Freshwater ecosystems are highly biodiverse and provide essential ecosystem services, yet they are highly endangered, with approximately one in three freshwater species at risk of extinction due to human activity. Among other taxa, aquatic insects are a significant component of freshwater biodiversity. Their immense intrinsic value derives from their status as the most diverse taxonomic group of animals, encompassing high richness of species and traits and occupying numerous positions within food webs. Because of their different sensitivities to water pollution, they are widely used as bioindicators of ecosystem health. However, delineating the global distributions of aquatic insects has been hindered by the limited availability of species occurrence data and the lack of scalable hydrographic data processing tools that would allow assessing their environmental preferences and mapping their populations. This thesis suggests a novel, open-science approach to assess and map global freshwater biod- iversity at a high spatial resolution, with an emphasis on aquatic insects. My research aims were threefold: i) to create a comprehensive, standardised global dataset of aquatic insect occurrences, ii) to develop intuitive tools for complex hydrographic data processing and provide reproducible workflow examples, and iii) to explore the spatial patterns of ecological niche breadths of aquatic insects at the global scale. Therefore, the thesis is divided into three parts. First, I compiled the Global EPTO Database by standardising 50 datasets of Ephemeroptera, Plecoptera, Trichoptera and Odonata georeferenced occurrences at the genus level and attributing them with additional environmental and topographic information. I mapped the global distributions of aquatic insect genera, revealing biodiversity hotspots and knowledge gaps across the different regions of the world. Second, I co-lead the development of the ’hydrographr’ R-package, a tool that enables large-scale freshwater-specific longitudinal connectivity and network analyses, as well as the processing of numerous types of spatial data. Further, I created reproducible workflows of case studies that involve species distribution modelling and network distance and connectivity ana- lyses, aiming to facilitate the use of the package by freshwater ecologists. Third, I explored the large-scale spatial patterns in the ecological niche breadth of aquatic insects using worldwide occurrence records from the Global EPTO Database. The study showed that spatial patterns of assemblage niche breadth are likely shaped by evolutionary origins and dispersal history of EPTO, challenging the common assumption that niches are consistently narrower in species-rich tropical regions. Overall, this thesis represents a valuable contribution to spatial freshwater biodiversity science by providing the first comprehensive and standardised global dataset of aquatic insect occurrences, intuitive tools for complex hydrographic data processing, and novel insights into the spatial patterns of ecological niche breadth of aquatic insects at the global scale. All three outcomes are of high importance in freshwater ecological research, not only by tackling knowledge gaps on global aquatic insect biodiversity distributions, but also by suggesting an integrative approach that can be applied to other freshwater taxa.
