Residence time and human-mediated propagule pressure at work in the alien flora of Galapagos

Introduced species present the greatest threat to the unique terrestrial biodiversity of the Galapagos Islands. We assess the current status of plant invasion in Galapagos, predict the likelihood of future naturalizations and invasions from the existing introduced flora, and suggest measures to help limit future invasions. There has been a 1.46 fold increase in plant biodiversity in Galapagos due to alien plant naturalizations, reflecting a similar trend on islands elsewhere. There are 870 alien plant species recorded in the archipelago. Of evaluated species, 34% species have naturalized. Within this group are the invasive species (16% of evaluated) and the transformers (3.3% of evaluated). We show that, as expected, naturalized species have been present in the archipelago longer than non-naturalized species. We also find that a higher human-mediated propagule pressure is associated with a greater human population and with properties that have been settled longer. This, combined with the relatively recent introduction of most species, leads us to the conclusion that Galapagos is at an early stage of plant invasion. We predict that more species from the existing alien flora will find an opportunity to naturalize and invade as propagule pressure increases alongside rapid human population growth associated with immigration to serve the booming tourism industry. In order to reduce future invasion risk, we suggest reviewing inter-island quarantine measures and continuing community education efforts to reduce human-mediated propagule pressure.     

Invaders at the doorstep: Using species distribution modeling to enhance invasive plant watch lists

Watch lists of invasive species that threaten a particular land management unit are useful tools because they can draw attention to invasive species at the very early stages of invasion when early detection and rapid response efforts are often most successful. However, watch lists typically rely on the subjective selection of invasive species by experts or on the use of spotty occurrence records. Further, incomplete records of invasive plant occurrences bias these watch lists towards the inclusion of invasive plant species that may already be present in a land management unit, because the occurrences have not been formally integrated into publicly accessible biodiversity databases. However, these problems may be overcome by an iterative approach that guides more complete detection and compilation of invasive plant species records within land management units. To address issues from unobserved or unrecorded occurrences, we combined predicted suitable habitat from species distribution models and aggregated invasive plant occurrence records to develop ranked watch lists of 146 priority invasive plant species on >4000 land management units from five different administrative types within the United States. Based on this analysis, we determined that on average 84% of priority invasive plants with suitable habitat within a given land management unit were as yet unobserved, and that 41% of those were ‘doorstep species’ – found within 50 miles of the unit boundary yet not detected within the unit. Two case studies, developed in collaboration with staff at U.S. Fish and Wildlife Service Refuges, showed that by combining both habitat suitability models and invasive plant occurrence records, we could identify additional problematic invasive plants that had been previously overlooked. Model-based watch lists of ‘doorstep species’ are useful tools because they can objectively alert land managers to threats from invasive plants with high likelihood of establishment.     

Preventing establishment: an inventory of introduced plants in Puerto Villamil, Isabela Island, Galapagos

As part of an island-wide project to identify and eradicate potentially invasive plant species before they become established, a program of inventories is being carried out in the urban and agricultural zones of the four inhabited islands in Galapagos. This study reports the results of the inventory from Puerto Villamil, a coastal village representing the urban zone of Isabela Island. We visited all 1193 village properties to record the presence of the introduced plants. In addition, information was collected from half of the properties to determine evidence for potential invasiveness of the plant species. We recorded 261 vascular taxa, 13 of which were new records for Galapagos. Most of the species were intentionally grown (cultivated) (73.3%) and used principally as ornamentals. The most frequent taxa we encountered were Cocos nucifera (coconut tree) (22.1%) as a cultivated plant and Paspalum vaginatum (salt water couch) (13.2%) as a non cultivated plant. In addition 39 taxa were naturalized. On the basis of the invasiveness study, we recommend five species for eradication (Abutilon dianthum, Datura inoxia, Datura metel, Senna alata and Solanum capsicoides), one species for hybridization studies (Opuntia ficus-indica) and three species for control (Furcraea hexapetala, Leucaena leucocephala and Paspalum vaginatum).     

