Risk Of Reinvasion Research Articles

RISK ASSESSMENT FOR THE DEVELOPMENT OF THE EXEMPLIFIED TERRITORIES

The paper explores the risks associated with exempted and liberated territories that were previously used for certain industrial, commercial, agricultural or other activities. Such territories were captured or used by military forces during the war and then liberated or abandoned and left unattended, or were disturbed by natural disasters, man-made accidents, etc. The aim of the article is to analyze the possibility of their further use and rehabilitation. The following indicators of risk sources can be identified in such areas: presence of explosive objects; level of soil and water contamination; presence of chemical, biological or radiation contamination; degree of damage to infrastructure and building structures; risk of dangerous situations and accidents; impact on the health and safety of the local population; possibility of spreading infectious diseases; presence of unexploded or uncontrolled explosive materials; risk of re-invasion by enemy forces; potential environmental damage; and potential environmental impact. Based on the analysis of these indicators, they were summarized and grouped into six main risk indicators: demining of territories; efficiency of demining and disposal of remnants of military equipment, mines, etc.; safety and efficiency of demining and disposal technologies; degree of contamination of the demined territories after demining and disposal; level of safety assessment of the population living in these territories; return of vital infrastructure. An expert assessment methodology was applied, which includes an analysis of the severity of the consequences and the likelihood of their occurrence. The risks were ranked using the method of pairwise comparisons. The results of the study can be used to develop strategies for the further use and rehabilitation of the affected areas. The results of the study indicate the need for systematic monitoring and control of the exempted and liberated territories in order to prevent possible environmental and socio-economic problems. To ensure sustainable development and conservation of natural resources, due attention should be paid to the issues of environmental safety and rehabilitation of these territories. Further research in this area will allow developing more effective strategies for the use and rehabilitation of exempted areas, taking into account current environmental and socio-economic challenges.

Eradicating an invasive mammal requires local elimination and reduced reinvasion from an urban source population.

Invasive mammal eradications are increasingly attempted across large, complex landscapes. Sequentially controlled management zones can be at risk of reinvasion from adjacent uncontrolled areas, and managers must weigh the relative benefits of ensuring complete elimination from a zone or minimizing reinvasion risk. This is complicated in urban areas, where habitat heterogeneity and a lack of baseline ecological knowledge increase uncertainty. We applied a spatial agent-based model to predict the reinvasion of a well-studied species, the brushtail possum (Trichosurus vulpecula), across an urban area onto a peninsula that is the site of an elimination campaign in Aotearoa New Zealand. We represented fine-scale urban habitat heterogeneity in a land cover layer and tested management scenarios that varied four factors: the density of possums remaining following an elimination attempt, the maintenance trap density on the peninsula, and effort expended toward preventing reinvasion by means of a high-density trap buffer at the peninsula isthmus or control of the source population adjacent to the peninsula. We found that achieving complete elimination on the peninsula was crucial to avoid rapid repopulation. The urban isthmus was predicted to act as a landscape barrier and restrict immigration onto the peninsula, but reliance on this barrier alone would fail to prevent repopulation. In combination, complete elimination, buffer zone, and source population control could reduce the probability of possum repopulation to near zero. Our findings support urban landscape barriers as one tool for sequential invasive mammal elimination but reaffirm that novel methods to expose residual individuals to control will be necessary to secure elimination in management zones. Work to characterize the urban ecology of many invasive mammals is still needed.

Prioritising the eradication of invasive species from island archipelagos with high reinvasion risk

Abstract Eradicating invasive species from islands is a proven method for safeguarding threatened and endangered species from extinction. Island eradications can deliver lasting benefits, but require large up‐front expenditure of limited conservation resources. The choice of islands must therefore be prioritised. Numerous tools have been developed to prioritise island eradications, but none fully account for the risk of those eradicated species later returning to the island: reinvasion. In this paper, we develop a prioritisation method for island eradications that accounts for the complexity of the reinvasion process. By merging spatially explicit metapopulation modelling with stochastic dynamic optimisation techniques, we construct a decision‐support tool that optimises conservation outcomes in the presence of reinvasion risk. We applied this tool to two different case studies—rat (Rattus rattus) invasions in the Seaforth archipelago in New Zealand, and cane toad (Rhinella marina) invasions in the Dampier archipelago in Australia—to illustrate how state‐dependent optimal policies can maximise expected conservation gains. In both case studies, incorporating reinvasion risk dramatically altered the optimal order of island eradications, and improved the potential conservation benefits. The increase in benefits was larger in Dampier than Seaforth (42% improvement versus 6%), as a consequence of both the characteristics of the invasive species, and the arrangement of the islands. Synthesis and applications. Our results illustrate the potential consequences of ignoring reinvasion risk. We recommend that reinvasion risk be explicitly included in any island eradication prioritisation involving an archipelago, particularly when some islands are close to the mainland.

