Range-wide salamander densities reveal a key component of terrestrial vertebrate biomass in eastern North American forests

Characterizing the population density of species is a central interest in ecology. Eastern North America is the global hotspot for biodiversity of plethodontid salamanders, an inconspicuous component of terrestrial vertebrate communities, and among the most widespread is the eastern red-backed salamander, Plethodon cinereus. Previous work suggests population densities are high with significant geographic variation, but comparisons among locations are challenged by lack of standardization and failure to accommodate imperfect detection. We present results from a range-wide monitoring network that accounts for detection uncertainty using systematic survey protocols and robust quantitative models. We analyzed mark-recapture data from 19 study areas across the range. Estimated salamander densities ranged from 1950 to 34300 salamanders/ha, with a median of 9965 salamanders/ha. We compare these results to previous estimates for P. cinereus and other abundant terrestrial vertebrates. We demonstrate that overall biomass of P. cinereus, a secondary consumer, is of similar or greater magnitude to widespread primary consumers such as white-tailed deer and Peromyscus mice, and 2-3 orders of magnitude greater than common high-biomass omnivorous species and other secondary consumer species. Our results add empirical evidence that P. cinereus specifically, and amphibians in general, are an outsized component of terrestrial vertebrate communities in temperate ecosystems.