Robin E. Jung

Modeling Anuran Detection and Site Occupancy on North American Amphibian Monitoring Program (NAAMP) Routes in Maryland

Abstract One of the most fundamental problems in monitoring animal populations is that of imperfect detection. Although imperfect detection can be modeled, studies examining patterns in occurrence often ignore detection and thus fail to properly partition variation in detection from that of occurrence. In this study, we used anuran calling survey data collected on North American Amphibian Monitoring Program routes in eastern Maryland to investigate factors that influence detection probability and site occupancy for 10 anuran species. In 2002, 17 calling survey routes in eastern Maryland were surveyed to collect environmental and species data nine or more times. To analyze these data, we developed models incorporating detection probability and site occupancy. The results suggest that, for more than half of the 10 species, detection probabilities vary most with season (i.e., day-of-year), air temperature, time, and moon illumination, whereas site occupancy may vary by the amount of palustrine forested wetland habitat. Our results suggest anuran calling surveys should document air temperature, time of night, moon illumination, observer skill, and habitat change over time, as these factors can be important to model-adjusted estimates of site occupancy. Our study represents the first formal modeling effort aimed at developing an analytic assessment framework for NAAMP calling survey data.

Evaluation of terrestrial and streamside salamander monitoring techniques at Shenandoah National Park

In response to concerns about amphibian declines, a study evaluating and validating amphibian monitoring techniques was initiated in Shenandoah and Big Bend National Parks in the spring of 1998. We evaluate precision, bias, and efficiency of several sampling methods for terrestrial and streamside salamanders in Shenandoah National Park and assess salamander abundance in relation to environmental variables, notably soil and water pH. Terrestrial salamanders, primarily redback salamanders (Plethodon cinereus), were sampled by searching under cover objects during the day in square plots (10 to 35 m2). We compared population indices (mean daily and total counts) with adjusted population estimates from capture-recapture. Analyses suggested that the proportion of salamanders detected (p) during sampling varied among plots, necessitating the use of adjusted population estimates. However, adjusted population estimates were less precise than population indices, and may not be efficient in relating salamander populations to environmental variables. In future sampling, strategic use of capture-recapture to verify consistency of ps among sites may be a reasonable compromise between the possibility of bias in estimation of population size and deficiencies due to inefficiency associated with the estimation of p. The streamside two-lined salamander (Eurycea bislineata) was surveyed using four methods: leaf litter refugia bags, 1 m2 quadrats, 50 × 1 m visual encounter transects, and electric shocking. Comparison of survey methods at nine streams revealed congruent patterns of abundance among sites, suggesting that relative bias among the methods is similar, and that choice of survey method should be based on precision and logistical efficiency. Redback and two-lined salamander abundance were not significantly related to soil or water pH, respectively.

Stream salamanders as indicators of stream quality in Maryland, USA

Biological indicators are critical to the protection of small, headwater streams and the ecological values they provide. Maryland and other state monitoring programs have determined that fish indicators are ineffective in small streams, where stream salamanders may replace fish as top predators. Because of their life history, physiology, abundance, and ubiquity, stream salamanders are likely representative of biological integrity in these streams. The goal of this study was to determine whether stream salamanders are effective indicators of ecological conditions across biogeographic regions and gradients of human disturbance. During the summers of 2001 and 2002, we intensively surveyed for stream salamanders at 76 stream sites located west of the Maryland Coastal Plain, sites also monitored by the Maryland Biological Stream Survey (MBSS) and City of Gaithersburg. We found 1,584 stream salamanders, including all eight species known in Maryland, using two 15 × 2 m transects and two 4 m2 quadrats that spanned both stream bank and channel. We performed removal sampling on transects to estimate salamander species detection probabilities, which ranged from 0.67-0.85. Stepwise regressions identified 15 of 52 non-salamander variables, representing water quality, physical habitat, land use, and biological conditions, which best predicted salamander metrics. Indicator development involved (1) identifying reference (non-degraded) and degraded sites (using percent forest, shading, riparian buffer width, aesthetic rating, and benthic macroinvertebrate and fish indices of biotic integrity); (2) testing 12 candidate salamander metrics (representing species richness and composition, abundance, species tolerance, and reproductive function) for their ability to distinguish reference from degraded sites; and (3) combining metrics into an index that effectively discriminated sites according to known stream conditions. Final indices for Highlands, Piedmont, and Non-Coastal Plain regions comprised four metrics: number of species, number of salamanders, number of intolerant salamanders, and number of adult salamanders, producing classification efficiencies between 87% and 90%. Partial validation of these indices was obtained when a test of the number of salamanders metric produced an 82% correct classification of 618 MBSS sites surveyed in 1995-97. This study supports the use of stream salamander monitoring and a composite stream salamander index of biotic integrity (SS-IBI) to determine stream quality in Maryland.

