Abstract
Spatial synchrony between populations emerges from endogenous and exogenous processes, such as intra- and interspecific interactions and abiotic factors. Understanding factors contributing to synchronous population dynamics help to better understand what determines abundance of a species. This study focuses on spatial and temporal dynamics in the Eurasian red squirrel (Sciurus vulgaris) using snow-track data from Finland from 29 years. We disentangled the effects of bottom-up and top-down forces as well as environmental factors on population dynamics with a spatiotemporally explicit Bayesian hierarchical approach. We found red squirrel abundance to be positively associated with both the abundance of Norway spruce (Picea abies) cones and the predators, the pine marten (Martes martes) and the northern goshawk (Accipiter gentilis), probably due to shared habitat preferences. The results suggest that red squirrel populations are synchronized over remarkably large distances, on a scale of hundreds of kilometres, and that this synchrony is mainly driven by similarly spatially autocorrelated spruce cone crop. Our research demonstrates how a bottom-up effect can drive spatial synchrony in consumer populations on a very large scale of hundreds of kilometres, and also how an explicit spatiotemporal approach can improve model performance for fluctuating populations.
Highlights
Population dynamics often show positive spatial autocorrelation
The spatial range estimate in the best-fit spatiotemporal model reaches 655 ± 90 km, which is the distance where the spatial autocorrelation becomes negligible between red squirrel populations on average
The correlograms do not show where the populations become fully disconnected on average as the negative synchrony appears to continue beyond the spatial coverage of the data
Summary
Population dynamics often show positive spatial autocorrelation. Changes in abundance in neighbouring populations occur simultaneously and in the same direction, and this synchrony abates with distance (Liebhold et al 2004). Possible reasons underlying synchrony include dispersal (Ranta et al 1995; Kendall et al 2000), regional stochasticity due to environmental factors (Moran effect; Moran 1953; Royama 1992), nomadic predators (Norrdahl and Korpimäki 1996; Korpimäki et al 2005) and trophic interactions with another species that shows synchrony (Byholm et al 2002; Satake et al 2004; Cattadori et al 2005). A common cause of synchrony in consumer populations is a spatially autocorrelated food resource. Autocorrelation of the resources can in turn be caused by environmental conditions, which in this context is a form of Moran effect. Understanding synchronous population dynamics and factors contributing to them can help to better understand core issues in ecology, like what determines abundance and trend of a population.
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