DEMOGRAPHY OF A SALAMANDER (AMBYSTOMA-MACULATUM) POPULATION STUDIED BY SKELETOCHRONOLOGY

Two hundred and twelve (212) adults of the yellow-spotted salamander, Ambystoma maculatum, were caught in the springs of 1989 and 1990 with unbaited minnow traps in two adjacent temporary ponds located in a deciduous forest in Trois-Rivieres (Quebec). The sex ratio was approximately 2:1 in favor of males. Snout-vent length (SVL) was significantly higher in females (90.2 +/- 6.3 mm) than in males (82.9 +/- 5.5 mm). Age was determined in cross sections of phalanges by counting the number of growth lines in the bone. Most of the salamanders were between 2 and 18 years of age, with a major peak distribution at 7 in both sexes and a secondary peak at 15 in males. The oldest animal was 32 years old. The study shows that most females are mature by the age of 7 at SVL > 78 mm, but many males reach maturity between the ages of 2 and 6 at SVL > 63 mm. Back calculation of growth curves reveals that females are already longer than males at 3 years old. Differences in age at maturity, reproductive frequency, and survival explain the observed sex ratio. Sexual dimorphism in body length is due to the rapid growth of females and their delayed maturity, not to a difference in longevity.