Inverse priority effects: A role for historical contingency during species losses.

Communities worldwide are losing multiple species at an unprecedented rate, but how communities reassemble after these losses is often an open question. It is well established that the order and timing of species arrival during community assembly shapes forthcoming community composition and function. Yet, whether the order and timing of species losses can lead to divergent community trajectories remains largely unexplored. Here, we propose a novel framework that sets testable hypotheses on the effects of the order and timing of species losses-inverse priority effects-and suggests its integration into the study of community assembly. We propose that the order and timing of species losses within a community can generate alternative reassembly trajectories, and suggest mechanisms that may underlie these inverse priority effects. To formalize these concepts quantitatively, we used a three-species Lotka-Volterra competition model, enabling to investigate conditions in which the order of species losses can lead to divergent reassembly trajectories. The inverse priority effects framework proposed here promotes the systematic study of the dynamics of species losses from ecological communities, ultimately aimed to better understand community reassembly and guide management decisions in light of rapid global change.

Biological invasions are a population-level rather than a species-level phenomenon.

Biological invasions pose a rapidly expanding threat to the persistence, functioning and service provisioning of ecosystems globally, and to socio-economic interests. The stages of successful invasions are driven by the same mechanism that underlies adaptive changes across species in general-via natural selection on intraspecific variation in traits that influence survival and reproductive performance (i.e., fitness). Surprisingly, however, the rapid progress in the field of invasion science has resulted in a predominance of species-level approaches (such as deny lists), often irrespective of natural selection theory, local adaptation and other population-level processes that govern successful invasions. To address these issues, we analyse non-native species dynamics at the population level by employing a database of European freshwater macroinvertebrate time series, to investigate spreading speed, abundance dynamics and impact assessments among populations. Our findings reveal substantial variability in spreading speed and abundance trends within and between macroinvertebrate species across biogeographic regions, indicating that levels of invasiveness and impact differ markedly. Discrepancies and inconsistencies among species-level risk screenings and real population-level data were also identified, highlighting the inherent challenges in accurately assessing population-level effects through species-level assessments. In recognition of the importance of population-level assessments, we urge a shift in invasive species management frameworks, which should account for the dynamics of different populations and their environmental context. Adopting an adaptive, region-specific and population-focused approach is imperative, considering the diverse ecological contexts and varying degrees of susceptibility. Such an approach could improve and refine risk assessments while promoting mechanistic understandings of risks and impacts, thereby enabling the development of more effective conservation and management strategies.

Mimicking functional elements of the natural flow regime promotes native fish recovery in a regulated river.

Streamflow regimes that maintain vital functions and processes of aquatic ecosystems are critical to sustaining ecosystem health. In rivers with altered flow regimes, restoring components of the natural flow regime is predicted to conserve freshwater biodiversity by supporting ecological functions and geomorphological processes to which native communities are adapted. However, the effectiveness of environmental flow restoration is poorly understood because of inadequate monitoring and uncertainty in ecological responses to managed changes in specific, quantifiable aspects of the annual streamflow regime. Here, we used time series models to analyze 25 years of fish assemblage data collected before and after environmental flow implementation in a dammed river in California, USA. We examined the response of the fish community to changes in individual components of the flow regime known to support ecosystem functions. We found that as functional flow components shifted toward their predicted natural range, the quasi-extinction risk (likelihood of population declines of >80%) decreased for the native fish assemblage. Following environmental flow implementation, observed changes toward natural ranges of dry season duration, fall pulse flow magnitude, and wet season timing each reduced quasi-extinction risk by at least 40% for the native assemblage. However, functional flow components that shifted away from their predicted natural range, including lower spring recession flows and higher dry season baseflow, resulted in greater quasi-extinction risk for native species. In contrast, non-native species decreased in abundance when flow components shifted toward predicted natural ranges and increased when components shifted away from their natural range. Although most functional flow components remained outside of their natural range following environmental flow implementation, our results indicate that even moderate shifts toward a natural flow regime can benefit native and suppress non-native fish species. Overall, this study provides the most compelling evidence to date of the effectiveness of functional environmental flows in supporting native fish recovery in a highly regulated river.

Do community changes persist after irruptive population dynamics? A case study from an invasive species boom and bust.

