Competition and the life table of cladocerans from a tropical shallow lake

Abstract

AbstractLaboratory experiments were carried out to investigate the influence of competition for food, with different combinations of species, using life table data. In Experiment 1, the cultivated chlorophycean Desmodesmus spinosus (Chodat) Hegewald, at a low concentration (0.25 mg C L−1), was used to feed the cladocerans Daphnia gessneri Herbst and Diaphanosoma birgei Kořínek; in Experiment 2, the same alga was used in an even lower concentration (0.15 mg C L−1) to feed three species, D. gessneri, D. birgei, and Ceriodaphnia richardi Sars, in pairs. Three treatments were set up in Experiment 1 (four replicates each): a. control with the species alone; and b. in shared cultures. For Experiment 2, six treatments were set up (three replicates each): a. control with the species alone; and b. pairs of species in shared cultures. Competition for the chlorophycean occurred in Experiment 1, when D. birgei significantly reduced the average life span of D. gessneri, and D. gessneri significantly reduced the gross and net reproductive rates of D. birgei, despite the greater efficiency in all parameters, of survival and reproduction, of the second species. D. birgei was the only species that reproduced under extreme food limitation; in Experiment 2, despite gross and net reproductive rates, generation time, population growth rate and reproductive effort negatively influenced by C. richardi and D. gessneri, in addition to the average life span, also affected by D. gessneri. D. birgei was competitively superior to the other two species being able to reproduce and grow at very low food concentrations.