Abstracts

Evolution of Species and Ecosystems: Theoretical Analysis and Computer-Assisted Modeling

The work deals with the functioning of a closed “producer-consumer” aquatic system with spatially separated components where each component consists of a mixed culture. Microalgae Chlorella vulgaris and Scenedesmus sp. were used as producers, infusoria Paramecium caudatum and rotifers Brachionis sp. were used as consumers. Competition of predators was studied with predators consuming a mixed culture of algae, the competition of algae – under nitrogen-limited growth conditions. Experimental and theoretical modeling made in the “producer” component showed that Scenedesmus algae exhibiting higher specific growth rate are more competitive than chlorella. When growth is limited by the substrate concentration the competition is primarily determined by the shape of dependence of specific growth rate of a given population on the substrate concentration. Provided the dependencies do not cross the species with higher specific growth rate is advantageous over the entire substrate concentration range. The experiment has turned up that in the “consumer” component there are two predators (Paramecium caudatum and Brachionis sp.), 3 preys (bacteria, chlorella and Scenedesmus) and one biogenic element (nitrogen) limiting growth of the predators. The theoretical assertion for the coexistence of a mixed culture of predators – the possible number of predator species coexistent in equilibrium does not exceed the number of prey species which, in its turn, is not more than the sum of the number of predator species and the number of density-dependent-growth-controlling factors holds. In its extended form the Gause principle which means that the number of species m in an ecosystem cannot be more than the number of growth limiting factors n:
m<=n,

Yet in the “consumer” component the predators have not been found to coexist, Paramecium caudatum protozoa had been ousted by Brachionis sp. rotifers. One of the possible forms of metabolite interaction of the populations is the effect of the metabolic products of algae on the growth of protozoa. Batch cultivation of Paramecium caudatum protozoa with addition of supernatant of chlorella and Scenedesmus turned up negative effect of metabolic products of Scenedesmus on reproduction of the protozoa. Thus, absence of coexistence of populations in the “consumer” component is explained by the inhibition of growth of paramecia by algal metabolites. Effect of this factors in a closed system may be larger than in open systems.

Note. Abstracts are published in author's edition

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