Flooding and hydrologic connectivity modulate community assembly in a dynamic river-floodplain ecosystem

Dynamic river-floodplain systems host aquatic communities shaped by fluctuating water conditions. While prior research has shown that hydrology influences species distribution, the exact mechanisms remain unclear. It was already known that connectivity affects dispersal and resource availability. However, no prior work had resolved how flooding interacts with these patterns. This gap motivated the need to track community changes across connectivity gradients. Researchers sought to determine if deterministic or stochastic processes dominate during stable and flood periods. They also aimed to assess how flooding alters assembly mechanisms. This study adds new insights into the interplay between hydrology and biodiversity.

The study aimed to evaluate how hydrologic connectivity and flooding influence aquatic community assembly in a dynamic river-floodplain system. Researchers focused on benthic invertebrates, tracking their responses to connectivity and flood events. The goal was to determine if deterministic or stochastic processes drive community changes. They also sought to assess how flooding alters assembly dynamics. The study examined a lateral connectivity gradient in the Tagliamento River. Four flood events occurred during the year-long study. These events allowed the team to compare pre- and post-flood patterns. The findings could clarify how biodiversity relates to hydrology in natural systems.

The team collected benthic chironomids and oligochaetes from the Tagliamento River over a year. Sampling occurred across a lateral connectivity gradient in a semi-natural floodplain. Four bankfull flood events were recorded during the study period. Researchers assessed how flooding and connectivity influenced community assembly. They measured invertebrate density, richness, and diversity. Multivariate ordinations were used to track faunal composition changes. The study compared patterns during stable and flood periods. Local abiotic features were also analyzed to assess deterministic processes.

Invertebrate density and richness increased with higher connectivity. Diversity patterns, however, showed no significant correlation with connectivity. Species turnover increased as connectivity decreased. Contrary to expectations, connectivity did not affect how floods changed community metrics. Invertebrate composition changed predictably after floods. During stable periods, communities assembled deterministically. Beta-diversity and co-occurrence patterns were non-random. After floods, these signals declined despite no habitat homogenization.

The study found that flooding shifts community assembly from deterministic to stochastic processes. Deterministic sorting occurred during stable periods with strong beta-diversity signals. Floods disrupted these patterns, likely resetting assembly to earlier stages. Connectivity influenced species turnover but not flood responses. Diversity remained uncorrelated with connectivity levels. The findings suggest that hydrology modulates assembly mechanisms. Biodiversity may exhibit complex relationships with connectivity. This study highlights the need to consider temporal dynamics in floodplain ecosystems.