David M. Marsh

Current Trends in Plant and Animal Population Monitoring

Animal and plant population monitoring programs are critical for identifying species at risk, evaluating the effects of management or harvest, and tracking invasive and pest species. Nevertheless, monitoring activities are highly decentralized, which makes it difficult for researchers or conservation planners to get a good general picture of what real-world monitoring programs actually entail. We used a Web-based survey to collect information on population monitoring programs. The survey focused on basic questions about each program, including motivations for monitoring, types of data being collected, spatiotemporal design of the program, and reasons for choosing that design. We received responses from 311 people involved in monitoring of various species and used these responses to summarize ongoing monitoring efforts. We also used responses to determine whether monitoring strategies have changed over time and whether they differed among monitoring agencies. Most commonly, monitoring entailed collection of count data at multiple sites with the primary goal of detecting trends. But we also found that goals and strategies for monitoring appeared to be diversifying, that area-occupied and presence-absence approaches appeared to be gaining in popularity, and that several other promising approaches (monitoring to reduce parameter uncertainty, risk-based monitoring, and directly linking monitoring data to management decisions) have yet to become widely established. We suggest that improved communication between researchers studying monitoring designs and those who are charged with putting these designs into practice could further improve monitoring programs and better match sampling designs to the objectives of monitoring programs.

Fine-scale population differentiation and gene flow in a terrestrial salamander ( Plethodon cinereus ) living in continuous habitat

Several recent studies have shown that amphibian populations may exhibit high genetic subdivision in areas with recent fragmentation and urban development. Less is known about the potential for genetic differentiation in continuous habitats. We studied genetic differentiation of red-backed salamanders (Plethodon cinereus) across a 2-km transect through continuous forest in Virginia, USA. Mark-recapture studies suggest very little dispersal for this species, whereas homing experiments and post-Pleistocene range expansion both suggest greater dispersal abilities. We used six microsatellite loci to examine genetic population structure and differentiation between eight subpopulations of red-backed salamanders at distances from 200 m to 2 km. We also used several methods to extrapolate dispersal frequencies and test for sex-biased dispersal. We found small, but detectable differentiation among populations, even at distances as small as 200 m. Differentiation was closely correlated with distance and both Mantel tests and assignment tests were consistent with an isolation-by-distance model for the population. Extrapolations of intergenerational variance in spatial position (σ2<15 m2) and pair-wise dispersal frequencies (4Nm<25 for plots separated by 300 m) both suggest limited gene flow. Additionally, tests for sex-biased dispersal imply that dispersal frequency is similarly low for both sexes. We suggest that these low levels of gene flow and the infrequent dispersal observed in mark-recapture studies may be reconciled with homing ability and range expansion if dispersing animals rarely succeed in breeding in saturated habitats, if dispersal is flexible depending on the availability of habitat, or if dispersal frequency varies across the geographic range of red-backed salamanders.

TREATMENT OF SPINAL TUMORS USING CYBERKNIFE FRACTIONATED STEREOTACTIC RADIOSURGERY: PAIN AND QUALITY-OF-LIFE ASSESSMENT AFTER TREATMENT IN 200 PATIENTS

OBJECTIVEBenign and malignant tumors of the spine significantly impair the function and quality of life of many patients. Standard treatment options, including conventional radiotherapy and surgery, are often limited by anatomic constraints and previous treatment. Image-guided stereotactic radiosurgery using the CyberKnife system (Accuray, Inc., Sunnyvale, CA) is a novel approach in the multidisciplinary management of spinal tumors. The aim of this study was to evaluate the effects of CyberKnife stereotactic radiosurgery on pain and quality-of-life outcomes of patients with spinal tumors. METHODSWe conducted a prospective study of 200 patients with benign or malignant spinal tumors treated at Georgetown University Hospital between March 2002 and September 2006. Patients were treated by means of multisession stereotactic radiosurgery using the CyberKnife as initial treatment, postoperative treatment, or retreatment. Pain scores were assessed by the Visual Analog Scale, quality of life was assessed by the SF-12 survey, and neurological examinations were conducted after treatment. RESULTSMean pain scores decreased significantly from 40.1 to 28.6 after treatment (P < 0.001) and continued to decrease over the entire 4-year follow-up period (P < 0.05). SF-12 Physical Component scores demonstrated no significant change throughout the follow-up period. Mental Component scores were significantly higher after treatment (P < 0.01), representing a quality-of-life improvement. Early side effects of radiosurgery were mild and self-limited, and no late radiation toxicity was observed. CONCLUSIONCyberKnife stereotactic radiosurgery is a safe and effective modality in the treatment of patients with spinal tumors. CyberKnife offers durable pain relief and maintenance of quality of life with a very favorable side effect profile.

