Risk management to prioritise the eradication of new and emerging invasive non-native species

Robust tools are needed to prioritise the management of invasive non-native species (INNS). Risk assessment is commonly used to prioritise INNS, but fails to take into account the feasibility of management. Risk management provides a structured evaluation of management options, but has received little attention to date. We present a risk management scheme to assess the feasibility of eradicating INNS that can be used, in conjunction with existing risk assessment schemes, to support prioritisation. The Non-Native Risk Management scheme (NNRM) can be applied to any predefined area and any taxa. It uses semi-quantitative response and confidence scores to assess seven key criteria: Effectiveness, Practicality, Cost, Impact, Acceptability, Window of opportunity and Likelihood of re-invasion. Scores are elicited using expert judgement, supported by available evidence, and consensus-building methods. We applied the NNRM to forty-one INNS that threaten Great Britain (GB). Thirty-three experts provided scores, with overall feasibility of eradication assessed as ‘very high’ (8 species), ‘high’ (6), ‘medium’ (8), ‘low’ (10) and ‘very low’ (9). The feasibility of eradicating terrestrial species was higher than aquatic species. Lotic freshwater and marine species scored particularly low. Combining risk management and existing risk assessment scores identified six established species as priorities for eradication. A further six species that are not yet established were identified as priorities for eradication on arrival as part of contingency planning. The NNRM is one of the first INNS risk management schemes that can be used with existing risk assessments to prioritise INNS eradication in any area.     

Analysis of the Trojan Y-Chromosome eradication strategy for an invasive species

The Trojan Y-Chromosome (TYC) strategy, an autocidal genetic biocontrol method, has been proposed to eliminate invasive alien species. In this work, we analyze the dynamical system model of the TYC strategy, with the aim of studying the viability of the TYC eradication and control strategy of an invasive species. In particular, because the constant introduction of sex-reversed trojan females for all time is not possible in practice, there arises the question: What happens if this injection is stopped after some time? Can the invasive species recover? To answer that question, we perform a rigorous bifurcation analysis and study the basin of attraction of the recovery state and the extinction state in both the full model and a certain reduced model. In particular, we find a theoretical condition for the eradication strategy to work. Additionally, the consideration of an Allee effect and the possibility of a Turing instability are also studied in this work. Our results show that: (1) with the inclusion of an Allee effect, the number of the invasive females is not required to be very low when the introduction of the sex-reversed trojan females is stopped, and the remaining Trojan Y-Chromosome population is sufficient to induce extinction of the invasive females; (2) incorporating diffusive spatial spread does not produce a Turing instability, which would have suggested that the TYC eradication strategy might be only partially effective, leaving a patchy distribution of the invasive species.     

Evaluation of machine learning methods for predicting eradication of aquatic invasive species

In the work, we evaluate the performance of machine learning approaches for predicting successful eradication of aquatic invasive species (AIS) and assess the extent to which eradication of an invasive species depends on the certain specified ecological features of the target ecosystem and/or features that characterize the planned intervention. We studied the outcomes of 143 planned attempts for eradicating AIS, where each attempt was described by ecological and eradication-strategy-related features of the target ecosystem. We considered several machine learning approaches to determine whether one could produce a classifier that accurately predicts weather an invasive species will be eradicated. To assess each learner’s performance, we examined its tenfold cross-validated prediction accuracy as well as the false positive rate, the F-measure, and the Area Under the ROC Curve. We also used Kaplan–Meier survival analysis to determine which features are relevant to predicting the time required for each eradication program. Across the five typical machine learning approaches, our analysis suggests that learners trained by the decision tree work well, and have the best performance. In particular, by examining the trained decision tree model, we found that if an occupied area was not large and/or containments of AIS dispersal were employed, the eradication of AIS was likely to be successful. We also trained decision tree models over only the ecological features and found that their performances were comparable with that of models trained using all features. As our trained decision tree models are accurate, decision makers can use them to estimate the result of the proposed actions before they commit to which specific strategy should be applied.     

Pheromone trapping models for insect pest control

Pheromones have recently been suggested for use in insect pest control. We formulate a discrete version of a model with virgin females (or female equivalent of pheromone) in traps, and explore conditions under which this mechanism can eradicate the pest. Our model is density independent, thus when eradication is not possible, the pest increases without bound, in reality density dependent effects limit population growth. Successive refinements incorporating various features, show that delayed mating together with monogamy has a strong influence on the outcome, whereas other aspects of mating behaviour are relatively unimportant. All our models show that when males are in excess control is impossible but when some virgins are left unmated each day the outcome depends on the parameters. As the birth rate or survivorship increase, control by this method becomes more difficult.     