Coupling Scirpus recruitment with Spartina control guarantees recolonization of native sedges in coastal wetlands

Recruiting native coastal vegetation and preventing the reinvasion of exotic Spartina alterniflora is a major challenge in China, due to harsh tidal environment for vegetation establishment and rapid Spartina colonization. This paper first reviewed the revegetation course of native Scirpus mariqueter in a coastal wetland in the Yangtze Estuary, where the adjacent Spartina was effectively eliminated. From 2014 to 2019, the area of planted Scirpus increased by 26.7 times, and the plant density and biomass growth amounted to the levels of mature sedge community. The establishment of Scirpus promoted the sedimentary accretion with an annual sedimentary rate of 9.2 cm yr−1, which was significantly higher than that in the mudflat. Six years of monitoring revealed that the revegetation approach with belowground propagules (corms) was effective for Scirpus establishment under strong hydrodynamic disturbances in the tidal mudflat because the morphology and germination rate of corms benefited the anchoring function of seedlings. Both recruited Scirpus and the original community expanded constantly due to positive feedback between plant progradation and sedimentary accretion. Then, we implemented a model simulation under the scenario of Spartina retention. The prediction showed that the high-speed invasion of Spartina would colonize and replace the whole Scirpus community in the study area during the period of 2014–2019. Hence, our results highlighted the importance of coupling Scirpus recruitment with Spartina eradication in guaranteeing recolonization of native coastal sedges. As a long-lasting management strategy, unremitting field monitoring and assistant decision-making tools (such as the forecasting models) on Spartina reinvasion risk are highly suggested for preserving the restoration of native marshes.

Common deficiencies of actions for managing invasive alien species: a decision-support checklist

Despite the increasing number of invasive species, protocols devoted to assess the feasibility (i.e., probability of success or failure) of management actions in the field are scarce, yet success depends on a broad scope of issues beyond the biology of species and the ecosystem to be managed. In this paper we make a retrospective analysis of 90 actions and management proposals developed in Andalusia (southern Spain) in 2004 to 2018. Actions included 59 terrestrial and aquatic taxa. We identified items that in case of deficiency were responsible for either the rejection of action proposals (n = 44) or failure of implemented actions for which the goal was not achieved (n = 22). The most frequent deficiencies included the absence of funding during the necessary time to achieve the goals, the risk of reinvasion and an insufficient removal rate to achieve the specific objective. Based on the deficiencies found, we built a comprehensive, broad-scope compliance checklist to assist decision-makers to identify deficiencies before action. In addition, implemented actions for which the goal was achieved (n = 24) were used for validating the checklist. The checklist contains 40 items related to IAS features, administrative features, methodology effectiveness, efficiency and impacts of the action, and invaded ecosystem features. The checklist is valid across all taxa and habitats. The use of this checklist will help reduce the degree of arbitrariness and subjectivity of actions aimed at managing IAS, and a more efficient use of resources.

Quantifying site-level usage and certainty of absence for an invasive species through occupancy analysis of camera-trap data

Efficient implementation of management programs for invasive species depends on accurate surveillance for guiding prioritization of surveillance and control resources in space and time. Occupancy probabilities can be used to determine where surveillance should occur. Conversely, knowledge of the certainty of site-level absence is of special interest in situations where the objective is to completely remove populations despite substantial risk of re-invasion. Indeed, the decision to shift from emphasizing control activities over the full range to emphasizing reinvasion prevention, surveillance, and response near the borders, depends on accurate knowledge of absence across space. We used a dynamic occupancy model to monitor changes in the distribution of an invasive species, feral swine (Sus scrofa), based on camera-trap data collected as part of a management program from June 2014 to January 2016 in San Diego County, California. Site usage of feral swine declined overall. The most informative predictors of site usage were spatial (latitude and longitude). Site-level non-usage rates increased over time and in response to management removal efforts; and site-level usage rates were heavily impacted by having neighboring sites that were used. Combining the detection probability estimated from the occupancy model and Bayes Theorem, we demonstrated how certainty of local (site-level) absence can be estimated iteratively in time in areas with negative surveillance (no detections) data. Our framework provides a means for using management-based surveillance data to quantify certainty of site-level absence of an invasive species, allowing for adaptive prioritization of surveillance and control resources. Our approach is flexible for application to other species and types of surveillance (e.g., track-plates, eDNA).

