Reporting costs for invasive vertebrate eradications

Testing transgenerational transfer of personality in managed wildlife populations: a house mouse control experiment

Pest species control operations are most effective if every individual in a population is targeted. Yet, individual personality drives variation in animal responses to devices such as traps and baits. Failing to account for differences in behavior during control operations may drive a selective removal, resulting in residual animals with biased expressions of personality. If these biased traits are passed onto offspring, control operations would become increasingly problematic. To test if biased trait expressions in founding populations are passed on to offspring, we quantified personality traits in wild-caught house mice (Mus musculus) and created founder populations selected for biased (high, low) or intermediate expressions of activity. We released the behaviorally biased populations into outdoor yards to breed to the F₁ generation and, 10 weeks later, removed the mice and quantified the personality traits of the offspring. Despite the strong personality bias in founder populations, we observed no transgenerational transfer of personality and detected no personality bias in the F₁ generation. Our results provide reassuring evidence that a single intensive control operation that selects for survivors with a personality bias is unlikely to lead to a recovering population inherently more difficult to eradicate, at least for house mice.

CONTAIN: Optimising the long-term management of invasive alien species using adaptive management

Invasive Alien Species (IAS) threaten biodiversity, ecosystem functions and services, modify landscapes and impose costs to national economies. Management efforts are underway globally to reduce these impacts, but little attention has been paid to optimising the use of the scarce available resources when IAS are impossible to eradicate, and therefore population reduction and containment of their advance are the only feasible solutions.

CONTAIN, a three-year multinational project involving partners from Argentina, Brazil, Chile and the UK, started in 2019. It develops and tests, via case study examples, a decision-making toolbox for managing different problematic IAS over large spatial extents. Given that vast areas are invaded, spatial prioritisation of management is necessary, often based on sparse data. In turn, these characteristics imply the need to make the best decisions possible under likely heavy uncertainty.

Our decision-support toolbox will integrate the following components:

(i) the relevant environmental, social, cultural, and economic impacts, including their spatial distribution;

(ii) the spatio-temporal dynamics of the target IAS (focusing on dispersal and population recovery);

(iii) the relationship between the abundance of the IAS and its impacts;

(iv) economic methods to estimate both benefits and costs to inform the spatial prioritisation of cost-effective interventions.

To ensure that our approach is relevant for different contexts in Latin America, we are working with model species having contrasting modes of dispersal, which have large environmental and/or economic impacts, and for which data already exist (invasive pines, privet, wasps, and American mink). We will also model plausible scenarios for data-poor pine and grass species, which impact local people in Argentina, Brazil and Chile.

We seek the most effective strategic management actions supported by empirical data on the species’ population dynamics and dispersal that underpin reinvasion, and on intervention costs in a spatial context. Our toolbox serves to identify key uncertainties driving the systems, and especially to highlight gaps where new data would most effectively reduce uncertainty on the best course of action. The problems we are tackling are complex, and we are embedding them in a process of co-operative adaptive management, so that both researchers and managers continually improve their effectiveness by confronting different models to data. Our project is also building research capacity in Latin America by sharing knowledge/information between countries and disciplines (i.e., biological, social and economic), by training early-career researchers through research visits, through our continuous collaboration with other researchers and by training and engaging stakeholders via workshops. Finally, all these activities will establish an international network of researchers, managers and decision-makers. We expect that our lessons learned will be of use in other regions of the world where complex and inherently context-specific realities shape how societies deal with IAS.

Controlling invasive rodents via synthetic gene drive and the role of polyandry

House mice are a major ecosystem pest, particularly threatening island ecosystems as a non-native invasive species. Rapid advances in synthetic biology offer new avenues to control pest species for biodiversity conservation. Recently, a synthetic sperm-killing gene drive construct called t-Sry has been proposed as a means to eradicate target mouse populations owing to a lack of females. A factor that has received little attention in the discussion surrounding such drive applications is polyandry. Previous research has demonstrated that sperm-killing drivers are extremely damaging to a male's sperm competitive ability. Here, we examine the importance of this effect on the t-Sry system using a theoretical model. We find that polyandry substantially hampers the spread of t-Sry such that release efforts have to be increased three- to sixfold for successful eradication. We discuss the implications of our finding for potential pest control programmes, the risk of drive spread beyond the target population, and the emergence of drive resistance. Our work highlights that a solid understanding of the forces that determine drive dynamics in a natural setting is key for successful drive application, and that exploring the natural diversity of gene drives may inform effective gene drive design.

