Size and Cycle in Dusky Salamanders

Abstract

The equal fitness paradigm (EFP) is a life-history model in which the currency of fitness is usable energy rather than individuals, and the principal trade-off is between survival, evaluated as generation time, and productivity, evaluated as growth and reproductive rates. In the current study I examined variation in generation time, age at first reproduction, productivity, and mortality in salamanders of the genus Desmognathus within the framework of the EFP. Desmognathus salamanders are restricted to eastern North America, with a center of distribution in the southern Appalachian Mountains. The data sources of the present report are published studies of life histories and demographics of five species of Desmognathus that include the smallest and largest members of the genus. The analysis showed that Desmognathus salamanders have greater ages at first reproduction, lengthier generation times, lower productivities, and lower mortality rates than are predicted by the scaling functions of the EFP for vertebrates of equivalent sizes. The differences among species in these parameters are correlated with variation in adult body size and the association between body size and habitat utilization in the genus, wherein the largest species are aquatic in mountain streams and the smallest are terrestrial in mesic forests. Streamside species of intermediate size exploit a broader range of habitats and are more widely distributed than the stream- and forest-dwelling forms. It is likely that the streamside mode of life in Desmognathus represents an adaptation promoting dispersal. Adaptive radiation in the genus is expressed in extreme life-history and body-size diversification mediated through variation in age at first reproduction and generation time.