Inoculation with native soil improves seedling survival and reduces non-native reinvasion in a grassland restoration

Losses of grasslands have been largely attributed to widespread land-use changes, such as conversion to row-crop agriculture. The remaining tallgrass prairie faces further losses due to biological invasions by non-native plant species, often with resultant ecosystem degradation. Of critical concern for conservation, restoration of native grasslands has been met with little success following eradication of non-native plants. In addition to the direct and indirect effects of non-native invasive plants on beneficial soil microbes, management practices targeting invasive species may also negatively affect subsequent restoration efforts. To assess mechanisms limiting germination and survival of native species and to improve native species establishment, we established six replicate plots of each of the following four treatments: (1) inoculated with freshly collected prairie soil with native seeds; (2) inoculated with steam-pasteurized soil with native seeds; (3) noninoculated with native seeds; or (4) noninoculated/nonseeded control. Inoculation with whole soil did not improve seed germination; however, addition of whole soil significantly improved native species survival, compared to pasteurized soil or noninoculated treatments. Inoculation with whole soil significantly decreased reestablishment of non-native invasive Bothriochloa bladhii (Caucasian bluestem); at the end of the growing season, plots receiving whole soil consisted of approximately 30% B. bladhii cover, compared to approximately 80% in plots receiving no soil inoculum. Our results suggest invasion and eradication efforts negatively affect arbuscular mycorrhizal hyphal and spore abundances and soil aggregate stability, and inoculation with locally adapted soil microbial communities can improve metrics of restoration success, including plant species richness and diversity, while decreasing reinvasion by non-native species.     

我国外来入侵生物防控科技进展

随着全球经济一体化的发展,外来入侵生物的危害日益加重。我国针对当前各类重大外来生物的入侵,按照基础研究、共性关键技术与重大产品研发、典型应用示范3个层面,部署了一系列项目,并取得了一定成果:揭示了入侵生物的入侵特性和入侵机理,以及入侵植物与脆弱生态系统的相互作用机制;研发了重大新发农业入侵物种风险评估及防控技术,建立了生物威胁数据库和生物入侵突发事件可视化智能决策支持平台,以及重大入侵动植物的治理模式和技术体系;建立了主要入侵生物标本资源库。今后应以跨境动植物有害生物为主要目标,开展入侵扩散与成灾机制、早期预防预警、快速检测监测、识别追踪溯源、点面拦截狙击、区域防灾减灾等技术研究。     

Successful information exchange between restoration science and practice

The science‐practice gap is often cited as a limitation to successful restoration outcomes; however, the existence of such a gap in information exchange is rarely measured. Here, we quantify the gap by focusing on common recommendations from both scientists (i.e. researchers) and managers (i.e. practitioners, land managers) on what is needed for successful restoration. We surveyed 45 managers associated with 244 invasive species (Tamarix spp.) removal projects across the southwestern U.S. to determine the degree to which they have utilized four strategies advocated by scientists: (1) collaborate widely, (2) monitor beyond cursory visual methods, (3) use a variety of information sources, and (4) consider project goals beyond invasive species removal. Half of these managers were also interviewed to assess managers' perceptions of the role of science in restoration. Twenty‐three scientists specializing in Tamarix‐related research in this region were also surveyed to assess how much they understood and/or shared the concerns of land managers. We found that managers were following scientists' recommendations and that managers' perceptions of the role of science in land management did not have any bearing on the management actions taken. Scientists reported being influenced by managers, and the concerns of scientists and managers were more overlapping than expected. Boundary organizations and river‐wide partnerships were often cited as important in facilitating effective communication between land managers and scientists. A lack of funding for monitoring and for longer‐term projects was cited by both groups as a limitation to incorporating scientists' recommendations into restoration.     

Impacts of the emerald ash borer (EAB) eradication and tree mortality: potential for a secondary spread of invasive plant species

Since the discovery of the emerald ash borer in 2002, eradication efforts have been implemented in an attempt to eliminate or contain the spread of this invasive beetle. The eradication protocol called for the removal of every ash tree within a 0.8 km radius around an infested tree. In 2005 this study was established to identify environmental changes attributed to the eradication program and measure subsequent shifts in forest community composition and structure. We conducted this study in Ohio and compared areas that received the eradication treatment (ash trees cut down), to areas that were left uncut, (ash still standing). The goal of this project was to identify how the plant community is responding in these two areas. The eradication protocol accelerated the formation and size of gaps within the forest and thus increased the duration and intensity of light penetrating through to the forest floor. In addition, the use of track vehicles for removal of cut trees resulted in significant soil compaction. The resultant plant community had greater species diversity (H′). When specific species composition differences were compared, an increase in the establishment of invasive plant species was detected in areas that received eradication efforts compared to those that did not. Invasive species accounted for 18.7% of the total herbaceous cover in this highly disturbed environment which included Cirsium arvense, Rhamnus cathartica and 2 species of Lonicera. In contrast, invasive species accounted for <1% of the total herbaceous cover in the undisturbed uncut areas.     

Predicting invasiveness in exotic species: do subtropical native and invasive exotic aquatic plants differ in their growth responses to macronutrients?

