ASsessing effects of biological Invasions and Climate Change (ASICS)

Climate in the coldest regions on Earth is changing at an unprecedented rate, triggering poleward and upward species redistribution, and increasing the likelihood of biological invasions. However, we know little about the impacts of newly colonizing species in high-elevation and high-latitude ecosystems, and how species invasions are likely to interact with other global change factors, such as climate and land-use changes. Here, we aim to combine expertise and an unprecedentedly huge dataset from cold environments all around the world (sub-Antarctic islands, Arctic, Antarctic and alpine regions) to better understand the combined effects of climate changes and biological invasions on contemporary species redistributions. Long-term surveys and georeferenced records from sub-Antarctic islands and alpine regions will be used as benchmark model systems and further extended to other cold environments (Arctic, Antarctic) to address the following research questions: (i) Changes of climatic conditions on sub-Antarctic islands and along elevation gradients are expected to shape vegetation belts, but do they trigger differences in elevational diversity patterns and in the speed of species redistribution between native and non-native plants? (ii) As native species have evolved under cooler conditions, are native plants and invertebrates expanding upwards more quickly than their non-native counterparts? (iii) Have/will the different rates of expansion (asynchrony) cause novel species interactions? (iv) How much does the redistribution of native and non-native species affect patterns of spatio-temporal variation in functional biodiversity metrics? The project is a collaborative effort from several European research teams led by David Renault from the Unversity of Rennes. Within the overall project framework, the Austrian contribution will mainly concentrate on the flora of sub-antarctic islands. We will try to predict the next generation of invading plant species on these islands and develop and apply a model to simulate how patterns of native and non-native plant species composition and richness will delveop over the 21st century.

This project has increased our understanding of the risk that invasive plant species pose to the sub-Antarctic. We modelled a large portion of globally invasive plant species to investigate whether they can survive in the sub-Antarctic region under current climatic conditions as well as under the conditions that arise under different scenarios of climate change in the years 2071-2100. As a result of the unique sub-Antarctic climate, ecological modelling as commonly performed is not as effective and prone to errors. We hence conducted an exploratory study prior to modelling, identified the challenges when predicting species distributions under these circumstances, and made recommendations to address them. After implementing these recommendations in this projects' models, the predictions showed that many invasive plant species would be able to survive in the sub-Antarctic even under current conditions. In the future, the number of species that could establish in the sub-Antarctic is predicted to rise with increasing severity of climate change. However, there is notable variation in the predicted amount of species among the islands. Whereas the more northern, and more temperate, islands are predicted to support the largest number of novel invasive plant species, the colder islands in closer proximity to Antarctica are expected to remain somewhat protected from the majority of plant invaders. Nevertheless, it is the colder islands that see the highest proportional increase in alien species numbers, when those species would actually be introduced. Climate change can furthermore lead to profound changes in the islands' ecology, as trees and shrubs are predicted to be able to survive on islands that are currently dominated by herbaceous vegetation and mosses. Notably, on all islands at least one invasive shrub or tree species is predicted to survive with projected climate change. Lastly in this project, we studied the history of alien plant species introduction to the islands since the late 18th century. We found three separate periods during which the majority of currently present alien plants were brought to the islands. These periods coincide with moments in time where human activity and exploitation of the sub-Antarctic were most pronounced, including high times of whaling in the 19th century and the increase in tourism at the end of the previous century. The modern-day shipping network of the sub-Antarctic has shifted from the global north to the global south, connecting a new set of potential plant invaders to the islands. The results of the species' climate suitability models show that many of these potential newcomers could survive upon arrival. This highlights the need for adequate biosecurity measures to protect the sub-Antarctic's unique flora and vegetation against competitive replacement by an ever increasing number of invasive species.