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Climate change is increasing the proportion of river networks experiencing flow intermittence, which in turn reduces local diversity (i.e., α-diversity) but enhances variation in species composition among sites (i.e., β-diversity), with potential consequences on ecosystem stability. Indeed, the multiscale theory of stability proposes that regional stability can be attained not only by local processes but also by spatial asynchrony among sites. However, it is still unknown whether and how scale-dependent changes in biodiversity associated with river flow intermittence influence stability across spatial scales. To elucidate this, we here focus on multiple metacommunities of French rivers experiencing contrasting levels of flow intermittence. We clearly show that the relative contribution of spatial asynchrony to regional stability was higher for metacommunities of intermittent than perennial rivers. Surprisingly, spatial asynchrony was mainly linked to asynchronous population dynamics among sites, but not to β-diversity. This finding was robust for both truly aquatic macroinvertebrates and for taxa that disperse aerially during their adult stages, implying the need to conserve multiple sites across the landscape to attain regional stability in intermittent rivers. By contrast, metacommunities of truly aquatic macroinvertebrates inhabiting perennial rivers were mainly stabilized by local processes. Our study provides novel evidence that metacommunities of perennial and intermittent rivers are stabilized by contrasting processes operating at different spatial scales. We demonstrate that flow intermittence enhances spatial asynchrony among sites, thus resulting in a regional stabilizing effect on intermittent river networks. Considering that climate change is increasing the proportion of intermittent rivers worldwide, our results suggest that managers need to focus on the spatial dynamics of metacommunities more than on local-scale processes to monitor, restore, and conserve freshwater biodiversity., (© 2024 John Wiley & Sons Ltd.)

Floodplain landscapes are highly fragmented by river regulation resulting in habitat degradation and flood regime perturbation, posing risks to population persistence. Climate change is expected to pose supplementary risks in this context of fragmented landscapes, and especially for river systems adaptation management programs are developed. The association of habitat quality and quantity with the landscape dynamics and resilience to human-induced disturbances is still poorly understood in the context of species survival and colonization processes, but essential to prioritize conservation and restoration actions. We present a modelling approach that elucidates network connectivity and landscape dynamics in spatial and temporal context to identify vital corridors and conservation priorities in the Loire river and its tributaries. Alteration of flooding and flow regimes is believed to be critical to population dynamics in river ecosystems. Still, little is known of critical levels of alteration both spatially and temporally. We applied metapopulation modelling approaches for a dispersal-limited tree species, white elm; and a recruitment-limited tree species, black poplar. In different model steps the connectivity and natural dynamics of the river landscape are confronted with physical alterations (dams/dykes) to species survival and then future scenarios for climatic changes and potential adaptation measures are entered in the model and translated in population persistence over the river basin. For the two tree species we highlighted crucial network zones in relation to habitat quality and connectivity. Where the human impact model already shows currently restricted metapopulation development, climate change is projected to aggravate this persistence perspective substantially. For both species a significant drawback to the basin population is observed, with 1/3 for elm and ¼ for poplar after 25 years already. But proposed adaptation measures prove effective to even bring metapopulation strength and persistence up to a level above the current level., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

In a context of increasing landscape modifications and climatic changes, scale hierarchy becomes an ever more crucial issue to integrate in the analysis of drivers and stressors of biological communities, especially in river networks. To cope with this issue, we developed (i) spatial hierarchical models of functional diversity of stream invertebrate communities to assess the relative influence of local- vs. regional-scale factors in structuring community assembly, and (ii) analysis of metacommunity elements to determine the ecological processes behind the structuring. The spatial structuring of benthic invertebrate communities was investigated over 568 sites in South-eastern France. Community structure was mainly driven by the altitudinal gradient and spring flow variation at broad scales, with functional diversity gradually decreasing with elevation and being maximized at intermediate levels of flow variability. According to the 'elements of metacommunity structure' analysis, the prevailing influence of the altitudinal gradient was also supported by a Clementsian structuration of invertebrate communities. Conversely, the influence of observed climatic changes in temperature and rainfall was weak and observed only at fine scales. As a result, natural environmental filters were stronger drivers of the functional diversity of communities than human-induced stressors (e.g. water pollution and hydromorphological alterations). More broadly, our results suggest that management needs to embrace the possibilities of gathering high spatial and taxonomical resolution data when analysing and predicting flow variation and climate change effects in order to preserve and restore functionally diverse communities. Moreover, to develop environmental flow schemes or restoration and climate change adaptation strategies for freshwater communities, local and regional processes need to be addressed simultaneously; equally responsible as drivers of community diversity., (Copyright © 2016 Elsevier B.V. All rights reserved.)