Invertebrate abundance and river drying data from Europe and South America: family and genus-level taxonomic resolution for perennial and non-perennial reaches

Drying river networks include non-perennial reaches that cease to flow or dry, and drying is becoming more prevalent with ongoing climate change. Biodiversity responses to drying have been explored mostly at local scales in a few regions, such as Europe and North America, limiting our ability to predict future global scenarios of freshwater biodiversity. Locally, drying acts as a strong environmental filter that selects for species with adaptations promoting resistance or resilience to desiccation, thus reducing aquatic α-diversity. At the river network scale, drying generates complex mosaics of dry and wet habitats, shaping metacommunities driven by both environmental and dispersal processes. By repeatedly resetting community succession, drying can enhance β-diversity in space and time. To investigate transferability of these concepts across continents, we compiled and analyzed a unique dataset of 43 aquatic invertebrate metacommunities from drying river networks in Europe and South America. In Europe, α-diversity was consistently lower in non-perennial than perennial reaches, whereas this pattern was not evident in South America. Concomitantly, β-diversity was higher in non-perennial reaches than in perennial ones in Europe but not in South America. In general, β-diversity was predominantly driven by turnover rather than nestedness. Dispersal was the main driver of metacommunity dynamics, challenging prevailing views in river science that environmental filtering is the primary process shaping aquatic metacommunities. Lastly, α-diversity decreased as drying duration increased, but this was not consistent across Europe. Overall, drying had continent-specific effects, suggesting limited transferability of knowledge accumulated from North America and Europe to other biogeographic regions. As climate change intensifies, river drying is increasing and our results underscore the importance of studying its effects across different regions. The importance of dispersal also suggests that management efforts should seek to enhance connectivity between reaches to effectively monitor, restore, and conserve freshwater biodiversity.

Methods
Aquatic invertebrate metacommunity datasets from Europe and South America were identified and compiled. Selection was based on four criteria. Drying was the main source of environmental variation and sampled rivers were minimally or least impacted with moderate to high water quality. For each metacommunity, each reach was sampled at least once before and once after drying to capture the local effects of the drying on metacommunity dynamics. Sampling methods were quantitative or semi-quantitative. Nine datasets were compiled, spanning 12 countries, 41 rivers, 43 metacommunities, and 2505 samples from 696 unique reaches and 249 sampling campaigns. Communities were sampled between 2004 to 2022 and covered a wide environmental gradient across both continents, ranging from first-order gravel-bed headwater streams to fifth-order sand-bed rivers. DRN catchment areas ranged between 13 and 1076 km². Datasets included 3–8 environmental variables from stream velocity, wetted width, maximum depth, temperature, pH, conductivity, dissolved oxygen, and discharge.