Kristen K. Cecala

Effects of Urbanization on Occupancy of Stream Salamanders

Urban development is the most common form of land conversion in the United States. Using a before-after control-impact study design, we investigated the effects of urbanization on larval and adult stages of southern two-lined salamanders (Eurycea cirrigera) and northern dusky salamanders (Desmognathus fuscus). Over 5 years, we estimated changes in occupancy and probabilities of colonization and survival in 13 stream catchments after urbanization and in 17 catchments that were not urbanized. We also examined effects of proportion of urbanized area in a catchment and distance of the salamander population to the nearest stream on probabilities of colonization and survival. Before urbanization, adult and larval stages of the two salamander species occupied nearly all surveyed streams, with occupancy estimates ranging from 1.0 to 0.78. Four years after urbanization mean occupancy of larval and adult two-lined salamanders had decreased from 0.87 and 0.78 to 0.57 and 0.39, respectively. Estimates of mean occupancy of larval northern dusky salamanders decreased from 1.0 to 0.57 in urban streams 4 years after urbanization; however, adult northern dusky salamander occupancy remained close to 1.0 in urban streams over 5 years. Occupancy estimates in control streams were similar for each species and stage over 5 years. Urbanization was associated with decreases in survival probabilities of adult and larval two-lined salamanders and decreases in colonization probabilities of larval dusky salamanders. Nevertheless, proportion of impervious surface and distance to nearest stream had little effect on probabilities of survival and colonization. Our results imply that in the evaluation of the effects of urbanization on species, such as amphibians, with complex life cycles, consideration of the effects of urbanization on both adult and larval stages is required.

Diet of Larval Red Salamanders (Pseudotriton ruber) Examined Using a Nonlethal Technique

Abstract Stream salamanders may play important roles as predators within streams, but we know little about actual predation by stream salamanders on other organisms. Because larval stream salamanders are more abundant within streams than adults, feed and forage throughout the year, and may spend multiple years in streams before transformation, larvae may play a more important role than adults in trophic interactions within streams. We conducted a study using larval Red Salamanders (Pseudotriton ruber) to determine (1) the prey composition of larval salamanders, (2) whether feeding rates are affected by stream water temperature, (3) whether larval size affects the diversity of prey items, and (4) whether nonlethal stomach flushing is an effective technique for examining the diet of larval salamanders. We found that larvae consumed a wide diversity of prey items including individuals of the families Chironomidae (36.52% of prey items) and Sphaeriidae (15.17%) as well as terrestrial prey (7.87%) and other salamanders (2.25%). We also found that feeding rates were negatively correlated with stream water temperature, and larger larvae consumed a wider diversity of prey items than smaller individuals. Our results also suggest that nonlethal stomach flushing did not affect survivorship. These findings suggest that larval Red Salamanders are generalist predators that can play important trophic roles in stream ecosystems.

Patterns of Trombiculid Mite (Hannemania dunni) Parasitism among Plethodontid Salamanders in the Western Piedmont of North Carolina

Trombiculid mites are known to parasitize a variety of amphibian species, yet few comparisons of mite parasitism among amphibian species have been made. In this study, we investigated patterns of trombiculid mite parasitism among 3 plethodontid salamanders (Desmognathus fuscus, Eurycea cirrigera, and Plethodon cylindraceus) in the western Piedmont of North Carolina. All 3 salamander species were parasitized by a single species, Hannemania dunni. Desmognathus fuscus harbored mites more frequently (60.4% of individuals) than E. cirrigera (11.1%) or P. cylindraceus (14.6%). Desmognathus fuscus also had higher parasite loads than E. cirrigera or P. cylindraceus (P < 0.001). Mites on D. fuscus were found more frequently on the limbs than other body locations (P < 0.001). We found no correlation between salamander size and mite abundance (P = 0.689), but salamander collection sites influenced the abundance of mites on D. fuscus (P = 0.002). We found no effect of season on mite abundance in D. fuscus (P = 0.952). Salamander habitat preferences and edaphic or climatic differences among study sites may influence patterns of Hannemania sp. parasitism of salamanders.