We investigated whether plasticity in growth responses to nutrients could predict invasive potential in aquatic plants by measuring the effects of nutrients on growth of eight non-invasive native and six invasive exotic aquatic plant species. Nutrients were applied at two levels, approximating those found in urbanized and relatively undisturbed catchments, respectively. To identify systematic differences between invasive and non-invasive species, we compared the growth responses (total biomass, root:shoot allocation, and photosynthetic surface area) of native species with those of related invasive species after 13 weeks growth. The results were used to seek evidence of invasive potential among four recently naturalized species. There was evidence that invasive species tend to accumulate more biomass than native species ( P  = 0.0788). Root:shoot allocation did not differ between native and invasive plant species, nor was allocation affected by nutrient addition. However, the photosynthetic surface area of invasive species tended to increase with nutrients, whereas it did not among native species ( P  = 0.0658). Of the four recently naturalized species, Hydrocleys nymphoides showed the same nutrient-related plasticity in photosynthetic area displayed by known invasive species. Cyperus papyrus showed a strong reduction in photosynthetic area with increased nutrients. H. nymphoides and C. papyrus also accumulated more biomass than their native relatives. H. nymphoides possesses both of the traits we found to be associated with invasiveness, and should thus be regarded as likely to be invasive.     

Eradication of Feral Pigs From Pinnacles National Monument

Abstract: Feral pigs (Sus scrofa) have caused considerable damage where they have been introduced around the world. At Pinnacles National Monument, California, USA, managers were concerned that feral pigs were damaging wetland habitats, reducing oak regeneration, competing with native wildlife, and dispersing nonnative plant species through soil disturbance. To address these threats the National Park Service constructed an exclosure around 57 km² of monument land and through cooperation with the Institute for Wildlife Studies eradicated all feral pigs within the area. Trapping, ground-hunting, hunting dogs, and Judas techniques were used to remove feral pigs. Trapping techniques removed most pigs, but a combination of techniques was required to cause eradication. A series of bait sites and transects across the monument helped focus removal efforts and facilitated detection of the last remaining feral pigs in the exclosure. Consistent funding and cooperation from the National Park Service allowed for a seamless and comprehensive program that provided intensive removal of feral pigs. The successful eradication of feral pigs at Pinnacles National Monument should encourage managers in other areas to implement future control or eradication programs.     

Evaluating the “recovery level” of endangered species without prior information before alien invasion

For maintaining social and financial support for eradication programs of invasive species, quantitative assessment of recovery of native species or ecosystems is important because it provides a measurable parameter of success. However, setting a concrete goal for recovery is often difficult owing to lack of information prior to the introduction of invaders. Here, we present a novel approach to evaluate the achievement level of invasive predator management based on the carrying capacity of endangered species estimated using long‐term monitoring data. In Amami‐Oshima Island, Japan, where the eradication project of introduced small Indian mongoose is ongoing since 2000, we surveyed the population densities of four endangered species threatened by the mongoose (Amami rabbit, the Otton frog, Amami tip‐nosed frog, and Amami Ishikawa's frog) at four time points ranging from 2003 to 2011. We estimated the carrying capacities of these species using the logistic growth model combined with the effects of mongoose predation and environmental heterogeneity. All species showed clear tendencies toward increasing their density in line with decreased mongoose density, and they exhibited density‐dependent population growth. The estimated carrying capacities of three endangered species had small confidence intervals enough to measure recovery levels by the mongoose management. The population density of each endangered species has recovered to the level of the carrying capacity at about 20–40% of all sites, whereas no individuals were observed at more than 25% of all sites. We propose that the present approach involving appropriate monitoring data of native organism populations will be widely applicable to various eradication projects and provide unambiguous goals for management of invasive species.     

Native seed addition as an effective tool for post-invasion restoration

Invasive plant species reduce biodiversity, alter ecosystem processes, and cause economic losses. Control of invasive plants is therefore highly desired by land managers and policy makers. However, invasive plant control strategies frequently fail, partly because management often concentrates only on the eradication of invasive plants and not on revegetation with native species that use the available resources and prevent reinvasion. In this study, we focused on the intracontinental invader Rumex alpinus L., which was introduced by humans from the Alps to the lower mountains of Central Europe, where it has spread to semi-natural meadows, suppresses local biodiversity, and reduces the quality of hay used as cattle fodder. The species can be effectively removed using herbicide, but this leaves behind a persistent seed bank. Without further treatment, the invader rapidly regenerates and reinvades the area. We supplemented the herbicide treatment by adding the seeds of native grasses. Addition of native-seed effectively suppressed the regeneration of the invader from the seed bank, reduced its biomass, and consequently, prevented massive reinvasion. While the invader removal was successful, the restored community remained species-poor because the dense sward of native grasses blocked the regeneration of native forbs from the seed bank. Nevertheless, the addition of native seed proved to be an effective tool in preventing reinvasion after the eradication of the invasive plant.     

