Chaoborus populations: response to food web manipulation and potential effects on zooplankton communities

Chaoborus populations were studied in two lakes in which fish predation was experimentally reduced, and in a reference lake. In Tuesday Lake, major reduction of fish predation led to substantial increases in density of Chaoborus punctipennis. Analysis of crop contents and estimates of consumption rates suggested that C. punctipennis caused declines of rotifer and copepod populations following the manipulations. In Peter Lake, lesser changes in fish predation caused no major change in density of Chaoborus flavicans, perhaps because food limitation compensated for effects of reduced predation. In both Peter Lake and the reference lake, Paul Lake, C. flavicans preyed heavily and selectively on Daphnia less than about 1.4 mm in total length. Bioenergetic calculations indicated that up to 46% of the daphnids were consumed daily. At some times of the year, certain zooplankton populations (especially noncolonial rotifers, small copepods, and small cladocerans) were strongly influenced by Chaoborus predation.

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