Comparative Population Dynamics of Daphnia rosea and Holopedium gibberum in Four Oligotrophic Lakes

Seasonal abundance patterns of Daphnia rosea and Holopedium gibberum showed great variability over the period 1974–83 in four coastal montane lakes of British Columbia. Though the lakes differed considerably in size, depth, and history of experimental disturbance (fish introductions, fertilization, plankton harvesting}, these differences apparently had much less influence on seasonal abundance patterns than did interannual variation in environmental factors shared by all the lakes. Spring rates of population increase differed strongly among years and were positively correlated between the two species. The timing and magnitude of summer population maxima also differed significantly among years, but were not correlated between the species. Adult mortality rates tended to increase through each season for both species, but showed no clear correlations either between the species or between years. Annual differences in growth and mortality rates and peak abundances were not associated with any obvious differences in environmental factors (insolation, rainfall, water temperature). There was no evidence of direct competition between the species, in terms of negative correlations in abundance. This is surprising in view of their similar life histories and feeding ecologies.