Island Eradications Research Articles

Rodent management in Aotearoa New Zealand: approaches and challenges to landscape-scale control.

Aotearoa-New Zealand has only four rodent species, all introduced. In order of arrival, they are Pacific rat Rattus exulans, brown rat R. norvegicus, house mouse Mus musculus, and black rat R. rattus. Rodent management in New Zealand aims mainly to conserve indigenous biodiversity rather than to protect crops or manage diseases, as is usual elsewhere. We describe four major "regimes" and one major vision for rodent control in New Zealand to meet ecological restoration objectives. Current challenges for island eradications are for large islands that are remote or populated by people. Aerial 1080 is the only large-scale (tens of thousands of hectares) option for black rat control, but its application requires adjustment to counter subsequent rapid black rat repopulation. Unfenced "ecosanctuaries" (mean 720 ha) use ground-based traps and poisons to target mainly black rats and face constant reinvasion. Ecosanctuaries with mammal-resistant fences (up to 3500 ha) limit reinvasion and target more pest species and have enabled the return of previously extirpated taxa to the main islands. Predator Free 2050 aims to eradicate the rat species (but not mice) plus some other introduced mammals from New Zealand by 2050. This vision is not attainable with current tools, but research and experimental management is exploring techniques and technologies. The large scale (to 100000 ha) at which black rats are now targeted for control to extremely low abundance seems to be unique to New Zealand.

The next frontier: assessing the feasibility of eradicating mammalian pests from Auckland Island

Auckland Island, the fifth largest island in New Zealand, is the only island in New Zealand’s subantarctic region where introduced mammalian pests remain (pigs, Sus scrofa; mice, Mus musculus; cats, Felis catus). The island has unique biodiversity and is a key site for progressing New Zealand’s goal to be free of several introduced predators by 2050. Recent island eradication successes have rekindled interest in eradicating pests from Auckland Island, and for the first time considering all three pests in one project.

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.

Do Invasive Mammal Eradications from Islands Support Climate Change Adaptation and Mitigation?

Climate change represents a planetary emergency that is exacerbating the loss of native biodiversity. In response, efforts promoting climate change adaptation strategies that improve ecosystem resilience and/or mitigate climate impacts are paramount. Invasive Alien Species are a key threat to islands globally, where strategies such as preventing establishment (biosecurity), and eradication, especially invasive mammals, have proven effective for reducing native biodiversity loss and can also advance ecosystem resilience and create refugia for native species at risk from climate change. Furthermore, there is growing evidence that successful eradications may also contribute to mitigating climate change. Given the cross-sector potential for eradications to reduce climate impacts alongside native biodiversity conservation, we sought to understand when conservation managers and funders explicitly sought to use or fund the eradication of invasive mammals from islands to achieve positive climate outcomes. To provide context, we first summarized available literature of the synergistic relationship between invasive species and climate change, including case studies where invasive mammal eradications served to meet climate adaptation or mitigation solutions. Second, we conducted a systematic review of the literature and eradication-related conference proceedings to identify when these synergistic effects of climate and invasive species were explicitly addressed through eradication practices. Third, we reviewed projects from four large funding entities known to support climate change solutions and/or native biodiversity conservation efforts and identified when eradications were funded in a climate change context. The combined results of our case study summary paired with systematic reviews found that, although eradicating invasive mammals from islands is an effective climate adaptation strategy, island eradications are poorly represented within the climate change adaptation and mitigation funding framework. We believe this is a lost opportunity and encourage eradication practitioners and funders of climate change adaptation to leverage this extremely effective nature-based tool into positive conservation and climate resilience solutions.

Trophic niche changes associated with the eradication of invasive mammals in an insular lizard: an assessment using isotopes.

Invasive species are a major threat to island biodiversity, and their eradications have substantially contributed to the conservation of island endemics. However, the consequences of eradications on the trophic ecology of native taxa are largely unexplored. Here, we used the eradication of invasive black rats Rattus rattus and European rabbits Oryctolagus cuniculus from the Berlenga Island, in the western coast of Portugal, as a whole-ecosystem experiment to investigate the effects of the eradication of invasive mammals on the trophic niche and body dimensions of the island-restricted Berlenga wall lizard Podarcis carbonelli berlengensis over a 2-year period. Our results suggest an expansion of the isotopic niche and an intensification of the sexual dimorphism of the lizard following mammal eradication. Additionally, we found considerable variability in isotopic niche across the island and detected evidence of sex-specific and season-modulated nutritional requirements of this threatened reptile. Our findings support that the eradication of 2 of the planet’s most problematic invasive vertebrates led to changes in the lizard trophic niche and sexual dimorphism in just 2 years. This suggests that the ecological pressures—for example, prey availability and habitat structure—to which lizards are exposed have substantially changed post-eradication. Our study emphasizes the scientific value of island eradications as experiments to address a wide range of ecological questions and adds to the increasing body of evidence supporting substantial conservation gains associated with these restoration interventions.

