Effects of individual variability on the outcome of competition between cladoceran species

Simulation modeling was performed to study the impact of individual variability on the population dynamics of particular cladoceran populations and the outcome of interspecific competition at low and high temperatures. The study was performed on one species of small size (Ceriodaphnia quadrangula O.F. Müller) and one species of large size (Simocephalus vetulus O.F. Müller). Laboratory experiments were performed to estimate the average values of principal demographic parameters of these species and their coefficients of variability at two temperatures, 18 and 27°C. Population dynamics of the two species in mono- and mixed cultures was simulated with and without accounting for individual variability using available published data and our own data on demographic parameters. Individual variability was shown to help populations survive unfavorable trophic conditions and to give competitive advantage over populations in which all individuals of the same age are identical. Individual variability decreased with rising temperatures due to probable acceleration of physiological processes.