Identifying inconsistencies in exotic pet regulations that perpetuate trade in risky species.

Regulatory inconsistencies at different jurisdictional levels have contributed to the global expansion of the exotic pet trade, with resultant increases in the spread of invasive species and pathogens. Researchers have enumerated multiple limitations and environmental risks posed by international and national rules that govern the exotic pet trade, yet little attention has focused on the regulation of the exotic pet trade within national borders. We reviewed state-level regulations that apply to the trade of vertebrate animal taxa in the United States. Definitions and classifications for regulating different vertebrate taxa varied greatly across states, and the terms pet and companion animal were poorly defined and inconsistent across states. States implemented regulations that permit trade in exotic vertebrate pets that are banned from import into the United States owing to public health and conservation concerns. Once species have been imported into the United States, inconsistent internal regulations facilitate the movement of animals that pose substantial invasion and disease risks. Violations of state laws were typically listed as misdemeanors, and the median fine for violating state wildlife trade laws was $1000. Inconsistent and incomplete regulation of exotic vertebrate pets across state borders, in conjunction with limited penalties for violating regulations, has facilitated continued possession of exotic pets in states where these animals are banned. Based on our review of regulatory weaknesses, we conclude that a transition to a federally enforced list of vertebrate species that may be traded as pets is needed, with all other vertebrate species banned from the exotic pet trade unless their potential invasion and disease risks have been assessed and demonstrated to be low or nonexistent.

Identificación de las inconsistencias en las regulaciones de las mascotas exóticas que perpetúan el mercado de especies riesgosas Resumen Las inconsistencias regulatorias en diferentes niveles regulatorios han contribuido a la expansión mundial del mercado de mascotas exóticas, con un incremento resultante en la dispersión de especies invasoras y patógenos. Los investigadores han enumerado varias limitaciones y riesgos ambientales que representan las normas nacionales e internacionales que dictan el mercado de mascotas exóticas, pero se ha puesto poca atención en la regulación de este mercado dentro de las fronteras nacionales. Revisamos las regulaciones a nivel estatal que aplican al mercado de taxones de vertebrados en los Estados Unidos (EU). Entre los estados, las definiciones y clasificaciones para regular el mercado de los diferentes taxones de vertebrados variaron mucho y los términos mascota y animal de compañía contaban con definiciones deficientes e incoherentes. Los estados implementaron regulaciones que permiten el mercado de vertebrados como mascotas exóticas cuya importación está prohibida para los EU debido a cuestiones de salud pública y conservación. Una vez que las especies han sido importadas a los EU, las regulaciones internas incoherentes facilitan el traslado de animales que representan un riesgo importante de invasión y de enfermedad. Con frecuencia, las violaciones a las leyes estatales se denominaban delitos menores y la multa promedio por violar las leyes estatales de comercio de fauna era de $1,000. La regulación incompleta e incoherente del mercado de mascotas exóticas entre los límites estatales, en conjunto con las penalizaciones limitadas por violar las regulaciones, ha facilitado la posesión continua de mascotas exóticas en estados en donde estos animales están prohibidos. Con base en nuestra revisión de las debilidades regulatorias, concluimos que se necesita transitar a una lista con aplicación federal de especies de vertebrados que pueden ser comercializadas como mascotas, con todas las demás especies de vertebrados vetadas del mercado a menos de que se haya evaluado su riesgo potencial de invasión y de enfermedad y se haya demostrado que es bajo o inexistente.

Introduction of artificial light at night increases the abundance of predators, scavengers, and parasites in arthropod communities.

While recent studies explore the negative impacts of light pollution on arthropods, few studies investigated community-level responses to artificial light. Using an array of landscaping lights and pitfall traps, we track community composition over 15 consecutive days and nights, including a five-night pre-light period, a five-night during-light period, and a five-night post-light period. Our results highlight a trophic-level response to artificial nighttime lighting with shifts in the presence and abundance of predators, scavengers, parasites, and herbivores. We show that associated trophic shifts occurred immediately upon the introduction of artificial light at night and are limited to nocturnal communities. Lastly, trophic levels reverted to their pre-light state, suggesting many short-term changes in communities are likely the result of behavioral shifts. These trophic shifts may become common as light pollution increases, implicating artificial light as a cause of global arthropod community change and highlighting light pollution's role in global herbivorous arthropod decline.

Sampling environmental DNA from trees and soil to detect cryptic arboreal mammals.

