Small mammals often play a crucial role during plant succession; for example, from semi-desert to grassland (Brown & Heske 1990) or from open grassland to forest (Jensen & Nielsen 1986). Although the effect of seed predation on succession has been discussed for more than two decades (Janzen 1971), it is still controversial (Davidson 1993; Hulme 1996a). Rodents have been shown both to enhance and to hinder succession. Their habit of collecting seeds and then burying them elsewhere, as distant as 20–30 m from the collecting site, aids the dispersal of the plants (Abbott & Quink 1970). Although the seeds are clearly stored for future consumption, seeds frequently survive to germination (Vander Wall 1990). On the other hand, seed predation by rodents, particularly after dispersal, is one of the most important mechanisms of slowing down old-field succession (De Steven 1991; Gill & Marks 1991). It follows that any seed preference of the granivores has a potential effect on species-specific regeneration rates and on colonization, and hence might affect the community structure.
Although many studies have focused on seed preferences of small mammals in deserts (Hay & Fuller 1981; Abramsky 1983; Kelrick et al. 1986) and in temperate regions of North America (Mittelbach & Gross 1984; Whelan et al. 1990; Willson & Whelan 1990; Myster & Pickett 1993; Schwantes Boman & Casper 1995), seed predation in European temperate vegetation is poorly investigated (but see Hulme 1996b; Hulme & Borelli, in press). Moreover, we are not aware of any study in which consistencies of seed predation were compared among seasons, years and sites. Because seed rain is often seasonal, for example, in temperate fleshy-fruited species (Kollmann 1994), seasonal differences in seed predation have a high potential impact on recruitment.
The two objectives of this paper are to investigate (1) spatio–temporal consistencies in seed preferences and (2) the reasons underlying these preferences. We tested seed predation of rodents among 12 fleshy-fruited species in early successional forest. Selectivity was compared among four seasons and 2 years in south-west Germany and during one summer in south England. The animals responsible for predation were identified with selectively accessible seed dishes and live traps. Where strong and consistent preferences occurred, we attempted to explain them by looking at basic seed characteristics.