Dispersal and Population Ecology of the Red-backed Salamander (Plethodon cinereus)

Abstract

Terrestrial salamanders are major components of ecosystems in eastern North America. One species, the Red-backed Salamander (Plethodon cinereus), may be the most abundant vertebrate throughout its range. Red-backed Salamanders are commonly monitored as indicators of ecosystem health and to assess the effects of forest management practices. In order to address poorly understood aspects of the ecology of Red-backed Salamanders, I conducted a 4-y mark-recapture study of a population in Maryland, resulting in 2,745 records of 752 marked salamanders, along with a complementary genetic analysis of six microsatellite loci.

I estimated growth rates and age at sexual maturity using a hierarchical Bayesian model fitted by mark-recapture measurements, then measured home range size and seasonal and annual movement distances by immatures and adults, before and after the experimental removal of 98 conspecifics. Males grow and mature more slowly than females, despite reaching slightly larger asymptotic sizes; they may also face greater competition for space: adult males occupy the largest home ranges and show the largest increase in home range size after the removal of conspecifics. The largest between-year movements were made by individuals as they transitioned from immaturity to maturity.

Using mark-recapture population models, I found that estimates of survival, detection, and abundance varied temporally along with the age and sex of the individuals present, both within and among seasons. Encounter probability varied among weekly sampling occasions, and models with separate parameters for each sex were strongly preferred. Survival was approximately the same over winters and summers, and lower for males than for females; this may be an artifact of sex-biased dispersal, as the majority of encountered immature individuals were estimated to be males, with models indicating a pulse of emigration in the fall and an influx of immature males onto the study site in the spring.

An FST randomization test of multilocus genotypes showed a significant male bias in dispersal. Of salamanders captured repeatedly as both immatures and adults, males moved significantly farther before maturity than females did. Together, these results provide a comprehensive assessment of sex-biased dispersal at fine spatial and temporal scales in a terrestrial ectothermic vertebrate.