Irruptive or boom-and-bust population dynamics, also known as 'outbreaks', are an important phenomenon that has been noted in biological invasions at least since Charles Elton's classic book was published in 1958. Community-level consequences of irruptive dynamics are poorly documented and invasive species provide excellent systems for their study. African Jewelfish (Rubricatochromis letourneuxi, "jewelfish") are omnivores that demonstrate opportunistic carnivory, first reported in Florida in the 1960s and in Everglades National Park (ENP) in 2000. Twelve years after invasion in ENP, jewelfish underwent a 25-fold increase in density in one year. By 2016, jewelfish represented 25-50% of fish biomass. Using a 43-year fish community dataset at two sites (1978-2021), and a 25-year dataset of fish and invertebrate communities from the same drainage (1996-2021), with additional spatial coverage, we quantified differences in fish and invertebrate communities during different phases of invasion. During jewelfish boom, abundant, native cyprinodontiform fishes decreased in density and drove changes in community structure as measured by similarity of relativized abundance. Density of two species declined by > 70%, while four declined by 50-62%. Following the jewelfish bust, some species recovered to pre-boom densities while others did not. Diversity of recovery times produced altered community structure that lagged for at least four years after the jewelfish population declined. Community structure is an index of ecological functions such as resilience, productivity, and species interaction webs; therefore, these results demonstrate that irruptive population dynamics can alter ecological functions of ecosystems mediated by community structure for years following that population's decline.

Tissue damage, antioxidant capacity, transcriptional and metabolic regulation of red drum Sciaenops ocellatus in response to nanoplastics exposure and subsequent recovery.

Nanoplastics are recognized as emerging contaminants that can cause severe toxicity to marine fishes. However, limited researches were focusing on the toxic effects of nanoplastics on marine fish, especially the post-exposure resilience. In this study, red drum (Sciaenops ocellatus) were exposed to 5 mg/L polystyrene nanoplastics (100 nm, PS-NPs) for a 7-day exposure experiment, and a 14-day recovery experiment that followed. The aim was to evaluate the dynamic alterations in hepatic and branchial tissue damage, hepatic antioxidant capacity, as well as hepatic transcriptional and metabolic regulation in the red drum during exposure and post-exposure to PS-NPs. Histopathological observation found that PS-NPs primarily triggered hepatic lipid droplets and branchial epithelial liftings, a phenomenon persistently discernible up to the 14 days of recovery. Although antioxidant capacity partially recovered during recovery periods, PS-NPs resulted in a sustained reduction in hepatic antioxidant activity, causing oxidative damage throughout the entire exposure and recovery phases, as evidenced by decreased total superoxide dismutase activities and increased malondialdehyde content. At the transcriptional and metabolic level, PS-NPs primarily induced lipid metabolism disorders, DNA damage, biofilm disruption, and mitochondrial dysfunction. In the gene-metabolite correlation interaction network, numerous CcO (cytochrome c oxidase) family genes and lipid metabolites were identified as key regulatory genes and metabolites in detoxification processes. Among them, the red drum possesses one additional CcO6B in comparison to human and zebrafish, which potentially contributes to its enhanced capacity for maintaining a stable and positive regulatory function in detoxification. This study revealed that nanoplastics cause severe biotoxicity to red drum, which may be detrimental to the survival of wild populations and affect the economics of farmed populations.

Forest Insect Biosecurity: Processes, Patterns, Predictions, Pitfalls.

The economic and environmental threats posed by non-native forest insects are ever increasing with the continuing globalization of trade and travel; thus, the need for mitigation through effective biosecurity is greater than ever. However, despite decades of research and implementation of preborder, border, and postborder preventative measures, insect invasions continue to occur, with no evidence of saturation, and are even predicted to accelerate. In this article, we review biosecurity measures used to mitigate the arrival, establishment, spread, and impacts of non-native forest insects and possible impediments to the successful implementation of these measures. Biosecurity successes are likely under-recognized because they are difficult to detect and quantify, whereas failures are more evident in the continued establishment of additional non-native species. There are limitations in existing biosecurity systems at global and country scales (for example, inspecting all imports is impossible, no phytosanitary measures are perfect, knownunknowns cannot be regulated against, and noncompliance is an ongoing problem). Biosecurity should be a shared responsibility across countries, governments, stakeholders, and individuals.