What we don’t seed: the role of long-lived seed banks as hidden legacies of invasive plants

Acacia dealbata is an invasive south-eastern Australian tree that produces a persistent soil seed bank. In order to characterize the seed bank in plots invaded by A. dealbata and to understand its implications for management and re-invasion risk, density, germinability, and viability of the seed bank were evaluated in five sites in central Portugal. Soil samples were collected in A. dealbata invaded plots and adjacent areas and screened for seeds, which were then quantified and germinated at 25 °C. A subset of seeds was first exposed to 60 °C to assess the effect of high soil temperature on dormancy breaking. Variables influencing differences between sites were explored with generalized linear mixed models with a Poisson distribution. Inside A. dealbata invaded plots the seed bank averaged 4608 seeds/m2, reaching up to 62,747 seeds/m2; in adjacent areas, up to 14 m from the plots, only 9 seeds/m2 were found. Seed bank densities were mostly influenced by stoniness, number of fires in the last 10 years, and density of trees and roots. Almost 90% of seeds were viable, but only 8.6% germinated without treatment. Nearly 70% of seeds exposed to 60 °C germinated without any physical stimulation, suggesting that high soil temperatures can effectively break seed dormancy. The high density and viability of A. dealbata’s seed bank and its ability to disperse seeds far from the parent plants contribute to the species’ invasive success. These features combined with heat events that can overcome seed dormancy need to be considered in the management of this species.

Eradication of invasive Carpobrotus sp.: effects on soil and vegetation

AbstractInvasive species management (eradication or control) can be used to promote native plant restoration. The objective of this study is to evaluate different treatments to guide the selection of future modalities for the eradication (i.e. elimination of all individuals in a population) of Carpobrotus sp. from a strict nature reserve. Two removal methods were tested: (1) living Carpobrotus removal; (2) living Carpobrotus and litter removal. To assess the effectiveness of each treatment, we studied the recolonization of native vegetation, the recolonization of Carpobrotus, and soil erosion and compared these metrics to those taken in native vegetation and in patches of intact Carpobrotus. We also tested the capacity of a 50‐cm‐wide Carpobrotus strip to retain soil. The removal of Carpobrotus together with its litter led to high rates of soil erosion. The Carpobrotus strips were found to retain the soil rather well. Removing live Carpobrotus while leaving its litter in place reduced soil erosion and led to higher native plant species recolonization. The composition of the vegetation 10 months after applying the treatments was biased in favor of native pioneer species. These are typically the first species to establish (Aetheoriza bulbosa and Arisarum vulgare resprouted, Frankenia hirsuta and Lotus cytisoides germinated, and Sonchus sp. benefited from long‐distance dispersal). Few weedy species were recorded (e.g. Sonchus asper asper). Whatever the treatment, the risk of reinvasion from the seed bank or from resprouting stems is nonnegligible, so long‐term monitoring is vital to the ultimate success of the eradication program.

Inferential and forward projection modeling to evaluate options for controlling invasive mammals on islands.

