|SREL Reprint #1118|
Demography and Life History of Two Species of Chorus
Frogs (Anura: Hylidae) in South
The demography and life history of two populations
of two species of chorus frogs (Pseudacris ornata and P. nigrita)
were studied for 4 yearrs 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 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
SREL Reprint #1118
Caldwell, J.P. 1987. Demography and life history of two species of chorus frogs (Anura: Hylidae) in South Carolina. Copeia 1987:114-127.