Assessing the Use of Non-lethal Tail Clips for Measuring Stable Isotopes of Plethodontid Salamanders

Stable isotopes are increasingly used in ecology to study the diets, trophic position, and migratory patterns of wildlife including herpetofauna. When using stable isotopes, it is important to consider which tissues can or should be sampled, and how selecting tissues may affect the inferences drawn from stable isotope data. Amphibians offer fewer tissues than other larger organisms that can be harvested in sufficient quantity without killing the animal; however, many salamanders have tails that readily autotomize and regenerate. We used three species of plethodontid salamander (Plethodon cinereus, P. metcalfi, and Desmognathus quadramaculatus) to determine whether distal tail tissue had carbon and nitrogen stable isotope values comparable to commonly used tissues (liver and whole carcass [minus the liver and gonads]) that must be collected lethally. We found that variation in carbon values (δ13C) within and among tissues was negatively correlated with C:N (an indication of high lipid content). Nitrogen (δ15N) and Carbon (δ13C) values (once adjusted for C:N) of tail tissue were positively correlated with values for carcass tissue, and tail δ15N values were positively correlated and biased with δ15N values for liver tissue. Adjusted δ13C values for tail tissue were unbiased and had weaker positive correlations with δ13C values for liver tissue compared to whole carcass. The weak correlation between adjusted δ13C values of tail and liver tissues may reflect differences in turnover rates between the two tissues. Our data show that, with calibration, non-lethal collection of tail clips is a suitable substitute to lethal tissue collection for measuring δ13C and δ15N of plethodontid salamanders

Trophic polymorphism in a terrestrial salamander

Question: Does habitat heterogeneity promote trophic polymorphism in a terrestrial salamander? Hypothesis: Eastern red-backed salamanders (Plethodon cinereus) in upland and lowland habitats differ morphologically because their prey’s size differs between those habitats. Field site: Five mature hardwood forests in central New York and northern Pennsylvania, USA, with known differences in diet between upland and lowland habitats. Methods: We collected animals and examined their stomach contents and their cranial morphology, the latter with digital stereomicroscope images and morphometric methods. Results: We found morphological differences between upland and lowland salamanders, although there was a considerable phenotypic range for both habitats. Lowland salamanders generally had relatively shorter heads and a lower jaw/head ratio, and upland salamanders generally had the converse. Within and among habitats, cranial morphology was associated with diet, where salamanders with lowland-like morphology consumed more large prey and fewer small prey, and salamanders with upland-like morphology consumed the converse. Conclusions: The observed trophic polymorphism and association with food use within populations suggests that this variation may accentuate variation at larger scales, and may play an important role in diversification within the genus

Identifying Priority Species and Conservation Opportunities Under Future Climate Scenarios: Amphibians in a Biodiversity Hotspot

Climate change is driving shifts in the distribution of plants and animals, and prioritizing management actions for such shifts is a necessary but technically difficult challenge. We worked with state agencies in the southeastern United States to identify high-priority amphibian species, to model the vulnerabilities of those species to regional climate change, and to identify long-term climatic refugia within the context of existing conservation lands. Directly interfacing with state natural resource experts ensured that 1) species prioritization schemes extend beyond political boundaries and 2) our models resulted in conservation-relevant applications. We used a correlative model to project midcentury distributions of suitable climate for priority species and to evaluate each species\u27 vulnerability to climate change. Using spatially explicit projected climate distributions, we ranked existing protected areas relative to their ability to provide climatic refugia for priority species in 2050. We identified 21 species as regional high-priority species. Fifteen of the 21 species are forecast to lose more than 85% of their climatically suitable habitat. Regions in the Appalachian Mountains, the Florida Panhandle, and the north-central region of Alabama are projected to lose the most climatic habitat for priority amphibian species. We identified many existing protected areas as midcentury climatic refugia in the Appalachians; however, our projections indicated refugia in the Southeast Coastal Plain to be exceedingly scarce. Although the topographic relief present in the Appalachians appears to provide future conservation opportunities via climatic refugia, the Coastal Plain affords fewer such opportunities and conservation of amphibians in that region is likely to be more challenging. The approach outlined here could be applied across a broad range of taxa and regions

