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Wild pigs (Sus scrofa) are the most widely distributed invasive wild ungulate in the United States, yet the factors that influence wild pig dispersal and colonization at the regional level are poorly understood. Our objective was to use a population genetic approach to describe patterns of dispersal and colonization among populations to gain a greater understanding of the invasion process contributing to the expansion of this species. We used 52 microsatellite loci to produce individual genotypes for 482 swine sampled at 39 locations between 2014 and 2016. Our data revealed the existence of genetically distinct subpopulations (FST = 0.1170, p < 0.05). We found evidence of both fine-scale subdivision among the sampling locations, as well as evidence of long term genetic isolation. Several locations exhibited significant admixture (interbreeding) suggesting frequent mixing of individuals among locations; up to 14% of animals were immigrants from other populations. This pattern of admixture suggested successive rounds of human-assisted translocation and subsequent expansion across Florida. We also found evidence of genetically distinct populations that were isolated from nearby populations, suggesting recent introduction by humans. In addition, proximity to wild pig holding facilities was associated with higher migration rates and admixture, likely due to the escape or release of animals. Taken together, these results suggest that human-assisted movement plays a major role in the ecology and rapid population growth of wild pigs in Florida.

Fil: Peri, Pablo Luis. Instituto Nacional de Tecnología Agropecuaria; Argentina. Universidad Nacional de la Patagonia Austral; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

1. Global change, such as exotic invasions, dramatically affects ecosystem functioning. However, the mechanisms behind the impacts are often unclear and despite extensive experimental work, we know little about the importance of biodiversity loss as a component of global change effects in real-world ecosystems. 2. We disentangled several mechanisms by which an exotic invader affected ecosystem functioning in East African drylands in Kenya and Ethiopia. We used structural equation modelling to separate direct effects of a woody invader Prosopis juliflora on a range of ecosystem functions from indirect effects mediated through changes in biodiversity (plant species richness) and ecosystem functioning (herbaceous biomass). We analysed effects on ecosystem functions linked to soil biogeochemical cycling and transfer of energy between trophic levels. 3. We found that the mean size of individual indirect effects mediated by biodiversity and herbaceous biomass was about twice as large as the mean size of individual direct effects of Prosopis on ecosystem functions, showing that indirect effects are an important component of the invader's overall environmental impacts. Changes in both herbaceous biomass and biodiversity were approximately equally important as drivers of indirect effects, indicating that we need to expand our view of indirect effects to consider a wider range of mechanisms. Simple univariate models failed to capture some Prosopis invader effects because positive direct effects on soil stability and predatory invertebrates were counteracted by negative indirect effects on biodiversity or biomass loss. The majority of effects were similar in both study systems. Suggestions that woody invaders are able to increase certain ecosystem functions may therefore have arisen because these negative indirect effects were not considered. 4. Synthesis. Our study indicates that successful management of exotic invasions is likely to require not only control of the invader but also restoration of diverse and productive herbaceous communities as they are important for many ecosystem functions. This highlights the importance of biodiversity as a driver of ecosystem functioning also in real-world systems.

Processes that drive plant invasions play out across multiple spatial and temporal scales. Understanding individual steps along the introduction-naturalization-invasion continuum and its drivers is crucial for management. This review, targeting the broad audience of invasion scientists, field ecologists and land managers, summarizes the state-of-the-art and potential of remote sensing (RS) in plant invasion science and management. It identifies challenges and research gaps, discusses the discrepancies between technology, science and practice, and suggests ways of addressing some of these issues. Mapping, modelling and predicting invasion processes across scales is a major challenge since they are dynamic and highly complex. Integration of RS data collected at different spatial and temporal scales (“rocking” across scales) has the potential to elucidate the dynamics of invasions and to reveal its drivers, thereby improving the efficiency of control measures. Increasing spatial/temporal resolution of imagery from satellites and drones has much potential to (i) precisely identify even less conspicuous invasive species; (ii) map invasion dynamics; and (iii) provide information on environmental variables and landscape structure at scales fine enough to capture underlying ecological processes. Until now, RS research has focussed primarily on spatio-temporal patterns of plant invasions. Other more challenging topics, such as early monitoring, and revealing the invasion mechanisms and impacts have received less attention. Despite the power of RS technology and recent developments, large discrepancies remain between possibilities and actual implications in research and practical management of invasions. Although recent technological advances, such as powerful algorithms, cloud solutions, and data streams from citizen science, might overcome some limitations, the mutual dialog among field ecologists, managers, invasion scientists and RS specialists remains crucial; our review contributes to such communication.

1. Much attention has been paid to negative effects of alien species on resident communities but studies that quantify community-level effects of a number of invasive plants are scarce. We address this issue by assessing the impact of 13 species invasive in the Czech Republic on a wide range of plant communities. 2. Vegetation in invaded and uninvaded plots with similar site conditions was sampled. All species of vascular plants were recorded, their covers were estimated and used as importance values for calculating the Shannon diversity index H', evenness J and Sørensen index of similarity between invaded and uninvaded vegetation. 3. With the exception of two invasive species, species richness, diversity and evenness were reduced in invaded plots. Species exhibiting the greatest impact reduced species numbers per plot and the total number of species recorded in the communities sampled by almost 90%. A strong reduction of species number at the plot scale resulted in a marked reduction in the total species number at the landscape scale, and in less similarity between invaded and uninvaded vegetation. The decrease in species richness in invaded compared to uninvaded plots is largely driven by the identity of the invading species, whereas the major determinants of the decrease in Shannon diversity and evenness are the cover and height of invading species, and differences between height and cover of invading and dominant native species, independent of species identity. 4. Synthesis. Management decisions based on impact need to distinguish between invasive species, as their effects on diversity and composition of resident vegetation differ largely. Tall invading species capable of forming populations with the cover markedly greater than that of native dominant species exert the most severe effects on species diversity and evenness. Since a strong impact on the community scale is associated with reduction in species diversity at higher scales, invaders with a high impact represent a serious hazard to the landscape.