Impacts of rodent eradication on seed predation and plant community biomass on a tropical atoll

AbstractInvasive rodent eradications are frequently undertaken to curb island biodiversity loss. However, the breadth of rodents’ ecological impact, even after eradication, is not always fully recognized. For example, the most widespread invasive rodent, the black rat (Rattus rattus), while omnivorous, eats predominantly seeds and fruit. Yet, the effects of seed predation release after eradication on plant communities and ecological functions are not well understood, posing a gap for island restoration. We examined the role of seed predation release following black rat eradication in changes to tree composition and aboveground biomass across an islet network (Palmyra Atoll) in the Central Pacific. We conducted repeated surveys of seed, juvenile, and adult tree biomass and survival in permanent vegetation plots before and after the eradication of rats. We observed a 95% reduction in seed predation for an introduced, previously cultivated tree population (Cocos nucifera). Juvenile tree biomass of all species increased 14‐fold, with C. nucifera increasing the most, suggesting that eradication increased this tree's competitive advantage. Indeed, based on stage‐structured demographic models, rat eradication led to a 10% increase in C. nucifera population growth rate. The effect of invasive rodent seed predation varies considerably among the plant species in a community and can shift competitive dynamics, sometimes in favor of invasive plants. These bottom‐up effects should be considered in evaluating the costs and benefits of eradication. Documenting the variation in invasive rodent diet items, along with long‐term surveys, can help prioritize island eradications where restoration is most likely to be successful.

Recent advances of quantitative modeling to support invasive species eradication on islands

AbstractThe eradication of invasive species from islands is an important part of managing these ecologically unique and at‐risk regions. Island eradications are complex projects and mathematical models play an important role in supporting efficient and transparent decision‐making. In this review, we cover the past applications of modeling to island eradications, which range from large‐scale prioritizations across groups of islands, to project‐level decision‐making tools. While quantitative models have been formulated and parameterized for a range of important problems, there are also critical research gaps. Many applications of quantitative modeling lack uncertainty analyses, and are therefore overconfident. Forecasting the ecosystem‐wide impacts of species eradications is still extremely challenging, despite recent progress in the field. Overall, the field of quantitative modeling is well‐developed for island eradication planning. Multiple practical modeling tools are available for, and are being applied to, a diverse suite of important decisions, and quantitative modeling is well placed to address pressing issues in the field.

Treating Cancer as an Invasive Species.

To cure a patient's cancer is to eradicate invasive cells from the ecosystem of the body. However, the ecologic complexity of this challenge is not well understood. Here we show how results from eradications of invasive mammalian species from islands-one of the few contexts in which invasive species have been regularly cleared-inform new research directions for treating cancer. We first summarize the epidemiologic characteristics of island invader eradications and cancer treatments by analyzing recent datasets from the Database of Invasive Island Species Eradications and The Cancer Genome Atlas, detailing the superior successes of island eradication projects. Next, we compare how genetic and environmental factors impact success in each system. These comparisons illuminate a number of promising cancer research and treatment directions, such as heterogeneity engineering as motivated by gene drives and adaptive therapy; multiscale analyses of how population heterogeneity potentiates treatment resistance; and application of ecological data mining techniques to high-throughput cancer data. We anticipate that interdisciplinary comparisons between tumor progression and invasive species would inspire development of novel paradigms to cure cancer.

Anticoagulant Rodenticides, Islands and Animal Welfare Accountancy.

