We lack a thorough understanding of the ecological processes, like species interactions and dispersal, that mediate the ecological responses of whole ecosystems to global changes, and their variability in realistically complex ecosystems. These processes involve multiple interacting species that move freely about the landscapes and thus, understanding these processes demands measures that can account for this complexity, at both the local and landscape scale. I address this issue by combining the local population dynamics of complex food webs and their metacommunity dynamics (yielding so called meta-food-webs). This allows me to incorporate real-world complexity for both local and spatial processes to examine how food webs respond to global changes, focusing on land use changes that alter the spatial configuration of habitats. To delve into the underlying mechanisms governing the impacts of global changes on multitrophic communities in complex landscapes, and to explore variations in these responses among species, trophic groups, landscapes and global change drivers, I develop new theoretical frameworks in which I combine ecology and mathematics. I demonstrate that local and spatial processes mediate meta-food-web responses to global changes in complex landscapes. Specifically, I show that there is a strong trophic dependency in the response of species to land use changes and emphasize that especially (large-bodied) consumer species at high trophic positions have elevated extinction risks when habitat becomes increasingly isolated (research chapters 1 and 2). In research chapter 3, by jointly considering multiple aspects of global change (land use changes and biological invasions), I demonstrate the interdependence of different environmental stressors. Overall, this thesis presents a major step towards a clearer understanding of food web responses to global change impacts.
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