UBC Theses and Dissertations

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UBC Theses and Dissertations

The relative importance of food availability and predation to the juvenile survival of Diacyclops thomasi Bowerman, Joy E.


In situ enclosure experiments were conducted in Placid Lake, British Columbia to determine the effect of food availability and predation on the naupliar survival of D. thomasi. These experiments revealed that food limitation due to competition from the grazing assemblage, interspecific predation by D. kenai and intraspecific predation by D. thomasi adults could all substantially affect the survival of D. thomasi nauplii. Subsequent feeding studies showed that D. kenai at lake densities were capable of preying on nauplii at a rate of 20% of nauplii per predator per day and this seemed to account for most of the mortality of D. thomasi nauplii in enclosures with D. kenai. When these results were extrapolated to two oligotrophic montane lakes, cannibalism was judged to be the major mortality agent. In the Placid Lake community, the effect of interspecific predation and competition acted only earlier and later in the season respectively, and the magnitude of their effect was influenced by year to year variation in weather. In Eunice Lake, in which D. thomasi has recently become a community dominant, experimental results suggested that D. kenai had previously limited D. thomasi in the lake. The introduction of cutthroat trout and a mild winter seemed to be responsible for the decline in D. kenai and concurrent increase in D. thomasi.

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