Structure Transformation of the Anuran Amphibian Spawning Communities in Floodplain Lakes of the Medveditsa River Valley (Saratov Region) under Conditions of Long-Term Reduction of Water Content

Abstract

The structure of spawning taxocenoses of anuran amphibians in five floodplain lakes of the Medveditsa river valley in 2009-2018 is analysed. Two near-terrace lakes (Lebyazhye and Koblovo) and three lakes of the central floodplain (Sadok, Kruglen'koye, and Cherepashie) were used as model ones. The degradation of the populations of the three most numerous species, a decrease in the dominance degree of the common spadefoot toad were established. Degradation is more characteristic of species with a longerer distance of spawning migrations -the severity of changes consistently decreases in the row of species: Pelophylax ridibundus Pelobates fuscus Bombina bombina. Indices of the structure of amphibian communities in the near-terrace lakes Lebyazhye and Koblovo were stable. Against the background of low water content and unstable hydrological regime of the central floodplain lakes with a survey duration of five or more years, three periods were established to characterize the structure of spawning amphibian taxocenoses, namely: a stable structure, a sharp decrease in dominance and an increase in evenness, and an increase in the variability of the main attributes of the structure. At the end of the third period, which characterizes the structure of taxocenoses, some stabilization of the main parameters was noted with an extremely low number of mature individuals of all amphibian species. The high level of spring flood of the Medveditsa river in 2018 determined the beginning of the exit from the abnormally long period of low water content of the spawning lakes in the floodplain (from 2009 till 2017) and their functioning in the hydrological regime as temporary water bodies. The sudden increase in water content of the floodplain lakes and the extension of their hydroperiod allow the beginning of the recovery process of the population size and community structure of anuran amphibians to be noted.