UNTANGLING THE CAUSES OF DISAPPEARANCE FROM A LOCAL-POPULATION OF ROOT VOLES, MICROTUS-OECONOMUS - A TEST OF THE REGIONAL SYNCHRONY HYPOTHESIS

Ydenberg proposed that nomadic predators are responsible for the obser ved geographical synchrony in microtine population dynamics in Fennosc andia. I tested this hypothesis by studying an alpine assemblage of mi crotine species being out of phase with the neighboring areas by using mortality-collars and mark-recapture trapping. The studied population failed to increase during the summer although the females were breedi ng continuously. Predators caused a 82% mortality rate (25 of the 26 o bserved deaths) during summer among the adults, which is sufficient to synchronize otherwise asynchronous populations. Young root voles had lower persistence than adult root voles in the start of the summer but this trend was reversed in the latter part of the summer. Persistence of young voles was significant negatively correlated with the observe d dispersal rates of the adults. Adult dispersal occurred only in the first part of the summer. Survival rates of young root voles were not significantly correlated with the observed survival rates of the morta lity-collared adults. Hence, the very low apparent survival (persisten ce) of young root voles early in the summer was probably due to high d ispersal rates and not high in situ mortality rates.