Simple SummaryAnticoagulant rodenticides are a mainstay of rodent management in many domestic, municipal, agricultural, and conservation settings. Anticoagulant poisoning has poor welfare outcomes for mammals and birds and, worldwide, this means potentially very large numbers of animals are poisoned annually consequent (intended or not) to rodenticide use. Critical differences in use patterns of anticoagulants applied for ongoing rodent control, versus application for rodent eradication especially on islands, have clear implications for animal welfare costs measured as cumulative number of animals affected over time. Here we outline these differences and discuss how animal welfare considerations can be weighed in decisions to use anticoagulant rodenticides for island eradication attempts.Anticoagulant rodenticides are used to manage rodents in domestic, municipal, agricultural, and conservation settings. In mammals and birds, anticoagulant poisoning causes extensive hemorrhagic disruption, with the primary cause of death being severe internal bleeding occurring over days. The combined severity and duration of these effects represent poor welfare outcomes for poisoned animals. Noting a lack of formal estimates of numbers of rodents and nontarget animals killed by anticoagulant poisoning, the ready availability and worldwide use of anticoagulants suggest that very large numbers of animals are affected globally. Scrutiny of this rodent control method from scientific, public, and regulatory perspectives is being driven largely by mounting evidence of environmental transfer of residual anticoagulants resulting in harmful exposure in wild or domestic animals, but there is also nascent concern for the welfare of targeted rodents. Rodent control incurs a cumulative ledger of animal welfare costs over time as target populations reduced by poisoning eventually recover to an extent requiring another reduction. This ‘rolling toll’ presents a critical contrast to the animal welfare accountancy ledger for eradication scenarios, where rodent populations can be completely removed by methods including anticoagulant use and then kept from coming back (e.g., on islands). Successful eradications remove any future need to control rodents and to incur the associated animal welfare costs.

Enhancing the value of future island eradications needs improved understanding of past outcomes

Enhancing the value of future island eradications needs improved understanding of past outcomes

Optimizing confirmation of invasive species eradication with rapid eradication assessment

Summary Confirmation of invasive species eradication following management programmes is typically determined by waiting an arbitrary period of time before determining success or failure based upon the then obvious presence or absence of the target species. Rapid eradication assessment could be achieved more expediently by applying statistical models of the probability of detecting survivors and their offspring, using a grid of detection devices, for a given set of biological and monitoring parameters. We simulate estimation of the probability of eradication for invasive rodents on islands across a range of monitoring parameters in order to provide guidance to managers on the optimal values, diminishing returns and trade‐offs in monitoring to achieve a given level of confidence in successful eradication. We found that monitoring an island for survivors over 15–20 nights is optimal and that waiting longer than a year before commencing monitoring has a negligible impact on the estimated probability of success. The spacing between detection devices has a considerable influence on estimated probability of success but only when it is <60 m. Intrinsic biological parameters of the target species have a substantial impact on confirming the probability of success, but validated field data are lacking to reliably incorporate these in current rapid eradication assessment models. We present case studies demonstrating cost savings of at least 5% to managers when applying rapid eradication assessment to the eradication of house mice Mus musculus from Isla Pájaros and Isla Muertos in Arrecife Alacranes (Scorpion Reef) Mexico, and implement the rapid eradication assessment model in an HTML GUI interface for eradication managers (www.rea.is). Synthesis and applications. Rapid eradication assessment (REA) is a powerful tool for managers to design optimal invasive species eradication monitoring programmes. We recommend island eradication managers routinely implement REA on small islands for the demonstrated cost savings and to accelerate eradication confirmation, ultimately facilitating island restoration.

Eradication of common mynas Acridotheres tristis from Denis Island, Seychelles.

In Seychelles, the common myna has been shown to have a negative impact on endangered endemic birds on Denis Island, interfering with breeding attempts and attacking adult endemic birds at their nests. This stimulated an attempt to eradicate the island's mynas. The eradication was undertaken in three phases, overall killing 1186 mynas and lasting 5 years. Decoy trapping was the most effective method for catching mynas, but the last birds were shot. Decoy trapping was compromised by catches of non-target species. Data collection from killed birds indicated that trapping did not favour either sex, and that most breeding occurred during the wetter season, November to March. Eradication of mynas from small tropical islands is feasible. The Denis Island eradication was prolonged by difficulties in management and staffing. Using volunteers, the cost of the eradication was similar to that of eradicating rodents from the island. In future eradication attempts in Seychelles, possible food stress during the drier season (May to September) might facilitate trapping at this time. Habitat management, especially the removal of short mown grass, could enhance eradication progress. Continued monitoring is needed to confirm eradication and detect any immigration, and also to record responses in the endemic birds. © 2016 Society of Chemical Industry.

