Environment trumps predation and spatial factors in structuring cladoceran communities from Boreal Shield lakes

Abstract

Understanding local and regional controls on communities is a major theme in ecology. Are communities mainly determined by local environmental gradients, local biotic interactions, and (or) dispersal processes? To address this, subfossil Cladocera were enumerated from the surface sediments of 50 remote Boreal Shield lakes in northwestern Ontario, Canada, to examine three ecologically relevant explanatory categories. Variation partitioning analyses were used to test and quantify the unique and shared effects of local abiotic measures, local predation factors, and spatial variables as predictors of community composition. Thirty-nine taxa were identified and communities were typically composed of pelagic taxa, such as Bosmina , daphniids, and Holopedium gibberum . Environmental variables (i.e., pH, lake surface area, specific conductivity, and lake water total aluminum concentration) explained uniquely 8.8% of the variation, which was 2.5 times greater than the unique contributions of predation or dispersal-related spatial variables. Predation and dispersal processes assumed lesser roles in structuring communities. Considering the extensive geographic scale of this study, our paleolimnological approach indicates that broad-scale dispersal limitation of cladocerans seems negligible for the many taxa examined here. Our findings further support the utility of cladocerans as key biological indicators to track environmental changes within Boreal Shield lakes.