Demography and Life History of Two Species of Chorus Frogs (Anura: Hylidae) in South Carolina

Abstract

The demography and life history of two populations of two species of chorus frogs (Pseudacris ornata and P. nigrita) were studied for 4 yr on the Savannah River Plant near Aiken, South Carolina. Sexual maturity in both species is reached within the first year of life, and the population turnover is nearly annual. The sex ratio of adults that entered the breeding ponds each year at each locality was 1:1. The operational sex ratio was skewed toward males during the first breeding peak in P. ornata, but was 1:1 in P. nigrita. All females that entered the ponds for the first time were gravid, but the percentage of females depositing eggs within a season and within localities was variable. In general, when the number of adults breeding in one year was low, survival of these adults to the next breeding season was high, suggesting that there may be a cost to reproduction in terms of survival. Juvenile recruitment was highest in the wettest year of the study. Recruitment of P. nigrita was never as high as that of P. ornata. One of the study sites had an artificially lowered water level, and juvenile recruitment of P. ornata was low during all years at this site compared to the other pond. These species best fit a bet-hedging model of life history tactics. The breeding habitat is unpredictable in time and space. Juvenile mortality is predictably high, but where and when it occurs is random. Selection apparently has favored juvenile dispersal as an alternative to longevity and iteroparity of individual females.