Invasion by Exotic Earthworms Alters Litter- and Soil-dwelling Oribatid Mites

Exotic earthworms are drivers of biotic communities in invaded North American forest stands. Here we used ecologically important oribatid mite (Arachnida: Acari) communities, as model organisms to study the responses of litter- and soil-dwelling microarthropod communities to exotic earthworm invasion in a northern temperate forest. Litter- and soil-dwelling mites were sampled in 2008–2009 from forest areas: (1) with no earthworms; (2) those with epigeic and endogeic species, including Lumbricus rubellus Hoffmeister; and (3) those with epigeic, endogeic, and anecic earthworms including L. terrestris L. Species richness and diversity of litter- and soil-dwelling (0–2 cm soil depth) oribatid mites was 1–2 times higher in sites without earthworms than in sites with worms. Similarly, litter-dwelling oribatid mites were between 72 and 1,210 times more abundant in earthworm-free sites than in sites with worms. Among earthworm invaded sites, abundance of litter-dwelling oribatid mites in sites without the anecic L. terrestris was twice as high in May and 28 times higher in October, compared to sites with L. terrestris. Species richness, diversity, and abundance of oribatid mites were greater in litter-layers than in the soil-layers that showed a varied response to earthworm invasion. Species compositions of both litter- and soil-dwelling oribatid mite communities of forests with no earthworms were markedly different from those with earthworms. We conclude that exotic earthworm invasions are associated with significant declines of species diversity, numbers, and compositional shifts in litter- and soil-inhabiting communities. These faunal shifts may contribute to earthworm effects on soil processes and food web dynamics in historically earthworm-free, northern temperate forests

Life History and Habitat of the Rare Patch-nosed Salamander (Urspelerpes brucei)

We examined the life history and habitat characteristics for the Patch-nosed Salamander, Urspelerpes brucei. Body-size measurements of individuals captured using litter bags and by hand from 2008 to 2010 indicated that the larval period lasts at least 2 y, salamanders attain reproductive maturity at or shortly after metamorphosis, and adults have very little variation in body size. Occupied streams are characterized by small size, little water, and narrow, steep-walled ravines. Within occupied streams, larval capture rate was significantly and negatively related to mean water depth, underscoring the importance of protecting headwaters. We hypothesize that the only known population of U. brucei east of the Tugaloo River was isolated from the west-bank populations by the tremendous increase in w

Detrital stoichiometry as a critical nexus for the effects of streamwater nutrients on leaf litter breakdown rates

Nitrogen (N) and phosphorus (P) concentrations are elevated in many freshwater systems, stimulating breakdown rates of terrestrially derived plant litter; however, the relative importance of N and P in driving litter breakdown via microbial and detritivore processing are not fully understood. Here, we determined breakdown rates of two litter species, Acer rubrum (maple) and Rhododendron maximum (rhododendron), before (PRE) and during two years (YR1, YR2) of experimental N and P additions to five streams, and quantified the relative importance of hypothesized factors contributing to breakdown. Treatment streams received a gradient of P additions (low to high soluble reactive phosphorus [SRP]; ~10–85 μg/L) crossed with a gradient of N additions (high to low dissolved inorganic nitrogen [DIN]; ~472–96 μg/L) to achieve target molar N:P ratios ranging from 128 to 2. Litter breakdown rates increased above pre‐treatment levels by an average of 1.1–2.2× for maple, and 2.7–4.9× for rhododendron in YR1 and YR2. We used path analysis to compare fungal biomass, shredder biomass, litter stoichiometry (nutrient content as C:N or C:P), discharge, and streamwater temperature as predictors of breakdown rates and compared models containing streamwater N, P or N + P and litter C:N or C:P using model selection criteria. Litter breakdown rates were predicted equally with either streamwater N or P (R2 = 0.57). In models with N or P, fungal biomass, litter stoichiometry, discharge, and shredder biomass predicted breakdown rates; litter stoichiometry and fungal biomass were most important for model fit. However, N and P effects may have occurred via subtly different pathways. Litter N content increased with fungal biomass (N‐driven effects) and litter P content increased with streamwater P availability (P‐driven effects), presumably via P storage in fungal biomass. In either case, the effects of N and P through these pathways were associated with higher shredder biomass and breakdown rates. Our results suggest that N and P stimulate litter breakdown rates via mechanisms in which litter stoichiometry is an important nexus for associated microbial and detritivore effects

