title: The extended Moran effect and large-scale synchronous fluctuations in the size of great tit and blue tit populations.
abstract: 1. Synchronous fluctuations of geographically separated populations are in general explained by the Moran effect, i.e. a common influence on the local population dynamics of environmental variables that are correlated in space. Empirical support for such a Moran effect has been difficult to provide, mainly due to problems separating out effects of local population dynamics, demographic stochasticity and dispersal that also influence the spatial scaling of population processes. Here we generalize the Moran effect by decomposing the spatial autocorrelation function for fluctuations in the size of great tit Parus major and blue tit Cyanistes caeruleus populations into components due to spatial correlations in the environmental noise, local differences in the strength of density regulation and the effects of demographic stochasticity. 2. Differences between localities in the strength of density dependence and nonlinearity in the density regulation had a small effect on population synchrony, whereas demographic stochasticity reduced the effects of the spatial correlation in environmental noise on the spatial correlations in population size by 21.7% and 23.3% in the great tit and blue tit, respectively. 3. Different environmental variables, such as beech mast and climate, induce a common environmental forcing on the dynamics of central European great and blue tit populations. This generates synchronous fluctuations in the size of populations located several hundred kilometres apart. 4. Although these environmental variables were autocorrelated over large areas, their contribution to the spatial synchrony in the population fluctuations differed, dependent on the spatial scaling of their effects on the local population dynamics. We also demonstrate that this effect can lead to the paradoxical result that a common environmental variable can induce spatial desynchronization of the population fluctuations. 5. This demonstrates that a proper understanding of the ecological consequences of environmental changes, especially those that occur simultaneously over large areas, will require information about the spatial scaling of their effects on local population dynamics.
authors.affiliation: Department of Biology, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway. Bernt-Erik.Sather@bio.ntnu.no
authors.forename: Bernt-Erik
authors.initials: BE
authors.lastname: Saether
authors.forename: Steinar
authors.initials: S
authors.lastname: Engen
authors.forename: Vidar
authors.initials: V
authors.lastname: Grøtan
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Fiedler
authors.forename: Erik
authors.initials: E
authors.lastname: Matthysen
authors.forename: Marcel E
authors.initials: ME
authors.lastname: Visser
authors.forename: Jonathan
authors.initials: J
authors.lastname: Wright
authors.forename: Anders Pape
authors.initials: AP
authors.lastname: Møller
authors.forename: Frank
authors.initials: F
authors.lastname: Adriaensen
authors.forename: Hans
authors.initials: H
authors.lastname: van Balen
authors.forename: Dawn
authors.initials: D
authors.lastname: Balmer
authors.forename: Mark C
authors.initials: MC
authors.lastname: Mainwaring
authors.forename: Robin H
authors.initials: RH
authors.lastname: McCleery
authors.forename: Miriam
authors.initials: M
authors.lastname: Pampus
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Winkel
mesh_terms: D000818:Animals; D002980:Climate; D017753:Ecosystem; D005060:Europe; D016015:Logistic Models; D046109:Passeriformes; D011156:Population Density; D011157:Population Dynamics