UBC Theses and Dissertations

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UBC Theses and Dissertations

Predation interactions between zooplankton and two species of Chaoborus (Diptepa, Chaoboridae) in a small coastal lake Fedorenko, Alice Y.R.


Feeding habits of two coexisting species of Chaoborus, C.trivittatus and C.americanus, were investigated in lake and in laboratory experiments, and by an extensive survey of larval crop contents. The field study showed that C.trivittatus has a two year life cycle, migrates dielly during the summer season down to 20 m, and is the more abundant of the two Chaoborus species. C.americanus has a one year life cycle and migrates at most over a distance of only 5 m. Seasonal abundance and distribution of most plankton types found in Eunice Lake were monitored during 1971 and 1972. Zooplankton had a low standing crop and were mostly found above 6 m. Zooplankton size and swimming velocity and size of larval head parts were measured in the laboratory and, together with the above data on vertical distribution, were used to evaluate the availability of zooplankton as prey for Chaoborus. The lake and laboratory experiments showed that rates of larval feeding and digestion increase significantly with temperature. Temperature, however, does not seem to affect feeding rate of the 4th instar C.trivittatus larvae. Feeding rates increase with larval age and vary with prey type and density. From analysis of chaoborid crop contents, diet differences were found among all instars of the two species, and these were related to prey size, abundance, and distribution. The calculated percent of prey standing crop that the Chaoborus in Eunice Lake could potentially remove ranged from a minimum of 3% for nauplii to a maximum of 20% for Diaptomus kenai. Seasonal changes in Choaborus instar composition and in zooplankton species composition result in reduced predation on any single zooplankton group. The observed diet of Chaoborus larvae in Eunice Lake was shown to be closely related to the morphology of Chaoborus and their prey and to the relative distribution of predator and prey.

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