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Large river floodplains contain a high diversity of habitats and species but are highly threatened by human activities. River floodplain restoration is increasingly undertaken to reverse biodiversity loss and enhance ecosystem services., Few studies have examined the consequences on the biota of restoring lateral connectivity, a key variable that represents the exchange of materials and organisms between the river and its floodplain. We developed models to describe the richness and abundance of aquatic macroinvertebrates in 18 channels of the Rhône floodplain and predict how restoration (i.e. the increase in lateral connectivity of floodplain channels) should alter the native and alien communities., Models quantified how richness and abundance decrease for lentic taxa and increase for lotic and alien taxa with higher connectivity between the floodplain channels and the main channel. Predicted changes were weakly related to overall observed changes when all restored channels were combined, but consistent with observed changes when floodplain channels were grouped by restoration type. We highlighted that restoration interventions modifying lateral connectivity induced a change of lentic and lotic taxa richness in accordance with the predictions. Richness of alien taxa was favoured by restoration more than predicted; however, no interaction between alien species changes and native species was detected after restoration., Restoration of the ecosystem predictably transformed native communities and encouraged alien species, at least over the 4 years studied. Our findings demonstrate that lateral connectivity is a key variable driving macroinvertebrate communities in large river floodplains and that the response of macroinvertebrates to restoration of a disturbance-driven ecosystem can in part be predicted. Therefore, the outcome of restoration programmes can be optimised by quantifying lateral connectivity before and after restoration. [ABSTRACT FROM AUTHOR]

Rivers and floodplains are among the most threatened ecosystems. Hydroelectric power plants and embankments have reduced the hydrological connectivity between rivers and their floodplain channels, leading to loss of freshwater habitats and biological communities. To prevent and reverse such loss, numerous restoration programmes have aimed at rejuvenating the lateral hydrological connectivity between rivers and floodplain channels. Despite considerable global attention, we know remarkably little about the ecological benefits of floodplain restoration programmes., We analysed the functional diversity of different macroinvertebrate groups (natives and aliens) along a gradient of lateral hydrological connectivity on the Rhône river in France. We used 36 sampling sites to describe the functional diversity (Rao's quadratic entropy) before and after the enhancement of the lateral hydrological connectivity by restoration. The effects of restoration on functional diversity were tested for each macroinvertebrate group and at multiple spatial levels (alpha and beta)., Before restoration, alpha functional diversity of the entire macroinvertebrate community peaked in sites with a high lateral connectivity. The contribution of the native groups to functional diversity was higher than that of the alien group. The latter was not constrained by high values of lateral hydrological connectivity and reached a maximum in highly connected sites., After restoration, within-site functional diversity (alpha FD) declined linearly following the enhancement of lateral hydrological connectivity. The restoration operations increased the contribution of the aliens to functional diversity and reduced the contribution of a group of native taxa. In addition, among-sites functional diversity (beta FD) was successfully enlarged by restoration., Synthesis and applications. The lateral hydrological connectivity (LHC) represents a key parameter for explaining the functional diversity (FD) of macroinvertebrates in a floodplain ecosystem. Our results demonstrate that restoration-induced changes to functional diversity can be predicted. Controversially, restoration-induced enhancement of lateral hydrological connectivity increased the functional diversity of the alien macroinvertebrates. However, these species contributed only to a small part of the total macroinvertebrate functional diversity. We recommend that restoration programmes diversify the levels of lateral hydrological connectivity among the channels to ensure an optimal functional diversity at the floodplain scale. [ABSTRACT FROM AUTHOR]