POPULATION-DYNAMICS OF DAPHNIA-HYALINA LEYDIG (CRUSTACEA, CLADOCERA) IN A PRODUCTIVE AND AN UNPRODUCTIVE LAKE IN THE ENGLISH LAKE DISTRICT

The population dynamics of Daphnia hyalina Leydig in a productive lake, Esthwaite Water, and an unproductive lake, Buttermere, in the English Lake District have been compared. The winter is passed as resting eggs in the bottom sediments in Buttermere and as free-swimming individuals in the planktonic zone in Esthwaite Water. In Esthwaite Water seasonal periodicity was characterised by maxima in spring and autumn and a minimum in summer; in Buttermere, there was no spring maximum and the first increase in population density was in summer. Population densities were higher and adult females were larger and laid more eggs per clutch in Esthwaite Water than in Buttermere. In each lake males became numerous in autumn. Observed rates of population increase, 'r' and calculated birth rates, 'b' and death rates 'd' were nearly always higher in Esthwaite Water than in Buttermere. © 1979 Dr. W. Junk b.v. Publishers.