Environmental Gradients and Ecological Processes as Constraints in the Distribution Patterns of Freshwater Biological Communities

The hypothesis that I tested in my research was that, often, the relationship among distribution of organisms and environmental gradients can be successfully evaluated as a limiting factor using the proper analytical methods. Firstly, I used quantile regression to describe the limiting action of both physical habitat characteristics and other environmental variables, on macroinvertebrate density and diversity. This study was conducted in rivers and streams belonging to two countries: Italy and Finland. The results can contribute to the definition of bioassessment indices and can be used within habitat based models. I also evaluated the link between the characteristics of lake macroinvertebrate communities and their habitat. Twenty-one variables that represent chemical, physical and morphological characteristics of nine different lakes were measured. Using quantile regression to evaluate limiting responses, we selected sampling depth and oxygen saturation percent as the two variables that best explain the number of taxa and the diversity of a site. At a later stage, a new approach for the identification of environmental flows that sum up the limiting factor approach, basic ecological relationships and the use of appropriate spatial scale for different organisms was developed. This is one of the few examples available in the literature that shows how to consider together different biological communities, at different trophic levels, within an habitat based model. Finally, the impact of potential climate change on the hydrological and ecological status of the alpine stretch of the Serio was investigated. Future hydrological cycle was predicted; present and prospective habitat availability for fish and macroinvertebrates was investigated. The results display the potential for large flow decrease, and shift of seasonal flow peaks. Variable scenarios of habitat availability were investigated, with a potentially worse situation for all species.