Benjamin Girardot ( defended his PhD on June, 7 in Marseille, where he conducted his research about the analysis of disturbances on the structure and dynamic of food webs (

Benjamin was based in the Mediteranean Institute of Oceanography (MIO), and his thesis was supervised by JC Poggiale, M Gauduchon and F Ménard, all three affiliated to the same institute.


Usually, the relationships between, on the one hand, the fragility of food webs and their structure, and on the other hand, the generative processes responsible for these structures, are treated separately. We develop in this thesis an eco-evolutionary assembly model that allows usto study these two relationships in a unified framework. For each of these relationships, three levels of organization are considered: the network, the network motif (*i.e.* the triplets of species in the network), and the species. We study the role of the evolutionary history of communities in the emergence of these structures, as well as their fragility. We first highlight a key role of evolutionary environmental richness on the emerging structures of food webs and their associated fragilities. We also show that this environmental richness of evolution plays an important role in the type of controls ("bottom-up" *vs*"top-down") present in the communities. Particularly fragile network substructures are then highlighted; substructures that, in combination with other species-level indicators, can be used to strengthen predictions about the fragility of these species. Finally, we study the emergence of the characteristic distribution of these substructures, or network motifs: although common patterns are observed, for example inthe order of appearance, or "fixation", of some of these motifs, we show that the speed of emergence seems to depend on abiotic conditionsof evolution.