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Climate change poses several challenges to biological communities including changes in the frequency of encounters between closely related congeners as a result of range shifts. When climate change leads to increased hybridization, hybrid dysfunction or genetic swamping may increase extinction risk—particularly in range‐restricted species with low vagility. The Peaks of Otter Salamander, Plethodon hubrichti, is a fully terrestrial woodland salamander that is restricted to ~18 km of ridgeline in the mountains of southwestern Virginia, and its range is surrounded by the abundant and widespread Eastern Red‐backed Salamander, Plethodon cinereus. In order to determine whether these two species are hybridizing and how their range limits may be shifting, we assessed variation at eight microsatellite loci and a 1,008 bp region of Cytochrome B in both species at allopatric reference sites and within a contact zone. Our results show that hybridization between P. hubrichti and P. cinereus either does not occur or is very rare. However, we find that diversity and differentiation are substantially higher in the mountaintop endemic P. hubrichti than in the widespread P. cinereus, despite similar movement ability for the two species as assessed by a homing experiment. Furthermore, estimation of divergence times between reference and contact zone populations via approximate Bayesian computation is consistent with the idea that P. cinereus has expanded into the range of P. hubrichti. Given the apparent recent colonization of the contact zone by P. cinereus, future monitoring of P. cinereus range limits should be a priority for the management of P. hubrichti populations., This study uses population genetic approaches to assess whether hybridization between a severely range‐restricted mountaintop endemic salamander and a closely related widespread congener is contributing to the extinction risk of the former. While we find little to no evidence of hybridization, we do present evidence that the more common species is expanding into the range of the mountaintop endemic species. We discuss the conservation implications of this finding.

Reversible acclimation increases resilience to environmental stress, but acclimation may have hidden costs due to underlying linkages between related physiological traits. These linkages might result in trade‐offs that undermine whole‐organism performance if the change in a related trait reduces the net benefits of acclimation or increases susceptibility to alternative environmental stressors. Metabolic rate and water loss rate are two fundamental physiological traits that could interact due to their dependence on gas exchange across shared physical surfaces. Reductions in water loss rate in response to dehydration stress might reduce metabolic rate by constraining the flux of both water and oxygen. We examined acclimation of metabolic rate and water loss rate using a species of woodland salamander (Plethodon metcalfi) in response to temperature and humidity using a full factorial experimental design. We controlled the evaporative demand of the air across temperatures to assess temperature and humidity as independent cues for acclimation. We predicted that reductions in water loss rate would coincide with reductions in metabolic rate in response to temperature due to shared physical and chemical pathways. We also assessed acclimation of heart rates as a potential compensatory mechanism used to promote oxygen delivery. We integrated these responses into a biophysical model developed from first principles to demonstrate the potential for these interactions to influence habitat suitability. We found that reductions in water loss rates during thermal acclimation were associated with simultaneous reductions in metabolic rates, and we did not find a compensatory response in heart rates. We suggest that these linkages underlie whole‐organism strategies (e.g. physiological dormancy or arousal) for reducing the energetic costs imposed by warm temperatures. The biophysical model suggested that the interaction between these two traits potentially structures phenotypic variation in our population because certain combinations of trait values were incapable of reaching positive energy balance. Trade‐offs between linked physiological traits potentially structure whole‐organism strategies for responding to environmental stressors and constrain phenotypic variation. Therefore, predictions of the benefits of acclimation must be interpreted cautiously without knowledge of the underlying trade‐offs among linked physiological traits. A plain language summary is available for this article.

