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Size-dependent vertical distribution in natural systems. Frequency (number of individuals) of a small species (a) D. cucculata and a larger species. (b) Daphnia galeata in size classes from 0.5 to larger than 1.4 mm in surface and bottom waters of Lake Esch-Sur-Sure, Luxembourg (Thys & Hoffman 2005). Curves are fitted to data for clarity and arrow indicates where frequency curves cross, i.e. at which size the majority of Daphnia chose to avoid surface waters.
