Widespread declines in body size in Appalachian Plethodontid salamanders

Background/Question/Methods: Climate change models project widespread range contractions for Appalachian salamanders within the next decade, with greatest effects predicted for species in the southern Appalachians. Climate change can impact amphibians through shifts in species distributions, leaner body condition, and reduced growth.  These impacts may be detected in nature by quantifying changes in occupancy, population abundance, individual body size, and reproductive effort. Highton (2005) documented widespread declines in population abundance of 28 species of Plethodon in the eastern US by the 1980’s.  Between June–October 2011 and March–June 2012, we resurveyed 79 of Highton’s historical sites, which included 217 populations of 15 species of Plethodon. At each site, we sampled 3, 50 x 3m plots, capturing all salamanders found under cover objects.  We identified each capture to species, sex, and age class, and measured snout-vent length (SVL).  Using these animals and ~8,000 specimens collected from those same sites between 1957–1996, we analyzed change in SVL for each species over the period 1957–2012. To examine whether changes in SVL might have resulted from climate, we parameterized a biophysical model using historical, site-specific temperature data to estimate annual activity and metabolic expenditure over that same period. 

Results/Conclusions: In our re-surveyed samples, we found a total of 1,870 animals (8.6/site; range = 0–75) of 14 species. Using Bayesian linear mixed effects models, we found significant body size reductions (95% CRI for slope estimate was < 0) in 6 species (Plethodon cheoah, P. cinereus, P. cylindraceus, P. jordani, P. ventralis, and P. yonahlossee) and a significant increase in body size (95% CRI for slope estimate was > 0) for P. welleri.  Results of biophysical models indicated that the duration of annual activity did not change from 1957–2011, although metabolic expenditure increased by ~7% over that same time period. All else being equal, our result suggests that body size might be constrained due to less energy available to growth. Our results show reduced body size in Plethodon across sites within a 767 km region of the Appalachians, with the fastest rates of change in the southern latitudes. Our results support predictions of species loss from the southern Appalachians (Milanovich et al. 2009) and we hypothesize that these changes are driven by regional climate change patterns.