| Summary: | Abstract Freshwater ecosystems form unique environments with high biodiversity. However, freshwater biodiversity is increasingly threatened because of human activities, such as the ongoing climate change and land use alterations. To prevent the further decline in biodiversity, it is crucial to understand the factors that affect and modify biotic communities. For freshwater systems, information on the patterns and underlying echanisms of biodiversity is still inadequate, which may complicate any conservation and management efforts. Ecologists must often rely on different proxy variables in studies examining biodiversity-environment and biodiversity-space relationships due to difficulties in obtaining direct measures of numerous factors across large regions. Biodiversity patterns in streams have been shown to be structured by direct physical properties of the local habitat and by proxy features on the catchment and regional scales, but one problem has been related to only moderate explanatory power using such ‘traditional environmental variables’. The goal of this thesis was to study biodiversity patterns in northern streams by introducing the use of geographical proxy variables of environmental features (i.e. geodiversity) and dispersal (i.e. different geographical distances). More precisely, the aims were to 1) examine the effects of local environmental and geographical variables on stream biodiversity; 2) investigate how environmental and spatial distance types between stream sites affect the variation of stream insect communities; 3) compare the relative roles of habitat-scale geodiversity measures and traditional in-stream variables in explaining stream macroinvertebrate biodiversity and; 4) examine how catchment-scale geodiversity contributes to the variation in stream biodiversity in a boreal region. According to the results, traditional environmental variables contributed most to the variation in stream biodiversity. However, geographical proxies showed a clear usefulness in understanding ...
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