A Comparison of the Life History Features of a Temperate and a Subtropical Daphnia Species

Abstract

Life history features of the cladocerans Daphia magna Straus and D. laevis Birge were examined in the laboratory at high and low food (Chlamydomonas reinhardi) concentrations at 150, 210, and 270C. D. laevis, the largest limnetic, pond dwelling Daphnia species in Florida, had a significantly higher intrinsic rate of population growth (rm) than did D. magna at both high and low food concentrations at 210 and 270C. This advantage is accrued to D. laevis due to its significantly earlier age at first reproduction at elevated temperatures. Neither species had a reproductive advantage at 150C since both began reproduction relatively late in life. Survivorship of D. magna, a temperate pond-dwelling species, differs little from that of D. laevis at each temperature and food concentration. The fitness advantage accrued to D. laevis at elevated temperatures and low food concentrations may be partially responsible for the absence of larger daphnid species, including D. magna, from a Florida pond that lacks vertebrate predators. These results also shed light on the nature of widespread daphnid rarefaction in both subtropical and tropical aquatic habitats.