Changes in clonal composition of Daphnia taxa in Římov and Vír reservoirs at each of the three sampling stations ( dam , middle and upper ). Distribution of the most common clones (i.e. frequency > 10% in at least one sample) is shown. Remaining clones were pooled and classified as "rare" (white area, up to 100%). NA indicates dates when Daphnia were no longer present at the sampling site. A blank square across the graph indicates a date when there were too few individuals of the species available to calculate clone frequencies (n = 4).