Successful pest-mammal eradications from remote islands have resulted in important biodiversity benefits. Near-shore islands can also serve as refuges for native biota but require ongoing effort to maintain low-pest or pest-free status. Three management options are available in the presence of reinvasion risk: (1) control-to-zero density, in which immigration may occur but reinvaders are removed; (2) sustained population suppression (to relatively low numbers); or (3) no action. Biodiversity benefits can result from options one and two. The management challenge is to make evidence-based decisions on the selection of an appropriate objective and to identify a financially feasible control strategy that has a high probability of success. This requires understanding the pest species population dynamics and how it will respond to a range of potential management strategies, each with an associated financial cost. We developed a two-stage modeling approach that consisted of (1) Bayesian inferential modeling to estimate parameters for a model of pest population dynamics and control, and (2)a forward projection model to simulate a range of plausible management scenarios and quantify the probability of obtaining zero density within four years. We applied the model to an ongoing, six-year trapping program to control stoats (Mustela erminea) on Resolution Island, New Zealand. Zero density has not yet been achieved. Results demonstrate that management objectives were impeded by a combination of a highly fecund population, insufficient trap attractiveness, and a substantial proportion of the population that did not enter traps. Immigration is known to occur because the founding population arrived on the island by swimming from the mainland. However, immigration rate during this study was indistinguishable from zero. The forward projection modeling showed that control-to-zero density was feasible but required greater than a two-fold budget increase to intensify the trapping rate relative to population growth. The two-stage modeling provides the foundation for a management program in which broad-scale trials of additional trapping effort or improved trap lures would test model predictions and increase our understanding of system dynamics.

Genetic diversity and structure of Schistosoma japonicum within two marshland villages of Anhui, China, prior to schistosome transmission control and elimination.

Schistosomiasis is caused by the genus Schistosoma and affected more than 250 million people worldwide. Schistosoma japonicum was once seriously endemic in China and nearly 60years of efforts has seen great success in disease control. However, due to its zoonotic nature and complex life cycle, the schistosomiasis transmission control and final elimination would require, besides an intersectoral approach, deep understanding of population genetics of the parasite. We therefore performed a snail survey in two marshland villages of Anhui province of China and collected S. japonicum cercariae from infected snails. By using the recent developed microsatellite panel comprising seven loci, we genotyped the sampled parasites and analyzed the population genetic diversity and structure. The results showed much lower infection prevalence of S. japonicum in snails and low infected snail density in either marshland village. Through population genetic analyses, a considerable genetic diversity of parasites was revealed, whereas a small number of clusters were inferred and the sign of bottleneck effect was detected in each village. For the first time in S. japonicum in two villages, we provided estimates of effective population sizes with two different approaches. The results indicated that the parasite in two villages could eventually be eradicated with the ongoing integral control measures, but with potential risk of reinvasion of immigrant parasites through the Yangtze River. Such would be of great importance in assessment of the effects of ongoing control measures and prediction of the transmission capability for S. japonicum, thus guiding decisions on the choice of further control work.

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.

Self-Resetting Traps Provide Sustained, Landscape-Scale Control of a Rat Plague in New Zealand

Author(s): Carter, Anna; Peters, Darren | Abstract: Control of invasive mammals is central to the conservation and restoration of native habitats, especially in unique and vulnerable island ecosystems. While methods for eradication of pest mammals on offshore islands are well-established, long-term suppression at mainland sites and in other locations with an extremely high risk of re-invasion remains challenging. We examined the use of CO2-powered, self-resetting traps for control of rats during a beech forest mast on the New Zealand mainland. Goodnature® A24 automatic traps installed on a 100 × 50-m grid reduced tracking indices for ship rats from 68% to 0% within a 200-ha area over a period of four months. The extent of the trapped area was then increased to 700 ha, with the resolution of the trapping grid reduced to 100 × 100 m. Tracking indices within the expanded area decreased from 44% to 0% within an additional two months. Activity of rats in a non-treatment site remained at around 70% for the duration of the project. Tracking indices for house mice decreased from 22% to 0% within four months and remained low for the duration of the project, indicating that non-targeted control of house mice was also achieved within the project area. Our results show that Goodnature® A24 self-resetting traps can successfully knock down and suppress rats from plague levels within an unprotected, mainland site.

Incorporating Risk of Reinvasion to Prioritize Sites for Invasive Species Management

