Local and regional drivers of fish metacommunities in a temperate river catchment

In the last couple of decades, it has become apparent in ecology that community structure can be governed by both local (e.g. abiotic and biotic filtering) and regional processes (e.g. dispersal) – known as Metacommunity theory. However, management and restoration projects have lagged, still mostly focusing on the local environment for the benefit of certain species or communities – leading to failed projects and complicating cost-effective management. The aim of present study is to 1) look at temporal fish community change between 1990-1999 and 2010-2019, 2) identify metacommunities and the assembly rules structuring them in 2010-2019 and 3) assess the effects of past, present and future management on community structure. This was achieved by looking at temporal community turnover following shifts in management, and present local- and regional processes (via principle component analysis) relation (generalized linear model) to certain fish metacommunities (hierarchical clustering analysis). The results support the current knowledge of metacommunities: local, environmental filtering (i.e. species-sorting) is the main structuring force of isolated headwaters, while regional processes (i.e. mass-effect) is the main structuring force of highly connected, lowland rivers. However, lateral connectivity (i.e. wetlands adjacent to watercourse) seems to operate at smaller spatial scales than longitudinal connectivity, leading to mass-effects in areas where species-sorting previously functioned as structuring force. Present management and expected community change indicate that the focus on restoring connectivity in the catchment will cause turnover effects favouring highly dispersive species, causing homogenisation of species compositions. Additionally, climate change seem to have the potential to cause significant effect on the structuring of salmonid communities (Less)