A critical review of the precautionary approach of the IUCN impact classification for non-native taxa.

The International Union for the Conservation of Nature (IUCN) proposes the use of the Environmental Impact Classification for Alien Taxa to standardize the classification of introduced species (IS) based on their environmental impact. The IUCN invoked the precautionary principle (PP) via 2 rules: the impact assigned to a taxon must be the maximum recorded impact across different impact assessments, and when the main driver of environmental damage is unclear, it must be assumed to be caused by the IS. The validity of PP is conditioned on the degree of emergency that warrants urgent decisions and on the scientific evidence demonstrating the advantages of applying a preventive measure. The application of an impact classification system does not arise in the context of an emergency that requires management; it occurs before the decision-making phase. Thus, PP should not be used in early steps of the risk analysis process. The IUCN also did not provide enough scientific basis to justify the use of PP. Instead, the PP rules appear to be rooted primarily in the ethical value system underlying conservation science. Conservationists assign intrinsic value to native species by virtue of their roles and relationships within ecological and evolutionary systems and processes; thus, individuals introduced in new environments not only cease to have value because they are no longer part of that natural diversity and lack those links with the rest of the ecosystem, but they become a threat to what conservationists value most. The consequence of this belief is that all introduced taxa will have an impact at some level, suggesting that values justify the PP rules.

La Unión Internacional para la Conservación de la Naturaleza (UICN) propone usar la Clasificación del Impacto Ambiental para Taxones Exóticos (CIATE) para estandarizar la clasificación de las especies introducidas con base en su impacto ambiental. La UICN invocó el principio de precaución (PP) mediante dos reglas: el impacto asignado a un taxón debe ser el mayor impacto registrado en diferentes evaluaciones de impacto y cuando no sea claro el principal causante del daño ambiental, se debe asumir que lo causa la especie introducida. La validez del PP está condicionada por el grado de emergencia que amerite decisiones urgentes y por la evidencia científica que demuestre las ventajas de aplicar una medida preventiva. La aplicación de un sistema de clasificación de impactos no surge del contexto de una emergencia que requiere gestión, sino que ocurre antes de la fase de toma de decisiones. Por esto, el PP no debería usarse durante los primeros pasos del proceso de análisis de riesgo. La UICN tampoco proporcionó suficientes fundamentos científicos para justificar el uso del PP. En su lugar, las reglas del PP parecen estar ancladas principalmente en el sistema de valor ético subyacente a las ciencias de la conservación. Los conservacionistas les asignan un valor intrínseco a las especies nativas por su papel y sus relaciones dentro de los sistemas y procesos ecológicos y evolutivos; los individuos introducidos en ambientes nuevos no sólo dejan de tener valor porque ya no forman parte de la diversidad natural y carecen de esas conexiones con el resto del ecosistema, sino también se vuelven una amenaza para lo que más valoran los conservacionistas. Esta creencia tiene como consecuencia que todos los taxones introducidos tendrán un impacto a cierto nivel, lo que sugiere que el valor justifica las reglas del PP.

The challenge of managing threatened invasive species at a continental scale.

The European Union's (EU) environmental legislation establishes common measures to prevent the entry and spread of invasive non-native species and to minimize their impacts. However, species that are native to at least one member state but non-native and potentially invasive in others (NPIS) are in limbo because they are neither legally regulated at the EU level nor in most member states. We used the Communication and Information Resource Centre for Administrations, Businesses and Citizens (CIRCABC) raw data on NPIS (317 taxa) to analyze their distribution across the EU and identify which biogeographical regions are the main sources of invasions. We additionally evaluated the conservation challenge posed by NPIS that are threatened within their native ranges. We performed a pairwise analysis summarizing the number of species that are native to a given member state but non-native to another and vice versa. Although distribution patterns of NPIS varied across taxa groups, overall, southern and central EU countries were both donors and recipients of NPIS. Eastern countries were mainly a source, and western and northern countries mostly received NPIS. Around 27% of NPIS were threatened in some of their EU native ranges, which is a challenge for conservation and management because some of them have serious negative effects on European biodiversity, but hitherto remain outside the scope of the EU regulation of invasive non-native species. This highlights an unresolved paradox because efforts to manage species as invasive conflict with efforts to protect them as threatened within the same territory.

