Large-scale patterns of biodiversity in northern streams
insights from species, traits and phylogeny
Recently, ecologists and biogeographers have recognized the need of analyzing the multiscale phenomena of biodiversity in the light of a multifaceted concept: the investigation of multiple facets and multiple drivers operating at different spatial scales. The variation in species-based information has been the most commonly used approach to quantify how biodiversity varies through space and time, omitting the different evolutionary histories of each species and the fact that communities are constituted of species with different ecological roles. Stream biodiversity patterns have been demonstrated to be related to local-, catchment-, and regional-scale variables, but it is still an open question how these different sets of variables affect different facets of biodiversity in streams ecosystems (i.e., traits and phylogeny). The aim of this thesis was to investigate large-scale biodiversity patterns across northern streams by assessing the influence of different sets of variables (ranging from local habitat to large-scale geographical) underlying these patterns and through the investigation of different facets of biodiversity (i.e., species, traits and phylogenies). The results showed clearly the importance of local environmental variables and spatial factors in explaining large-scale biodiversity patterns in streams ecosystems, whilst the catchment and climate factors were less important. In addition, the results evidenced that the inference of trait-based and phylogeny-based biodiversity patterns might depend on an array of different mechanisms and complex factors that cannot be forecasted before the analysis. Overall, these findings elucidated that understanding both local- and large-scale factors are necessary for a better assessment of the mechanisms influencing the biodiversity and ecosystem processes of streams. Moreover, this thesis added trait-based and phylogeny-based views into the study of biodiversity patterns, enabling a better understanding of the different mechanisms associated with different facets of biological communities in streams.