Modeling the effects of life-history traits on estimation of population parameters for a cryptic stream species

Abstract. Estimating demographic values and rates for populations of cryptic stream species frequently is difficult because of prohibitively low capture probabilities. When assessing cryptic populations, researchers often are forced to make simplifying assumptions that could alter their conclusions about a population. We constructed models based on different assumptions about cohort structure, behavioral responses to capture, temporary emigration, and survival in a cryptic, larval population of red salamanders (Pseudotriton ruber) and fitted models to capture-mark-recapture data. Overall, models based on 2 cohorts were favored over models based on 1 cohort. Models based on assumptions of constant survival, behavioral responses to capture, and random temporary emigration were ranked higher than models lacking these assumptions. Consistent behavioral responses to capture demonstrated that using uncorrected counts to assess trends for this, and perhaps other larval amphibian populations, yields misleading results. Counts that are not corrected for trap-shy behavior may inherently show negative temporal trends. Temporary emigration was a critical assumption when describing larval salamander demography because only 27% of the larvae were active on the surface (the rest were in substratum habitats). Our study demonstrates the importance of making appropriate assumptions about demographic parameters and shows how population models can quantify aspects of the natural history of cryptic species.

Relationship between Behavioral Thermoregulation and Physiological Function in Larval Stream Salamanders

Abstract Relationships between behavioral regulation, environmental temperatures, and physiological tolerance are critical to conservation policy; however, these relationships may not be consistent among sister taxa. A species geographic range is influenced by various factors including physiological tolerance to temperature change. In this study, we investigated the effects of temperature variation on thermal preference and standard metabolic rates (SMR) of two species of larval salamanders, Eurycea cirrigera (Southern Two-Lined Salamander) and Eurycea wilderae (Blue Ridge Two-Lined Salamander). These species share similar life histories, but E. cirrigera is broadly distributed and E. wilderae occupies a smaller range. We measured SMR using volume of oxygen consumption during closed-circuit respirometery trials conducted at 5°C increments between 5°C and 25°C. Standard metabolic rates were influenced by temperature, with a range of temperature-independent SMRs observed at those temperatures above each species laboratory-determined thermal preference. Concordant with their thermal preference (15.70°C) and more-narrow geographic range, E. wilderae exhibited a smaller scope of temperatures at which SMR was temperature-independent, relative to E. cirrigera, and metabolic rates were depressed at 25°C. Therefore, preferred thermal temperatures corresponded with physiological maxima and environmental temperatures in each species. Our results support the importance of behavioral thermoregulation in maintaining optimal physiological function. Further, these findings indicate that the physiological specialization that occurs in species of narrow geographic ranges may preclude favorable responses to changing environmental temperatures caused by land-cover changes, including loss of riparian forest in the Eastern United States.

Patch occupancy of stream fauna across a land cover gradient in the southern Appalachians, USA

Abstract We modeled patch occupancy to examine factors that best predicted the prevalence of four functionally important focal stream consumers (Tallaperla spp., Cambarus spp., Pleurocera proxima, and Cottus bairdi) among 37 reaches within the Little Tennessee River basin of the southern Appalachian Mountains, USA. We compared 34 models of patch occupancy to examine the association of catchment and reach scale factors that varied as a result of converting forest to agricultural or urban land use. Occupancy of our taxa was linked to parameters reflecting both catchment and reach extent characteristics. At the catchment level, forest cover or its conversion to agriculture was a major determinant of occupancy for all four taxa. Patch occupancies of Tallaperla, Cambarus, and C. bairdi were positively, and Pleurocera negatively, correlated with forest cover. Secondarily at the reach level, local availability of large woody debris was important for Cambarus, availability of large cobble substrate was important for C. bairdi, and stream calcium concentration was important for P. proxima. Our results show the abundance of stream organisms was determined by the taxon-dependent interplay between catchment- and reach-level factors.

Detecting Enigmatic Declines of A Once Common Salamander in the Coastal Plain of Georgia

