Effects of landscape connectivity and predator-prey interactions on diving beetle assemblages in Finnish urban ponds

How does urban nature work? This question has fascinated many ecologists in recent decades. Biodiversity in urban nature is a core focus of urban ecology, because it benefits the well-being of urban residents by providing ecosystem services and nature-based solutions. However, most research about urban biodiversity has been conducted in terrestrial urban habitats, while the blue component, i.e. water surfaces, and biodiversity in urban blue have often been neglected. Recognising what urban habitats exist and understanding the ecological patterns and processes in such habitats are important in incorporating ecological knowledge into urban planning and biodiversity conservation. In this thesis, I use diving beetles (Dytiscidae) as my focal taxon to investigate how landscape connectivity and predator-prey interactions affect aquatic biodiversity in Finnish urban ponds. Chapters I and II focus on landscape features, investigating how dytiscid assemblages change along a gradient of urbanisation and how dytiscid community similarity responds to the structural connectivity of urban ponds. The results suggest that urban ponds have the capacity to support biodiversity but low structural connectivity between urban ponds can restrict the dispersal of dytiscids. Chapters III and IV focus on predator-prey interactions, investigating how dytiscid assemblages are affected by the presence of fish predators and how different levels of predation risk modify dytiscids’ habitat use and habitat selection. I found that the presence of fish decreases dytiscid species richness and abundance, and that dytiscids, especially small-sized species, prefer fishless habitats. The availability of spatial prey refugia can ease the high predation pressure in ponds with fish. To conclude, both landscape features and habitat-specific features affect dytiscids assemblages in urban ponds. Providing high pond density can improve structural connectivity between ponds and facilitate the dispersal of dytiscids, as well as other aquatic organisms. Retaining fishless habitats in an urban pondscape is crucial to support aquatic biodiversity. Provision of spatial prey refuges, such as aquatic vegetation, can facilitate the coexistence of predators and prey in urban ponds. The findings of this thesis provide insights into freshwater biodiversity conservation in urban regions