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| Home > Publications database > Dynamik und Persistenz eines mikrobiellen Räuber-Beute-Systems in Laborkulturen |
| Book/Report | FZJ-2018-04538 |
1993
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/19450
Report No.: Juel-2835
Abstract: The dynamics of microbial predator-prey systems have been studied extensively by experiments and mathematical models for more than 20 years. Confrontation ofexperimental results with predictions from mathematical models revealed that interactions and mechanisms that determine the population dynamics are considerablymore complex than was first expected . For example a contrasting experimental result was the stability and persistence of the system in laboratory cultures where large numbers of prey coexist with large numbers of active predators. The experiments reported in this work were undertaken using the ciliated protozoan $\textit{Tetrahyrnena thermophila}$ to represent the filter feeding predator and $\textit{Escherichia coli}$ as the bacterial prey source. Both were cultivated aerobically in carbon limited stationary cultures. The experiments have shown that beside the predatory interaction of these populations, carbon sources were recycled and thus bacterial growth partially compensated feeding pressure. It is suggested that these two mechanisms - predation and nutrient cycling - are sufficient to explain the stability of the predator-prey system. Growth kinetics of the bacteria feeding upon nutrients released mainly by the ciliates were assessed. In addition, growth of the bacteria on different substrates and effects of culture techniq ues were analysed in detail Later, the division and feeding kinetics of the protozoa were recorded and described as mathematical functions. This yields an astonishing result namely - the functional response of the protozoan could not be described by a hyperbolic saturation function (Bolling type II) as is usually believed. $\textit{Tetrahymena}$ seemed to adopt its uptake rate according to changing prey density in two (or more) steps showing a sigmoidal function at low prey densities. In addition, the population density of predators negatively affects the uptake of its bacterial food. Behavioural changes of $\textit{Tetrahymena}$ may explain these phenomena. The experimental results were summarized in a model of ordinary differential equations to describe the population dynamics of the system. Simulations showed that the stability of the predator-prey system mainly depends on the feeding behaviour of the predator. Nutrient cycling is less important but keeps the bacteria in a physiological active state. A sensitivity analysis showed that the model predictions do not change qualitatively if starting conditions or parameter values were altered. Thus there is now the possibility to explain a series of experimental results from this and previous works dealing with stationary and continuous cultures and sometimes with other microbes. This work emphasises the immense importance of adaptation and behavioural plasticity population dynamics not only of metazoan but also of microbial communities. In borderline situations especially, specific adaptation will cause more stability and coexistence of a predator and its prey as in the experiments documented here.
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