Upcoming thesis defences at LAE

Eugène Maurey will defend his thesis on Monday 29 September at 2pm in the Gallé lecture theatre (Presidency) at the Brabois engineering site (Vandoeuvre les Nancy).
The presentation is entitled ‘Quantification of the regulatory service provided by multi-taxonomic communities of predatory arthropods in an agricultural environment.’
He will present the work carried out over the past three years at LAE, under the supervision of Gaël Caro and Benjamin Bergerot.
Omar Hafidi's defence should follow in early autumn. We will provide more details as soon as possible.

Summary : 

Reducing pesticide use to control pest populations is a major challenge for the protection of biodiversity and human health. An alternative now widely recognized by the scientific community is to manage these populations not with chemical inputs, but through their natural enemies already present in agroecosystems. This process is referred to as the natural regulation of pests. These natural enemies encompass a wide range of taxonomic groups, particularly epigeic predatory arthropods such as ground beetles, spiders, and centipedes. To enhance the regulatory service provided by these communities, it is essential to improve our understanding of this service, the factors that drive its variability, and the methods used to quantify it. A promising approach to assessing the natural regulation exerted by epigeic predatory arthropods is to describe the structure of their communities through functional traits related to predation. However, a major challenge lies in the absence of a common functional trait directly linked to predation and applicable to all relevant taxa. To overcome this limitation, we reviewed predation-related traits across the main taxonomic groups of soil-dwelling predatory arthropods and proposed body size as a functional proxy, given its consistent relationship with predation. Based on body size, we estimated the predation potential of communities using the well-known relationships between predator size and prey size. Although body size proved to be informative, our results also highlighted its limitations. This trait alone is insufficient to capture the complexity of predation, which is influenced by ecological context as well as potential methodological biases. Moreover, this focus on body size reflects a lack of empirical data on other key traits related to predation. To evaluate the relevance of our approach, we compared it with a reference method based on modeling energy fluxes in food webs. Our descriptive approach, grounded in body size, successfully predicted predation fluxes within communities. However, we also found that natural regulation does not depend solely on predation: other ecological processes, independent of predator communities, also play a role. This challenges the idea that predation alone can represent the entirety of the regulatory service. Finally, we examined the influence of landscape structure on predation. The analysis of relationships between landscape variables and the predation function revealed little effect. In contrast, taxonomic structure showed a stronger response to landscape variables. This finding highlights the need to better understand the functional responses of communities and to investigate the response traits of predator communities. Indeed, while body size can help anticipate predation, it does not reflect how communities respond to environmental filters at the landscape scale. Nevertheless, an indirect link between landscape and biological control can be established by using taxonomic structure as an intermediary. Thus, by mobilizing taxonomic structure as a response proxy, we can reveal a connection between landscape and biological control. These relationships deserve further investigation in order to identify levers of action within landscapes to promote biological control. This dissertation highlights both the potential and the limitations of a functional approach to analyzing pest regulation by epigeic predatory arthropods. While body size provides a useful starting point, future research should develop multi-trait frameworks that combine effect traits and response traits. Such approaches would provide a more robust and mechanistic understanding of ecological functions and their relationship to landscape structure, ultimately contributing to more effective management of natural regulation in agriculture.