SYNCHRONY IN POPULATION-DYNAMICS

Our data are long-term population dynamics of a set of species in diff erent localities in Finland. There is considerable level of species-sp ecific synchrony in population fluctuations among the localities. The degree of synchrony levels off with increasing distance among the popu lations compared. Climatic perturbations and dispersal have been propo sed as pace-making factors for synchrony. According to Moran's theorem , local populations sharing a common structure of density dependence s hould become synchronized under the influence of a spatially correlate d density-independent factor. This predicts synchrony to decay slower with increasing distance between local populations than if the synchro ny is caused by dispersal. To explore the significance of the Moran ef fect and dispersal in explaining the observed regional synchrony, we u sed a metapopulation system. The Moran effect and dispersal are both c apable to synchronize alone local population fluctuations. However, wi th dispersal the level of synchrony decreases with distance among the populations. Adding Moran's effect does not greatly affect the level o f synchrony, nor the negative correlation between synchrony and distan ce. This finding makes it difficult to tell apart whether an observed negative correlation between the level of synchrony and distance among the compared populations is caused by dispersal alone, or both disper sal and Moran's effect acting together.