Growth, Survival and Reproduction of Plethodon jordani: Trade-Offs between Selective Pressures

Growth and survival of Plethodon jordani were determined from size distributions of large collections made three times per year for five years in the same location. Growth during the first year of life could not be measured because the young only appear above ground one year after being laid as eggs in May. Average growth in snout-vent length was 12.02 mm from May to Oct. during the second year, 1.90 mm from Oct. to the following May and 9.26 mm from May to Oct. of the third year. The increment of growth decreased in all subsequent years. Survival during the second and third years of life was calculated from samples of successive year classes as 0.364 and 0.484, respectively. Some individuals become mature during the summer three years after being laid as eggs. Judged by the condition of ovarian eggs, only one-fourth of the females will mate in Aug. and Sept. and lay eggs when four years old. The same proportion holds for the next year. Individuals six-years-old and older appear to oviposit in alternate years. On the assumption that the annual rate of survival of adults is constant with age, that rate was calculated as 0.81 per year. The calculation was based on the proportion of three-year-olds to those larger. The estimated survival rate permitted matching size and age distributions to obtain a growth curve for those ages not measurable directly. Fecundity was estimated from numbers of large ovarian eggs, corrected for clutch size by using data from P. glutinosus. A combination of the regression of clutch size on snout-vent length and the growth curve made fecundity age-specific. Long-term data revealed a virtually constant population size, permitting the assumption of a stationary life table. Survival during the first year of life would be 0.837 for the net reproductive rate to equal 1.0. Based on the balanced life table, the mean generation time is calculated as 9.8 years. Data on this population from the Balsam Mountains are compared with similar data from the Great Smoky Mountains, where a lower proportion of one-year olds was found. P. glutinosus collected at the same times gave data very similar to Highton's more extensive collections from Maryland and Pennsylvania. The calculated life table for P. jordani is compared with Tilley's for Desmognathus ochrophaeus. The principal differences are in his conclusions that D. ochrophaeus females breed annually, and that there is no statistically significant relation between age and fecundity among mature females. The data for P. jordani cannot be reconciled with these conclusions about D. ochrophaeus. Both competition and predation have been important as selective pressures shaping this life history.