Joint species models reveal the effects of environment on community assemblage of freshwater mussels and fishes in European rivers

Aim Given that riverine systems exhibit longitudinal environmental gradients from headwater to the mouth of a river, habitat heterogeneity appears to be a major driver of spatial variation in community composition among riverine localities. As freshwater ecosystems are amongst the most endangered ecosystems in the world, community-based conservation and multiple-species management are necessary to maintain ecosystem integrity. We used joint species distribution models (JSDMs) to investigate the relative importance of abiotic and biotic factors that are responsible for the distribution and co-occurrence of species in riverine ecosystems. Location Central and northern Europe. Methods We examined the general patterns of species assemblage of two endangered freshwater mussel species (Margaritifera margaritifera and Unio crassus) and their associated fish communities. We examined the patterns of positive or negative co-occurrence in mussel and fish species and identified shared abiotic responses between mussel-host pairs. Results We found that the relative importance of abiotic and residual factors and patterns of significant species correlations varied among taxa: significant residual correlations were prevalent among fish species, whereas mussel occurrences were exclusively explained by abiotic factors. Mussels and their fish hosts generally had shared abiotic responses with some mismatched responses between mussel-host pairs. Main conclusions Given that the composition of communities were tightly linked with abiotic factors and residual correlations, the results have significant implications for the conservation and restoration of aquatic communities. This study highlights the necessity to simultaneously consider environmental factors and species co-occurrences in the modelling of species distributions and assemblages of riverine communities. Such a holistic community conservation approach can reveal ecological similarities and differences among species, which can help us avoid conflicts among target-species conservation plans.