Environmental DNA (eDNA) approaches to monitoring biodiversity in terrestrial environments have largely focused on sampling water bodies, potentially limiting the geographic and taxonomic scope of eDNA investigations. We assessed the performance of two strictly terrestrial eDNA sampling approaches to detect arboreal mammals, a guild with many threatened and poorly studied taxa worldwide, within two central New Jersey (USA) woodlands. We evaluated species detected with metabarcoding using two eDNA collection methods (tree bark vs. soil sampling), and compared the performance of two detection methods (qPCR vs. metabarcoding) within a single species. Our survey, which included 94 sampling events at 21 trees, detected 16 species of mammals, representing over 60% of the diversity expected in the area. More DNA was found for the 8 arboreal versus 8 non-arboreal species detected (mean: 2466 vs. 289 reads/sample). Soil samples revealed a generally similar composition, but a lower diversity, of mammal species. Detection rates for big brown bat were 3.4 × higher for qPCR over metabarcoding, illustrating the enhanced sensitivity of single-species approaches. Our results suggest that sampling eDNA from on and around trees could serve as a useful new monitoring tool for cryptic arboreal mammal communities globally.

Alternative stable ecological states observed after a biological invasion.

Although biological invasions play an important role in ecosystem change worldwide, little is known about how invasions are influenced by local abiotic stressors. Broadly, abiotic stressors can cause large-scale community changes in an ecosystem that influence its resilience. The possibility for these stressors to increase as global changes intensify highlights the pressing need to understand and characterize the effects that abiotic drivers may have on the dynamics and composition of a community. Here, we analyzed 26 years of weekly abundance data using the theory of regime shifts to understand how the structure of a resident community of dung beetles (composed of dweller and tunneler functional groups) responds to climatic changes in the presence of the invasive tunneler Digitonthophagus gazella. Although the community showed an initial dominance by the invader that decreased over time, the theory of regime shifts reveals the possibility of an ecological transition driven by climate factors (summarized here in a climatic index that combines minimum temperature and relative humidity). Mid and low values of the driver led to the existence of two alternative stable states for the community structure (i.e. dominance of either dwellers or tunnelers for similar values of the climatic driver), whereas large values of the driver led to the single dominance by tunnelers. We also quantified the stability of these states against climatic changes (resilience), which provides insight on the conditions under which the success of an invasion and/or the recovery of the previous status quo for the ecosystem are expected. Our approach can help understand the role of climatic changes in community responses, and improve our capacity to deal with regime shifts caused by the introduction of exotic species in new ecosystems.

Combining surface and soil environmental DNA with artificial cover objects to improve terrestrial reptile survey detection.

Reptiles are increasingly of conservation concern due to their susceptibility to habitat loss, emerging disease, and harvest in the wildlife trade. However, reptile populations are often difficult to monitor given the frequency of crypsis in their life history. This difficulty has left uncertain the conservation status of many species and the efficacy of conservation actions unknown. Environmental DNA (eDNA) surveys consistently elevate the detection rate of species they are designed to monitor, and while their use is promising for terrestrial reptile conservation, successes in developing such surveys have been sparse. We tested the degree to which inclusion of surface and soil eDNA sampling into conventional artificial-cover methods elevates the detection probability of a small, cryptic terrestrial lizard, Scincella lateralis. The eDNA sampling of cover object surfaces with paint rollers elevated per sample detection probabilities for this species 4-16 times compared with visual surveys alone. We readily detected S. lateralis eDNA under cover objects up to 2 weeks after the last visual detection, and at some cover objects where no S. lateralis were visually observed in prior months. With sufficient sampling intensity, eDNA testing of soil under cover objects produced comparable per sample detection probabilities as roller surface methods. Our results suggest that combining eDNA and cover object methods can considerably increase the detection power of reptile monitoring programs, allowing more accurate estimates of population size, detection of temporal and spatial changes in habitat use, and tracking success of restoration efforts. Further research into the deposition and decay rates of reptile eDNA under cover objects, as well as tailored protocols for different species and habitats, is needed to bring the technique into widespread use.

