Abstract
The surface area occupied by cities continues to increase, especially in the Mediterranean region. This process of urbanization profoundly alters the environment at both local and landscape scales, posing a global threat to biodiversity, particularly in soils. However, urban areas contain green spaces with diverse uses (food production, recreational, roadside landscaping) that can contribute to biodiversity conservation. Among soil communities, earthworms and ants play key ecological roles and serve as valuable bioindicators to assess habitat disturbances. Additionally, these organisms exhibit differences in dispersal abilities and dietary strategies, which can lead to distinct responses to disturbances at local and landscape scales. Furthermore, the Mediterranean region is considered a global biodiversity hotspot for these groups. Nevertheless, there have been very few studies conducted on these organisms in Mediterranean urban contexts.This thesis aims to identify environmental factors influencing earthworm and ant communities within different urban green spaces in the Mediterranean city of Montpellier, using a multi-scale, multi-taxa approach. Three complementary research axes were developed: axis 1 investigates ant responses in 24 urban forests distributed along an urbanization gradient; axis 2 examines the response of earthworm and ant communities in 40 urban sites, including food production areas and recreational or roadside green spaces, also distributed along an urbanization gradient; and finally, axis 3 explores earthworm distribution patterns using a genetic and phylogeographic approach within a subset of sites from axis 2.Axes 1 and 2 revealed a homogenization of communities across the metropolis, despite the considerable variability of green spaces studied, ranging from urban forests to a variety of open habitats. Local and landscape factors influencing these communities were also identified, with effects at multiple scales on earthworm communities, but a lack of response from ant communities to landscape factors. Axis 3 allowed for a refined analysis of earthworm distribution in Montpellier and highlighted a high genetic diversity of earthworms, as well as innovative results in an urban context. This thesis thus isolated environmental factors affecting earthworms and ants at various scales, from local to landscape, as well as from gene to community.