Retos en la gestión de las especies invasoras amenazadas a escala continental Resumen La legislación ambiental de la Unión Europea (UE) establece medidas comunes para prevenir la entrada y dispersión de especies invasoras no nativas y para minimizar su impacto. Sin embargo, las especies que son nativas en al menos uno de los estados miembros, pero no nativas y potencialmente invasoras (ENPI) en los demás, están en un limbo ya que no están reguladas en la UE ni en la mayoría de los estados miembros. Usamos los datos brutos del Centro de Recursos de Información y Comunicación para las Administraciones, Empresas y Ciudadanos (CIRCABC) sobre las ENPI (317 taxones) para analizar su distribución en la UE e identificar qué regiones biogeográficas funcionan como principales orígenes de las invasiones. Además, evaluamos el reto que representan las ENPI amenazadas dentro de su distribución nativa. Realizamos un análisis por pares que resumió el número de especies nativas en un estado miembro pero no nativa en otro y viceversa. Aunque los patrones de distribución de las ENPI variaron entre los grupos taxonómicos, en general fueron los países del sur y centro de la UE quienes donaron y recibieron a las ENPI. Los países del este fueron principalmente un origen de ENPI; la mayoría de los del oeste y el norte fueron receptores. Un 27% de las ENPI están amenazadas en alguna de sus distribuciones nativas en la UE, lo que representa un reto para la conservación y la gestión porque algunas de las especies tienen efectos negativos serios sobre la biodiversidad europea, pero hasta ahora permanecen fuera del alcance de la regulación de la UE para las especies invasoras no nativas. Lo anterior resalta una paradoja sin resolver ya que los esfuerzos para manejar a las especies como invasoras entran en conflicto con los esfuerzos por protegerlas como amenazadas dentro del mismo territorio.

Molecular analyses of turf algae reveal a new species and an undetected introduction in the Pterosiphonieae (Rhodomelaceae, Rhodophyta).

Introduced seaweeds and undescribed species often remain undetected because marine regional floras are as yet poorly understood. DNA sequencing facilitates their detection, but databases are incomplete, so their improvement will continue to lead the discovery of these species. Here we aim to clarify the taxonomy of two turf-forming red algal Australian species that morphologically resemble the European Aphanocladia stichidiosa. We also aim to elucidate whether either of these species could have been introduced in Europe or Australia. We studied their morphology, analyzed 17 rbcL sequences of European and Australian specimens, examined their generic assignment using a phylogeny based on 24 plastid genomes, and investigated their biogeography using a taxon-rich phylogeny including 52 rbcL sequences of species in the Pterosiphonieae. The rbcL sequences of one of the Australian species were identical to A. stichidiosa from Europe, considerably expanding its known distribution. Unexpectedly, our phylogenetic analyses resolved this species in the Lophurella clade rather than in Aphanocladia and the new combination L. stichidiosa is proposed. The other Australian species is described as L. pseudocorticata sp. nov. Although L. stichidiosa was originally described in the Mediterranean ca. 70 years ago, our phylogenetic analyses placed it in a lineage restricted to the southern hemisphere, showing that it is native to Australia and introduced to Europe. This study confirms that further work using molecular tools is needed to characterize seaweed diversity, especially among the poorly explored algal turfs, and showcases the usefulness of phylogenetic approaches to uncover introduced species and to determine their native ranges.

Effects of substratum type and orientation on the recruitment of bryozoans in an artificial area of the Western Atlantic.

Bryozoans are commonly associated with various artificial structures in marine environments and have been responsible for several bioinvasion events worldwide. Understanding the interactions between bryozoans and artificial structures is therefore essential to prevent the establishment and spread of potential bioinvaders. This study investigated bryozoan recruitment on four different substrates (PET, nautical ropes, metal, and PVC) placed in three orientations (vertical, horizontal facing down and facing up) in an area of the Western Atlantic. In total, 15 species of bryozoans were found. The results revealed significant variations in assemblages' richness, with bryozoans showing a preference for settling on PVC (14 species found) and on the underside of horizontal substrates (15 species found), resulting in the higher representativity observed in this study. Cryptogenic (nine species) and exotic (five species) bryozoans dominated the assemblages in all treatments, indicating that the type of substrate (especially artificial) and its orientation can favor the settlement of bryozoans, particularly non-native species. Therefore, the availability of multiple types of artificial substrates in marine environments should be treated as a cause for concern.

