Population Dynamics of Tubifex tubifex, Studied by Means of a New Model

Abstract

The difficulties connected with the study of tubificid population dynamics and production have long been recognized (Kennedy, 1966; Johnson and Brinkhurst, 1971; Jónasson and Thorhauge, 1976; Waters, 1977; Bonomi and Adreani, 1978). The problems encountered are mostly of a taxonomic nature, as it is often difficult, if not impossible, to describe the populations in terms of biologically meaningful compartments. Even in the unusual case of a single species population, the complicated biological cycle strongly limits the possibility of a suitable description; indeed, it is well known that after the cocoon laying period, the tubificids undergo a regression of the reproductive system (Černosvitov, 1930; Poddubnaya, 1971) that makes the regressed animals quite similar to the true young, that have not yet undergone any reproductive period. Only Poddubnaya and co-workers, as far as we know, have been able to account for the state of regression of the reproductive system in their work on the tubificids of Rybinsk Reservoir (Poddubnaya, 1972; Arkhipova, 1976). Moreover, the possibility of describing the cocoon (or egg) population numbers has been either neglected or not taken into consideration for the lack of description of the cocoons specific characters.