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

Abstract

Laboratory 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.

Competition of Cladocerans for Natural Seston from a Tropical Shallow Lake

“…Our results agree with several studies that report a greater sensitivity of juveniles with the increasing body size of the species [2,5,6,41]. In other studies with cladocerans of Lake Monte Alegre, there was already an indication of the greater sensitivity of young D. gessneri regarding limiting food [25], which resulted in lower rates of juvenile growth compared to C. richardi [42]. In addition, the low reproductive rates of D. gessneri fed seston in the present study agree with work by [43], who reported the low growth of this species in the seston of Lake Monte Alegre, although the quantity and quality of edible algae were favorable to cladocerans, particularly in summer.…”

“…Unlike D. gessneri, the life table parameters of C. richardi were not affected by the competitor. The superiority of C. richardi over D. gessneri agrees with experimental studies with the edible chlorophycean Desmodesmus spinosus [10,25]. The smaller species excluded the larger one in a few days of the experiment at low but not high food concentrations of the edible chlorophycean [10].…”

“…Although the threshold food concentration (TFC) for D. birgei is unknown, the species showed through its reproductive rates that the TFC may be even lower than that found for the species D. gessneri and C. richardi. In experiments with a chlorophycean, at very low concentrations, D. birgei was the only one able to reproduce compared to C. richardi and D. gessneri, even experiencing the effects of competition with them [25].…”

“…The experiments followed a standard procedure used in the laboratory described by [25]: "the cladocerans were initially kept in 140 mL glass bottles, and then transferred to 600 mL bottles, after the increase of the organisms, for avoiding the crowding effect. The bottles were filled with lake water filtered on glass fiber membrane (Millipore AP20), plus 1 mg C L −1 of the chlorophycean D. spinosus as food.…”

“…Studies on competition between cladocerans from Lake Monte Alegre have focused on laboratory experiments, with defined concentrations of a single species of edible alga and controlled conditions of temperature, light, and photoperiod [10,25]. However, the current study used natural seston, with all its variability in algal composition and size, to test the possibility of competition in the environment, including the limnetic and littoral zones.…”