Individual Specialisation in Established Biological Invasions: importance and Ecological Impact

Differences among individuals are the substance on which natural selection acts. However, little is known about how individual traits influence invasion dynamics, to the extent that it has been argued that either bold, aggressive, highly competitive individuals, or individuals that are shy or cautious, and less competitive, may make successful invaders. Thus empirically identifying the constituent individual traits of successful invaders is key; but what is also missing is an understanding of the consequences of any such individual variation among invasive individuals for the native biota and communities. This information is vital for informing management actions. This project utilises a natural experiment across invaded islands to determine the extent, covariance and persistence of individual variation across multiple traits (dietary, behavioural and cognitive) simultaneously in two invasive rat species in the wild. This approach explicitly tests how the fundamental ecological processes of competition and predation affect successful trait combinations, and will identify specific trait combinations, i.e. individual phenotypes, that cause particular individuals to have disproportionate impacts on native biota within an invasive species. The project examines hypotheses untested in either invasive species, or individuals of any species in natural contexts.

This work has revealed substantial inter- and intra-specific variation in behavioural traits that have the potential to be exploited to achieve management objectives. The field research component of this project and its results have contributed to the design of experimental work that forms a component of a multi-million dollar grant awarded to the crown research institute Landcare Research/Manaaki Whenua that is investigating the last survivors of eradication programs. Leveraging personality differences in these 'last 10%' to successfully remove them will ensure significant progress is made towards Predator Free 2050, New Zealand's 'moonshot' of eradicating numerous invasive mammalian predators. Success here will both inspire and enable advances in techniques around the world addressing this global problem.

Work carried out during the project involved field data collection on invasive rodents across five island locations that vary in their total invasive species composition. Behavioural and cognitive trials were conducted on all captured individuals, alongside the collection of associated metadata and physiological samples. Laboratory analyses on physiological samples have begun, but have not been completed as a result of the global pandemic leading to laboratory closures and subsequent backlogs. Thus a number of final conclusions remain pending within the timeframe of the grant itself, although work remains ongoing on a number of aspects. Behavioural variation was substantial both among individuals and across locations (and thus contexts), although results suggest this may contain site-specific components that are not necessarily clearly related to the complexity of the suite of invaders present on an island. Delays in laboratory-based analyses mean that multivariate statistical approaches addressing how the individual behavioural, dietary and microbiome variation present are interconnected, and whether predictions can be made across this ecological-behavioural-physiological axis, have yet to be concluded. However, all components show significant among-individual variation, and most show strong within-individual consistency. The research has led to a number of additional avenues of inquiry (connections between behaviour and the microbiome, the economic impacts of invasions, see below), and has resulted in scientific publications and broader public engagement with the early results of the research at governmental and research organisation, NGO and community group levels. Papers have been produced on the impacts and management of rodents on islands, including collaborations examining the likelihood for current management techniques to achieve eradication goals and potential obstacles to success, the impacts of invasive mice on island foodwebs and the potential to leverage individual behavioural variation to enhance management of vertebrates.

Additional lines of invesigation and enquiry have also been established with state-of-the-art and wider societal implications. Firstly, the experienced researcher has joined Invacost - part of the AlienScenario program. This truly global international collaboration seeks to develop a more comprehensive understanding of the economic costs of biological invasions, inspired by a newly compiled comprehensive database. A number of descriptive and synthetic papers have been published or are in preparation following an intensive (pre-pandemic) workshop and subsequent online communications. The outcomes from this project are expected to have an influence on a broad range of fields outwith ecology as they comprehensively highlight for the first time the widescale impacts of biological invasions on human socio-economic and One Health interests. Secondly, a successful pilot project was established investigating links between the individual microbiome and key invasive traits. The full results of this latter work have been delayed by pandemic related laboratory delays, and by the need for additional methodological analyses. However, they reveal clear and intriguing variation in microbiome diversity across individuals, and these promising initial findings resulted in an expansion of this data collection to multiple fieldsites for the final fieldwork component of the project.

Periodic Reporting for period 2 - ISEBI (Individual Specialisation in Established Biological Invasions: importance and Ecological Impact)

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