外来入侵种——苹果绵蚜在中国的适生区预测

苹果绵蚜Eriosoma lanigerum(Hausmann)是我国重要的检疫性害虫,主要为害苹果、海棠等苹果属(Malus Mill.)植物。目前,该种害虫已在我国一些苹果主产区迅速扩散,并给我国的苹果产业造成了较为严重的经济损失。为了对其进行有效监控,控制其蔓延,制定合理的防治策略,本研究利用GARP和MAXENT两种生态位模型,结合其寄主地理分布,预测苹果绵蚜在我国的潜在地理分布区。研究结果表明:GARP和MAXENT预测结果相似,但前者预测面积比后者广泛。苹果绵蚜在我国的最适适生区主要分布在东北(辽宁南部)、华北(河北东、南部、北京、天津和山西南部)、华东(山东大部)、华中(河南北部)和西北(陕西中部)。另外,河北南部、山东和河南南部、甘肃东部、四川中南部、陕西大部、云南与西藏的零星地区是苹果绵蚜的中度适生区;黑龙江、吉林、新疆等20个省份(市、自治区)的全境是苹果绵蚜低度适生区或不适生区。此外,刀切法(Jackknifetest)检验结果表明,1月份平均最高温是影响苹果绵蚜分布最重要的环境变量。最后,提出几点管理苹果绵蚜的方法和防治策略,避免该种害虫传播或入侵到其它苹果产区。     

Landscape diversity slows the spread of an invasive forest pest species

According to the associational resistance hypothesis, diverse habitats provide better resistance to biological invasions than monocultures. Host‐plant abundance has been shown to affect the range expansion of invasive pests, but the effect of landscape diversity (i.e. density of host/non‐host patches and diversity of forest habitat patches) on invasions remains largely untested. We used boundary displacement models and boosted regression tree analyses to investigate the effects of landscape diversity on the invasion of Corsica by the maritime pine bast scale Matsucoccus feytaudi over an 18‐yr period. Taking the passive wind dispersal of the scale into account, we showed that open habitats and connectivity between host patches accelerated spread by up to 13%, whereas landscapes with high tree diversity and a high density of non‐host trees decreased scale spread by up to 14%. We suggest a new mechanism for such associational resistance to pest invasion at the landscape level, which we term ‘the pitfall effect’.     

Economics of invasive species policy and management

This article examines the use of economic analysis to inform bioinvasion management, with particular focus on forest resources. Economics is key for understanding invasion processes, impacts, and decision-making. Biological invasions are driven by and affect economic activities at multiple scales and stages of an invasion. Bioeconomic modeling seeks to inform how resources can be optimally allocated across invasion management activities—including prevention, surveillance programs for early detection and management, and controlling invasion populations and spread—to minimize the long-term costs and damages. Economic analysis facilitates understanding of decisions by public and private decision-makers, gaps between these, and the design of policies to achieve socially desirable outcomes. Private decision-makers may undercontrol invasions relative to socially optimal levels, because they generally account for their own costs and benefits of control but less often for broader ecosystem impacts or future spread across the landscape. Economic analysis considers approaches for increasing private invasion management and evaluates feedbacks between ecological and economic systems that can affect policy outcomes. Future research should continue evaluation and design of control strategies across the biosecurity continuum and across species to enhance cost-effectiveness, better incorporate uncertainty into policy design, increase focus on incentives and behavioral tools to influence private behaviors that affect invasion spread, and incorporate invasive species consideration within broader systems-focused science. In addition, challenges in valuing biodiversity and ecosystem service impacts and the costs and effectiveness of control measures are key data gaps. Greater collaboration between decision-makers and researchers will facilitate development and communication of usable economic research.     

Evaluation system for management measures of invasive alien species

The introduction and spread of invasive alien species is a serious threat to ecosystem structures, functions and services worldwide. At enormous cost and effort, attempts are being made to stop and reduce the ongoing appearance of alien species in ecosystems to protect the regional and native biodiversity. Still, management of invasive alien species in particular is often not successful. One reason is a lack of robust toolkits for the management of these species. Guidance on measures which are efficient and effective and which have no negative impact on the environment and human health is urgently needed for decision-making. As a result of an expert workshop, we present a set of three evaluation criteria: effectiveness, ecological impact, and impact on human health. These criteria allow an evaluation of management measures for the prevention, eradication, control and utilisation/disposal of invasive alien species for nature conservation purposes. We applied this evaluation system for 168 invasive and potentially invasive alien species of five taxonomic groups (fungi, non-vascular plants, vascular plants, invertebrates and vertebrates) involving 3619 different management measures. The evaluation of management measures and resulting recommendations for their application are a necessary basis for appropriate, ecologically necessary and professionally sound management. This new approach provides an essential framework for future decisions on management measures, for example in accordance with the provisions of the new Regulation (EU) No 1143/2014 of the European Parliament and of the Council of 22 October 2014 on the prevention and management of the introduction and spread of invasive alien species.     

