Abstract:The 48 h-LC50 of Pb2+ to M. macrocopa was determined by an acute toxicity test, and the effects of different concentrations (0.2, 0.4, 0.6, 0.8 and 1.0 mg/L) of Pb2+ at three densities (0.5×106, 1.0×106, 2.0×106 cells/mL) of algae Scenedesmus obliquus on life table demography of M. macrocopa was studied by a life table experiment. The result showed that the 48 h-LC50 of Pb2 to M. macrocopa was 10.5 mg/L. Compared with the controls at every algal concentrations, except that Pb2+ at 0.2 mg/L prolonged significantly the life expectancy at birth of M. macrocopa cultured at the algal densities of 0.5×106 and 1.0×106 cells/mL, and Pb2+ at 0.4 mg/L increased the net reproductive rate and Pb2+ at 0.4-0.8 mg/L increased the intrinsic rate of population growth of the animals cultured at the algal density of 0.5×106 cells/mL, Pb2+ at higher concentrations shortened the life expectancy at birth, decreased the gross reproductive rate, the net reproductive rate and the intrinsic rate of population growth. With the rise of the algal density, the threshold of Pb2+ concentration decreasing the gross reproductive rate and the net reproductive rate had a decline tendency, but the reverse was also true for that shortening the generation time. Pb2+ concentration, algal density, and their interactions had significant effects on all the life table demography of M. macrocopa (P<0.05). When the algal densities were 0.5×106 and 1.0×106 cells/mL, there were significant dose-effect relationships between Pb2+ concentration and each of all the life table demography. When the algal density was 2.0×106 cells/mL, there were dose-effect relationships between Pb2+ concentration and the life expectancy at birth, the gross reproductive rate as well as the net reproductive rate. The life expectancy at birth, the net reproductive rate and the intrinsic rate of population increase of M. macrocopa had different sensitivities to Pb2+ pollution with different food densities.