El interés por la conservación de los reptiles es cada vez mayor debido a su susceptibilidad ante la pérdida del hábitat, enfermedades emergentes y la captura para el mercado de fauna. Sin embargo, las poblaciones de reptiles son difíciles de monitorear por lo frecuente que es la cripsis en sus historias de vida. Esta dificultad deja incierto el estado de conservación de muchas especies y desconocida la eficacia de las acciones de conservación. Los censos de ADN ambiental (DNAa) elevan sistemáticamente la tasa de detección de las especies que monitorean, y aunque su uso es prometedor para la conservación de los reptiles terrestres, han sido escasos los éxitos en el desarrollo de dichos censos. Analizamos el grado al que la inclusión del muestreo de DNAa superficial y del suelo a los métodos convencionales de cobertura artificial eleva la probabilidad de detección de una pequeña lagartija terrestre críptica: Scincella lateralis. El muestreo de DNAa de las superficies con cobertura de objetos con rodillos de pintura elevó las probabilidades de detección por muestra para esta especie 4-16 veces más que los censos visuales. Detectamos fácilmente el DNAa de S. lateralis bajo los objetos de cubierta hasta dos semanas después de la última detección visual y en algunos objetos de cubierta en donde no se había observado en los meses previos a S. lateralis. Con suficiente intensidad de muestreo, el análisis de DNAa del suelo bajo objetos de cubierta produjo probabilidades de detección por muestra comparables como métodos de rodillo superficial. Nuestros resultados sugieren que la combinación del DNAa y los métodos de objetos de cobertura puede incrementar considerablemente el poder de detección de los programas de monitoreo de reptiles, lo que permite estimaciones más precisas del tamaño poblacional, detección de los cambios espaciales y temporales en el uso de hábitat y el éxito de rastreo de los esfuerzos de restauración. Además, se necesita la investigación sobre las tasas de depósito y descomposición del DNAa de reptiles bajo objetos de cubierta, así como los protocolos hechos para diferentes especies y hábitats, para que la técnica entre al uso difundido.

The International Vertebrate Pet Trade Network and Insights from US Imports of Exotic Pets.

The international trade in exotic vertebrate pets provides key social and economic benefits but also drives associated ecological, ethical, and human health impacts. However, despite its clear importance, we currently lack a full understanding of the structure of the pet trade, hampering efforts to optimize its benefits while mitigating its negative effects. In the present article, we represent and review the structure of the pet trade as a network composed of different market actors (nodes) and trade flows (links). We identify key data gaps in this network that, if filled, would enable network analyses to pinpoint targets for management. As a case study of how data-informed networks can realize this goal, we quantified spatial and temporal patterns in pets imported to the United States. Our framework and case study illustrate how network approaches can help to inform and manage the effects of the growing demand for exotic pets.

Managing propagule pressure to prevent invasive species establishments: propagule size, number, and risk-release curve.

There is considerable evidence that keeping propagule pressure low can drastically reduce establishment probability of potential invasive species. Yet, most management plans and research efforts fail to explicitly acknowledge all three of the components of propagule pressure: size, number, and the risk-release relationship. It is unclear how failing to specify one or more of these components can influence the efficacy of management plans in preventing invasive species establishment. Furthermore, even if all components are acknowledged and quantified, there currently is no mathematical tool available to calculate the levels of propagule pressure that ensure attainment of a predetermined, and system-specific, target establishment probability. Here, we quantify the resulting uncertainty in establishment probability when one or more components of propagule pressure is unknown by using parameter uncertainty analysis on realistic values of propagule pressure. In addition, to aid in the development of management plans that explicitly set propagule pressure limits, we develop a propagule-pressure sensitivity analysis that we use to determine the required reduction in levels for propagule size and number (representative of management actions) to maintain a target establishment probability. We show that the precision of establishment estimates is highly dependent on knowledge of all three propagule pressure components, where the possible range of values for establishment probability can vary by over 50% without full specification. In addition, our sensitivity analysis showed that propagule size and number can be altered independently or in conjunction to lower establishment probability below a target level. Importantly, our sensitivity analysis was able to specifically quantify how much reduction in a propagule pressure component(s) is needed to reach a given target establishment probability. Our findings suggest that quantifying the three components of propagule pressure should be a priority for invasive species prevention moving forward. Furthermore, our sensitivity analysis tool can serve to guide the development of new invasive species management plans in a transparent and quantitative manner. Together with information on the costs associated with approaches to reducing propagule pressure, our tool can be used to identify the most cost-effective approach to prevent invasive species establishments.

Mapping shifts in spatial synchrony in grassland birds to inform conservation planning.

