The effect of energy reserves on interspecific competition in cladocerans

Abstract

Interspecific competition may lead to oscillatory or stable coexistence, or the extinction o f some o f the interacting species. One contributing factor to oscillatory coexistence is time lags, caused, for example, by energy reserves in one or both species. GouLDEN & HoRNIG (1980) performed a series of laboratory experiments on single species and competition systems, examining the interactions between Daphnia ga/eata mendotae, a large cladoceran with energy reserves, and Bosmina longirostris, a small cladoceran with no visible energy reserves. In the single species experiments, Daphnia was found to continue reproduction in periods with little available food, rendered possible by their energy reserves. In addition to adult Daphnia, the newbom suppressed food density, and then the newboms starved and died. The energy reserves thus produced a time lag in the population development, which was in tum the main cause of the population oscillations. The Daphnia energy reserves were also found to have consequences for the competition with Bosmina, the latter having no energy reserves to sustain reproduction during food shortage. In a follow-up study, the food availability was found to be essential to the outcome of the competition experiments. Bosmina could coexist with Daphnia, probably because Bosmina adults could survive the oscillation cycles in the Daphnia population and exploit the resources effectively during the period in which the Daphnia population consisted of mostly juveniles (GoULDEN et al. 1982). The Daphnia-Bosmina competition experiment has been described by a structured population model (McCAULEY et al. 1996); however, these models include a large number of parameters, and it is thus difficult to perform general analyses. Our aim was to show that simple delay-differential models with energy reserves are capable of satisfactorily capturing the dynamics of Daphnia and Bosmina, and that combining these equations adequately describe the Daphnia-Bosmina competition experiment, with only a few parameters included.