PhD projects

The emergence of tick-borne animal and zoonotic diseases is influenced by complex interactions between ticks, transmitted agents, vertebrate reservoir hosts and their habitats. Changes in the composition of the landscape can strongly alter the relationships between species and the abundance of populations, thereby affecting the 'acarological risk', defined as the density of ticks infected by a pathogen.

This PhD is set within the major challenges related to the erosion of aquatic biodiversity. After several decades of improvement, recent studies indicate a slowdown, or even a reversal, of this trend for the richness and abundance of aquatic macroinvertebrates. This situation raises questions about the existence of pressures for which current river protection measures remain insufficient, particularly toxic chemical contamination. Indeed, multi-contamination has been identified as a major threat to aquatic biodiversity, yet its specific effects remain insufficiently characterized and quantified within ecosystems. The recent development of active biomonitoring techniques, now deployed nationwide in France, offers new prospects for specifically qualifying this pressure within the environmental variability, a first step toward addressing the operational challenges of river protection and restoration.

Urban regions face environmental risks that are exacerbated by climate change (CC). By controlling and planning the conversion, restoration, or conservation of natural spaces, spatial planning directly affects the well-being of populations and their resilience to these risks. Indeed, natural spaces contribute to health and well-being and represent an important asset for adaptation and resilience due to the ecological functions they perform and the ecosystem services (ES) they provide (regulation of temperatures, floods, and pollution; recreation and reduction of anxiety; awareness-raising and education about biodiversity; etc.). Yet, planning decisions are rarely studied through the lens of who loses or gains from changes in natural spaces and their ecosystem services.

French forests suffer the combined effects of climatic, health and human disturbances, while at the same time being identified as one of the solutions to the ecological transition. As a result, controversy over the future of forests and associated ecosystem services intensifies. These debates could reflect, on the ground, more profound changes in the interactions between humans and these environments and be embodied in new modes of governance. Drawing on the theories of care, the ontological turn and ethnobotany, our research involves investigating the collective transformations underway in the Livradois-Forez Regional Nature Park.

Anthropogenic pressure on aquatic environments in the SOUTH region is intensifying, amplified by marked climate warming. It manifests as habitat fragmentation, reduced river flow, and warming of water bodies, leading to impacts on fish growth, reproduction, tolerance to hypoxia, and resistance to parasites and contaminants. When these constraints become too severe, multiple hybridizations emerge, linked to the overlap of ecological niches. In this context, the assessment of hybridization rates appears essential, but its implementation on a large scale remains technically and financially challenging. The advent of metabarcoding and environmental barcoding (non-invasive, rapid, inexpensive) allows for a considerable reduction of sampling efforts and species-level identifications.

The thesis aims to understand the impact of biodiversity loss on ecosystem services and to support the ecological transition of agriculture. To achieve this, it relies on a novel approach that models ecosystem multifunctionality, focusing on the synchrony between soil and plants. The objective is to identify the conditions and controlling factors (such as climate, soil, and species diversity) that govern ecosystem functioning. The research also includes both field and laboratory experiments to test these models.

A European study has shown that populations of farmland birds have declined by nearly 60% over the last 40 years, and that intensive agriculture is the main pressure associated with this decline (Rigal et al. 2023). It also shows that the impact of intensive agriculture is compounded by the growing impact of climate change on these populations. However, this large-scale study is based on an approximation of agricultural intensity, measured by the value of pesticide and fertilizer purchases per hectare. This approach is not sufficient for analyzing the role of the multiple facets of agricultural intensification on long-term trends in bird populations. The relative weight of each of these components, as well as their spatial and temporal interactions, still need to be elucidated in order to understand the mechanisms behind the observed decline.

Permanent grasslands play an essential role in maintaining grass-fed livestock and providing key ecosystem services for the agro-ecological transition (pollination, pest control, soil fertility) and society (carbon storage, water purification, aesthetic value). In France, permanent grasslands are one of the most diversified ecosystems but also one of the most threatened at the national scale. Indeed, their surface has considerably decreased over the last decades, which hinders the functioning of agricultural landscapes as well as the conservation of a unique heritage biodiversity. Moreover, global changes are likely to influence the characteristics of the remaining grasslands. However, we lack knowledge on the temporal dynamics of biodiversity and ecosystem services of permanent grasslands at the French national scale, as well as on the underlying causes and consequences of these dynamics.

The project aims to understand the way in which the biological activity of agroforestry systems is structured, in time and space, in relation to the soil multifunctionality in Mediterranean and semi-arid tropical environments. The project will be divided into three lines of research. The first will focus on community structures and soil interaction networks according to different spatial and temporal heterogeneity gradients. The aim is to identify patterns of community assembly and interaction networks at different scales (i) spatial and (ii) temporal.

Lakes and ponds of the Aquitaine Atlantic coast are unique natural ecosystems, not only at the national but also at the European scale. These systems host a high taxonomic diversity, especially for aquatic plants. Indeed, isoetid communities represent a set of species with high conservation value, also including one endemic species. These communities are however highly threatened, especially by anthropogenic activities, and most of the coastal Aquitaine’s lakes have already experienced their extinction. Knowledge on these species is still however scarce, particularly concerning their genetic diversity. While conservation and restoration actions are emerging with the redaction of a National Plan for preserving these communities, understanding their genetic diversity, their relationships with taxonomic and functional diversity appear as a major issue.