Aquatic diversity in a connected floodplain system: the role of environmental, spatial, and dispersal traits on macroinvertebrate communities

Abstract

Since 1970, approximately 83% of global freshwater species have declined, particularly in neotropical regions, highlighting the urgent need for conservation efforts in these ecosystems. This study investigates the factors shaping the taxonomic and functional diversity of macroinvertebrate communities in the Middle Paraná River, Argentina, a minimally regulated area, offering a unique opportunity to examine biodiversity alongside river ecosystem interactions. Our study examines the complex ecosystem of the Middle Paraná River, characterized by hydromorphological interactions between main waters, secondary channels, and lakes across its extensive floodplains. We analyzed data from 166 sites, identifying 160 species of benthic invertebrates. Spatial and environmental variables were assessed to characterize ecological conditions (e.g., patch type, habitat connectivity and shape, hydrometric phase, depth, granulometry, and conductivity) and to disentangle their influence on biotic patterns through variation partitioning analysis. The species composition, taxonomic, and functional beta diversity of the communities were assessed. The taxonomic diversity of invertebrates was influenced by spatial and niche-based factors, depending on their dispersal mode. While the longitudinal dimension was important, smaller-scale variations, especially lateral ones, played a crucial role in community diversity, aligning with flood pulse and flow pulse theories. Functional diversity was influenced by mesohabitat and microhabitat scales rather than along the longitudinal dimension, suggesting that lateral variability might impact detritivore diversity. Food sources were not restrictive, allowing detritivores to thrive during normal hydrometric levels, with high beta diversity and functional redundancy. The heterogeneity of the river-floodplain system boosted species turnover and high coexistence, preventing species dominance and benefiting detritivores, resulting in high local diversity and significant functional redundancy. These findings suggest that a dispersal group-based approach improves the understanding of community patterns and can be useful for monitoring, conservation, and restoration strategies in riverine ecosystems.