Vole cycles in western France: an old question revisited with modern tools

Cyclic dynamics are observed in many rodents. In a first step, single explanations were searched for explaining all cycles. However, more local studies have shown that causes of cycles are often different depending on the species or the habitat concerned. It is therefore important to work at a local level to understand the specific dynamics shown by cyclic populations. In this thesis, I sought to understand the cyclical dynamics of voles in the agricultural plains of western France. Three axes were mainly addressed: 1) the structure of density dependence; 2) The changes in demographic traits (survival and reproduction) responsible for the different phases of the cycles; 3) The relationships between demographic traits and agriculture. Modeling approaches, analysis of empirical data and experimental data were used. The main results are that the vole cycles show two density dependent phases. The decline phase takes place in winter and is due to a reproduction change through direct density dependence. The second is the low phase. The latter is probably multifactor and due to delayed density dependence mechanisms. Finally, we have shown that agricultural practices and crop type had a strong impact on the demographic traits and those depend on the season. This thesis gives a consistent pattern explaining how our common vole population enter and maintain cyclic dynamic. However, the underlying mechanisms remain unclear. In this context, some works have been initiated concerning research of maternal effects or resource depletion.