Structures and Dynamics of Populations of the Salamader Desmognathus Ochrophaeus Cope in Different Habitats

Abstract

Two populations of Desmognathus ochrophaeus, one inhabiting a wet rockface created during the construction of a tunnel portal on the Blue Ridge Parkway and the other a wooded cover 145 m away, were compared with respect to size at maturity, growth rates, age structure, and fecundity. Woodland animals are larger at maturity than rockface animals. This is because of their faster juvenile growth rates, not delayed maturity as previously believed. Woodland juveniles then continue to grow faster than rockface individuals after they mature, possibly because food resources are more extensive and dependable in leaf litter than on wet rockfaces. In the rockface population, growth rates appear to vary slightly from year to year. Body sizes and egg production are positively correlated in both populations, and the larger body sizes of woodland females enables them to achieve a mean clutch size nearly 50% greater than that of the rockface population. Body—size variation among populations of D. ochrophaeus is a complex phenomenon, possibly involving genetic differentiation of populations at different elevatons as well as non—evolutionary differences in growth rates between populations in different habitats. Further studies will be required to show whether other differences among rockface populations and between rockface and woodland populations have genetic bases. In the rockface population, proportions of second—summer juveniles and males in their 1st yr of sexual maturity appear to decrease during the summer. The cause of this phenomenon is unknown, and there is no evidence for it in the woodland population. Both populations have similar age structures in the early summer, before changes in the structure of the rockface population have occurred. Continued sampling of the rockface population over four successive summers resulted in a decline in the ratio of adult males to 1st yr juveniles, especially after the summer of 1971 when collecting was particularly intense. Estimates of the normal number of adult males in the population and the amount of yearly recruitment were made from capture—release—recapture data on another rockface population of similar density. Sustained collecting, which should have resulted in a greater decline in mean number of testis lobes per male than was observed, showed that older males may have been underrepresented in samples because of their more secretive habits.