Climate change is causing profound and lasting changes to living conditions within ecosystems, leading to major changes in the communities that inhabit them. More than a third of theworld’s vertebrates live in freshwater ecosystems, and their decline is more alarming than in other ecosystems (terrestrial and marine ones). Despite this, the knowledge needed to implement management measures to protect these environments and adapt uses to them remains incomplete.The aim of this phD was to provide information on the spatial structuration of aquatic communities on a large scale, in a context of climate change, with a view to meeting highly applied needs.

First, we discuss, the choice between direct environmental variables (e.g. water temperature, hydraulic variables) or proximal variables (air temperature, discharge) for the living conditions of organisms. The spatial structuration of fish and macroinvertebrate communities in the Loire catchmentwas then described using multivariate analyses. The value of the cross-taxa approach, i.e. the combination of fish and macroinvertebrate data, was demonstrated in view of the lack of spatial concordance between the two biological compartments studied. Thus, Loire communities are structured along the upstream-downstream environmental gradient, by water temperature, hydraulic conditions and topography.

Species distribution modelling (SDM) is the method of choice for identifying the major environmental determinants of species structuration and anticipating potential future changes in distribution. Most SDMs are based solely on presence-absence data, whereas the use of abundance data, although more complex to model, provides valuable information on the health of populations and their resilience capacity in a changing environment. A method for modelling abundance classes using machine learning was proposed, with the application of technical solutions to resolve the difficulties inherent in abundance data. These SDMs were then used to project potential future species distributions for the 2050 and 2080 time horizons and to assess the impact of climate change on the abundances of fish and macroinvertebrate communities.

Finally, a comparison of the similarity of the spatial structuration patterns of the aquatic communities of the major French river basins, the Loire, Seine, Rhône and Garonne, was carried out in order to assess the scope of the work carried out on the Loire river basin. Keywords : species distribution models ; SDM; abundance ; fish ; macroinvertebrates ; aquatic communities.

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Cite the thesis

Coline Picard. Structuration spatiale des communautés aquatiques à large échelle : influence des facteurs environnementaux dans un contexte de changement climatique. Sciences de l'environnement. Université Claude Bernard - Lyon I, 2023. Français. ⟨NNT : 2023LYO10177⟩. ⟨tel-04744394⟩

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