Résumé
This study aims at estimating the effect of landscape composition on the availability of small mammal preys (in terms of biomass) to predators on a sectorial scale (n x 1km2). Four study sites, representative of different stages of agriculture intensification, were selected in eastern France according to landscape composition. The population dynamics of Microtus arvalis, Arvicola terrestris, Clethrionomys glareolus and Apodemus sp. were monitored from 1992 to 1996 by using index methods and trapping. M. arvalis and A. terrestris population biomasses were stable in landscapes with low percentage of permanent grassland. M. arvalis populations displayed greater biomass variations with sharp declines, in the sites where the proportion of permanent grassland to farmland was greater than 50%. A. terrestris populations were very unstable in one study site where the proportion of permanent grassland to farmland was greater than 85%. Synchronic patterns between M. arvalis populations and the populations of hedgerow rodents were suspected at sites with large fluctuations of M. arvalis: every decline of the populations of hedgerow rodents was concomitant with the M. arvalis decline. Those results suggest that two kinds of ecological systems in terms of prey-resource variations for mammalian predators can be distinguished: (i) stable in landscapes with lower proportion of permanent grassland, and (ii) unstable, with grassland species crashes and synchronous declines of the rodent community, in landscapes with higher proportion of permanent grassland. Moreover, the population dynamics of small mammals were asynchronous between the four sites situated at relatively short distance (some tens kilometres).