Reproductive ecology of muskellunge (Esox masquinongy), an introduced predator, in the lower Wolastoq/Saint John River, New Brunswick, Canada.

Introduced predators can have harmful top-down effects on their newly colonized system through competition with and direct predation on native species. Following an initial introduction of muskellunge in Lac Frontière, Québec in the 1970s at the headwaters of the Wolastoq/Saint John River, the species rapidly migrated downstream, expanding its range by ~500 km over ~20 years. Despite this expansive colonization and concern over possible threats to native species, little is known about the basic ecology of muskellunge in this system. The last downstream barrier is the hydroelectric facility, Mactaquac Generating Station (MGS), 150 km upstream of the sea. While there are no downstream fish passage facilities at MGS, adult muskellunge have been recorded downstream. In this study, muskellunge (n = 23) were surgically tagged with very-high-frequency (VHF) radio or combined acoustic radio telemetry (CART) tags and tracked over two spawning seasons. We sought to determine if there was a reproducing population downstream of MGS and tracked Tagged muskellunge over two spawning seasons. We tracked fish to locate and confirm spawning sites, and followed up with egg and/or juvenile sampling surveys. Tagged muskellunge (90%) moved upstream towards the MGS during the spawning period in each year (2016 and 2017), where they remained throughout the entire spawning period. No spawning or nursery sites were confirmed near MGS, but in 2016 three distinct spawning locations and six distinct nursery sites were confirmed 10-12 km downstream amongst a chain of flooded islands. In 2016, eggs, sac-fry and juveniles were collected and confirmed as muskellunge by genetic sequencing, providing the first empirical observation of successful spawning downstream of MGS.

Population genetic structure, parasite infection and somatic condition of pumpkinseed Lepomis gibbosus (Actinopterygii: Centrarchidae) in the Oder river basin.

In Poland, distribution of non-native pumpkinseed Lepomis gibbosus (Centrarchidae) is strictly limited to the Oder river basin, where it was introduced in the early 20th century. Recently, several populations have been found in waterbodies adjacent to the Oder, particularly in its lower reaches. In this study, we compare the genetic relatedness of populations in the Oder basin with other European populations using nuclear (microsatellite) and mitochondrial (partial cytochrome c oxidase subunit I; cox1) markers. Microsatellite analysis indicated that four populations in the lower Oder form a separate cluster, while one in the middle Oder clustered with Danubian populations, from where probably having been introduced. Microsatellite data suggested that the lower Oder populations differ from other non-native European populations, making it impossible to estimate the source of introduction. Nevertheless, analysis of cox1 indicated that Oder pumpkinseeds belong to the same haplotype as the vast majority of European populations. Parasitological examination confirmed the presence of two North American species, the monogenean Onchocleidus dispar and trematode Posthodiplostomum centrarchi, in the lower Oder, both previously unknown in the region. Fifteen other parasite species were acquired, including glochidia of invasive Sinanodonta woodiana. In the middle Oder, parasite infection was more limited. Fish from the Gryfino Canal, considered one of the most invasive populations in Europe, showed the highest parasite abundance and diversity, and the highest somatic condition and growth rate due to warm water released from the Dolna Odra power plant. Our results highlight significant differences in somatic condition and parasite infection in long-established non-native pumpkinseed populations in the same river system, reflecting mainly environmental conditions.

Hydrology and water quality shape macroinvertebrate patterns and facilitate non-native species dispersals in an inter-basin water transfer system.

Understanding biotic assemblage variations resulting from water diversions and other pressures is critical for aquatic ecosystem conservation, but hampered by limited research. Mechanisms driving macroinvertebrate assemblages were determined across five lakes along China's South-to-North Water Diversion Project, an over 900-km water transfer system connecting four river basins. We assessed macroinvertebrate patterns from 59 sites in relation to water quality, climatic, spatial, and hydrologic factors. Macroinvertebrate density, biomass, and species richness increased from upriver to downriver lakes, and were higher during the water transfer period than in the non-water transfer period. Non-native species including Nephtys sp., Paranthura japonica, Potamillacf acuminata, Capitekkidae spp. and Novaculina chinensis, were distributed along the entire study system, some become dominant in upriver lakes. High species turnover occurred in two upriver lakes. Hydrology and water quality are critical factors in shaping these macroinvertebrate patterns. Hydrological disturbance by water transfer boosted macroinvertebrate abundance during the water transfer period while facilitated non-native species dispersals and increased biotic homogenization. This study indicates the need for: 1) an effective ecosystem monitoring system; 2) unified system management standards; 3) external pollution controls; and 4) limiting the dispersal of non-native species.