An evaluation of population index and estimation techniques for tadpoles in desert pools

Abstract Using visual (VI) and dip net indices (DI) and double-observer (DOE), removal (RE), and neutral red dye capture-recapture (CRE) estimates, we counted, estimated, and censused Couchs spadefoot (Scaphiopus couchii) and canyon treefrog (Hyla arenicolor) tadpole populations in Big Bend National Park, Texas. Initial dye experiments helped us determine appropriate dye concentrations and exposure times to use in mesocosm and field trials. The mesocosm study revealed higher tadpole detection rates, more accurate population estimates, and lower coefficients of variation among pools compared to those from the field study. In both mesocosm and field studies, CRE was the best method for estimating tadpole populations, followed by DOE and RE. In the field, RE, DI, and VI often underestimated populations in pools with higher tadpole numbers. DI improved with increased sampling. Larger pools supported larger tadpole populations, and tadpole detection rates in general decreased with increasing pool volume and surface area. Hence, pool size influenced bias in tadpole sampling. Across all techniques, tadpole detection rates differed among pools, indicating that sampling bias was inherent and techniques did not consistently sample the same proportion of tadpoles in each pool. Estimating bias (i.e., calculating detection rates) therefore was essential in assessing tadpole abundance. Unlike VI and DOE, DI, RE, and CRE could be used in turbid waters in which tadpoles are not visible. The tadpole population estimates we used accommodated differences in detection probabilities in simple desert pool environments but may not work in more complex habitats.

Amphibian Research and Monitoring Initiative (ARMI): a successful start to a national program in the United States

Most research to assess amphibian declines has focused on local-scale projects on one or a few species. The Amphibian Research and Monitoring Initiative (ARMI) is a national program in the United States mandated by congressional directive and implemented by the U.S. Department of the Interior (specifically the U.S. Geological Survey, USGS). Program goals are to monitor changes in populations of amphibians across U.S. Department of the Interior lands and to address research questions related to amphibian declines using a hierarchical framework of base-, mid- and apex-level monitoring sites. ARMI is currently monitoring 83 amphibian species (29% of species in the U.S.) at mid- and apex-level areas. We chart the progress of this 5-year-old program and provide an example of mid-level monitoring from 1 of the 7 ARMI regions.

Stream salamander species richness and abundance in relation to environmental factors in Shenandoah National Park, Virginia

Abstract Stream salamanders are sensitive to acid mine drainage and may be sensitive to acidification and low acid neutralizing capacity (ANC) of a watershed. Streams in Shenandoah National Park, Virginia, are subject to episodic acidification from precipitation events. We surveyed 25 m by 2 m transects located on the stream bank adjacent to the water channel in Shenandoah National Park for salamanders using a stratified random sampling design based on elevation, aspect and bedrock geology. We investigated the relationships of four species (Eurycea bislineata, Desmognathus fuscus, D. monticola and Gyrinophilus porphyriticus) to habitat and water quality variables. We did not find overwhelming evidence that stream salamanders are affected by the acid-base status of streams in Shenandoah National Park. Desmognathus fuscus and D. monticola abundance was greater both in streams that had a higher potential to neutralize acidification, and in higher elevation (>700 m) streams. Neither abundance of E. bislineata nor species richness were related to any of the habitat variables. Our sampling method preferentially detected the adult age class of the study species and did not allow us to estimate population sizes. We suggest that continued monitoring of stream salamander populations in SNP will determine the effects of stream acidification on these taxa.

Large-scale habitat associations of four desert anurans in Big Bend National Park, Texas

Abstract We used night driving to examine large scale habitat associations of four common desert anurans in Big Bend National Park, Texas. We examined association of soil types and vegetation communities with abundance of Couchs Spadefoots (Scaphiopus couchii), Red-spotted Toads (Bufo punctatus), Texas Toads (Bufo speciosus), and Western Green Toads (Bufo debilis). All four species were disproportionately associated with frequently inundated soils that are relatively high in clay content. Bufo punctatus was associated with rocky soil types more frequently than the other three species. Association between all four species and vegetation types was disproportionate in relation to availability. Bufo debilis and Bufo punctatus were associated with creosote and mixed scrub vegetation. Bufo speciosus and Scaphiopus couchii were associated with mesquite scrub vegetation. Bufo debilis, Scaphiopus couchii, and B. speciosus were more tightly associated with specific habitat types, whereas B. punctatus exhibited a broader distribution across the habitat categories. Examining associations between large-scale habitat categories and species abundance is an important first step in understanding factors that influence species distributions and presence-absence across the landscape.

