Synchronization of gypsy moth outbreaks along an invasion front

Herbivourous forest insects can become pest when local population fluctuations are geographically synchronized to result in regionalized outbreaks. The spatial synchrony is important in at at least four different ways. First, it dilutes the regulating effects of any natural enemy that could otherwise provide local control. Second, it reduces the ecological landscape’s ability for buffering because most areas within a watershed or greater ecosystem will experience simultaneous disturbance. Third, it greatly exacerbates  the economic burden on any individual stake-holder because a majority of his/her tract of land may be damaged during any given outbreak. Finally, the massive geographical scale of many of these outbreaks -- for example the 65 million cumulative acres defoliated by the gypsy moth over the last 25 years -- vastly overwhelms the budgetary and logistical capabilities of federal or state agencies to suppress populations and thereby mitigate impacts. Despite its ecological significance, studying the process of synchronization is difficult because most fluctuating populations are, at least locally, fully or partially synchronized. In this study we show that Gypsy moth offers an interesting opportunity for studying synchronization because outbreaks along the invasion front are initially out of phase with well-established populations, yet synchronize with 'the great attractor’ within 15-20 years of invasion. We develop a spatial-extended theoretical model for the system and show that the initial asynchrony is caused by a strong Allee effect in nascent populations. We further use the model to explore plausible causes for the rapid synchronization.