Islands in the ice: Potential impacts of habitat transformation on Antarctic biodiversity.

Antarctic biodiversity faces an unknown future with a changing climate. Most terrestrial biota is restricted to limited patches of ice-free land in a sea of ice, where they are adapted to the continent's extreme cold and wind and exploit microhabitats of suitable conditions. As temperatures rise, ice-free areas are predicted to expand, more rapidly in some areas than others. There is high uncertainty as to how species' distributions, physiology, abundance, and survivorship will be affected as their habitats transform. Here we use current knowledge to propose hypotheses that ice-free area expansion (i) will increase habitat availability, though the quality of habitat will vary; (ii) will increase structural connectivity, although not necessarily increase opportunities for species establishment; (iii) combined with milder climates will increase likelihood of non-native species establishment, but may also lengthen activity windows for all species; and (iv) will benefit some species and not others, possibly resulting in increased homogeneity of biodiversity. We anticipate considerable spatial, temporal, and taxonomic variation in species responses, and a heightened need for interdisciplinary research to understand the factors associated with ecosystem resilience under future scenarios. Such research will help identify at-risk species or vulnerable localities and is crucial for informing environmental management and policymaking into the future.

Aquatic invasion patterns across the North Atlantic.

Biological invasions are a major driver of biodiversity loss and socioeconomic burden globally. As invasion rates accelerate worldwide, understanding past invasion dynamics is essential to inform predictions of future invaders and impacts. Owing to a high diversity of pathways and current biosecurity gaps, aquatic systems near urban centres are especially susceptible to alien species establishments. Here, we compiled and compared alien species lists for three different aquatic recipient regions spanning the North Atlantic: Chesapeake Bay, Great Lakes-St. Lawrence River and North and Baltic Seas. Each system is a major trade centre, with a history of invasions, and characterized by a strong natural salinity gradient. Our goal was to compare the alien species across systems, to test for similarities in the taxonomic composition and geographic origin as well as species overlap among the three regions. We selected specific macroinvertebrate, algal and fish taxa for analysis, to control for uneven taxonomic and biogeographic resolution across regions. Cumulatively, we identified 326 individual alien species established in these aquatic systems, with the North and Baltic Seas most invaded overall (163), followed by Great Lakes-St. Lawrence River (84) and Chesapeake Bay (79). Most invasions were from Ponto-Caspian, Eurasian, Northwest Pacific, Northwest Atlantic and North American origins, and mostly comprised Arthropoda, Chordata, Mollusca and Annelida. However, origins and taxonomies differed significantly among destinations, with Ponto-Caspian species particularly successful invaders to the North and Baltic Seas then Great Lakes-St. Lawrence River, but less so to Chesapeake Bay. Nevertheless, approximately eight-tenths of invaders established in only one region, indicating disparate invasion patterns and a high potential for future aliens to accrue from increasingly diverse source pools and pathways. These results support biosecurity strategies that consider a broad range of geographic origins and taxonomic groups to limit the translocation, arrival and spread of alien species worldwide.

A keystone mutualism promotes resistance to invasion.