Abstract For amphibian species suspected of undergoing enigmatic declines, it is important to determine the effort required to confidently establish species absence. Desmognathus auriculatus (Southern Dusky Salamander) has purportedly gone from being quite common throughout the southeastern US Coastal Plain to now being enigmatically rare. We used repeated standardized surveys of 5 historically occupied streams and their adjacent riparian zones between 2007 and 2010 to estimate detection rate of Southern Dusky Salamanders. We detected Southern Dusky Salamanders at 3 of 5 historic sites. Mean detection rate across streams known to be occupied at least once during the study was moderately low (mean ± 1 SE = 0.20 ± 0.12 for a double-sampled 50-m survey), improved at 2 sites with increasing time since drought, and varied among streams. For comparison, we evaluated detection rates of several other stream salamanders and found those rates to range from 0.37 (± 0.07) for Eurycea quadridigitata (Dwarf Salamander) to 0.08 (± 0.01) for Siren intermedia (Lesser Siren). Based on mark—recapture along a 200-m section of stream and the associated riparian habitat at the site where Southern Dusky Salamanders were most often detected, we estimated 43 (± 15) and 97 (± 161) individuals to be present February—May 2009 and October 2009–May 2010, respectively. Despite abundant adults, Southern Dusky Salamanders were the only species that we failed to detect as larvae; however, we observed many newly metamorphosed Southern Dusky Salamanders–usually under logs with saturated soil and often near entrances to crayfish burrows. Our results generally support the characterizations of Southern Dusky Salamanders as having become enigmatically uncommon. Because landcover change in the study area has been minimal, we suspect habitat damage from Sus scrofa (Feral Pig) may be responsible for the variation in Southern Dusky Salamander presence and abundance among sites. Because of the low detectability of Southern Dusky Salamanders, future work to identify factors driving Southern Dusky Salamander distribution and abundance will require intensive sampling at sites to provide robust estimates of occupancy or population size.

Ecology of juvenile Northern watersnakes ( Nerodia sipedon ) inhabiting low-order streams

The juvenile stage for many reptiles is considered “the lost years” because of low capture probabilities, however understanding factors impacting juvenile survivorship and recruitment is critical for conservation of populations. We studied the ecology of juvenile Northern watersnakes, Nerodia sipedon, by intensively sampling a first-order stream and determined the occupancy of juveniles in 30 low-order streams in the Piedmont of North Carolina. Juveniles were relatively abundant within a single stream (n = 62 ± 9), and their capture probabilities were positively related to increasing stream-water temperatures. We also found that juveniles had high survivorship (ϕ = 0.87 ± 0.017). Occupancy of juvenile N. sipedon in low-order, Piedmont streams may be greater at streams that have confluences with high order streams or lakes, which potentially support adult N. sipedon populations. This study provides important information regarding the natural history of juvenile reptiles and indicates the importance of low order streams as habitat for N. sipedon populations.

Negative Phototaxis Results from Avoidance of Light and Temperature in Stream Salamander Larvae

Abstract Forest removal is a global threat to amphibian diversity. Declines occur within these areas, but many amphibians also avoid moving into or through disturbed areas. Understanding which cues result in avoidance may provide targets for preservation of amphibian occupancy and population connectivity. Negative phototaxis is known from many amphibians, but light can serve as a cue or as a proxy for other environmental cues like temperature. This study sought to evaluate whether larval salamander habitat selection was influenced most by light or temperature cues. Because some individuals choose to remain in deforested habitat, we also assessed whether differences in habitat selection existed between individuals from forested and deforested habitat. Using a laboratory experiment, we found that salamanders use both light and temperature cues for habitat selection. Although salamanders demonstrated larger responses to temperature, they were willing to move into warmer habitats to avoid light. Individuals from deforested regions preferred brighter and warmer areas than individuals from forested regions although plasticity was higher with respect to light relative to temperature. We also noted that salamander thermal preferences were lower than daytime temperatures in small (< 60 m) deforested regions. Overall, a combination of light and thermal cues following forest removal may contribute to avoidance of deforested regions, but more research is necessary to understand why some salamanders continue to occupy warm and bright-disturbed areas.

Response of stream salamanders to experimental drought in the southern Appalachian Mountains, USA

Droughts act as significant disturbances to freshwater animals and their ecosystems. Given the impending threat of more frequent and persistent droughts because of global climate change, the lack of data on the responses of many aquatic animals to drought is a cause for concern. This study examined the body condition of the most commonly detected species (Desmognathus quadramaculatus) and abundance of commonly found species after two years of experimental drought in two first-order streams in the southern Appalachian Mountains. Our results indicated negative effects of drought on the stream salamander community. The body condition of D. quadramaculatus larvae in experimental drought transects was significantly lower than larvae captured in control reaches, which may have resulted from lower macroinvertebrate production in experimental reaches. Additionally, larval D. quadramaculatus abundance declined 47% in experimental drought transects, and Eurycea wilderae larvae and D. ocoee adults were 70% less likely to be captured in experimental stream transects. Our findings contribute additional evidence that stream plethodontids have little resistance to drought. With extended droughts resulting from climate change more likely in the future, more research is necessary to determine if reduced body condition, production, and lowered abundance have effects on long-term population viability.