The relationship between landscape pattern and the distribution and spread of exotic spe- cies is an important determinant of where and when management actions are best applied. We have developed an interdisciplinary approach for prioritizing treatment of harmful, nonnative, invasive plants in National Park landscapes of the Mid-Atlantic USA. The approach relies upon a detailed model of reinvasion risk that combines information on: (1) global factors representing park-level infestation from seed and sprout, (2) landscape factors including disturbance-based spread vectors and neighborhood seed density, and (3) local factors determining establishment probability based on habitat suitability. Global seed rain estimates are derived empirically from park inventory data and modified by informa- tion on species reproductive strategies. Landscape-level propagule pressure is modeled spatially using species life history characteristics including dispersal attributes, connectivity to nearby plant populations, and increased propagule pressure through disturbance. The local-scale habitat suitability model uses a Mahalanobis distance approach, parameterized from plant inventory plot data and GIS-based data on plot wetness, land cover, slope, radiation, and soil characteristics. We illustrate the model for Ailanthus altissima (tree-of-heaven) in Antietam National Battlefield Park. The results of the A. altissima modeling highlight regions of the park where eradication would be most prudent and feasible based on current infestation patterns and landscape heterogeneity. Although the success of different treatment modalities is often considered in invasive species management, a spatially explicit assessment of likely treatment success is rarely undertaken. Our approach provides a valuable tool to assist natural resource practitioners to prioritize management options in confronting biological invasions.

Genetic correlations within and between isolated tsetse populations: What can we learn?

Isolated tsetse populations constitute a target for tsetse control programmes in endemic countries, since their isolation, if demonstrated, allows control without reinvasion risk from neighbouring populations. Population genetic parameters, such as the fixation index, have proven useful to assess isolation status, and should also give important information on the divergence time since isolation. We gathered results obtained from different datasets regarding several examples of putatively totally isolated tsetse populations of different tsetse species: Glossina palpalis gambiensis in Guinea, in the Niayes of Senegal, and in the sacred wood of Bama in Burkina Faso; G. tachinoides from Bitou and Pama in South-East Burkina Faso. The different levels of isolation were compared to differentiation between the two subspecies G. p. gambiensis and G. p. palpalis which both occur allopatrically along the Comoe River in Ivory Coast. We also use some historical evidence to calibrate differentiation speed and give estimates of time since separation for the different cases studied. Discrepancies mostly come from underestimate of effective population sizes, and we propose improving sampling design and genetic markers quality to circumvent such caveats.

Genetic signature of a recent southern range shift in Glossina tachinoides in East Burkina Faso

In the eastern part of Burkina-Faso, the riverine tsetse fly, Glossina tachinoides Westwood, transmits African animal trypanosomosis that constitute a major constraint to sub-Saharan agriculture. To organize an efficient vector control campaign against this vector, it is crucial to identify and target isolated populations in order to prevent any risk of reinvasion. Previous entomological data using traps in this part of the country have suggested that G. tachinoides has now become discontinuously distributed with a western and an eastern tsetse belt. In this paper, we studied population genetics on G. tachinoides trapped in two sites, separated by 150kms, on the western and eastern sides of this “gap”. We found that a significant differentiation does exist between the two sites and that it is fairly above than what was expected given the geographic distance. A comparison between observed and expected differentiation allowed estimating that the total separation between these two sites could have occurred around 10years ago (i.e. between 1 and 21years), which is in line with the dates of environmental changes that occurred in this area. This result will help the national PATTEC project to organize the tsetse eradication in this area.

Understanding local population genetics of tsetse: The case of an isolated population of Glossina palpalis gambiensis in Burkina Faso

Tsetse flies are the vectors of human and animal trypanosomiases. For tsetse eradication programs, it is crucial to be able to identify and target isolated populations, because they can be targeted for eradication without risk of reinvasion. However, most data that are available on non-isolated populations fail to find how these populations are locally structured, because Wahlund effect (admixture of individuals from genetically different units) always interfere with interpretations. In this paper, we investigated the genetic population structure of a possibly isolated population of Glossina palpalis gambiensis in a sacred wood in South Burkina Faso, using microsatellite DNA markers. We found that genotypic proportions in this population were in agreement with random mating model and that these tsetse were genetically highly differentiated from other populations of the same Mouhoun river basin only a few kilometers away, confirming its genetic isolation. The population also displayed substantial temporal differentiation in a two years period that lead to an estimate of effective population size of ∼100 individuals. The fact that no Wahlund effect was identified allowed us to accurately measure the basic genetic parameters of this isolated population. Identifying such isolated and small populations is crucial for eradication programs and should be implemented more often.

