Landscape effects on the population dynamics of small mammal communities: A preliminary analysis of prey-resource variations

This study aims at estimating the effect of landscape composition on the av ailability of small mammal preys (in terms of biomass) to predators on a se ctorial scale (n x 1 km(2)). Four study sites, representative of different stages of agriculture intensification, were selected in eastern France acco rding to landscape composition. The population dynamics of Microtus arvalis, Arvicola terrestris, Clethrion omys glareolus and Apodemus sp. were monitored from 1992 to 1996 by using i ndex methods and trapping. M. arvalis and A. terrestris population biomasses were stable in landscapes with low percentage of permanent grassland. M. arvalis populations display ed greater biomass variations with sharp declines in the sites where the pr oportion of permanent grassland to farmland was greater than 50%. A. terres tris populations were very unstable in one study site where the proportion of permanent grassland to farmland was greater than 85%. Synchronic pattern s between M. arvalis populations and the populations of hedgerow rodents we re suspected at sites with large fluctuations of M. arvalis: every decline of the populations of hedgerow rodents was concomitant with the M. arvalis decline. These results suggest that two kinds of ecological systems in terms of prey -resource variations for mammalian predators can be distinguished: (i) stab le in landscapes with lower proportion of permanent grassland, and (ii) uns table, with grassland species crashes and synchronous declines of the roden t community, in landscapes with higher proportion of permanent grassland. Moreover, the population dynamics of small mammals were asynchronous betwee n the four sites situated at relatively short distance (some tens kilometre s).