Spatial synchrony, defined as the correlated fluctuations in abundance of spatially separated populations, can be caused by regional fluctuations in natural and anthropogenic environmental population drivers. Investigations into the geography of synchrony can provide useful insight to inform conservation planning efforts by revealing regions of common population drivers and metapopulation extinction vulnerability. We examined the geography of spatial synchrony and decadal changes in these patterns for grassland birds in the United States and Canada, which are experiencing widespread and persistent population declines. We used Bayesian hierarchical models and over 50 years of abundance data from the North American Breeding Bird Survey to generate population indices within a 2° latitude by 2° longitude grid. We computed and mapped mean local spatial synchrony for each cell (mean detrended correlation of the index among neighboring cells), along with associated uncertainty, for 19 species in 2, 26-year periods, 1968-1993 and 1994-2019. Grassland birds were predicted to increase in spatial synchrony where agricultural intensification, climate change, or interactions between the 2 increased. We found no evidence of an overall increase in synchrony among grassland bird species. However, based on the geography of these changes, there was considerable spatial heterogeneity within species. Averaging across species, we identified clusters of increasing spatial synchrony in the Prairie Pothole and Shortgrass Prairie regions and a region of decreasing spatial synchrony in the eastern United States. Our approach has the potential to inform continental-scale conservation planning by adding an additional layer of relevant information to species status assessments and spatial prioritization of policy and management actions. Our work adds to a growing literature suggesting that global change may result in shifting patterns of spatial synchrony in population dynamics across taxa with broad implications for biodiversity conservation.

La sincronía espacial, definida como las fluctuaciones correlacionadas de la abundancia de poblaciones separadas espacialmente, puede deberse a las fluctuaciones regionales de los conductores ambientales naturales y antropogénicos de las poblaciones. Los análisis de la geografía de las sincronías pueden proporcionar conocimiento útil para guiar los esfuerzos de planeación de la conservación al revelar regiones de conductores comunes de población y la vulnerabilidad de extinción de las metapoblaciones. Examinamos la geografía de la sincronía espacial y los cambios por década en estos patrones para las aves de pastizal en los Estados Unidos y Canadá, las cuales están experimentando declinaciones poblacionales extensas y persistentes. Usamos modelos bayesianos jerárquicos y más de 50 años de datos de abundancia tomados del Censo Norteamericano de Aves Reproductoras para generar índices poblacionales dentro una cuadrícula de 2° de latitud por 2° de longitud. Calculamos y mapeamos la sincronía espacial local media para cada celda (la correlación con deducción de tendencia de la media del índice entre las celdas vecinas), además de la incertidumbre asociada, para 19 especies en dos períodos de 26 años: 1968 - 1993 y 1994 - 2019. Se predijo que las aves de pastizal aumentarían su sincronía espacial en donde aumentarán la intensificación agrícola, el cambio climático o las interacciones entre ambos. No encontramos evidencia de un aumento generalizado de la sincronía entre las especies de aves de pastizal. Sin embargo, con base en la geografía de estos cambios, hubo una heterogeneidad espacial considerable entre las especies. Como promedio entre las especies, identificamos módulos de sincronía espacial en aumento en las regiones de Prairie Pothole y Shortgrass Prairie así como una región de sincronía espacial en declive al este de los Estados Unidos. Nuestra estrategia tiene el potencial para guiar a la planeación de la conservación a escala continental al añadir una capa adicional de información relevante a los análisis del estado de las especies y a la priorización espacial de las acciones de manejo y de políticas. Nuestro trabajo contribuye a una creciente literatura que sugiere que el cambio mundial podría derivar en patrones cambiantes de sincronía espacial en las dinámicas poblacionales de muchos taxones con implicaciones amplias para la conservación de la biodiversidad. Mapeo de los Cambios en la Sincronía Espacial de las Aves de Pastizal para Guiar la Planeación de la Conservación.

Changes in taxonomic and phylogenetic diversity in the Anthropocene.

To better understand how ecosystems are changing, a multifaceted approach to measuring biodiversity that considers species richness (SR) and evolutionary history across spatial scales is needed. Here, we compiled 162 datasets for fish, bird and plant assemblages across the globe and measured how taxonomic and phylogenetic diversity changed at different spatial scales (within site α diversity and between sites spatial ß diversity). Biodiversity change is measured from these datasets in three ways: across land use gradients, from species lists, and through sampling of the same locations across two time periods. We found that local SR and phylogenetic α diversity (Faith's PD (phylogenetic diversity)) increased for all taxonomic groups. However, when measured with a metric that is independent of SR (phylogenetic species variation, PSV), phylogenetic α diversity declined for all taxonomic groups. Land use datasets showed declines in SR, Faith's PD and PSV. For all taxonomic groups and data types, spatial taxonomic and phylogenetic ß diversity decreased when measured with Sorensen dissimilarity and phylogenetic Sorensen dissimilarity, respectively, providing strong evidence of global biotic homogenization. The decoupling of α and ß diversity, as well as taxonomic and phylogenetic diversity, highlights the need for a broader perspective on contemporary biodiversity changes. Conservation and environmental policy decisions thus need to consider biodiversity beyond local SR to protect biodiversity and ecosystem services.

