ИСТИНА

A long-term study (1987–2007) on a Rana arvalis population in Moscow province focused on body length of males and females, and age-dependent reproductive characteristics. Correlations between egg diameter and reproductive effort with female body length weakened with age, whereas the relationship between body length and fecundity was characterized by positive allometry. Significant directional interannual changes in body length and reproductive characteristics paralleled with a relative decrease of the mature part of the population. The survival of mature females and males depended on premetamorphic survival, and was higher in earlier study years characterized by more favorable conditions in the aquatic phase. A decrease in net reproduction rate (R0) and, therefore, a limitation of population growth, was revealed both at relatively high and low levels of initial cohort size. The increase in the estimated recruitment exerts a strong influence on R0 via the decrease in the premetamorphic survival and, to a lesser extent, via a decrease in body length and fecundity of three- and four-year-old females. Changes in the annual number of breeding females were rather abrupt; however, a general long-term tendency for a decrease in female numbers was observed from 1992 to 1998, and the numbers remained low until present. The main reason for this decrease was a considerable deterioration of premetamorphic conditions, i.e. a decrease in carrying capacity of the aquatic environment. Sexual dimorphism in body length and growth rates (males were larger as a group and in an each given age, so they grew faster), maturation rates (2- or 3-year-old males became mature more often) and survival (males had lower survival relative to the initial cohort size) were revealed. These sexual differences remained present despite a gradual increase in the size of mature frogs, and a decrease of their survival, corresponding to the decrease in population size.