William B. Sutton

Landscape-level influences of terrestrial snake occupancy within the southeastern United States.

Habitat loss and degradation are thought to be the primary drivers of species extirpations, but for many species we have little information regarding specific habitats that influence occupancy. Snakes are of conservation concern throughout North America, but effective management and conservation are hindered by a lack of basic natural history information and the small number of large-scale studies designed to assess general population trends. To address this information gap, we compiled detection/nondetection data for 13 large terrestrial species from 449 traps located across the southeastern United States, and we characterized the land cover surrounding each trap at multiple spatial scales (250-, 500-, and 1000-m buffers). We used occupancy modeling, while accounting for heterogeneity in detection probability, to identify habitat variables that were influential in determining the presence of a particular species. We evaluated 12 competing models for each species, representing various hypotheses pertaining to important habitat features for terrestrial snakes. Overall, considerable interspecific variation existed in important habitat variables and relevant spatial scales. For example, kingsnakes (Lampropeltis getula) were negatively associated with evergreen forests, whereas Louisiana pinesnake (Pituophis ruthveni) occupancy increased with increasing coverage of this forest type. Some species were positively associated with grassland and scrub/shrub (e.g., Slowinskis cornsnake, Elaphe slowinskii) whereas others, (e.g., copperhead, Agkistrodon contortrix, and eastern diamond-backed rattlesnake, Crotalus adamanteus) were positively associated with forested habitats. Although the species that we studied may persist in varied landscapes other than those we identified as important, our data were collected in relatively undeveloped areas. Thus, our findings may be relevant when generating conservation plans or restoration goals. Maintaining or restoring landscapes that are most consistent with the ancestral habitat preferences of terrestrial snake assemblages will require a diverse habitat matrix over large spatial scales.

Snake co‐occurrence patterns are best explained by habitat and hypothesized effects of interspecific interactions

Snakes often occur in species-rich assemblages, and sympatry is thought to be facilitated primarily by low diet overlap, not interspecific interactions. We selected, a priori, three species pairs consisting of species that are morphologically and taxonomically similar and may therefore be likely to engage in interspecific, consumptive competition. We then examined a large-scale database of snake detection/nondetection data and used occupancy modelling to determine whether these species occur together more or less frequently than expected by chance while accounting for variation in detection probability among species and incorporating important habitat categories in the models. For some snakes, we obtained evidence that the probabilities that habitat patches are used are influenced by the presence of potentially competing congeneric species. Specifically, timber rattlesnakes (Crotalus horridus) were less likely than expected by chance to use areas that also contained eastern diamond-backed rattlesnakes (Crotalus adamanteus) when the proportion of evergreen forest was relatively high. Otherwise, they occurred together more often than expected by chance. Complex relationships were revealed between habitat use, detection probabilities and occupancy probabilities of North American racers (Coluber constrictor) and coachwhips (Coluber flagellum) that indicated the probability of competitive exclusion increased with increasing area of grassland habitat, although there was some model uncertainty. Cornsnakes (Pantherophis guttatus or Pantherophis slowinskii) and ratsnakes (Pantherophis alleghaniensis, Pantherophis spiloides, or Pantherophis obsoletus) exhibited differences in habitat selection, but we obtained no evidence that patterns of use for this species pair were influenced by current interspecific interactions. Overall, our results are consistent with the hypothesis that competitive interactions influence snake assemblage composition; the strength of these effects was affected by landscape-scale habitat features. Furthermore, we suggest that current interspecific interactions may influence snake occupancy, challenging the paradigm that contemporary patterns of snake co-occurrence are largely a function of diet partitioning that arose over evolutionary time.

High susceptibility of the endangered dusky gopher frog to ranavirus

Amphibians are one of the most imperiled vertebrate groups, with pathogens playing a role in the decline of some species. Rare species are particularly vulnerable to extinction because populations are often isolated and exist at low abundance. The potential impact of pathogens on rare amphibian species has seldom been investigated. The dusky gopher frog Lithobates sevosus is one of the most endangered amphibian species in North America, with 100-200 individuals remaining in the wild. Our goal was to determine whether adult L. sevosus were susceptible to ranavirus, a pathogen responsible for amphibian die-offs worldwide. We tested the relative susceptibility of adult L. sevosus to ranavirus (103 plaque-forming units) isolated from a morbid bullfrog via 3 routes of exposure: intra-coelomic (IC) injection, oral (OR) inoculation, and water bath (WB) exposure. We observed 100% mortality of adult L. sevosus in the IC and WB treatments after 10 and 19 d, respectively. Ninety-five percent mortality occurred in the OR treatment over the 28 d evaluation period. No mortality was observed in the control treatment after 28 d. Our results indicate that L. sevosus is susceptible to ranavirus, and if adults in the wild are exposed to this pathogen, significant mortality could occur. Additionally, our study demonstrates that some adult amphibian species can be very susceptible to ranavirus, which has been often overlooked in North American studies. We recommend that conservation planners consider testing the susceptibility of rare amphibian species to ranavirus and that the adult age class is included in future challenge experiments.

