Population consequences of a physiological model for individuals

For many applications, it is important to identify the traits of individuals that are essential for the dynamical behaviour of populations. On the basis of computer simulations, which used a realistic model for size-dependent ingestion, reproduction and survival of individuals, we evaluated population consequences in homogeneous simple habitats. Even at constant food supply rates, populations oscillate due to a synchronization of life cycles of individuals. Although such a synchronization is observed in actual populations of Daphnia magna Straus, which the simulations aim to mimic, it is not so pronounced. By introducing a small scatter on the parameter settings of the individuals, the synchronization and so the oscillation is greatly reduced. In situations of strict food limitation the ageing process dominates population dynamics and model details on growth and reproduction prove unimportant, but become important as soon as this condition no longer applies due to, for example, predation. A consequence is that significant sublethal effects of toxic compounds on reproduction will not show up at population level as long as food limitation applies. This confounds the interpretation of field data. Key-words: Fed-batch cultures, energy budgets, ageing process, biological variability, toxic sublethal effects

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