All ecosystems on Earth are undergoing rapid human-induced changes. One important component of these changes is the transport of species to new ecosystems, where they often establish and spread, and cause ecological disruption as invasive species. Behaviour plays a major role in this process, not only by enabling species to spread or establish, but also in the native species’ response to invasion. These behavioural changes drive population dynamics, and the speed at which they happen are crucial. The shared evolutionary history between two species influences how fast or effective these changes happen. To study these complicated interactions, this thesis combines a comparative study of the existing literature with novel concepts and metadata, as well as analyses of laboratory experiments and field data.
For Chapter 1, a large cross-taxonomical dataset on behavioural changes in biological invasions was gathered and analysed. It is the first to include native and non-native species, to identify types of behaviour and mechanisms of change and to quantify the speed of the behavioural change. This gave us the opportunity to test hypotheses in invasion ecology, but also to explore the distribution of learning across types of behaviour and its implications for the speed of behavioural change. All analyses were conducted considering the biases in the data and differences in the ecology of native and invasive species.
In Chapter 2, the behavioural differences between an established non-native crayfish species, the spiny-cheek crayfish Faxonius limosus, and the novel non-native marbled crayfish (Procambarus virginalis) were experimentally quantified, and findings were used to predict the invasion success of the latter species. Experiments were designed to show the outcome of inter-specific agonistic interactions, activity and exploration. Finally, not only inter-specific differences were tested but also between both sexes of the spiny-cheek crayfish, and between lab-reared and wild-caught individuals of the marbled crayfish. Apart from predicting invasion success, these analyses help to better understand behavioural plasticity in this special clonal species.
Chapter 3 contains the application of two classification schemes - of animal innovation and eco-evolutionary experience - to the dataset of Chapter 1. I encourage the use of this general quantification scheme of animal innovation to mine a broader range of behavioural changes. The scheme was applied in this study to specifically investigate if big changes in behaviour help native species to cope with invasion. It was also tested if high eco-evolutionary experience with that species buffers negative population consequences for native species. We reject the first hypothesis and accept the latter and found as well a negative relationship between both parameters, as lower experience necessitates bigger change. Therefore, these classifications can help a priori predictions of invasion impact on specific native species.
In Chapter 4, the population dynamics and nesting behaviour of the common eider (Somateria mollissima) in West Iceland was analysed from field data. The dataset encompasses yearly nest count data on 134 islands over up to 123 years. Therefore, we were able to investigate how long-term climate dynamics affect the eider colonies and how that changed with the invasion of the American mink (Neovison vison) into the region in 1948. Similarly, the arctic fox (Vulpes lagopus), the only native terrestrial nest predator, was absent from the study area for decades and we compared the behavioural response to both predators. The differences between the effects of specific predators help to direct targeted conservation efforts to protect the common eider.
Finally, Chapter 5 presents population dynamics of the American mink in Iceland, Denmark, Germany and its native range in the USA estimated from hunting bag data using a novel method. Effects of anthropogenic factors on the hunting bag were quantified, namely the global price of American mink fur, the production of fur in the respective country, and hunting effort and legislation connected to hunting and fur production. While we were able to test several hypotheses on American mink population dynamics in Europe - for example, if it follows a boom-bust dynamic - the utility of this method stretches beyond this system and can be applied whenever population numbers are estimated from hunting bag data.
My thesis explores a novel dataset on behavioural changes in biological invasions (Chapter 1). It includes experimental results on the role of behaviour in an over-invasion scenario of crayfish in Europe (Chapter 2) and expands the horizon of behavioural studies in invasions by introducing classification schemes for eco-evolutionary experience and animal innovation (Chapter 3). Finally, the introduction of the American mink in Europe is studied, by its consequences for the Icelandic avifauna (Chapter 4) and the estimation of its population dynamics through hunting bag data in several countries (Chapter 5)