Phylogenetic Relationships of the Endangered Shenandoah Salamander (Plethodon shenandoah) and Other Salamanders of the Plethodon cinereus Group (Caudata: Plethodontidae)

Abstract The Shenandoah Salamander (Plethodon shenandoah), known from isolated talus slopes on three of the highest mountains in Shenandoah National Park, is listed as state-endangered in Virginia and federally endangered under the U.S. Endangered Species Act. A 1999 paper by G. R. Thurow described P. shenandoah-like salamanders from three localities further south in the Blue Ridge Physiographic Province, which, if confirmed, would represent a range extension for P. shenandoah of approximately 90 km from its nearest known locality. Samples collected from two of these three localities were included in a molecular phylogenetic study of the known populations of P. shenandoah, and all other recognized species in the Plethodon cinereus group, using a 792 bp region of the mitochondrial cytochrome-b gene. Phylogenetic estimates were based on Bayesian, maximum likelihood, and maximum parsimony methods and topologies examined for placement of the new P. shenandoah-like samples relative to all others. All topologies recovered all haplotypes of the P. shenandoah-like animals nested within P. cinereus, and a statistical comparison of the best likelihood tree topology with one with an enforced (Thurow + Shenandoah P. shenandoah) clade revealed that the unconstrained tree had a significantly lower –ln L score (P < 0.05, using the Shimodaira-Hasegawa test) than the constraint tree. This result and other anecdotal information give us no solid reason to consider the Thurow report valid. The current recovery program for P. shenandoah should remain focused on populations in Shenandoah National Park.

Evaluation of Canoe Surveys for Anurans along the Rio Grande in Big Bend National Park, Texas

Abstract Surveys for amphibians along large rivers pose monitoring and sampling problems. We used canoes at night to spotlight and listen for anurans along four stretches of the Rio Grande in Big Bend National Park, Texas, in 1998 and 1999. We explored temporal and spatial variation in amphibian counts and species richness and assessed relationships between amphibian counts and environmental variables, as well as amphibian-habitat associations along the banks of the Rio Grande. We documented seven anuran species, but Rio Grande leopard frogs (Rana berlandieri) accounted for 96% of the visual counts. Chorus surveys along the river detected similar or fewer numbers of species, but orders of magnitude fewer individuals compared to visual surveys. The number of species varied on average by 37% across monthly and nightly surveys. We found similar average coefficients of variation in counts of Rio Grande leopard frogs on monthly and nightly bases (CVs = 42–44%), suggesting that canoe surveys are a fairly precise technique for counts of this species. Numbers of Rio Grande leopard frogs observed were influenced by river gage levels and air and water temperatures, suggesting that surveys should be conducted under certain environmental conditions to maximize counts and maintain consistency. We found significant differences in species richness and bullfrog (Rana catesbeiana) counts among the four river stretches. Four rare anuran species were found along certain stretches but not others, which could represent either sampling error or unmeasured environmental or habitat differences among the river stretches. We found a greater association of Rio Grande leopard frogs with mud banks compared to rock or cliff (canyon) areas and with seepwillow and open areas compared to giant reed and other vegetation types. Canoe surveys appear to be a useful survey technique for anurans along the Rio Grande and may work for other large river systems as well.

Conservation genetics of the endangered Shenandoah salamander (Plethodon shenandoah, Plethodontidae)

The Shenandoah salamander (Plethodon shenandoah) is restricted to three isolated talus outcrops in Shenandoah National Park, VA, USA and has one of the smallest ranges of any tetrapod vertebrate. This species was listed as endangered under the US Endangered Species Act in 1989 over concern that direct competition with the red-backed salamander ( Plethodon cinereus), successional habitat changes, and human impacts may cause its decline and possible extinction. We address two issues herein: (1) whether extensive introgression (through long-term hybridization) is present between the two species and threatens the survival of P. shenandoah, and (2) the level of population structure within P. shenandoah. We provide evidence from mtDNA haplotypes that shows no genetic differentiation among the three isolates of P. shenandoah, suggesting that their fragmentation is a geologically recent event, and/or that the isolates are still connected by occasional gene flow. There is also no evidence for extensive introgression of alleles in either direction between P. cinereus and P. shenandoah, which suggests that P. shenandoah may not be in danger of being genetically swamped out through hybridization with P. cinereus.