. California fish and game. Fisheries -- California; Game and game-birds -- California; Fishes -- California; Animal Population Groups; Pêches; Gibier; Poissons. Station VIII :l :l a is Q pulicana length [n FIGURE 5. Daphnia pulicana egg density, mean size of reproductive females, and size frequency distribution at Stations III and VIM, Big Bear Lake, California, January-November 1978. During stratification the D. pulicaria population was concentrated just above the thermocline (Figure 6). Dissolved oxygen depletion in the hypolimnion apparently restricted the D. pulicaria population to the up
. California fish and game. Fisheries -- California; Game and game-birds -- California; Fishes -- California; Animal Population Groups; Pêches; Gibier; Poissons. Station VIII :l :l a is Q pulicana length [n FIGURE 5. Daphnia pulicana egg density, mean size of reproductive females, and size frequency distribution at Stations III and VIM, Big Bear Lake, California, January-November 1978. During stratification the D. pulicaria population was concentrated just above the thermocline (Figure 6). Dissolved oxygen depletion in the hypolimnion apparently restricted the D. pulicaria population to the upper strata. In the spring, prior to stratification, D. pulicaria was concentrated near middepth during the day and exhibited a distinct noctural ascent (Figure 6). Ceriodaphnia, a potential competitor of Daphnia (Lynch 1978), exhibited a similar life history, but one slightly out of phase with D. pulicaria in Big Bear Lake (Figure 4). Ceriodaphnia quadrangula population maxima generally occurred earlier than D. pulicaria maxima. The nonsynchrony of population trends of these two cladocerans may be, in part, a reflection of competitive interactions. Daphnia and Ceriodaphnia share the same resource base and both can limit the abundance of their resources (phytoplankton and bacteria) (Lynch 1978). Competition between adult Ceriodaphnia and juvenile Daphnia may have lim- ited the spring maximum of D. pulicaria. Although D. pulicaria brood size was highest in the spring, the annual population maximum did not occur until late in the year. Replacement of D. pulex by Ceriodaphnia as the dominant member of the zooplankton community has been related to competition between adult Ceriodaphnia and juvenile D. pulex (Lynch 1978). Competitive interactions of this type may be mediated by predation by planktivorous fish in Big Bear Lake. Ceriodaphnia quandrangula life history in Big Bear Lake was similar to that of D. pulicaria. The winter was passed either as large free-swimming reproductive
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