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Thermo-mineral springs are specific ecosystems with extreme environmental conditions that constitute interesting models for studying metacommunity processes. Since these springs can be considered as islands within a terrestrial context, we first aimed to test some predictions of the theory of island biogeography and the distance-decay hypothesis on benthic diatom communities. Then, we aimed to quantify the influence of physical, chemical, climatic and spatial factors on species assemblages. We evaluated the species-area relationship for all springs and for several group of springs classified according to their environmental and hydrochemical composition. The influence of environmental variables on α-diversity was tested. We also investigated whether β-diversity was related to spring isolation or changes in environmental conditions. Finally, we determined the importance of environmental and spatial variables in shaping diatom communities using ordination and variation partitioning. We did not find any species-area relationship whatever the group of springs investigated, and no geographical distance-decay pattern was observed. We found a significant effect of physical and chemical parameters on α-diversity and composition. Thus, diatoms communities of thermo-mineral springs did not seem to be influenced by dispersal processes at the scale of our study but appeared to be patterned by physical and chemical factors. [ABSTRACT FROM AUTHOR]