Regulation of population numbers in the Rana arvalis frog according to the results of long-term observations on the same population

Abstract

An analysis of the results of long-term stationary studies (1987–1996) on a Rana arvalis population showed that the mean body length and reproductive parameters of females increased with age. Significant interannual changes in body length and egg size (but not in fecundity and reproductive effort) were also accounted for by conditions of the warm season preceding the breeding season. The dependence of egg diameter and reproductive effort on the female body length weakened with age, and only the relationship between body length and fecundity was characterized by positive allometry. The survival rate of mature females depended on the premetamorphic survival rate and, therefore, was higher in earlier generations, in which the aquatic phase proceeded under more favorable conditions. The rate of reproduction (R0) decreased and, therefore, further population growth slowed down only after the initial abundance of the generation had reached a relatively high level. An increase in the initial abundance of the generation exerts a strong influence on R0 via a decrease in the survival of premetamorphic animals and, to a lesser extent, via a decrease in the body length and fecundity of tree-and four-year-old females. Changes in the annual abundance of breeding females in R. arvalis were more abrupt and less prolonged than those in the sympatric R. temporaria population. The holding capacity of the environment for the aquatic phase of the R. arvalis life cycle was higher than that for R. temporaria. Therefore, the population abundance of R. arvalis, compared to R. temporaria, was not subject to stringent negative feedback regulation dependent on the initial number of animals.