Literature Review and Meta-Analysis of Vegetation Responses to Goat and European Rabbit Eradications on Islands

Introduced goats and European rabbits have caused devastating effects on island vegetation, and many successful efforts to eradicate these introduced animals have taken place mainly since the 1950s. Yet, a comprehensive review of vegetation response to goat and rabbit eradications is lacking. We conducted a literature search for articles on vegetation assessments before and after eradications. We conducted two kinds of reviews of species richness and cover response to eradication: a literature review for studies that provided qualitative or species-by-species responses to eradications and a meta-analysis on quantitative vegetation cover and species richness data. A key finding from our literature search was a significant information gap in the reporting of vegetation responses after eradication. Of over 200 successful island eradications that have been conducted since the 1800s, we found only 23 eradication studies that met our criteria for inclusion in the present analysis. Plant richness and vegetation cover increased more often than they decreased after eradication. Results varied according to region, herbivore type, habitat, and vegetation type, suggesting island-specific circumstances influence responses. The effect of eradication on Sub-Antarctic tundra species richness and on tropical vegetation percentage cover was higher than for other types of vegetation. Few cases differentiate responses of native versus exotic plant species, despite native biodiversity protection being one common goal of introduced herbivore eradication. We strongly recommend before and after eradication vegetation monitoring to understand how island ecosystems respond to eradication. Continuous monitoring would provide guidance on whether active restoration strategies need to be implemented to recover key native species and on the development of a general model of expected vegetation response, which is an integral first step to accelerate our predictive ability of vegetation responses.

The Power of Partnerships: Eradicating Invasive Mice from Allen Cay, The Bahamas

Author(s): Alifano, Aurora; Moore, Predensa; Mackin, William; Iverson, John; Griffiths, Richard; Fabres, Boris; Jolley, Wesley; Holmes, Nick D. | Abstract: Developing countries often have urgent national commitments regarding protection of biodiversity, but can be experience- or resource-limited to undertake conservation action. The eradication of invasive alien vertebrates (IAV), requiring a specialized set of skills and experience and sometimes significant capital investments, is a case in point. Building international collaborations to eradicate IAVs from islands is a potential approach to enhance the conservation of threatened species within countries that do not have sufficient capacity or funding. Here, we present a case study, the successful removal of invasive house mice from Allen Cay, Exuma Islands, The Bahamas. The goal of the project was to protect Audubon’s shearwaters and improve breeding habitat for the endemic Allen Cay rock iguana. The project was collaboratively planned and implemented by two previously unassociated organizations, the Bahamas National Trust (BNT) and Island Conservation (IC). Both organizations brought unique skillsets to the project: BNT provided compliance and local biological expertise, and IC provided eradication project management. Local capacity to implement future eradication projects was strengthened through BNT’s ownership and management of the project, and a strong partnership now exists to increase the scale and efficacy of future Bahamian island eradication projects to protect threatened species. Efforts to expand and coordinate an international network of practitioners conducting IAV eradications will require an improved understanding of the threats posed by IAVs, access to technical support, exposure to best practices, and the empowerment of local agencies to invest in the protection of biodiversity on islands.

Tracing the Tiger: Population Genetics Provides Valuable Insights into the Aedes (Stegomyia) albopictus Invasion of the Australasian Region

BackgroundThe range of the Asian tiger mosquito Aedes albopictus is expanding globally, raising the threat of emerging and re-emerging arbovirus transmission risks including dengue and chikungunya. Its detection in Papua New Guinea's (PNG) southern Fly River coastal region in 1988 and 1992 placed it 150 km from mainland Australia. However, it was not until 12 years later that it appeared on the Torres Strait Islands. We hypothesized that the extant PNG population expanded into the Torres Straits as an indirect effect of drought-proofing the southern Fly River coastal villages in response to El Nino-driven climate variability in the region (via the rollout of rainwater tanks and water storage containers).Methodology/Principal FindingsExamination of the mosquito's mitochondrial DNA cytochrome oxidase I (COI) sequences and 13 novel nuclear microsatellites revealed evidence of substantial intermixing between PNG's southern Fly region and Torres Strait Island populations essentially compromising any island eradication attempts due to potential of reintroduction. However, two genetically distinct populations were identified in this region comprising the historically extant PNG populations and the exotic introduced population. Both COI sequence data and microsatellites showed the introduced population to have genetic affinities to populations from Timor Leste and Jakarta in the Indonesian region.Conclusions/SignificanceThe Ae. albopictus invasion into the Australian region was not a range expansion out of PNG as suspected, but founded by other, genetically distinct population(s), with strong genetic affinities to populations sampled from the Indonesian region. We now suspect that the introduction of Ae. albopictus into the Australian region was driven by widespread illegal fishing activity originating from the Indonesian region during this period. Human sea traffic is apparently shuttling this mosquito between islands in the Torres Strait and the southern PNG mainland and this extensive movement may well compromise Ae. albopictus eradication attempts in this region.