North America is home to both native and invasive earthworms acting as ecosystem engineers as they build burrows that can serve as habitat for other species or otherwise alter soil structure, affecting nutrient cycling and other ecosystem processes. Here I determine where and what earthworm species commonly occur in my study area, and compare effects of native and invasive earthworms on the common woodland salamander, Plethodon cinereus, in field surveys and laboratory experiments. The native earthworm Eisenoides carolinensis was the most common earthworm, followed by two invasive species Dendrobaena octaedra and Octolasion tyrtaeum. The presence of O. tyrtaeum was associated with a narrower O-horizon (i.e., organic layer in the soil). Using structural equation modeling to explore direct and indirect pathways of these three most common earthworm species on salamanders, I found O. tyrtaeum occurrence was negatively correlated with nighttime salamander counts, a proxy for total salamander numbers, mediated by negative effects on O-horizon depth and microinvertebrate numbers. In the laboratory, O. tyrtaeum and D. octaedra consumed more leaf litter per gram of earthworm per day than the native E. carolinensis. However, salamanders consumed earthworms and used burrows of all native and invasive species of earthworms similarly. The potential for negative indirect effects of the invasive earthworm O. tyrtaeum on P. cinereus was demonstrated both in the field and laboratory, highlighting that seemingly small differences between native and invasive ecosystem engineers have the potential to significantly alter the effects of these closely related native and invasive organisms.

Multiple pathways exist for species to respond to changing climates. However, responses of dispersal‐limited species will be more strongly tied to ability to adapt within existing populations as rates of environmental change will likely exceed movement rates. Here, we assess adaptive capacity in Plethodon cinereus, a dispersal‐limited woodland salamander. We quantify plasticity in behavior and variation in demography to observed variation in environmental variables over a 5‐year period. We found strong evidence that temperature and rainfall influence P. cinereus surface presence, indicating changes in climate are likely to affect seasonal activity patterns. We also found that warmer summer temperatures reduced individual growth rates into the autumn, which is likely to have negative demographic consequences. Reduced growth rates may delay reproductive maturity and lead to reductions in size‐specific fecundity, potentially reducing population‐level persistence. To better understand within‐population variability in responses, we examined differences between two common color morphs. Previous evidence suggests that the color polymorphism may be linked to physiological differences in heat and moisture tolerance. We found only moderate support for morph‐specific differences for the relationship between individual growth and temperature. Measuring environmental sensitivity to climatic variability is the first step in predicting species' responses to climate change. Our results suggest phenological shifts and changes in growth rates are likely responses under scenarios where further warming occurs, and we discuss possible adaptive strategies for resulting selective pressures.

In addition to creating or modifying habitat, ecosystem engineers interact with other species as predators, prey, or competitors. The earthworm, Lumbricus terrestris, interacts with the common woodland salamander, Plethodon cinereus, via: (1) ecosystem engineering, by providing burrows that are used as a refuge, (2) direct effects as a prey item, and (3) indirectly, by competing with microinvertebrates, another prey item for P. cinereus. Using enclosures in the forest, I examined the relative strengths of these component pathways between seasons and salamander age classes. I found that the relative strength (partial eta2) of the positive direct (trophic) effect of L. terrestris on the change in mass of P. cineresus was greater than that of the negative indirect effect, but only in summer. Positive effects of ecosystem engineering were only evident over the winter as increased adult survival. This research has implications for how habitat provisioning complements more well-studied species interactions, such as competition and predation, within communities.

Studies examining the influence of habitat provisioning by one species on the behavior of other species can provide key insights regarding impacts of ecosystem engineers on the availability of resources to other species. More specifically, an organism’s use of additional habitat provided by ecosystem engineers may affect the interpretation of observational or demographic data. We chose to examine the possible influence of earthworms, as ecosystem engineers, on the behavior of terrestrial salamanders, common forest vertebrates in North America. We conducted two experiments in microcosms to examine whether the earthworm Lumbricus terrestris acted as an ecosystem engineer by providing additional habitat (burrows) for Plethodon cinereus, a common woodland salamander. We also examined whether the behavioral changes of the non-burrowing, fossorial P. cinereus differed across age classes. Adults and juveniles responded similarly, with both adults and juveniles found under cover objects more often when earthworms were absent and using earthworm burrows when available. Our field data supported our experimental data in that greater numbers of earthworms on field plots were associated with a lower proportion of cover objects being occupied by salamanders (i.e., salamanders were likely underground). We found no differences in the response of adults and juveniles to the presence of earthworms. By providing underground habitat for a common terrestrial amphibian, the presence of earthworms may impact demographic studies on salamanders and conclusions drawn from those studies regarding aboveground faunal communities in eastern North America.

