THE TRANSIENT-BEHAVIOR OF FOOD-CHAINS IN CHEMOSTATS

Classical chemostat models such as the Monod, Marr-Pirt and Droop mode ls are formulated at the population level. These models are unstructur ed, which means that all individuals in the population are treated as being identical. Such models fail to describe the experimental data of Dent ct al. (1976, Arch. Microbiol. 109, 187-194) in detail. They gre w vegetative myxamoebae of the cellular slime mould Dictyostelium disc oideum in continuous culture with a bacterial food source, Escherichia cell B/r fed glucose. In this paper a new structured model is propose d, based on dynamic energy budgets (DEB)for conspecific individuals wh ich only interact via a common resource. The model fit for the time-co urse data of glucose, bacteria and myxamoebae is very good; it covers variations in mean cell volumes of both bacteria and myxamoebae. Compa rison with curve fitting results for the classical models reveals the mechanisms that are responsible for the better performance of the DEB model. We show that elements from different models, specifically maint enance (Marr-Pirt, gives stability) and energy reserves (Droop, gives oscillations) must be combined to produce acceptable fits. Therefore w e reject the assumption made by Bazin & Saunders (1978, Nature, Lend. 275, 52-54) that additional intra-specific interactions must be postul ated to explain the data.