Interior fences can reduce cost and uncertainty when eradicating invasive species from large islands

Summary The conservation of many threatened species can be advanced by the eradication of alien invasive animals from islands. However, island eradications are an expensive, difficult and uncertain undertaking. An increasingly common eradication strategy is the construction of ‘interior fences’ to partition islands into smaller, independent eradication regions that can be treated sequentially or concurrently. Proponents argue that, while interior fences incur substantial up front construction costs, they reduce overall eradication costs. However, this hypothesis lacks an explicit theoretical or empirical justification. We formulate a general theory that relates the number of interior fences to the magnitude and variation of the economic cost of island eradication. We use this theory to explore the conditions under which interior fences represent a defensible management strategy, under cost and risk minimisation objectives. We then specifically consider the forthcoming eradication of cats Felis catus from Dirk Hartog Island, Western Australia, by parameterising our general theory using published data on the cost and success of previous projects. Our results predict that under a wide range of reasonable conditions, interior fences can reduce the expected cost of a successful invasive alien animal eradication from large islands. On Dirk Hartog Island, interior fences will marginally reduce eradication costs, with two fences reducing expected costs by 3%. Interior fences have a much more substantial effect on the variability of eradication costs: two fences reduce the width of the 95% confidence bounds by more than one‐third and halve the size of the average project cost overrun/underrun. Our results reveal that the construction of interior fences is a defensible management strategy for eradicating alien invasive species from islands. However, the primary benefit of interior fences will be risk management, rather than a reduction in expected project costs.

Bait consumption by Sooty Terns: implications for island eradication programmes

SummaryRat Rattus spp. predation is widely recognised as a major threat to insular seabird populations. Rodent eradication programmes have advanced over the last two decades with purported benefits to ecosystems and seabird conservation. However, the danger of non-target poisoning to seabirds has rarely been examined, despite hundreds of insular eradication efforts. We initiated research to assess the risk of rodenticide bait to nesting Sooty Terns Sterna fuscata on Wake Atoll Complex. Placebo bait with a fluorescing dye was used in a control treatment design to track exposure and ingestion. Camera-based observations and faecal samples, post-mortem inspections and live chick observations suggested that bait exposure and consumption occurred, but that it was infrequent. Results indicated that poison bait eradication should occur outside the chick rearing phase to minimise risks to nesting seabirds. Our study also documents previously unreported environmental fluorescence, which may increase false positive results in pre-eradication assessments of bait palatability, bait uptake rates, and bait application methods that use inactive fluorescing test baits. We recommend that future conservation efforts begin with an evaluation of environmentally-based fluorescence before formal biomarker studies.

Nontarget Risk and Environmental Fate of the Broadcast Application of a Diphacinone Rodenticide at Mōkapu and Lehua Islands, Hawai'i