Cumulative meta-analysis identifies declining but negative impacts of invasive species on richness after 20 yr.

A principal impact of invasive species is that they reduce local species richness. However, it is unknown whether the magnitude of the richness decrease has been consistent over the past two decades of published research. We used cumulative meta-analysis to synthesize evidence from 240 articles evaluating whether this cumulative evidence base generally supports, or refutes, the association between invasive species presence and richness declines. First, we determined whether evidence accumulation lowered the mean effect size of invasive species on local native richness through time; termed the "decline effect." Then, as mean effect sizes changed over time, we identified when accumulated evidence reached sufficiency, indicating that the mean effect direction (positive or negative) was unlikely to be reversed by unpublished research. We also assessed whether the mean effect size reached a threshold of stability over publication years. To date, no research has tested mechanisms of the decline effect, and here we determine whether publication bias, sample size, time since invasion, or invader trophic position are driving a decline effect in the published evidence base. We found a clear decline in the cumulative mean effect of invasive species on local native species richness as published evidence accumulated between 1999 and 2016. Despite this decline, an average negative association was stable and sufficiently robust to unpublished studies by 2007, showing a 21% mean richness decrease by 2016. Contrary to our expectation, the decline effect manifested consistently regardless of invasive species trophic position, time since invasion, or journal rank. Within taxonomic subgroups, trees, insects, and herbaceous plants exhibit a decline effect, yet still show sufficient and stable negative impacts on richness. However, many other taxonomic subgroups (e.g., crustaceans, fish, mammals) lack evidence for average negative impacts on richness, or have not met sufficiency or stability thresholds.

The relationship between propagule pressure and establishment success in alien bird populations: a re-analysis of Moulton & Cropper (2019).

A recent analysis by Moulton & Cropper (2019) of a global dataset on alien bird population introductions claims to find no evidence that establishment success is a function of the size of the founding population. Here, we re-analyse Moulton & Cropper's data and show that this conclusion is based on flawed statistical methods-their data in fact confirm a strong positive relationship between founding population size and establishment success. We also refute several non-statistical arguments against the likelihood of such an effect presented by Moulton & Cropper. We conclude that a core tenet of population biology-that small populations are more prone to extinction-applies to alien populations beyond their native geographic range limits as much as to native populations within them.

Moving eDNA surveys onto land: Strategies for active eDNA aggregation to detect invasive forest insects.

The use of environmental DNA (eDNA) surveys to monitor terrestrial species has been relatively limited, with successful implementations still confined to sampling DNA from natural or artificial water bodies and soil. Sampling water for eDNA depends on proximity to or availability of water, whereas eDNA from soil is limited in its spatial scale due to the large quantities necessary for processing and difficulty in doing so. These challenges limit the widespread use of eDNA in several systems, such as surveying forests for invasive insects. We developed two new eDNA aggregation approaches that overcome the challenges of above-ground terrestrial sampling and eliminate the dependency on creating or utilizing pre-existing water bodies to conduct eDNA sampling. The first, "spray aggregation," uses spray action to remove eDNA from surface substrates and was developed for shrubs and other understorey vegetation, while the second, "tree rolling," uses physical transfer via a roller to remove eDNA from the surface of tree trunks and large branches. We tested these approaches by surveying for spotted lanternfly, Lycorma delicatula, a recent invasive pest of northeastern USA that is considered a significant ecological and economic threat to forests and agriculture. We found that our terrestrial eDNA surveys matched visual surveys, but also detected L. delicatula presence ahead of visual surveys, indicating increased sensitivity of terrestrial eDNA surveys over currently used methodology. The terrestrial eDNA approaches we describe can be adapted for use in surveying a variety of forest insects and represent a novel strategy for surveying terrestrial biodiversity.

A conceptual map of invasion biology: Integrating hypotheses into a consensus network.

