Spatial synchrony of exploited or economically important taxa should, theoretically, have substantial impacts for humans, as synchrony can produce high-amplitude oscillations through time in the total populations of large spatial regions. However, synchrony has seldom been investigated empirically for exploited species, and its importance for management is not often considered. We investigated causes and consequences of synchrony in white-tailed deer (Odocoileus virginianus) in Wisconsin, including whether deer synchrony had subsequent impacts on human populations through deer-vehicle collisions (DVCs), and whether deer synchrony may impact hunting success. We used county-level data spanning several decades, and a variety of wavelet-based analytic techniques, some developed recently.
Results/Conclusions
We found that deer were strongly synchronized across Wisconsin, principally on 3–7-year timescales. Synchronized environmental variation (i.e., Moran effects) over the winter months, related to snow depth, the El Niño Southern Oscillation, and the Pacific Decadal Oscillation, explained up to 88% of deer synchrony. Synchrony of numbers of hunters in each county did not explain synchrony of deer, except possibly at very short timescales (2-2.5 years), where little deer synchrony occurred. DVCs were in turn synchronized by deer populations at 3–7-year timescales, indicating that Moran effects cascaded through the system. Timescale-specific synchrony resulted in large, state-wide fluctuations of both deer and DVCs on 3–7-year timescales that would not occur if the synchrony were absent. Peak-trough distances of these fluctuations were >250,000 deer and >2500 DVCs, constituting a major phenomenon and likely affecting industries related to hunting and DVC recovery. This study provides a novel mechanism for population cycling that operates on large spatial scales. This study is the first we know of to show how synchrony in exploited taxa can impact humans across large spatial scales.