Sustainability as a Framework for Considering Gene Drive Mice for Invasive Rodent Eradication

Gene drives represent a dynamic and controversial set of technologies with applications that range from mosquito control to the conservation of biological diversity on islands. Currently, gene drives are being developed in mice that may one day serve as an important tool for reducing invasive rodent pests, a key threat to island biodiversity and economies. Gene drives in mice are still in development in laboratories, and wild release of modified mice is likely a distant reality. However, technological changes outpace the existing capacity of regulatory frameworks, and thus require integrated governance frameworks. We suggest sustainability—which gives equal consideration to the environment, economy, and society—as one framework for addressing complexity and uncertainty in the governance of emerging gene drive technologies for invasive species management. We explore the impacts of rodent gene drives on island environments, including potential conservation and restoration of island biodiversity. We outline considerations for rodent gene drives on island economies, including impacts on agricultural and tourism losses, and reductions in biosecurity costs. Finally, we address the social dimension as an essential space for deliberation that will be integral to evaluating the potential deployment of gene drive rodents on islands.

Eradicating invasive rodents from wet and dry tropical islands in Mexico

Eradications of invasive rodents from tropical islands have a lower success rate compared to temperate islands. In the tropics the wide range of physical and biological conditions results in a wide variety of island biomes, with unique challenges and windows of opportunity for rodent eradications. We describe and compare research and operational details of six successful eradications of invasive mice Mus musculus and ship rats Rattus rattus carried out during 2011–2015. The work was conducted on six islands in two distinct tropical archipelagos in Mexico (one dry in the Gulf of Mexico; one wet in the Caribbean), and included the first eradication of rats from a mangrove-dominated island > 500 ha. Invasive rodent populations varied among species and islands, even neighbouring islands; overall density was higher on wet islands. Physical and biological features, including the presence of land crabs, determined eradication timing and rates of bait broadcast (higher on wet islands). An interval of 6–10 days between the two bait applications per island was sufficient to eradicate actively breeding mouse and rat populations. Impacts on non-target species were negligible, including those on wild and captive iguanas. Eradication success was rapidly confirmed based on ground monitoring and statistical modelling. Rodent eradications on larger tropical islands should be achievable with directed research to inform planning and implementation.

A review of biodiversity outcomes from possum-focused pest control in New Zealand

Worldwide, introduced vertebrate pests impact primary production, native biodiversity, and human health. In New Zealand, extensive pest control (~10 million ha) is undertaken to protect native biota and to prevent losses to the primary sector from wildlife vectors of bovine tuberculosis (TB), primarily possums (Trichosurus vulpecula). Control is conducted by TBfree New Zealand and by conservation agencies. Remote, forested terrain is treated using the toxin 1080 via aerial delivery in bait with a return time of ~5 years. Ground-based control is conducted annually using traps and/or poison bait. Possums are controlled to very low abundance by these operations. Aerial 1080 is effective against another forest-dwelling vertebrate pest, the ship rat (Rattus rattus). Possum control has reduced TB rates, but collateral benefits for native biodiversity have not been quantified, making it difficult to demonstrate a return on investment. We review information from 47 accounts of responses of native biota to possum control. Of these, 60% quantified responses to aerial 1080; the remainder were ground-based. Possum control benefited vegetation by increasing foliage and fruit production, and by reducing tree mortality. Controlling ship rats and possums together improved bird populations, but rats recovered rapidly and long-term outcomes for rat-vulnerable birds are unknown.Large-bodied invertebrates also benefited from extensive pest control. We conducted a meta-analysis of 84 response measures from 35 of these 47 studies in order to provide a quantitative assessment of these findings. The analysis demonstrated that both ground and aerial control of this invasive pest in New Zealand has provided substantial collateral benefits for native biota. Few studies have taken advantage of decades of extensive pest control in New Zealand to monitor ecosystem-level outcomes, which have received only short-term attention thus far. Non-treatment experimental controls and replicate sites that enable validated assessments of outcomes for native biota are vital. Future studies would benefit from a standardised set of biodiversity indicators from a range of taxonomic and functional groupings, and from standardising experimental designs so individual studies can contribute to future meta-analyses, to strengthen the evidence base for the impacts of invasive pests on native biota in New Zealand and worldwide.