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Title: Geographic variation in North American gypsy moth cycles: subharmonics, generalist predators, and spatial coupling
Author: Bjornstad, Ottar N.; Robinet, Christelle; Liebhold, Andrew M.
Publication: Ecology. 91(1): 106-118.
Key Words: allee effect, gypsy moth, Lymantria dispar, nonparametric spatial covariance function, Northeastern United States, space-time defoliation data, spatiotemporal dynamics, virus-insect interactions
Abstract: Many defoliating forest lepidopterans cause predictable periodic deforestation. Several of these species exhibit geographical variation in both the strength of periodic behavior and the frequency of cycles. The mathematical models used to describe the population dynamics of such species commonly predict that gradual variation in the underlying ecological mechanisms may lead to punctuated (subharmonic) variation in outbreak cycles through period-doubling cascades. Gypsy moth, Lymantria dispar, in its recently established range in the northeastern United States may represent an unusually clear natural manifestation of this phenomenon. In this study we introduce a new statistical spatial-smoothing method for estimating outbreak periodicity from space-time defoliation data collected with spatial error. The method statistically confirms the existence of subharmonic variation in cyclicity among different forest types.
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