Особенности географического распространения пресноводных моллюсков

Abstract

Under the conditions of the Ukraine from the south-west to the north-east the fall of some species and groups of species of fresh-water mollusks is observed. The northern boundaries of the areals of these species spread from the north-west to south-east. Comparison of areal boudaries of some fresh-water mollusks with the summer (July) isotherms does not explain this phenomenon because summer temperatures of the air are near the optimal ones for their activity. Comparison of the mentioned boundaries with winter (January) isotherms points to the common character in their spreading. In the north-eastern direction not only decrease of January temperatures is observed, but also advancement of spring and winter thresholds of cold period, i. e. advancing from the south-west to the north-east the duration of the winter increases, as a result of this the winter in the far north-east lasts almost two months longer. Thus, the northern areal boundaries of fresh-water mollusks are determined by the winter temperatures.