It is not uncommon for one or a few species, and their interactions, to have disproportionate effects on other species in ecological communities. Such keystone interactions might affect how communities respond to the invasion of non-native species by preventing or inhibiting the establishment, spread or impact of non-native species. We explore whether a keystone mutualism among a hummingbird-mistletoe-marsupial promotes ecological resistance to an invasive pollinator, the bumblebee Bombus terrestris, by comparing data collected at sites prior to bumblebee invasion to data collected 11 years after the invasion in sites with and without the keystone mutualism. We built pollination networks and focused on network motifs, regarded as building blocks of networks, to identify the central pollinators and estimate the change in their interactions after invasion of B. terrestris. We also estimated the interaction rewiring across the season in post-invasion networks and tested it as a possible mechanism explaining how the keystone mutualism increased ecological resistance to invasion. We found two times more species in post-invasion sites with the keystone mutualism than in post-invasion sites without the keystone mutualism. Moreover, we found that invasive bumblebee reduced the strength and interaction niche of the five central pollinator species while increasing its own strength and interaction niche, suggesting a replacement of interactions. Also, we found that the keystone mutualism promoted resistance to B. terrestris invasion by reducing its negative impacts on central species. In the presence of the keystone mutualism, central species had three times more direct interactions than in sites without this keystone mutualism. The higher interaction rewiring, after invasion of B. terrestris, in sites with the keystone mutualism indicates greater chances of central pollinators to form new interactions and reduces their competence for resources with the non-native bumblebee. Our results demonstrate that a keystone mutualism can enhance community resistance against the impacts of a non-native invasive pollinator by increasing species diversity and promoting interaction rewiring in the community. This study suggests that the conservation of mutualisms, especially those considered keystone, could be essential for long-term preservation of natural communities under current and future impacts of global change.

Es común que una o unas pocas especies y sus interacciones tengan efectos desproporcionado sobre otras especies en las comunidades. Estas especies y sus interacciones claves podrían afectar el modo en que las comunidades responden a la invasión de especies no nativas al prevenir o disminuir su establecimiento, su propagación o el impacto de las mismas. En este estudio evaluamos si un mutualismo clave entre un colibrí, un muérdago y un marsupial promueve la resistencia de la comunidad frente a un polinizador invasor, el abejorro Bombus terrestris, mediante la comparación de datos colectados en sitios previos a la invasión del abejorro y datos colectados 11 años después de su invasión, en sitios con y sin el mutualismo clave. Construimos redes ecológicas planta-polinizador y nos centramos en los modos de interacción ("interaction motifs"), los cuales son usados como bloques en la construcción de las redes, para identificar los polinizadores centrales y estimar el cambio en sus interacciones después de la invasión de B. terrestris. Además, en las redes posteriores a la invasión estimamos la reconexión de interacciones a lo largo de la temporada y la evaluamos como un posible mecanismo mediante la cual el mutualismo clave aumentó la resistencia a la invasión. En sitios posteriores a la invasión con el mutualismo clave encontramos dos veces más especies que en sitios posteriores a la invasión ausentes de éste. Además, en los sitios ausentes del mutualismo clave, encontramos que el abejorro invasor redujo la fuerza y el nicho de interacción de los cinco polinizadores centrales mientras incrementó su propia fuerza y nicho de interacciones, sugiriendo un reemplazo de interacciones. Asimismo, encontramos que el mutualismo clave promovió la resistencia de la comunidad a la invasión de B. terrestris al reducir sus impactos negativos sobre las especies centrales. En presencia del mutualismo clave, las especies centrales presentaron tres veces más interacciones directas que en sitios ausentes de esta interacción. La gran reconexión de interacciones encontrada en sitios posteriores a la invasión con el mutualismo clave indica mayores probabilidades de que los polinizadores centrales formen nuevas interacciones y reduzcan la competencia por recursos con el abejorro no nativo. Nuestros resultados demuestran que un mutualismo clave puede mejorar la resistencia de la comunidad frente a los impactos de especies invasoras al incrementar la diversidad de especies y promover la reconexión de interacciones en la comunidad. Este estudio sugiere que la conservación de las interacciones mutualistas, principalmente aquellas consideradas claves, podría ser esencial para preservar las comunidades naturales frente a los impactos del cambio global.

Removal of invasive Scotch broom increases its negative effects on soil chemistry and plant communities.

Recovery of ecosystem properties following removal of invasive plants likely varies with characteristics of the plant and the relative soil quality at a given site. These factors may influence the occurrence of soil legacies and secondary invasions, hindering the effectiveness of restoration strategies. We assessed the potential for ecosystem recovery following removal of N-fixing Scotch broom for 4 years at two sites that contrasted strongly in soil quality in western Washington and Oregon, USA. Comparisons were made among plots, where Scotch broom was never present (uninvaded), retained, or removed. Scotch broom removal increased PAR and soil temperature but had limited effects on soil moisture. Concentrations of soil Ca, Mg, K, and P were significantly lower with Scotch broom removal, with the effect being most pronounced at the low-quality site. NMS ordinations indicated that the treatments differed in vegetation composition, with limited recovery following broom removal. Non-native and native species varied inversely in their abundance responses, where non-native species abundance was greatest in the removal treatment, intermediate in the retained treatment, and lowest in the uninvaded treatment, indicating occurrence of a secondary invasion following removal. As with the soil response, effects were more pronounced at the low-quality site. Our findings indicate that Scotch broom removal exacerbates negative effects on soil chemistry and plant communities, with little evidence of recovery over our study period. These findings highlight the importance of controlling Scotch broom invasions immediately after the species establishes, especially on low-quality sites that are more susceptible to Scotch broom invasion.