The stalk-eyed seed bug Chauliops fallax is an important agricultural pest of soybean and was first reported to occur outside East Asia. Here, the native evolutionary history, recent invasion history, and potential invasion threats of C. fallax were reported for the first time based on population genetic methods and ecological niche modelling. Four native genetic groups (EA, WE, TL, and XZ) and an east-west differentiation pattern consistent with the geographical characteristics of three-step landforms were well supported in China. The Kashmir sample was found to come from a recent invasion event, and the invasive source was determined to be the populations of the coastal areas of southern China. North America might have high a risk of invasion, which poses a serious threat to local soybean production. Our results provided new insights into the monitoring and management of Chauliops fallax in the early invasion stage. The short stay at the beginning of the invasion process is a critical time for invasive species identification and preventing invasive species from developing a wider distribution and significant economic impact. The stalk-eyed seed bug Chauliops fallax is an important agricultural pest of soybean and was first reported to occur outside East Asia. Here, we reported the native evolutionary history, recent invasion history, and potential invasion threats of C. fallax for the first time based on population genetic methods and ecological niche modelling. The results showed that four native East Asian genetic groups (EA, WE, TL, and XZ) were well supported, showing an east-west differentiation pattern consistent with the geographical characteristics of three-step landforms in China. Two main haplotypes existed: Hap1 might have experienced a rapid northwards expansion process after the LGM period, and Hap5 reflected local adaptation to the environment in southeastern China. The Kashmir sample was found to come from the recent invasion of populations in the coastal areas of southern China. Ecological niche modelling results suggested that North America has a high risk of invasion, which might pose a serious threat to local soybean production. In addition, with future global warming, the suitable habitat in Asia will move towards the higher latitude region and gradually deviate from the soybean planting area, which indicates the threat of C. fallax to soybean production in Asia will decrease in the future. The results could provide new insights into the monitoring and management of this agricultural pest in the early invasion stage.

There are thousands of case studies documenting invasive species’ impacts and these have led to the development of over 30 hypotheses that describe how invasions occur and their impacts manifest. The proliferation of invasion hypotheses over the decades has spurred several efforts to identify conceptual overlap and increase clarity of impact mechanism in the field. What is still lacking, however, is a comprehensive accounting of the evidence base on invasive species impacts, especially in regard to the biological scales, temporal scales, and taxonomic groups that receive research. Identifying the ‘known unknowns’ of empirical invasion impact research serves a critical function in the effort to evaluate support for existing hypotheses and generate novel hypotheses. We built a taxonomically and geographically comprehensive database of over 1500 research articles that report measures of invasive species’ ecological impacts published over the past 18 years (1999–2016). We found that, field-wide, published measures of invasive species’ impacts are highly skewed toward those measured at the population or community-level with scarce information on impacts at other biological scales (e.g., physiology, behavior). We also show that existing impact evidence stems most often from one-off studies of single invasive species. Yet, even for species that receive consistent attention, impacts have rarely been documented across more than one biological scale, beyond very short time periods, or in several ecosystems. In order to predict and anticipate how impacts manifest in a variety of temporal and biological contexts, the evidence base informing existing invasion hypotheses must become more integrative both within and across publications.

1. The diversity of pathogens on highly abundant introduced hosts has been positively correlated with time since introduction, geographical range of the introduced species and diversity of invaded habitats. However, little is known about the ecological effects of pathogen accumulation on non-native invasive plants. 2. Pathogen accumulation on invasive plant species may result from ecological processes such as high plant densities, expanding geographical ranges and pathogen dispersal from the native range, or evolutionary mechanisms such as host range shifts and adaptation of native pathogens to invasive species. 3. Over time pathogen accumulation may cause decline in the density and distribution of invasive plants and facilitate recovery of native species. Alternatively, pathogens might build up on invasive species and then spill back onto co-occurring native species, further exacerbating the effects of invasions. 4. Synthesis. Research efforts should focus on determining the long-term outcomes of pathogen accumulation on invasive species. Such research will require multifaceted approaches including comparative studies of diverse invasive species and habitats, experimental manipulations of hosts and pathogens in nature and controlled environments, and predictive models of host-pathogen interactions within an invasion framework. Results of this research will improve our understanding and ability to predict the outcomes of biological invasions.

Invasive woody species like Callery pear (Pyrus calleryana Decne.) alter ecosystems directly and indirectly through effects on arthropod communities as well as chemical alterations of the soil. Evidence suggests that the aggressive spread and negative impacts are due to allelopathic chemicals present throughout plant tissues which reduce herbivory and add unique allochthonous inputs to the soil, thereby reducing germination of native species and furthering Callery pear's domination on the landscape. To assess the allelopathic potential of Callery pear, we collected leaf tissue from Callery pear, black cherry (Prunus serotina) as the native comparison, and wild peach (Prunus persica) to serve as a non-native but non-invasive representative. Callery pear leaves contained 32 unique compounds compared to our other two species tested, with 23 of these compounds belonging to the group of compounds called flavones, which are secondary metabolites known to build up in the roots of plants and cause autotoxicity, along with changes to the soil microbial community, including mycorrhizal fungi. While flavones are ubiquitous in nature, their presence in Callery pear suggests downstream effects on native plants and arthropod communities, and provides evidence for the empty niche theory of invasion. Further experiments are needed to confirm flavones in other Callery pear tissues and to assess the mediating chemical pathways that lead to their upregulation.