Anthropocene is characterised by significant, and in many ways outcompeting natural processes, the impact of human activities on natural ecosystems. The excessive emission of greenhouse gases caused by global-scale use of fossil fuels, anthropogenic land-use change, and drastic decrease in pristine areas, have all contributed to global climate change. Although the Earth’s climate has historically fluctuated, the current situation is novel as climatic change is occurring at an unprecedented rate and has mainly been driven by human behaviour. The rapid pace of environmental change forces living organisms to respond fast in order to survive and reproduce. The magnitude of such responses might be especially prominent in migratory species due to their diverse and dispersed habitat requirements. Migratory species connect habitats across the globe, coupling biodiversity and ecosystem services. By travelling long distances, migratory species move biomass between habitats; transporting energy, nutrients, and other organisms. Also, migratory species alter the dynamics of resident communities that they connect on their journeys by foraging and becoming prey in numerous habitats during their annual cycle. Therefore environmental alteration leading to disruption of long-distance migratory behaviour will have far-reaching consequences which may drastically affect synchrony and unity in natural ecosystems. The aim of this dissertation was to reveal climate-driven changes to populations of migratory bats, from a historical overview through to future perspectives. To understand the magnitude of ongoing changes in populations of bats, we require adequate reference points from the past. Here, I had a unique opportunity to study recent changes in migratory behaviour and distribution of common European migratory bat species, Nyctalus noctula, based on long term dataset. In the presented work, I combined different approaches such as stable hydrogen isotopes to reveal migratory destinations; analysis of demographic data to evaluate sex and age population dynamics; respirometry measurements to establish physiological parameters and environmental modelling to predict suitable for hibernation areas under three climate change scenarios. This variety of applied technics allowed for complex investigation of animal responses to climate change. The obtained results are reported in two peer-reviewed publications and one manuscript, which is in preparation for submission. The research outcome aims to bridge the most demanding gaps in knowledge related to climate-driven changes in populations of migratory animals. The first chapter contributed to the improvement of the method for studying migratory animals by using stable isotopes. The second chapter was dedicated to climate change responses, particularly to an investigation of the mechanism of climate-driven range changes in populations of migratory bats. The third chapter described and evaluated the novel mechanistic approach in environmental modelling of species distribution under the impact of climate change. In chapter one, I have contributed to the validation of the assumptions for stable hydrogen analysis. Stable isotopes are broadly applied for the identification of the geographical origin of bats via transfer function, which is consists of the isotope signature of animals of know origin. However, there was no age validation performed before for stable isotope signatures in bat tissues. The stable isotopes approach was planned as the main method for the assignment of migratory bats in a long-term dataset. Therefore, in chapter one, I presented a validation approach for age differences in stable isotope signatures to better understand variation around the transfer function and increase the precision in the prediction of the geographic origin. In chapter two using a transfer function, which included individuals of both age classes, I investigated migratory behaviour and demographic structure of N. noctula under the distribution shift. The common noctule bats increased their winter range by more than 500 km during several decades. Apart from the observed biogeographic pattern little was known regarding the mechanism relevant for the range change. I hypothesized that the generation shift is the mechanism relevant to the range change in migratory bats. To test the hypothesis, I looked at the long-term data set regarding the demographic structure of winter colonies in the recently occupied winter range and I used stable hydrogen analysis to establish the geographic origin of bats. My finding supported the hypothesis regarding the generational shift in migratory behaviour of bats which resulted in winter range change. Obtained results, for the first time, demonstrated the relevance of generation shift in the regulation of species distribution in mammals. Chapter three was dedicated to the elaboration of a mechanistic physiologically-based model for the evaluation and forecasting of suitable hibernation areas in migratory bats. Climate change is expected to affect the cost of hibernation in a given area and might ultimately modify species winter distribution. With a novel approach, I aimed to combine fine-scale thermoregulation data of noctule bats with environmental variables from their past and present winter ranges to model species occurrence dynamics. Firstly, this joint approach improved our understanding of species physiological requirements to external conditions. Secondly, it enabled us to refine the modelling of future species distribution under different climate change scenarios. The presented work had revealed climate-driven changes in migratory behaviour and distribution of common noctule bats. By incorporation various technics and methodological approaches, I could tackle the magnitude of responses to climate change on different levels of ecological organisation: from an organismal physiological response to environmental conditions; to change in migratory behaviour on a population level and change in geographic distribution on a species level. The main findings elaborate on physiological and behavioural mechanisms underlying climate-driven range change and provide evidence for migratory bats being able to respond fast to the rapid pace of climate change. However, the consistency of responses is conditioned by species-specific traits such as physiological flexibility, high mobility and dispersion rate, short generation life, and diversity of migratory strategies; and climate velocity, as a metric of speed, and direction of climate displacement.
