have focused on the effects of osmotic stress on larval development of the species, few have assessed its effect on adult specimens. This study investigated the effects of low salinity on the physiology of M. viridis by using its regenerative capacity as a proxy for physiologic performance. Specimens were collected in spring 2015 on sandy flats in Hempstead Bay (Long Island, New York), a site that falls within its native range. Worms were ablated between the 14th and 20th chaetigers and cultured at five different salinity treatments (24psu, 15psu, 10psu, 5psu and 0psu) that reflected the broad salinity regimes of its distributional range. Data for anterior regeneration were analysed and presented. Morphogenesis during anterior regeneration was characterized by the formation of a blastema from which the major anatomic structures emerged. All specimens cultured at 5–24psu successfully completed regeneration whereas 75% of specimens cultured at 0psu died and the survivors were unable to proceed beyond the blastema stage. Salinity did not have an effect on regeneration time (14.5–15.1 days) but did have an effect on the percentage of chaetigers regenerated (lowest – 77% at 5psu, highest – 97.5% at 15‰). The post‐regeneration phase was characterized by variability in pigmentation patterns in the regenerated anterior structures, which appear to be independent of salinity treatments. In conclusion, adult M. viridis appears to exhibit high tolerance to low salinity environments, which may have been inherited from its larval stages. In addition, the different pigmentation patterns observed in regenerated structures may allude to the variability of this feature in spionids.