THÈSE - Université de Franche-Comté

shown that farming practices can impact small mammal populations. For instance, Jacob et al.
(2001; 2003) demonstrated a gradient of short-term farming practice disturbances (mulching <
mowing < harvesting < grazing < harrowing < ploughing) on the common vole Microtus
arvalis populations (Jacob & Halle 2001; Jacob 2003; Jacob & Hempel 2003). Edwards,
Crawley & Heard (1999) showed that farming practices such as grazing, soil acidification and
plant removal could reduce molehill production in grassland parcels by reducing the
availability of mole Talpa europaea principal food source (earthworms).
In eastern France and in western Switzerland, cyclic population outbreaks of the fossorial form
of the water vole Arvicola terrestris scherman (Shaw 1801) have been observed on a large
scale since the 1970s in farmland, mainly in mid-altitude mountains (Jura, Massif Central,
Alps) (Saucy 1994; Giraudoux et al. 1997; Fichet-Calvet et al. 2000). In these locations,
population outbreaks are travelling waves, starting from clusters of communes (French
administrative units) called “epicentres”, where high density occurs first, and spreading to
“diffusion” communes on a 6-years cyclic pattern. High population density on a large extent
causes severe crop damage and important economic losses (Meylan 1981). They have also
been linked to a higher prevalence of human alveolar echinococcosis, a lethal parasitical
disease maintained via a fox - small mammal cycle (Raoul et al. 2001). Chemicals have been
used to control water vole population outbreaks but they may result in secondary poisoning of
non-target wild animals (Brakes & Smith 2005). Evidence has been provided that the risk of
population outbreak is related to landscape features, e.g. the ratio of Permanent Grassland
(optimal habitat for the water vole) to Agricultural Land (PG/AL), on the regional scale. This
has been termed: the landscape composition effect (Giraudoux et al. 1997; Fichet-Calvet et al.
2000). The authors also showed that population destabilization occurs when a particularly high
PG/AL ratio is found (> 85%). On a sectorial scale, Duhamel et al. (2000) showed that
epicentres are generally comprised of large grassland openfields (51 %) and few forest (22 %),
as compared to diffusion communes (respectively 32 and 46 %). This has been termed the
landscape structure effect.
On a parcel scale (n x 10 m) two earlier studies, carried out in the farmland of the Swiss Jura
mountains, suggested a bottom-up regulation of water vole populations. Capture-markrecapture
and radiotelemetry experiments indicated that the first vole colonies were distributed
in grassland parcels with abundant plant cover (Saucy 1988). In a long-term study, on the
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