Spatial Synchrony of Spruce Budworm Outbreaks in Eastern North America

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. We investigated the spatial synchrony of outbreaks of the spruce budworm, Choristoneurafumiferana, over much of its outbreak range in eastern North America during the period 1945-1988. Spatial synchrony decreased with distance between local populations and approached zero near 2000 km. Investigation of the synchrony of local population time series with cluster analysis revealed a pattern of geographically distinct blocks of clusters oriented along an east-west axis. Spatial synchrony also was identified in monthly temperature and precipitation time series at 18 weather stations over the same time period and geographical range as the spruce budworm outbreaks. Cross correlations decreased linearly with distance between stations and approached zero near 3000 km and 1800 km, respectively. We developed a spatially explicit lattice model for a single species occupying multiple patches. Within patches, the model had first order logistic dynamics, and patches were linked by dispersal that depended upon their separation distances. Both local and regional stochasticity (i.e., a Moran effect) were present. The modeled lattice had the same spatial configuration as the outbreak region to facilitate investigating the relative effects of a Moran effect and dispersal on spatial synchrony. Simulations with and without a simple regionwide Moran effect and three levels of dispersal did not produce the decrease in spatial synchrony with distance observed with spruce budworm time series. However, when run at the highest dispersal rate, those simulations produced cluster maps similar to that observed for spruce budworm defoliation. Simulations with a spatially autocorrelated disturbance that had either zero or high local variability and three levels of dispersal produced decreases in spatial synchrony with distance similar to that observed in the historical data. When run at the highest dispersal rate, simulations yielded cluster maps similar to the cluster map for defoliation. We discuss the potential significance of the spatially autocorrelated disturbance factor in understanding regional insect outbreaks. We also consider the plausibility of dispersal rates used in our simulations. We suggest in conclusion that spruce budworm outbreaks were synchronized by a combination of a spatially autocorrelated Moran effect and a high dispersal rate.

Spatial scale and the detection of density dependence in spruce budworm outbreaks in eastern North America

“…Although our study and those reviewed by Ray and Hastings (1996) focused on very different ranges of spatial scales, both appear to confirm the effect of averaging over subpopulations, which was postulated by those authors to lower the detection of density dependence at larger spatial scales. Our recent work on spatial synchrony of spruce budworm defoliation (Williams and Liebhold 2000) adds strength to this argument. Across eastern North America, spatial synchrony of defoliation times series decreased with distance between the series.…”

Are bark beetle outbreaks less synchronous than forest Lepidoptera outbreaks?

“…Using spatio-temporal analyses of I. typographus populations, Økland and Bjørnstad (2003) found that large windfall events may be a major synchronizer of beetle outbreaks. This strong association with precipitation and wind is generally not as great for forest Lepidoptera, and they may be more heavily influenced by variation in temperature (Koenig et al 1994;Koenig and Knops 1998;Koenig et al 1999;Koenig and Knops 2000;Williams and Liebhold 2000). Temperature fluctuations tend to be synchronous over longer distances than precipitation (Koenig 2002) or large windfall events (Økland and Bjørnstad 2003), and this may partially explain why Lepidoptera species exhibit more extended synchrony.…”

“…Although outbreak maps are good indicators of forest insect populations at high densities, the relationship between infestation level and actual population density is generally nonlinear, thresholded, and subject to considerable variation (Williams et al 1991;Liebhold et al 1993;Williams and Liebhold 2000), though the relationship for I. typographus appears to be linear (Lindelo¨w and Schroeder 2000). While there may remain some questions about whether the observed differences in synchrony reflect true differences in population densities or not, our results indicate that there are substantial differences in levels of spatial synchrony among different forest insect taxa.…”

Spatial dynamics of Microtus vole populations in continuous and fragmented agricultural landscapes

“…covering hundreds of square kilometres, have most often been associated with species exhibiting cyclic population dynamics, including lepidoptera (e.g. Myers 1998;Williams and Liebhold 2000;Klemola et al 2006), game birds (e.g. Ranta et al 1995a;Cattadori et al 1999) and mammals (e.g.…”