Trends in Ranavirus Prevalence Among Plethodontid Salamanders in the Great Smoky Mountains National Park

Emerging pathogens are a potential contributor to global amphibian declines. Ranaviruses, which infect ectothermic vertebrates and are common in aquatic environments, have been implicated in die-offs of at least 72 amphibian species worldwide. Most studies on the subject have focused on pool-breeding amphibians, and infection trends in other amphibian species assemblages have been understudied. Our primary study objective was to evaluate hypotheses explaining ranavirus prevalence within a lungless salamander assemblage (Family Plethodontidae) in the Great Smoky Mountains National Park, USA. We sampled 566 total plethodontid salamanders representing 14 species at five sites over a 6-year period (2007–2012). We identified ranavirus-positive individuals in 11 of the 14 (78.6%) sampled species, with salamanders in the genus Desmognathus having greatest infection prevalence. Overall, we found the greatest support for site elevation and sampling year determining infection prevalence. We detected the greatest number of infections in 2007 with 82.5% of sampled individuals testing positive for ranavirus, which we attribute to record drought during this year. Infection prevalence remained relatively high in low-elevation sites in 2008 and 2009. Neither body condition nor aquatic dependence was a significant predictor of ranavirus prevalence. Overall, our results indicate that life history differences among species play a minor role determining ranavirus prevalence compared to the larger effects of site elevation and yearly fluctuations (likely due to environmental stressors) during sampling years.

COPPERHEADS ARE COMMON WHEN KINGSNAKES ARE NOT: RELATIONSHIPS BETWEEN THE ABUNDANCES OF A PREDATOR AND ONE OF THEIR PREY

Abstract:  Common Kingsnakes (formerly known collectively as Lampropeltis getula) are experiencing localized declines throughout the southeastern United States. Because there have been limited studies to determine how snakes regulate prey populations, and because Kingsnake declines may result in ecosystem impacts, we evaluated the hypothesis that Kingsnakes regulate the abundance of one of their prey, the venomous Copperhead (Agkistrodon contortrix). We generated a database of captures of the two species across the southeastern United States and, while controlling for large-scale habitat preferences, identified a negative relationship between the relative abundance of Kingsnakes and the relative abundance of Copperheads. Our results are correlative but consistent with the hypothesis that Copperhead populations experience a release from predation pressure where Kingsnake abundances are low. We suggest that Kingsnake declines, which are occurring for unknown reasons, are having ecological effects in affected ecosystems. We further highlight the potential role that snakes play in influencing the population dynamics of their prey.

Decline of the Cheat Mountain Salamander over a 32-Year Period and the Potential Influence of Competition from a Sympatric Species

Abstract We evaluated trends in occupancy of the Cheat Mountain Salamander (Plethodon nettingi) over a 32-yr period and examined the potential influence of competition by sympatric salamander species on these changes. We conducted surveys at 36 locations along four transects on an elevational gradient in the Appalachian Mountains geographic province of West Virginia, USA. We used occupancy modeling to examine patterns in species distributions for three focal species: P. nettingi, a federally threatened species, the Eastern Red-Backed Salamander (Plethodon cinereus), and the Allegheny Mountain Dusky Salamander (Desmognathus ochrophaeus). The probability of occupancy for P. nettingi was considerably lower in 2011 compared to 1978–79 at medium and high elevations (1,169–1,378 m). Additionally, occupancy of P. nettingi was associated negatively with P. cinereus at the highest elevations. These data suggest that these P. nettingi populations have declined and P. cinereus have possibly expanded their vertical distribution. Thus, P. cinereus may be negatively affecting mid- and high-elevation populations of P. nettingi. Alternatively, environmental changes (e.g., habitat disturbance and altered weather patterns) may have contributed to declines of P. nettingi at mid- and high-elevation sites, facilitated by colonization by P. cinereus. Due to the endemic and federally threatened status of P. nettingi, conservation efforts to avoid fragmentation of P. nettingi habitat should be maintained and possibly enhanced, as ecological impacts of environmental changes can be exacerbated in high-elevation habitats.

Wetland Wildlife Monitoring and Assessment

Monitoring wetland wildlife is complex and requires use of various techniques to obtain robust population estimates. Herpetofauna, birds and mammals frequently inhabit wetlands and adjacent uplands. Sampling herpetofauna can include passive techniques such as visual encounter and breeding call surveys, and capture techniques that use nets and traps. Common bird monitoring techniques include scan surveys, point counts, nest searches, and aerial surveys. Some mammals, such as bats, can be sampled with audio devices, whereas mark-recapture techniques are most effective for other taxa. For all groups, the techniques used depend on the monitoring objective and target species. This chapter describes various techniques for monitoring populations of wetland wildlife. If these techniques are incorporated into a robust sampling design, they can be used to document changes in species occurrence, relative abundance, and survival.