All medusae had prey in their stomachs. The most
frequent zooplanktonic species in the lake during the
present study were species of the cladoceran Daphnia
galeata × hyalina × cucullata complex and the rotifer
Polyarthra sp. (Tab. 2). Copepods were represented
only by the calanoid E. padanus padanus. The most frequent
prey in the stomachs of C. sowerbii were young
daphniids of the Daphnia complex, mostly 0.9-1.6 mm
in length, while diaptomid copepodites were also found
in the stomachs, although their numbers were comparatively
low. Negative to positive selection was obtained
for members of the Daphnia complex and the rotifers
Polyarthra sp. and Trichocerca sp., in addition to the
dipteran Chaoborus flavicans (Tab. 2). In contrast with
reports in the literature (Spadinger & Maier 1999;
Pérez-Bote et al. 2006), diaptomids were not selected,
but the low density of these taxa in the community can
explain this inconsistency. While negative selection for
small rotifers has been demonstrated (Dodson & Cooper
1983), neutral selection for a big rotifer such as
Asplanchna sp. was unusual, being one of the preferred
prey of C. sowerbii according to the same literature.
All medusae had prey in their stomachs. The mostfrequent zooplanktonic species in the lake during thepresent study were species of the cladoceran Daphniagaleata × hyalina × cucullata complex and the rotiferPolyarthra sp. (Tab. 2). Copepods were representedonly by the calanoid E. padanus padanus. The most frequentprey in the stomachs of C. sowerbii were youngdaphniids of the Daphnia complex, mostly 0.9-1.6 mmin length, while diaptomid copepodites were also foundin the stomachs, although their numbers were comparativelylow. Negative to positive selection was obtainedfor members of the Daphnia complex and the rotifersPolyarthra sp. and Trichocerca sp., in addition to thedipteran Chaoborus flavicans (Tab. 2). In contrast withreports in the literature (Spadinger & Maier 1999;Pérez-Bote et al. 2006), diaptomids were not selected,but the low density of these taxa in the community canexplain this inconsistency. While negative selection forsmall rotifers has been demonstrated (Dodson & Cooper1983), neutral selection for a big rotifer such asAsplanchna sp. was unusual, being one of the preferredprey of C. sowerbii according to the same literature.
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