Influence of coating type, colour, and deployment timing on biofouling by native and non-native species in a marine renewable energy context.

Biofouling on marine renewable energy devices presents engineering challenges for this developing sector, and has implications for the spread of marine non-native species (NNS) in coastal waters. This is particularly true at sites with abundant energy resource, little existing infrastructure, and few established NNS. Device coatings, such as antifouling paints, could reduce the risk of NNS spread. Settlement on coatings of various types and colours, representing those likely to be used on renewable energy devices, was assessed in the Orkney Islands, northern Scotland. Assemblage composition, but not overall biofouling cover, varied initially among different coloured surfaces, although differences decreased over time. Different coating types (an anticorrosive paint, a biocidal paint and a fouling-release coating) differed in biofouling abundance and composition for the full duration of the experiment. NNS were mostly, but not completely, absent from antifouling surfaces. These results can help informing antifouling strategies for the marine renewable energy industry.

High mercury concentrations in steelhead/rainbow trout, sculpin, and terrestrial invertebrates in a stream-riparian food web in coastal California.

Stream and riparian food webs are connected by cross-habitat exchanges of invertebrate prey that can transfer contaminants including mercury. Marine fog has been identified as a source of methylmercury (MeHg) to some terrestrial food webs in coastal California, suggesting that terrestrial invertebrates might have elevated MeHg relative to stream invertebrates and might lead to higher mercury exposure in fish that consume terrestrial subsidies. As an initial step to examine this possibility, we analyzed mercury concentrations in terrestrial and aquatic invertebrates and two fish species, steelhead/rainbow trout (Oncorhynchus mykiss) and coastrange sculpin (Cottus aleuticus), in a small watershed. Mean MeHg and total mercury (THg) concentrations in terrestrial invertebrates were three to four times higher than in aquatic invertebrates of the same trophic level. MeHg was >1000 ng/g dw in some individual centipede and scorpion samples, and also relatively high (100-300 ng/g dw) in some terrestrial detritivores, including non-native isopods. Mean THg in age 0 trout was 400 ng/g dw compared to 1200-1300 ng/g dw in age 1+ trout and sculpin, and the largest trout sampled had THg >3500 ng/g dw. However, the similar mercury concentrations between age 1+ trout and sculpin, despite different diet types, indicated that Hg concentrations in fish were not related simply to differences in consumption of terrestrial invertebrates. The high mercury concentrations we found in terrestrial invertebrates and fish suggest that further research on the sources and bioaccumulation of mercury is warranted in this region where O. mykiss populations are threatened.

Biosecurity and the ornamental fish trade: A stakeholder perspective in England.

The freshwater and marine ornamental fish industry is a primary route of hazard introduction and emergence, including aquatic animal diseases and non-native species. Prevention measures are key to reducing the risk of hazard incursion and establishment, but there is currently little understanding of the biosecurity practices and hazard responses implemented at post-border stages of the ornamental fish supply chain. This study addresses this knowledge gap, using questionnaires to collate information on actual biosecurity behaviours and hazard responses practised by ornamental fish retailers and hobbyist communities in England. Actual behaviours varied considerably within retailers and hobbyists, suggesting that reliance on preventative practices by individuals in the post-border stages of the ornamental fish supply chain is likely to be ineffective in minimizing the risk of hazard incursion and establishment. Resources should be allocated towards improving and enforcing robust pre- and at-border control measures, such as risk-based surveillance of ornamental fish imports at border controls. In addition, these findings should be used to implement targeted awareness-raising campaigns and help create directed training on biosecurity practices for individuals involved in the post-border stages of the ornamental supply chain.