Ref ID : 5428
Udo Halbach and Gisela Halbach-Keup; [Quantitative Beziehungen zwischen Phytoplankton und der Populationsdynamik des Rotators Brachionus calyciflorus Pallas. Befunde aus Laboratoriums-experimenten und Freilanduntersuchungen] (Quantitative relations between phytoplankton and the population dynamics of the rotifer Brachionus calyciflorus Pallas. Results of laboratory experiments and field studies). Arch.Hydrobiol. 73(3):273-309, 1974
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The experimental analysis of the biotic interrelationships between the planktonic rotifer Brachionus calyciflorus and the unicellular green alga Chlorella pyrenoidosa demonstrates two antagonistic influences of the algae on the rotifers: 1. A positive influence as food resource. 2. A negative influence at high densities, e.g. by lowering the filtration rate. It is suggested that the latter effect is caused by toxic algal substances released into the medium by the algae. The opposite effects of the algae cause maxima of the following population parameters of the rotifers at certain values of algal density: filtration and feeding rate, life span, fertility, intrinsic rate of natural increase, and carrying capacity. Model simulations demonstrate that the maximum of the intrinsic rate of natural increase is due to the maxima of life span and fertility. The carrying capacity reaches its maxium at algal densities somewhat higher than the other population parameters. Capacity values can also be derived by calculation, if algal dose, life span and biomass of adult animals, and the efficiency coefficient (assimilated fraction of food) are known. However, in order to adjust these theoretical values to the empirical capacity data lower life span values and a reduction of the efficiency coefficient must be assumed at high algal doses. Field studies were made by using 589 quantitative samples of phyto- and zooplankton. Significant positive correlations were found between the egg ratio and the population growth rate on the one hand and dry weights of the green algae Oocystis borgei and Scenedesmus obliquus on the other hand. Best correlations were obtained by using the sum of both dry weights. In any limnetic community various positive and negative relationships exist not only between members of different trophic levels, but also between members of the same levels, such as competition. The importance of these interspecific relationships for the understanding of the community and its stability is discussed.