Invasive commensal rodents such as Rattus spp. and Mus spp. imperil many threatened and endangered native species including plants, invertebrates and birds within Hawai'i and U.S. territories and possessions in the Pacific. In some cases, the eradication or control of invasive rodents could allow natural recovery and active restoration of native species and ecosystems negatively impacted. The broad scale application of rodenticides is a necessary management tool for this purpose, but it is highly controversial to the public and regulatory agencies. There is great perceived and actual risk of nontarget mortality and environmental contamination. One of the conservation uses of rodenticides registered in Hawai'i is the aerial broadcast of rodenticide bait over large areas of native ecosystems on the main Hawai'ian islands, repeated periodically to maintain reduced rodent population levels. Recognizing that the success of this program depends on public and regulatory support, a coalition of state and federal agencies and private landowners have carefully designed Hawai'i’s rodent control program to minimize short- and longterm environmental impacts. In the early 1990s, diphacinone was selected as the primary rodenticide for conservation uses in Hawai'i because of its long track record of safe and effective use in agriculture worldwide. Hawai'i’s program has 5 components: research on efficacy and environmental impacts, regulatory compliance, developing and using local technical expertise, monitoring of rodenticide impacts and native species recovery and public outreach and engagement, particularly at the community level. After many years of generating the efficacy and safety data in support of regulatory approval by the U.S. Environmental Protection Agency (EPA) and the State of Hawai'i, a diphacinone product (Diphacinone–50, Hacco, Inc., Randolph, WI) was approved in 2007 for conservation uses in the U.S. Subsequently, rodenticide pellets containing the active ingredient diphacinone at 0.005% (50 ppm) were broadcast by helicopter in February 2008 on Mōkapu and in January 2009 on Lehua. Mōkapu was the first island in the world where the aerial broadcast of this less hazardous active ingredient was used to eradicate rats. Island eradications in other parts of the world have usually used broad-spectrum active ingredients that are far more persistent and bioaccumulative, thus imparting a much higher risk to nontarget species and the environment. Monitoring of nontarget and environmental effects on Mōkapu and Lehua did not detect diphacinone residues. A number of factors, including state of Hawai'i restrictions on bait entering the ocean, led to rats surviving on Lehua. These projects demonstrate that the aerial broadcast of a rodenticide containing diphacinone can be an effective and safer tool for conservation. Hawai'i is using the results from Mōkapu and Lehua to plan future rat eradication and control projects and continue development of a long-term program.

The Removal of Feral Cats from San Nicolas Island: Methodology

Feral cats are considered one of the most detrimental invasive species within island ecosystems. Non-native feral cats have been on San Nicolas Island (5,896 ha, or 14,562 acres) since at least 1952. In an effort to counter the negative impacts of feral cats on marine and terrestrial birds, the San Nicolas seabird restoration project, with the goal of eradicating cats, was initiated in June 2009. Although aimed at seabird restoration, feral cat eradication is expected to aid in the protection of endemic terrestrial species, including the federally threatened island night lizard, federally threatened western snowy plover, a subspecies of deer mouse, and the state threatened island fox. Methods including the use of altered padded leg-hold live traps, detection dogs, and hunting are being utilized to deliver a successful eradication within a short window of opportunity. In addition, a trap monitoring system, operated in tandem with field PCs and GIS, has proven effective in managing large numbers of traps. Since initiation, a rotation of staff has provided an average of 6 field personnel on-island at any one time to staff the project continuously over 10 months. Eradication was complicated by the similarly sized island fox, rugged topography, restricted access to parts of the island by Navy activities, marine mammal presence on the beaches, and sea and shore birds nesting and roosting. Island eradications require multiple methods to effectively remove all cats, and operations on larger islands benefit from the intensive use of management tools such as GIS. The systems developed on the San Nicolas Seabird Restoration Project will advance the global effort to reduce the threats of invasive species, particularly feral cats.

Intraguild predation and mesopredator release effect on long-lived prey

Complete extirpation of a species can generate cascading effects throughout an ecosystem, yet are precisely the goal of island eradications of pest species. “Mesopredator release effect”, an asymmetrical special case of intraguild predation, has been hypothesised as a possible indirect effect from eradications, where superpredator removal can generate a mesopredator increase which may increase the impact on their shared prey. Theoretically this suggests that for intraguild predators, the superpredator may protect the shared prey from mesopredation, and removal of superpredators alone is not recommended. We create a model of long-lived age-structured shared prey and explore the non-equilibrium dynamics of this system. The superpredator can impact all prey life-stages (adult survival and reproductive success) whereas the smaller mesopredator can only impact early life-stages (reproductive success). This model is independently tested with data from a closed oceanic island system where eradication of introduced intraguild predators is possible for conservation of threatened birds. Mesopredator release only occurs in strongly top-down moderated (resource-abundant) systems. Even when mesopredator release can occur, the negative impact of more mesopredators is outweighed by the benefit of superpredator removal, allowing recovery of the prey population. Results are robust to 10% variation in model parameters. The consideration of age-structured prey contradicts previous theoretical results for mesopredator release effect and intraguild predation. Superpredator eradication is vital for population recovery of long-lived insular species. Nonetheless island conservation must retain a whole-ecosystem perspective given the complex trophic relationships among multiple species on islands.