Life History and Demographic Variation in the California Tiger Salamander (Ambystoma californiense)

In December 1991, we initiated a long-term study of the California Tiger Salamander (Ambystoma californiense) at a breeding pond in Monterey County, California. Because of habitat loss, this species is a candidate for federal endangered species status, but many basic features of its life history and demography have not been studied in detail. During the first seven years of this study, we captured, measured, individually marked, and released 657 breeding adults and 1895 newly metamorphosed juveniles at the drift fence encircling this pond. We also used skeletochronology to investigate age structure in cohorts of breeding adults. Numbers of breeding adults varied by more than a factor of four among years, and annual juvenile production ranged from 121–775 metamorphs. Contrary to the results of related studies, total juvenile production was positively related to the total biomass of breeding females. Both skeletochronology and mark-recapture data indicate that most individuals do not reach sexual maturity until 4–5 years of age, and, although individual longevity can exceed 10 years, less than 50% of individuals returned to breed a second time. These results suggest that this breeding population was a reproductive sink during the period of this study and that isolated breeding ponds may be insufficient for the long-term maintenance of viable populations of A. californiense.

Fig. 1.

Mean ± 2 SE monthly fraction of total annual captures of male (squares) and female (circles) Ambystoma californiense at Blomquist Pond over seven seasons (1992–1998). Line represents monthly precipitation means normalized to centimeters per day

Fig. 2.

Annual breeding activity and reproductive success of Ambystoma californiense at Blomquist Pond. Bars show numbers of total breeding males (solid) and females (open) corrected for sampling efficiency; line illustrates numbers of juveniles surviving to metamorphosis per breeding female; point labels are corrected estimates of total metamorph production

Fig. 3.

Timing of summer captures of newly emerged metamorphic Ambystoma californiense at the Blomquist Pond drift fence. Asterisks indicate median date of “emergence,” arrows mark the date on which the pond dried completely, and years marked with the same letter exhibited similar timing of emergence (all Sheffé's P > 0.05)