BACKGROUND AND AIMS: Since its emergence in the mid-20th century, invasion biology has matured into a productive research field addressing questions of fundamental and applied importance. Not only has the number of empirical studies increased through time, but also has the number of competing, overlapping and, in some cases, contradictory hypotheses about biological invasions. To make these contradictions and redundancies explicit, and to gain insight into the field's current theoretical structure, we developed and applied a Delphi approach to create a consensus network of 39 existing invasion hypotheses. RESULTS: The resulting network was analysed with a link-clustering algorithm that revealed five concept clusters (resource availability, biotic interaction, propagule, trait and Darwin's clusters) representing complementary areas in the theory of invasion biology. The network also displays hypotheses that link two or more clusters, called connecting hypotheses, which are important in determining network structure. The network indicates hypotheses that are logically linked either positively (77 connections of support) or negatively (that is, they contradict each other; 6 connections). SIGNIFICANCE: The network visually synthesizes how invasion biology's predominant hypotheses are conceptually related to each other, and thus, reveals an emergent structure - a conceptual map - that can serve as a navigation tool for scholars, practitioners and students, both inside and outside of the field of invasion biology, and guide the development of a more coherent foundation of theory. Additionally, the outlined approach can be more widely applied to create a conceptual map for the larger fields of ecology and biogeography.

Influence of invasion history on rapid morphological divergence across island populations of an exotic bird.

There is increasing evidence that exotic populations may rapidly differentiate from those in their native range and that differences also arise among populations within the exotic range. Using morphological and DNA-based analyses, we document the extent of trait divergence among native North American and exotic Hawaiian populations of northern cardinal (Cardinalis cardinalis). Furthermore, using a combination of historical records and DNA-based analyses, we evaluate the role of founder effects in producing observed trait differences. We measured and compared key morphological traits across northern cardinal populations in the native and exotic ranges to assess whether trait divergence across the Hawaiian Islands, where this species was introduced between 1929 and 1931, reflected observed variation across native phylogeographic clades in its native North America. We used and added to prior phylogenetic analyses based on a mitochondrial locus to identify the most likely native source clade(s) for the Hawaiian cardinal populations. We then used Approximate Bayesian Computation (ABC) to evaluate the role of founder effects in producing the observed differences in body size and bill morphology across native and exotic populations. We found cardinal populations on the Hawaiian Islands had morphological traits that diverged substantially across islands and overlapped the trait space of all measured native North American clades. The phylogeographic analysis identified the eastern North American clade (C. cardinalis cardinalis) as the most likely and sole native source for all the Hawaiian cardinal populations. The ABC analyses supported written accounts of the cardinal's introduction that indicate the original 300 cardinals shipped to Hawaii were simultaneously and evenly released across Hawaii, Kauai, and Oahu. Populations on each island likely experienced bottlenecks followed by expansion, with cardinals from the island of Hawaii eventually colonizing Maui unaided. Overall, our results suggest that founder effects had limited impact on morphological trait divergence of exotic cardinal populations in the Hawaiian archipelago, which instead reflect postintroduction events.

Dissecting the null model for biological invasions: A meta-analysis of the propagule pressure effect.

A consistent determinant of the establishment success of alien species appears to be the number of individuals that are introduced to found a population (propagule pressure), yet variation in the form of this relationship has been largely unexplored. Here, we present the first quantitative systematic review of this form, using Bayesian meta-analytical methods. The relationship between propagule pressure and establishment success has been evaluated for a broad range of taxa and life histories, including invertebrates, herbaceous plants and long-lived trees, and terrestrial and aquatic vertebrates. We found a positive mean effect of propagule pressure on establishment success to be a feature of every hypothesis we tested. However, establishment success most critically depended on propagule pressures in the range of 10-100 individuals. Heterogeneity in effect size was associated primarily with different analytical approaches, with some evidence of larger effect sizes in animal rather than plant introductions. Conversely, no variation was accounted for in any analysis by the scale of study (field to global) or methodology (observational, experimental, or proxy) used. Our analyses reveal remarkable consistency in the form of the relationship between propagule pressure and alien population establishment success.

Invasion Science: A Horizon Scan of Emerging Challenges and Opportunities.

We identified emerging scientific, technological, and sociopolitical issues likely to affect how biological invasions are studied and managed over the next two decades. Issues were ranked according to their probability of emergence, pervasiveness, potential impact, and novelty. Top-ranked issues include the application of genomic modification tools to control invasions, effects of Arctic globalization on invasion risk in the Northern Hemisphere, commercial use of microbes to facilitate crop production, the emergence of invasive microbial pathogens, and the fate of intercontinental trade agreements. These diverse issues suggest an expanding interdisciplinary role for invasion science in biosecurity and ecosystem management, burgeoning applications of biotechnology in alien species detection and control, and new frontiers in the microbial ecology of invasions.