Implications of long-term dynamics of fish and zooplankton communities for among-lake comparisons

Understanding the environmental determinants of lake community composition has been a central pursuit in freshwater ecology. Previous studies have defined community composition based on temporally limited surveys, with the implicit assumption that interannual variation is negligible compared with among-lake variability. Using a long-term data set for fish and zooplankton communities in five north temperate lakes (Wisconsin, USA), we found that interannual, within-lake similarity in species composition (a measure of temporal stability in community composition) generally exceeded community similarity among lakes. Despite these differences, however, the strength of community-environment relationships were found to range widely (2%-99% explained variation) depending on the choice of single-year sample used in the analysis, a result of high temporal coherence in limnological and biological characteristics. Perhaps of greatest concern, interannual similarity in species composition showed consistent relationships with habitat variables commonly used to explain community differences among lakes. Decreasing lake area and shoreline perimeter (indicative of lower habitat heterogeneity) and seepage lakes were associated with low interannual similarity in community composition, thus confounding the ability to differentiate among lake communities according to their habitat characteristics. In light of our results, we offer a number of explicit recommendations for the selection and analysis of community data in future cross-lake studies.