Effects of Forest Connectivity on the Spatial Synchrony of Outbreaks of a Forest Defoliating Insect

Synchronous fluctuations in the densities or population growth of spatially disjunct populations are ubiquitous. The factors responsible for driving this spatial synchrony have long spurred speculation. Traditionally, spatial synchrony in populations is thought to be caused by synchrony in environmental factors (the “Moran effect”), trophic interactions with another species that exhibits synchronous population fluctuations, or dispersal among populations. Since the direct effects of dispersal are difficult to quantify, I investigated the relationship between forest connectivity and the spatial synchrony of outbreaks of the forest defoliating insect Lymantria dispar. Forest connectivity was modeled using circuit theory. Effects of forest connectivity were assessed both across different sampling scales and over different distances (10km, 25km, 50km, and 100km). I found significant positive effects of the connectivity of L. dispar host trees as well as significant positive and negative effects of all tree species combined on spatial synchrony across the different scales of analysis. This suggests that dispersal is a significant driver of the spatial synchrony in this system. This approach exploring the relationship between spatial synchrony and forest connectivity assessed through circuit theory can be used in future studies as a framework for investigating possible differences in the effects of dispersal on synchrony across spatial scales.