Synchrony in population dynamics

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Abstract
Our data are long-term population dynamics of a set of species in different localities in Finland. There is considerable level of species-specific synchrony in population fluctuations among the localities. The degree of synchrony levels off with increasing distance among the populations compared. Climatic perturbations and dispersal have been proposed as pace-making factors for synchrony. According to Moran's theorem, local populations sharing a common structure of density dependence should become synchronized under the influence of a spatially correlated density-independent factor. This predicts synchrony to decay slower with increasing distance between local populations than if the synchrony is caused by dispersal. To explore the significance of the Moran effect and dispersal in explaining the observed regional synchrony, we used a metapopulation system. The Moran effect and dispersal are both capable to synchronize alone local population fluctuations. However, with dispersal the level of synchrony decreases with distance among the populations. Adding Moran's effect does not greatly affect the level of synchrony, nor the negative correlation between synchrony and distance. 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 dispersal and Moran's effect acting together.