| Summary: | Climate change is affecting species distributions and phenologies. These changes may in turn affect how species interact with each other. Thus, species-specific effects of a changing environment are expected to affect the whole food web. Due to this dynamic complexity, community and ecosystem level responses to climate change are still relatively poorly understood. In this thesis I use the Arctic ecosystem to fill in some of this knowledge gap. For this, the interaction webs of Arctic communities are ideal, as they are simple enough to sample adequately. At the same time, the Arctic has been warming twice as fast as the rest of the globe, likely accentuating the effects of climate change. In my thesis, I concentrate on a module of the total food web, the insect parasitoids, insect herbivores and a widespread flowering plant, Mountain Avens (Dryas). I specifically study how climatic factors affect each species in the community, whether species’ responses be predicted based on species traits such as parasitism strategy (koinobiontism versus idiobiontism), and whether different trophic levels respond in concert. To strengthen my conclusions as based on a purely observational study design, I approach these questions at different spatial and temporal scales. I examine local altitudinal gradients within a walking distance. I organize a similar sampling at a geographical scale, which includes latitudinal variation in climate as well as regions which have experienced different types of climate change. Finally, I contrast these spatial snapshots against a real time series at a single location. In the first chapter I asses both how plant and arthropod phenologies respond to climatic factors over time, but also how the landscape level patterns in snow conditions are changing. I found phenological sensitivities of arthropods to vary with their feeding guild, supporting the idea of climate change induced changes in phenological matching between interacting species. The spatial pattern in the relative timing of snowmelt was ...
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