The hypothesis that zooplankton evolve tolerance to cyanobacteria on a fine scale was tested by comparing the intrinsic rates of population increase (r) of a dominant cladoceran, Simocephalus vetulus, from seven small isolated lakes with the distances from 2.2 to 31.7 km. The toxic cyanobacterium Microcystis aeruginosa (poor food) significantly depressed the r values, compared with a nutritious…