Integrating social interactions between chiropterans and variations in prey abundance to understand the distribution of chiropterans
The feeding behaviour of animals is of vital importance for the physical condition of individuals and is strongly influenced by the transfer of inter-individual information and competition. The study of these cause-effect relationships is particularly difficult for elusive taxa such as bats, whose extremely diverse hunting behaviour and strategies introduce a new degree of complexity. Bats increase the efficiency of their foraging by being attentive to the information-carrying behaviour of other individuals; they then adapt their own behaviour either to avoid competition or to increase it. Previous studies on this phenomenon of listening among bats have produced very different and partly contradictory results, probably because they generally focused on a single species, differed considerably in the rate of eavesdropping and generally did not take account of the activity of conspecifics. Taking these social interactions into account now seems essential both to advance our ‘global’ understanding of how chiropterans integrate social information into their decision-making, to explain species distribution patterns and to elucidate the mechanisms by which species coexist. This understanding will help to provide answers in the field of conservation in relation to the increase in anthropogenic pressures, such as lighting and the fragmentation of environments. The aim of this thesis is to identify the pairs of species that are most subject to competition, in order to understand the causes and perceive the consequences at the scale of the landscape and anthropogenic pressures (light pollution). A second objective will be to characterise the feeding areas and to study the spatio-temporal rearrangement of the food resource - measured directly - over time, and its consequences for chiropterans and their interactions. A third objective will be to apply these concepts to a practical case of anthropogenic modification of natural balances and to model the effects (causal model). The case will be that of the effect of light pollution, and will enable clear hypotheses to be put forward on the effect of light pollution (most of the arthropod prey of chiropterans being attracted and concentrated under light sources) and its consequences on the competitive equilibrium in chiropterans.
Assimilation of heterogeneous data in simulations of atmospheric dispersion of radionuclides at regional scale
Modeling and simulation provide essential knowledge on the aerial dispersion of gases and particles and the resulting environmental marking. This applies in particular to the releases that were generated by atmospheric nuclear tests carried out in the past by France in Polynesia. While regional-scale meteorological and dispersion calculations are reasonably reliable, their results have a degree of uncertainty and present discrepancies with heterogeneous measurements of activities or dose rates in the air, on the ground and in biological compartments. The thesis will aim to develop inversion methods, based on data assimilation, in order to reduce errors and uncertainties in simulations of regional dispersion of radionuclides. The application will concern certain nuclear tests in the atmosphere. However, the methods developed during the thesis, such as Monte Carlo sampling by Markov chains, will have a more general field of implementation. After a literature review on nuclear testing and data assimilation methods, original inverse modeling algorithms will be programmed, tested, and applied to the simulation of the dispersion of aerial releases from tests. This will allow us to estimate the anticipated important role of measurement assimilation in improving simulations.
Alteration mechanisms study of MOX spent fuel in the presence of cimentious bentonitic material (MREA). Experimental and modeling approaches
In France, the reference way remains the reprocessing of spent fuel and the recovery of certain materials such as uranium and plutonium through the elaboration of MOX fuels and its recycling. However, the direct storage of fuels (UOX and MOX) in deep geological repository is also being studied in order to ensure that French storage concepts (Cigéo) are suitable for spent fuels as requested and included in the National Plan for the Management of Radioactive Materials and Waste (PNGMDR). Therefore, it is essential to study the alteration mechanisms of the spent fuel matrices in the presence of environmental materials that are similar, on a laboratory scale, to the current storage concept of radioactive waste in deep geological disposal: HA cells dug in the Callovo-Oxfordian (COx) clay whose low-alloy steel liner is isolated from the clay by a cimentious bentonitic grout called MREA. There is various objectives : on the one hand, to determine the impact of the environment on the alteration mechanisms of the fuel matrix as well as on the radionuclides release, and on the other hand, to develop a geochemical model to account for the main physicochemical processes involved. These studies are carried out at the ATALANTE facility (DHA) of the CEA Marcoule, where leaching experiments and characterizations of MOX fuels are achievable. This work is performed as part of the COSTO project and is supported by Andra and EDF.