Explaining why fluctuations in abundances of spatially disjunct populations often are correlated through time is a major goal of population ecologists. We address two hypotheses receiving little to no testing in wild populations: a) that population cycling facilitates synchronization given weak coupling among populations, and b) that the ability of periodic external forces to synchronize oscillating populations is a function of the mismatch in timescales (detuning) between the force and the population. These hypotheses were evaluated by applying new analytical methods for quantifying the geography of synchrony to field survey data on gypsy moth outbreaks. We measured cross-wavelet synchrony and phase synchrony of gypsy moth defoliation in local neighborhoods across the study area at two timescale ranges, 2-4 years and 7-11 years.
Results/Conclusions
We report that at timescales associated with gypsy moth outbreaks (7-11 years), spatial synchrony and phase synchrony increased with population periodicity. The extent to which synchrony in temperature and precipitation influenced population synchrony was associated with the degree of mismatch in dominant timescales of oscillation. Partially synchronized fluctuations in precipitation at the 7-11 year timescales appeared to be the main abiotic driver of population synchrony, perhaps because there was less detuning (frequency mismatch) between the dominant timescales of fluctuations in defoliation (~7-11 years) and that of precipitation (~7-9 years) than between defoliation and temperature fluctuations (~3.9 years). Our study provides new empirical methods and rare empirical evidence that population cycling and low detuning can promote population spatial synchrony.