Variations inter-populations de la structure d'âge et de la croissance du Prosobranche Bithynia tentaculata L.

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Abstract
The main variations in age structure and growth of different generations were studied in 25 populations of the prosobranch Bithynia tentaculata in the St. Lawrence River (Québec). The general unbalanced age structures of the populations reflect a low recruitment encountered during an odd year because of a general disturbance in the environment. The age structure is correlated to temperature, sediments, and current velocity. Water chemistry is largely responsible for the spatial variations in lengths of the adults, but these variations do not seem to influence the age at sexual maturity. Population densities may be regulated by an increase in the growth rate of young which would reduce the age at sexual maturity in populations with low densities; this mechanism would, however, be of little use to compensate a sudden decrease in density or an unbalanced age structure in a population. These results and those of previous studies on this species reveal the important role played by abiotic factors in regulating the spatio-temporal variations of the demographic profile of this prosobranch which possesses a high phenotypic plasticity.[Journal translation]