Biologische Invasionen

Biological invasions Translocation of alien plant and animal species by human activities is one of the most serious environmental problems of our time. Following a period of acclimatisation, expansion is caused now by escapees and blind passageers. Only a small percentage of these alien species is able to establish themselves in the new habitats and even less become invasive and serious pests. But they cause enormous ecological and economical damage and sometimes necessitate expansive eradication programs.     

Eradication revisited: dealing with exotic species

Invasions of nonindigenous species threaten native biodiversity, ecosystem functioning, animal and plant health, and human economies. The best solution is to prevent the introduction of exotic organisms but, once introduced, eradication might be feasible. The potential ecological and social ramifications of eradication projects make them controversial; however, these programs provide unique opportunities for experimental ecological studies. Deciding whether to attempt eradication is not simple and alternative approaches might be preferable in some situations.     

Evaluating the Feasibility of Eradicating an Invasion

The detectability of invasive organisms influences the costs and benefits of alternative control strategies, and the feasibility of eradicating an infestation. Search theory offers a mathematically rigorous framework for defining and measuring detectability taking account of searcher ability, biological factors and the search environment. In this paper, invasive species detectability is incorporated into a population simulation model. The model is applied to a base set of parameter values that represent reasonable values for a hypothetical weed. The analysis shows the effects of detectability and search effort on the duration of an eradication program. For a given level of detectability and search time, the analysis shows that the variables with the greatest influence on the duration of the eradication effort are search speed, kill efficiency, germination rate and seed longevity. Monte Carlo simulations are performed on a set of four weed scenarios, involving different combinations of plant longevity, seed longevity and plant fecundity. Results of these simulations are presented as probability distributions and allow us to calculate how the probability of eradication will be affected by search strategy.     

Are invaders moving targets? The generality and persistence of advantages in size, reproduction, and enemy release in invasive plant species with time since introduction

Successful plant invasions are often attributed to increased plant size, reproduction, or release from natural enemies, but the generality and persistence of these patterns remains widely debated. Meta-analysis was used to quantitatively assess invasive plant performance and release from enemy damage and how these change with residence time and geographic distribution. Invasive plants were compared either in their introduced and home ranges or with native congeners in the introduced range. Invasive plants in the introduced range were generally larger, allocated more to reproduction, and had lower levels of herbivore damage compared with conspecifics in the home range; pathogen attack, however, varied widely. In congener comparisons, invasive and native plants did not differ in size or herbivory, but invaders did allocate less to reproduction and had lower levels of pathogen damage. Time since introduction was a significant nonlinear predictor of enemy release for both herbivores and pathogens, with initial release in recently arrived species and little to no release after 50 to 200 years. Geographic distribution was also a significant nonlinear predictor of enemy release. The observed nonlinear relationships are consistent with dynamic invasions and may define targets for eradication efforts if these patterns hold up for individual species.     

Unusual suspects in the usual places: a phylo-climatic framework to identify potential future invasive species

A framework for identifying species that may become invasive under future climate conditions is presented, based on invader attributes and biogeography in combination with projections of future climate. We illustrate the framework using the CLIMEX niche model to identify future climate suitability for three species of Hawkweed that are currently present in the Australian Alps region and related species that are present in the neighbouring region. Potential source regions under future climate conditions are identified, and species from those emerging risk areas are identified. We use dynamically downscaled climate projections to complement global analyses and provide fine-scale projections of suitable climate for current and future (2070–2099) conditions at the regional scale. Changing climatic conditions may reduce the suitability for some invasive species and improve it for others. Invasive species with distributions strongly determined by climate, where the projected future climate is highly suitable, are those with the greatest potential to be future invasive species in the region. As the Alps region becomes warmer and drier, many more regions of the world become potential sources of invasive species, although only one additional species of Hawkweed is identified as an emerging risk. However, in the longer term, as the species in these areas respond to global climate change, the potential source areas contract again to match higher altitude regions. Knowledge of future climate suitability, based on species-specific climatic tolerances, is a useful step towards prioritising management responses such as targeted eradication and early intervention to prevent the spread of future invasive species.     