Controlling sympatric pest mammal populations in New Zealand with self-resetting,toxicant-free traps: a promising tool for invasive species management

The control of invasive mammals is a key challenge for conservation biologists and management practitioners, particularly in locations with a high risk of re-invasion. Here, we tested whether sympatric populations of invasive mammal species could be suppressed simultaneously using self-resetting traps and toxicant-free baits. We used binomial GLM models to examine whether an intermittent pattern of trap checks could be used to predict kill rates under conditions of heavy scavenging. We also estimated the financial costs associated with deployment and maintenance of the multi-kill traps over 10 years, compared with those of aerial and ground-based poisoning methods. Trapping reduced the activity of all target species at the study site to ≤10 % within 9 months. Our results show that self-resetting traps are a promising tool for controlling multiple species of pest mammals on an island with a high potential for re-invasion.     

Multiple attractors of host-parasitoid models with integrated pest management strategies: eradication, persistence and outbreak

Host-parasitoid models including integrated pest management (IPM) interventions with impulsive effects at both fixed and unfixed times were analyzed with regard to host-eradication, host-parasitoid persistence and host-outbreak solutions. The host-eradication periodic solution with fixed moments is globally stable if the host’s intrinsic growth rate is less than the summation of the mean host-killing rate and the mean parasitization rate during the impulsive period. Solutions for all three categories can coexist, with switch-like transitions among their attractors showing that varying dosages and frequencies of insecticide applications and the numbers of parasitoids released are crucial. Periodic solutions also exist for models with unfixed moments for which the maximum amplitude of the host is less than the economic threshold. The dosages and frequencies of IPM interventions for these solutions are much reduced in comparison with the pest-eradication periodic solution. Our results, which are robust to inclusion of stochastic effects and with a wide range of parameter values, confirm that IPM is more effective than any single control tactic.     

Evaluating management options for aquatic invasive species: concepts and methods

In analyses that attempt to estimate the costs of species invasions, it has been typical to report the costs of management and/or to multiply per-unit costs by the number affected to arrive at a total. These estimates are of limited value for most policy questions. We start our discussion by recognizing that biological pollutants such as aquatic invasive species are like conventional pollutants in important ways and appeal to the well-developed literature on conventional pollution to guide our thinking into how best to conceptualize the problem. We use a standard pollution control framework to identify the margins over which costs and benefits should be estimated to guide wise decision-making. We then use examples from the literature to illustrate how transactions in related markets can be used to estimate the benefits of management. The roles of adaptation, mitigation, and species population growth have particular relevance and are highlighted. In the final section of the paper, we think through the conditions under which investing in genetic biocontrol methods would be economically justified.     

Optimal invasive species management under multiple uncertainties

The management programs for invasive species have been proposed and implemented in many regions of the world. However, practitioners and scientists have not reached a consensus on how to control them yet. One reason is the presence of various uncertainties associated with the management. To give some guidance on this issue, we characterize the optimal strategy by developing a dynamic model of invasive species management under uncertainties. In particular, focusing on (i) growth uncertainty and (ii) measurement uncertainty, we identify how these uncertainties affect optimal strategies and value functions. Our results suggest that a rise in growth uncertainty causes the optimal strategy to involve more restrained removals and the corresponding value function to shift up. Furthermore, we also find that a rise in measurement uncertainty affects optimal policies in a highly complex manner, but their corresponding value functions generally shift down as measurement uncertainty rises. Overall, a rise in growth uncertainty can be beneficial, while a rise in measurement uncertainty brings about an adverse effect, which implies the potential gain of precisely identifying the current stock size of invasive species.     

A systematic approach for prioritizing multiple management actions for invasive species

The successful management and eradication of invasive species is often constrained by insufficient or inconsistent funding. Consequently, managers are usually forced to select a subset of infested areas to manage. Further, managers may be unaware of the most effective methods for identifying priority areas and so are unable to maximize the effectiveness of their limited resources. To address these issues, we present a spatially explicit decision method that can be used to identify actions to manage invasive species while minimizing costs and the likelihood of reinvasion. We apply the method to a real-world management scenario, aimed at managing an invasive aquatic macrophyte, olive hymenachne (Hymenachne amplexicaulis), which is one of the most threatening invasives in tropical Australia, affecting water quality, freshwater biodiversity, and fisheries.