The Temporal Coherence of Zooplankton Population Abundances in Neighboring North-Temperate Lakes

We investigated the temporal coherence (i.e., the correlation or synchrony between time series) of annual abundances among populations of freshwater zooplankton in eight lakes in Ontario, Canada, from 1980 to 1992. We estimated temporal coherence using the intraclass correlation coefficient (r_i). While values of r_i were relatively low among comparisons of all eight lakes, they were statistically significant for three of the seven common cladoceran and copepod taxa (Bosmina longirostris, Leptodiaptomus minutus, and Mesocyclops edax). These significant positive correlations imply that a portion of the interannual variation in abundance was produced by factors operating on a scale larger than the individual lake catchments. Because the eight-lake analysis might obscure strong, but conflicting, patterns among lakes in the region, we identified homogeneous and temporally coherent subsets of lakes for each species using an exploratory stepwise deletion procedure. The resultant homogeneous subsets exhibited much greater temporal coherence, accounting for 47% (Eubosmina) to 84% (Leptodiaptomus) of the interannual variation in abundance. Our results suggest that the factors affecting annual variation in zooplankton abundance must be sought both within lakes and beyond their watersheds.