Alternative Demographic Models for Two Populations of the Seal Salamander, Desmognathus monticola
Variation among desmognathan salamanders in the timing of the female reproductive cycle is poorly understood. Although nesting tends to be seasonal, in the warmer months, females may not reproduce on a strictly annual cycle, but on a biennial or irregular schedule. In the present report, I examine the ramifications of annual and biennial female reproductive schedules on demography in two populations of Desmognathus monticola in the southern Blue Ridge Mountains of southwestern North Carolina. Provisional demographic models for each are developed based on published data on age structure, growth and developmental rates, and fecundity in the populations in question. The models indicate that biennial reproduction would require higher first-year survival than annual reproduction, at levels that appear tenable given our understanding of the ecology of nesting females and larvae of this species.
Gompertz growth equations, SLx = SL0e
, fitted to the “female” skeletochronological data, including unsexed juveniles, and immature and mature females, as described in the text. The slope is given by dSLx/dx = βSL0e
. Setting the second derivative, d2SLx/dx2 = 0, provides a formula for the age at the maximum rate of growth, xλ = ln (β/α)/α, which are 1.85 yr (Coweeta) and 1.71 yr (Wolf Creek). The corresponding SLs are 28.4 mm and 26.9 mm, respectively. The asymptote of the Gompertz function can be calculated by the alternative equation, SLx = SL∞e
, by setting x = 0 and solving SL∞ = SL0e(β/α). The values are 77.3 mm (Coweeta) and 73.0 mm (Wolf Creek). The ratio of size at age of maximum growth to asymptotic size is set at e−1 = 0.368. The lowermost graph plots the Gompertz growth equations for females of both populations.
Least-squares regressions of ln follicle number on ln standard length of Coweeta and Wolf Creek gravid females of Desmognathus monticola.
Contributor Notes
Associate Editor: B. L. Stuart.