Data and code for Joint Species Distribution Models unveil co-occurrences between freshwater mussels and their fish hosts

Aim: Techniques used for modelling species distributions often disregard the effect of biotic interactions, which can be a determinant factor, particularly for obligatory relationships such as the one between freshwater mussels (FM) and their fish hosts. FM are among the most threatened taxa in the world, partially due to the dependence on fish hosts, also highly threatened, to complete their life cycle. In this study, Joint Species Distribution Models (JSDMs) were applied to FM and fish hosts assemblages to uncover the drivers and patterns of their co-occurrences. Location: Douro River Basin (Iberian Peninsula) Taxon: Freshwater mussels and fish hosts Methods: JSDMs were fitted to presence-absence records for FM and fish species assemblages and resulting matrices of pairwise species co-occurrences were used to identify co-occurrence patterns. A variance partitioning analysis among environmental variables and random effects was conducted to determine the drivers of species’ distributions and co-occurrences. Results: Co-occurrences between FMs and the more important fish hosts were consistently captured by JSDMs. These co-occurrences were determined by the species’ shared response to the environmental characteristics, but also by biotic interactions. Overall, the environmental component determining the distribution of FM and their co-occurrence with fish hosts included variables related to climate (annual maximum temperature and annual average precipitation), topography (elevation and river order), and land use (cropland extent). The contribution of biotic interactions was particularly important for host-specialist mussel species. Main conclusions: The findings of this study validate the use of JSDMs for identifying the primary and more important fish hosts for each FM species, as well as for understanding what factors drive their distributions. This can have substantial practical implications, as FM’ conservation often demands in situ and ex-situ measures, such as captive breeding, habitat restoration, and translocations, among others, that also need to consider adequate conditions for fish hosts. Furthermore, by finding similarities and differences between the ecological requirements of co-occurring species, conservation measures can be oriented towards communities instead of single species, bringing a more holistic perspective to the protection of biodiversity.