The gypsy moth (Lymantria dispar) invasion is among one of the best documented in the United States. Despite the extensive amount of spatiotemporal distributional data that is currently available for this species, important gaps in our understanding of gypsy moth spread remain. For instance, we lack a clear understanding of how drivers of gypsy moth range expansion operate and interact at large spatial extents. In this study, we explored the roles of various anthropogenic and environmental factors in range expansion dynamics of this high profile pest. Specifically, we investigated the effects of these factors on the rate at which 5 by 5 km quadrats across the U.S. invasive range become invaded. To achieve this, we used an extensive database of annual gypsy moth trap catch data (from 1985 to 2015), spanning from North Carolina to Wisconsin, compiled by the USDA-sponsored Slow the Spread program. We applied an innovative Bayesian probabilistic framework to determine the invasion status of quadrats, and therefore calculate the number of years from first appearance of a gypsy moth to invasion (i.e. waiting time to invasion). To assess the effects of the various drivers on each quadrat’s waiting time to invasion, we performed LASSO regression models for three different regions within the invasive range, including a full range model.
Results/Conclusions
The findings of this study demonstrate the utility of big data and macroscale studies. Here, we were able to illustrate a hierarchy of drivers of range dynamics of a high-profile pest that is applicable across the U.S. invasive range. In this hierarchy, factors that enhance population growth, such as seasonal temperatures and precipitation, were more important determinants of invasion rate than natural and anthropogenic drivers of propagule pressure, such as human population density and fragmentation. Furthermore, our findings bring forth potential implications of climate change on gypsy moth range expansion. We found that winter temperatures are the strongest limits to range expansion, particularly in the northern parts of the range. Increasing global temperatures may lessen the strength of these limits, potentially resulting in faster spread rates in the northern leading edges.