Species Redundancy and Niche Overlap: Mechanisms Maintaining Fish Community Function in Yangtze River Lakes in the Face of Lateral Hydrologic Connectivity Obstruction

The obstruction of lateral hydrologic connectivity poses a significant threat to floodplain ecosystems, with fishes being particularly susceptible to the impacts of such disturbances. Existing research about the effects of human activities on fish communities in the Yangtze River basin primarily focused on measures of diversity such as species diversity, functional diversity, and beta diversity. This study goes beyond by examining patterns of fish species and functional diversity variation, as well as revealing the pattern of species disappearance and its implications for maintaining fish community structure and function. Our findings highlight the importance of understanding the role of fish species in maintaining ecosystem function. We revealed a significant decrease in both fish species richness and functional richness across temporal (1960s, 1980s, and 2000s) and spatial (connected lakes, partially connected lakes, and disconnected lakes) scales. Among the disappearing fish species, those belonging to small-sized and large-sized genera exhibited a higher frequency of disappearance compared to those in moderate-sized genera. Nevertheless, the complexity of fish communities' co-occurrence networks does not exhibit a significant decrease with a decrease in species/functional richness, potentially due to the presence of niche overlap species (e.g., coexistence species within a single genus in our study). Our findings support the species redundancy hypothesis in elucidating the mechanisms that uphold fish community function. This study underscores the importance of considering fish species correlation within a community for the effective management of ecosystems, biodiversity conservation, and ecological restoration.