Possible Impacts of the Invasive Plant Rubus niveus on the Native Vegetation of the Scalesia Forest in the Galapagos Islands

Originally from Asia, Rubus niveus has become one of the most widespread invasive plant species in the Galapagos Islands. It has invaded open vegetation, shrubland and forest alike. It forms dense thickets up to 4 m high, appearing to displace native vegetation, and threaten the integrity of several native communities. This study used correlation analysis between a R. niveus cover gradient and a number of biotic (vascular plant species richness, cover and vegetation structure) and abiotic (light and soil properties) parameters to help understand possible impacts in one of the last remaining fragments of the Scalesia forest in Santa Cruz Island, Galapagos. Higher cover of R. niveus was associated with significantly lower native species richness and cover, and a different forest structure. Results illustrated that 60% R. niveus cover could be considered a threshold for these impacts. We suggest that a maximum of 40% R. niveus cover could be a suitable management target.     

Consumers and establishment limitations contribute more than competitive interactions in sustaining dominance of the exotic herb garlic mustard in a Wisconsin, USA forest

The understory is a diverse component of temperate forest ecosystems, contributing significantly to forest ecosystem services. Despite their importance, many native understories face stresses from current and past land use, habitat fragmentation, invasive species, and overabundant herbivores. We established a four block, three factor experiment to evaluate the relative contribution of native plant establishment, competitive effects from the invasive herb garlic mustard (Alliaria petiolata), and herbivory from white-tailed deer (Odocoileus virginianus) to better understand the mechanisms promoting low native plant richness and cover and understory dominance by the biennial exotic herb garlic mustard in a NE Wisconsin, USA forest. Four years of garlic mustard removal failed to increase native plant richness or cover in non-restored plots. However, deer access and the introduction of native plants (restoration treatment) both significantly enhanced native plant cover and richness, with restored species cover in fenced plots approximately 216 % that of open-access plots, and the majority of these species flowered at significantly higher proportions inside of fenced areas. In contrast, deer access did not significantly alter the cover, or seed production of garlic mustard. We also found no significant effect of garlic mustard presence on the cover or flowering of restored native species. We conclude that multiple factors, including limited natural establishment by native species and selective herbivory drove low native, high exotic dominance at our site, suggesting that a shift in focus from invasive plant removal to combined native plant restoration and herbivore control is needed to maximize the recovery of this degraded forest understory.     

A mink-free GB: perspectives on eradicating American mink Neovison vison from Great Britain and its islands

This paper examines the case for, and plausibility of, eradicating American mink Neovison vison from mainland Great Britain and its associated offshore islands. This invasive species causes extensive damage to native fauna throughout Europe, and the UK Government is obliged to eradicate it, if feasible, under the Bern Convention. Current mink control buys time, but is patchy and dependent on substantial funding in perpetuity. If enacted, eradication would be cheaper in the long term and much more effective in preserving native wildlife. The methodology of an eradication campaign is explored, together with risks, challenges, and a tentative timeline and cost. We judge that mink eradication is now logistically feasible, due to technological developments and experience gained from landscape-scale control. Using live traps fitted with electronic sensors – ‘smart’ traps – as the primary means of catching mink would render the campaign efficient, humane and free of non-target mortality and negative environmental impacts. The ecological benefits of mink eradication would be profound, including greatly improving prospects for water vole Arvicola amphibius populations. Reinvasion is highly unlikely. The greatest logistical challenge is probably removing mink from Scottish west coast islands. Eradication might take around a decade and be dependent on co-ordination between many conservation, fishing, farming, and water-related organisations, together with the consent of landowners. By adding alarms to existing mink traps, land and water managers can pave the way to eradication now. A mink-free Great Britain would plausibly cost tens of millions of pounds, against which could be set the limitless future costs of mink control. Such a campaign would be by far the world's largest invasive predator eradication project by geographical area and would set a precedent for citizen-led conservation action globally. Regional trials would be extremely valuable in determining the costs and practicality of a GB-wide campaign.     

Integrating seabird restoration and mammal eradication programs on islands to maximize conservation gains

Colonial nesting seabirds frequently drive island ecosystem biodiversity by maintaining ecosystem functioning and community dynamics. Invasive mammal introductions to most of the world’s islands have ravaged insular seabird populations and had associated devastating ecosystem-wide effects. Eradication programs remove invasive mammals from islands, with the goal of conserving and restoring island species and systems. However, most eradication programs rely almost exclusively on passive seabird recovery to achieve these goals. Unfortunately, the life histories of most seabird species are not conducive to passive recovery within a contemporary timeframe. Seabird restoration techniques can effectively overcome life history related issues and significantly reduce recovery times for insular seabird populations, thereby reducing associated ecosystem-wide recovery times. By integrating seabird restoration and eradication programs, practitioners can maximize conservation gains, expand funding opportunities, and restore island ecosystems and the biodiversity they support.