THÈSE - Université de Franche-Comté

Summary
1. Small mammals are the most important vertebrate pests in Central European agriculture. In
Western continental Europe, cyclic outbreaks of Arvicola terrestris populations have caused
dramatic grassland damage since the 1970s. One explanation could be that intensive
agriculture has created homogeneous grassland ecosystems with a high risk of outbreaks.
While the role of the landscape structure on A. terrestris outbreaks has been identified on a
large scale, little is known about the quantitative effects of grassland management on a local
scale. We aimed to investigate the impact, on a parcel scale, of farming practices on the A.
terrestris population increases, in order to identify which practices may significant affect
population changes and how they could be used to minimize the risk of outbreaks.
2. We examined different phases of an A. terrestris population cycle in agricultural parcels :
low density, increase and high density. For each parcel, relative abundance of A. terrestris
were estimated by an index method. Talpa europaea populations were also taken into account,
as they may play an important role in the early stages of A. terrestris population increases.
Farmers were interviewed about their land-use practices related to fertilisation, mowing, soil
work and grazing.
3. Farming practices significantly influenced A. terrestris populations. Intensive farming
practices (organic fertilisation and mowing) stimulated an early and more rapid growth of the
A. terrestris population. In contrast, disturbances such as grazing and soil work were
unfavourable to the abundance level of the A. terrestris population at the high density phase.
4. During increase phase, the A. terrestris populations reached higher abundance levels in the
parcels where the relative abundance of T. europaea were initially higher.
5. Synthesis and applications. Habitat manipulation by land managers offers a promising
alternative in more integrated control of A. terrestris outbreaks. We outline that practices
indirectly disturb populations, such as grazing and ploughing dampened population dynamics
in more heterogeneous agrosystems. Thus, rethinking the spatial arrangement of grazed,
ploughed and mowed parcels may be an effective way to stabilize populations and facilitate
the implementation of other control methods (e.g. trapping or chemical rodenticides). We also
recommend controlling T. europaea and A. terrestris populations at low density phase.
Thèse C. Morilhat 2005 98