Low-to-moderate nitrogen and phosphorus concentrations accelerate microbially driven litter breakdown rates

Particulate organic matter (POM) processing is an important driver of aquatic ecosystem productivity that is sensitive to nutrient enrichment and drives ecosystem carbon (C) loss. Although studies of single concentrations of nitrogen (N) or phosphorus (P) have shown effects at relatively low concentrations, responses of litter breakdown rates along gradients of low‐to‐moderate N and P concentrations are needed to establish likely interdependent effects of dual N and P enrichment on baseline activity in stream ecosystems. We established 25 combinations of dissolved inorganic N (DIN; 55–545 μg/L) and soluble reactive P (SRP; 4–86 μg/L) concentrations with corresponding N:P molar ratios of 2–127 in experimental stream channels. We excluded macroinvertebrates, focusing on microbially driven breakdown of maple (Acer rubrum L.) and rhododendron (Rhododendron maximum L.) leaf litter. Breakdown rates, k, per day (d−1) and per degree‐day (dd−1), increased by up to 6× for maple and 12× for rhododendron over our N and P enrichment gradient compared to rates at low ambient N and P concentrations. The best models of k (d−1 and dd−1) included litter species identity and N and P concentrations; there was evidence for both additive and interactive effects of N and P. Models explaining variation in k dd−1 were supported by N and P for both maple and rhododendron ( = 0.67 and 0.33, respectively). Residuals in the relationship between k dd−1 and N concentration were largely explained by P, but residuals for k dd−1 and P concentration were less adequately explained by N. Breakdown rates were more closely related to nutrient concentrations than variables associated with measurements of two mechanistic parameters associated with C loss (fungal biomass and microbial respiration rate). We also determined the effects of nutrient addition on litter C : nutrient stoichiometry and found reductions in litter C:N and C:P along our experimental nutrient gradient. Our results indicate that microbially driven litter processing rates increase across low‐to‐moderate nutrient gradients that are now common throughout human‐modified landscapes

Integrating Ecophysiological and Agent-Based Models to Simulate How Behavior Moderates Salamander Sensitivity to Climate

Developing rigorous ecological models is a fundamental goal of conservation biologists seeking to forecast biotic responses to climate change. A limitation of many models is they are amechanistic and lack integration of behavior, which is fundamental to animal biology. We integrated biophysical and agent-based models (ABM) to examine how behavior could affect the sensitivity of Plethodontid salamander activity time to climate. Specifically, our model used a temperature differential to stimulate plant climbing, a widely observed behavior among salamanders, which would allow salamanders to reduce body temperatures and associated dehydration rates. Consistent with expectations, predicted activity time was positively correlated with precipitation. The model showed that climbing plants increased activity time in drier conditions, particularly for smaller salamanders. The predicted importance of climbing behavior, a form of behavioral plasticity, was highly sensitive to assumptions about the threshold of water loss an individual was willing to tolerate. Because activity time is associated with fitness, increased activity time as a consequence of climbing behavior could moderate salamander sensitivity to shifts in weather patterns. Our results demonstrate the potential and importance of integrating behaviors into ecophysiological models when evaluating a species' potential sensitivity to climate