Spatial synchronization of vole population dynamics by predatory birds

Northern vole populations exhibit large-scale, spatially synchronous popula tion dynamics(1,2). Such cases of population synchrony provide excellent op portunities for distinguishing between local intrinsic and regional extrins ic mechanisms of population regulation(3). Analyses of large-scale survey d ata and theoretical modelling(4-6) have indicated several plausible synchro nizing mechanisms. It is difficult, however, to determine the most importan t one without detailed data on local demographic processes(3,7). Here we co mbine results from two field studies in southeastern Norway-one identifies local demographic mechanisms and landscape-level annual synchrony among 28 enclosed experimental populations and the other examines region-level multi -annual synchrony in open natural populations. Despite fences eliminating p redatory mammals and vole dispersal, the growth rates of the experimental p opulations were synchronized and moreover, perfectly linked with vole abund ance in the region. The fates of 481 radio-marked voles showed that bird pr edation was the synchronizing mechanism. A higher frequency of risky disper sal movements in slowly growing populations appeared to accelerate predatio n rate. Thus, dispersal may induce a feedback-loop between predation and po pulation growth that enhances synchrony.