Size-Mediated Tradeoffs in Life-History Traits in Dusky Salamanders

Among salamanders of the genus Desmognathus, the larger species tend to be more aquatic and the smaller more terrestrial. I studied life histories in assemblages of Desmognathus in the southern Blue Ridge Mountains of North Carolina at sites in the Cowee and southern Nantahala Mountains. Traits evaluated included mortality/survival, age at first reproduction, fecundity, and body size. The first three are direct fitness traits that enter into the characteristic equation, _x = αΣ^∞l_xm_xe^−rx  =  1.0. One assemblage (Wolf Creek), in the Cowee Mountains, comprises three species, from larger to smaller, D. quadramaculatus, D. monticola, and D. ocoee. A second assemblage (Coweeta Creek), in the Nantahala Mountains, also includes D. quadramaculatus, D. monticola, and D. ocoee, as well as the smaller D. aeneus and D. wrighti. I also studied three species only (D. ocoee, D. aeneus, D. wrighti) in an assemblage of six species (Nantahala River) in the Nantahala Mountains just west of Coweeta Creek. In these assemblages, age at first reproduction and fecundity are greater in the larger, more aquatic species. Instantaneous mortality rate is lower in the larger species; however, the latter have lower survival to first reproduction than the smaller species because developmental time to sexual maturation is lengthier than in the smaller species. Among species, it appears that size-mediated tradeoffs exist among age at sexual maturation, fecundity, and survival. The tradeoff relationships of life-history traits among species in both the Cowee and Nantahala assemblages may reflect fitness invariance or symmetry, perhaps stemming from design constraints in the genus Desmognathus. What remain unclear are factors contributing to the correlation between body size and the position of species along the stream-to-forest habitat gradient.