Spatial synchrony describes how populations fluctuate in abundance or other life history variables in a coordinated way across space. Numerous factors can induce or disrupt synchrony, including dispersal, interspecific interactions, and environmental fluctuations (e.g. Moran effects). In freshwater systems, investigations of synchrony have primarily focused on annual plankton cycles, whereas the drivers of inter-annual oscillations over varying timescales has received less attention. The goal of our study was to assess the temporal scale at which spatial synchrony of plankton occurs within Kentucky Lake, KY, USA. We also determined spatial coherence among biotic and abiotic mechanisms that might explain synchrony patterns. We used 1990-2015 data from the Kentucky Lake long-term monitoring program that samples biological and physiochemical parameters from 16 sampling sites spread across the lower 30 km of the lake. For each site, we generated annual mean values for three herbivorous (Bosmina longirostris, Daphnia sp., Diaphanosoma birgei) and two predaceous zooplankton (Leptodora kindtii and Copepoda), and chlorophyll a, water temperature, pH, conductivity, dissolved oxygen, dissolved/total phosphorous, and dissolved/total nitrogen. We used wavelet analysis to assess synchrony patterns of each variable, and tested for spatial coherence across short (< 4 yrs) and long timescales (> 4 yrs).
Results/Conclusions
We found more significant spatial coherence patterns between pairs of biotic variables than pairs of biotic with abiotic variables. Predatory copepods and L. kindtii both exhibited significant spatial coherence with Daphnia sp. across long timescales, and copepods showed significant coherence at short timescales. Leptodora kindtii showed significant spatial coherence at both long and short timescales with B. longirostris, and marginally significant coherence with D. birgei at long timescales. Copepods and L. kindtii also showed significant coherence with each other at long but not short timescales. These findings indicate that synchrony patterns of certain predator species are disproportionately associated with synchrony patterns of prey in a species-specific manner. For herbivory, B. longirostris was the only species to show significant coherence with chlorophyll a, and only over short but not long timescales. For abiotic factors, copepods and Daphnia sp. showed significant spatial coherence with conductivity at long but not short timescales. Total and dissolved nitrogen and phosphorous showed very limited spatial coherence with chlorophyll a. Tests of spatial coherence were not significant among either water temperature or dissolved oxygen with all zooplankton taxa. Overall, we found greater support for species interactions as potential mechanisms inducing synchrony than abiotic factors.