The ability of animal species to disperse through matrix habitats is likely to have important implications for species' responses to habitat fragmentation. Within fragmented forests, open fields are among the most common matrix habitats. However, few empirical studies have measured the effects of open habitats on dispersal success of forest-dwelling species. We used two experiments to determine the effects of open habitats and distance on dispersal and colonization by red-backed salamanders, Plethodon cinereus. In the first experiment, salamanders were displaced from habitat edges 25 m and 55 m into an open field and farther into the forest. Return rates from salamanders crossing the field vs. the forest were then used to determine the barrier effects of open habitats. Although return rate declined with distance, salamanders returned successfully through open habitat as often as they returned successfully through forest. In the second experiment, we constructed “islands” of forest-like habitat within an o...

Recent concern over global amphibian population declines has highlighted a need for more extensive, rigorous monitoring programs. Two sources of variation, spatial variation and variation in detection probability, make the design and implementation of effective monitoring programs difficult. We used Pollock's robust design in a 3-year capture–recapture study to estimate detection probability and temporary emigration for Plethodon salamanders in Great Smoky Mountains National Park (Tennessee/North Carolina), USA. We used 12 competing models to determine the importance of temporary emigration, and we explored temporal and behavioral effects on conditional capture probabilities. The top 4 models all included random temporary emigration, and Akaike model weights indicated that this parameter was the most important. Models that contained behavioral effects in capture probabilities were selected more often than models with equal capture probabilities for marked and previously unmarked individuals. The ...

We compared the species richness and abundance of salamanders on six recent clearcuts ( 50 years old) in southern Appalachian forests in western North Carolina, U.S.A. Catches of salamanders from plots in mature forest stands were about five times higher than those on recent clearcuts. Almost all species and major taxonomic groups of salamanders were adversely affected by timber removal. Mean number of species collected per plot was about twice as great in mature forest stands as in clearcuts. Analyses of stand age versus salamander catch for 47 plots indicate that 50–70 years are required for populations to return to predisturbance levels following cutting. We conservatively estimate that clearcutting in U.S. national forests in western North Carolina results in a loss of nearly 14 millton salamanders annually. It also is chronically reducing regional populations by more than a quarter of a billion salamanders (9%) below that which could be sustained if mature forests were not cut. Nosotros comparamos la riqueza de especies y abundancia de las salamandras en seis recientes cortas totales de bosque ( 50 anos) en los bosques del sur de los Apalaches, en el oeste de Carolina del Norte, Estados Unidos. La captura de salamandras por plot en bosques de rodales maduros fue aproximadamente cinco veces mayor que en aquellos cortados recientemente. Casi todas las especies y los mayores grupos taxonomicos de salamandras fueron adversamente afectados por la tala. La media del numero de especies capturada por plot fue aproximadamente dos veces mayor en los rodales de bosques maduros que en los cortados recientemente. Los analisis de edad del rodal versus captura de salamandras para 47 plots indican que entre 50–70 anos son necesarios para que las poblaciones retornen a los niveles previos a la perturbacion ocasionada por la tala del bosque. Nosotros estimamos en una forma conservadora que la tala de los Bosques Nacionales en el oeste de Carolina del Norte trae como consecuencia una perdida de alrededor de 14 millones de salamandras anualmente. La tala tambien esta reduciendo cronicamente las poblaciones a nivel regional en mas de un cuarto de billones de salamandras (9%) por debajo del nivel que podria ser sostenido por los bosques maduros si no hubieran sido cortados.