Island prioritization for invasive rodent eradications with an emphasis on reinvasion risk

Invasive rodents occur on over 80% of the world's island groups, invasions are continuing, and rodent impacts on insular wildlife have been well demonstrated. The extent of this problem calls for tools to aid large-scale prioritisation among the many candidate eradication operations. As conservation funds are limited, biologists have responded with prioritisation systems based on financial cost-effec- tiveness. Instead, we claim that long-term conserva- tion gain should be the primary focus when prioritising islands for invasive rodent eradication. This concept is embodied mainly by invasive rodent reinvasion risk, which we categorise as natural or anthropogenic, based on the mechanism of reinvasion and our ability to mitigate the risk. The result is a first-pass triage system that prioritises eradication programmes by their long-term conservation potential, not their immediate value for money. To construct a prioritiza- tion list, we group islands into units for simultaneous eradication, to minimize inter-island reinvasion risk, and then assign weights to levels of unit reinvasion risk and unit conservation value. The choice of parameter weights may depend on capacity for biosecurity action (i.e. reduction in reinvasion risk) and a choice of tertiary filter variables can further discriminate within priority ranks. We illustrate our prioritization framework with a case study on rodents in New Caledonia but explain how our system can be adapted to suit any invasive rodent species or island configuration.

Archipelago-Wide Island Restoration in the Galápagos Islands: Reducing Costs of Invasive Mammal Eradication Programs and Reinvasion Risk

Invasive alien mammals are the major driver of biodiversity loss and ecosystem degradation on islands. Over the past three decades, invasive mammal eradication from islands has become one of society's most powerful tools for preventing extinction of insular endemics and restoring insular ecosystems. As practitioners tackle larger islands for restoration, three factors will heavily influence success and outcomes: the degree of local support, the ability to mitigate for non-target impacts, and the ability to eradicate non-native species more cost-effectively. Investments in removing invasive species, however, must be weighed against the risk of reintroduction. One way to reduce reintroduction risks is to eradicate the target invasive species from an entire archipelago, and thus eliminate readily available sources. We illustrate the costs and benefits of this approach with the efforts to remove invasive goats from the Galápagos Islands. Project Isabela, the world's largest island restoration effort to date, removed >140,000 goats from >500,000 ha for a cost of US$10.5 million. Leveraging the capacity built during Project Isabela, and given that goat reintroductions have been common over the past decade, we implemented an archipelago-wide goat eradication strategy. Feral goats remain on three islands in the archipelago, and removal efforts are underway. Efforts on the Galápagos Islands demonstrate that for some species, island size is no longer the limiting factor with respect to eradication. Rather, bureaucratic processes, financing, political will, and stakeholder approval appear to be the new challenges. Eradication efforts have delivered a suite of biodiversity benefits that are in the process of revealing themselves. The costs of rectifying intentional reintroductions are high in terms of financial and human resources. Reducing the archipelago-wide goat density to low levels is a technical approach to reducing reintroduction risk in the short-term, and is being complemented with a longer-term social approach focused on education and governance.

From small Maria to massive Campbell: Forty years of rat eradications from New Zealand islands

Over the last four decades the eradication of rats from islands around New Zealand has moved from accidental eradication following the exploratory use of baits for rat control to carefully planned complex eradications of rats and cats (Felis catus) on large islands. Introduced rodents have now been eradicated from more than 90 islands. Of these successful campaigns, those on Breaksea Island, the Mercury Islands, Kapiti Island, and Tuhua Island are used here as case studies because they represent milestones for techniques used or results achieved. Successful methods used on islands range from bait stations and silos serviced on foot to aerial spread by helicopters using satellite navigation systems. The development of these methods has benefited from adaptive management. By applying lessons learned from previous operations the size, complexity, and cost effectiveness of the campaigns has gradually increased. The islands now permanently cleared of introduced rodents are being used for restoration of island‐seabird systems and recovery of threatened species such as large flightless invertebrates, lizards, tuatara, forest birds, and some species of plants. The most ambitious campaigns have been on remote subantarctic Campbell Island (11 300 ha) and warm temperate Raoul Island (2938 ha), aimed to provide long‐term benefits for endemic plant and animal species including land and seabirds. Other islands that could benefit from rat removal are close inshore and within the natural dispersal range of rats and stoats (Mustela erminea). Priorities for future development therefore include more effective methods for detecting rodent invasions, especially ship rats (Rattus rattus) and mice (Mus musculus), broader community involvement in invasion prevention, and improved understanding of reinvasion risk management.