1. Relating processes occurring at a local scale to the natural variability of ecosystems at a larger scale requires the design of predictive models both to orientate stream management and to predict the effects of larger scale disturbances such as climate changes. Our study contributes to this effort by providing detailed models of the hydraulic preferences of 151 invertebrate taxa, mostly identified at the species level. We used an extensive data set comprising 580 invertebrate samples collected using a Surber net from nine sites of second and third order streams during one, two or three surveys at each site. We used nested nonlinear mixed models to relate taxon local densities to bed shear stresses estimated from FliesswasserStammTisch hemisphere numbers.2. An average model by taxon, i.e. independent from surveys, globally explained 25% of the density variations of taxa within surveys. A quadratic relationship existed between the average preferences and the niche breadth of taxa, indicating that taxa preferring extreme hemisphere numbers had a reduced hydraulic niche breadth. A more complete model, where taxa preferences vary across surveys, globally explained 38% of the variation of taxa densities within surveys. Variations in preferences across surveys were weak for taxa preferring extreme hemisphere numbers. 3. There was a significant taxonomic effect on preferences computed from the complete model. By contrast, season, site, average hemisphere number within a survey and average density of taxa within a survey used as covariates did not consistently explain shifts in taxon hydraulic preferences across surveys. 4. The average hydraulic preferences of taxa obtained from the extensive data set were well correlated to those obtained from two additional independent data sets collected in other regions. The consistency of taxon preferences across regions supports the use of regional preference curves for estimating the impact of river management on invertebrate communities. By contrast, the hydraulic niche breadths of taxa computed from the different data sets were not related.

1. We relate invertebrate assemblages to direct measurements of near-bed hydraulic conditions that integrate the complex three-dimensional structure of flow close to the bottom. 2. We sampled invertebrate taxa from a Mediterranean River along a spatial gradient of increasing shear stress in two seasons (spring and autumn) with different hydrological conditions. We used a recently described ordination technique, Outlying Mean Index (OMI) analysis, to study the response of stream invertebrates to near-bed hydraulic parameters. 3. The distribution of nearly 70% of the taxa collected was significantly related to the hydraulic parameters assessed. In both seasons, shear stress and Froude number were the most important hydraulic parameters whereas substratum particle size and bed roughness had less influence. Most of the 31 taxa collected in both seasons had a higher OMI (an index showing the deviation between the mean environmental conditions used by a taxon and the mean environmental conditions used by a theoretical taxon uniformly distributed across the studied gradient) in autumn (when flow was greater) and were found in samples with high shear stress and high Froude number. This suggests that benthic invertebrates changed their preferences according to flow conditions. 4. Taxon richness declined with increased shear stress during lower flow in spring. Finally, and agreeing with previous results, the proportion of filter feeders and collector-gatherers was inversely related to shear stress. 5. Our results are a first step towards better habitat suitability models that could inform management decisions.

Summary 1.Floodplains are species-rich environments often strongly impacted by human activities. In particular, the negative effects of progressive and rapid disconnection of secondary channels have led to restoration programmes and a growing interest in restoration ecology. 2. Current restoration strategies in large river floodplains focus on the macroinvertebrate response related to the increases in lateral connectivity of the secondary channels. We constructed a framework to assess a gradient of hydrological connectivity among 13 secondary channels and the main channel of a large river, and we modelled the response of a set of macroinvertebrate metrics to this gradient. Comparisons between predicted and observed metrics in restored channels allowed us to measure the effect of an increase in the hydrological connectivity on the biological characteristics of macroinvertebrate assemblages. 3. The pre-restoration framework enabled a clear ordering of channels into three types according to levels of hydrological connectivity. Rarefied richness and species traits, responding to the connectivity gradient, showed a net difference between disconnected channels and the main river channel. We were able to highlight a predation-colonization trade-off along the gradient of hydrological connectivity with a maximum colonization potential in the most connected channels. 4. Post-restoration sampling showed deviations of the restored channels from their expected ecological state. A large proportion of colonizers were favoured by the restoration operations and non-native species occurred in the restored channels. 5. Synthesis and applications. Macroinvertebrate biodiversity in large river floodplains is shaped by lateral hydrological connectivity. Increasing hydrological connectivity led to an increase in colonization rate. One year after restoration, the increase in lateral connectivity had shifted the restored sites away from the predicted state. This unpredictability is, in part, a consequence of the rapid colonization by non-native species of new habitats created by the restoration measures. We recommend that floodplain-scale restoration should focus on diversification of the hydrological connectivity of channels, thereby conserving a maximum of functional characteristics in macroinvertebrate communities.