EFFECTS OF FOREST ROADS ON THE ABUNDANCE AND ACTIVITY OF TERRESTRIAL SALAMANDERS

One of the major effects of deforestation is the creation of numerous edge zones where remaining forest meets nonforest habitat. At this interface, edge effects on forest habitats can include altered abiotic conditions, changes in rates of competition and predation, and altered community structure. While the edge effects resulting from clear- cuts and other open habitats are well-studied, little is known about the comparative edge effects of forest roads. We studied the effects of forest roads on the abundance, surface activity, and body condition of red-backed salamanders (Plethodon cinereus) and slimy salamanders (P. glutinosus and P. cylindraceus) in the Southern Appalachians of Virginia. We conducted surveys for salamanders at 21 sites where gravel roads bisected mature forest. These sites were divided into three data sets based on region and year of survey. We also carried out an enclosure experiment to determine whether road edges influenced the surface activity and detectability of red-backed salamanders. We found fewer red-backed salaman- ders near roads in all three data sets. These edge effects extended ,20 m into the forest in two of the three data sets but increased linearly out to 80 m in the data set collected during an unusually dry period. In contrast, slimy salamanders showed no clear responses to forest-road edges and had significantly different responses than those of red-backed salamanders. Within our experimental enclosures, red-backed salamander detectability did not differ between edge and interior habitats, suggesting that the patterns we observed were not simply due to changes in salamander activity patterns. Like red-backed salamander counts, soil moisture and cover object area also tended to decrease near roads. The steepness of the gradient in soil moisture was a significant predictor of the steepness of the decline in salamander counts, while there was no significant relationship between the decreases in cover object area and decreases in salamander counts. Collectively, these results show that edge effects from forest roads may be comparable to edge effects from clear-cuts or other types of silvicultural edges. Additionally, they suggest that, for terrestrial salamanders, variation in the magnitude of edge effects may be related to variation in soil moisture. Management approaches that minimize soil desiccation associated with road building and maintenance may reduce the impacts of roads on amphibian populations in adjacent forest.

Effects of roads on patterns of genetic differentiation in red-backed salamanders, Plethodon cinereus

Roads can fragment animal populations by reducing gene flow, which can lead to drift and the loss of genetic diversity. One of the principle signatures of reduced gene flow is increased genetic differentiation in isolated populations, and evidence that roads contribute to such differentiation has been reported for several species. We used microsatellites to examine whether six roads led to increased genetic differentiation in red-backed salamanders (Plethodon cinereus). These six roads included one divided interstate highway, one undivided four-lane highway, and four secondary roads. We found that the genetic distance between plots that were bisected by the interstate highway was significantly greater than the genetic distance between equidistant plots on the same side of the highway. However, for the five smaller roads, plots across the road were no more genetically distinct than were plots on the same side of the road. Bayesian clustering methods also supported both of these findings. The optimal clustering of plots for the interstate highway consisted of two clusters that corresponded to the two sides of highway. For the other five sites, the optimal grouping consisted of a single cluster containing all of the plots. Our findings suggest that gene flow across very large roads is rare and that bisected red-backed salamander populations are likely to diverge from one another. For smaller roads, our results imply that the indirect effects of roads on genetic population structure are probably less of a pressing concern for terrestrial salamanders than are the direct effects of mortality and habitat alteration.

Edge Effects of Gated and Ungated Roads on Terrestrial Salamanders

Abstract Roads through forest habitats reduce the abundance of many animal species. These reductions are often referred to as edge effects and their causes include roadkill, degradation of forest habitat, and changes in biotic interactions. Which of these causes are operating can have important implications for management. Terrestrial salamanders in the southern Appalachians have previously been shown to be subject to edge effects from forest roads that are open to traffic. In this study, I examined edge effects on red-backed salamanders (Plethodon cinereus) along forest roads that were either open or gated to prevent vehicle entry. I also included roads that varied in the width of the gravel surface, the width of the roadside verge, and the magnitude of habitat gradients at the forest edge. I found that ungated roads were associated with consistent edge effects on salamanders, whereas no detectable edge effects were found for gated roads. Road width was as good a predictor of the magnitude of edge effects as was the presence of a gate, though the width of the roadside verge was largely unrelated to the magnitude of edge effects. Gradients in habitat variables (soil moisture, temp, leaf litter thickness) were not closely related to the magnitude of edge effects. These results demonstrate that narrow, gated roads do not typically produce edge effects on terrestrial salamanders of the same magnitude as wider, ungated roads. In addition, the apparent importance of road type or road width and the relative unimportance of habitat characteristics suggest that traffic-related factors may be a substantial contributor to edge effects on terrestrial salamanders. These findings provide some support for the closing of redundant forest roads as a low-cost method for diminishing the negative effects of roads on forest ecosystems.

Evaluating methods for sampling stream salamanders across multiple observers and habitat types

While techniques for sampling pond-breeding amphibians are relatively well-established, comparable methods for stream amphibians are still being developed. Uncertainty about sampling techniques is particularly acute for approaches that involve multiple observers. I evaluated three techniques for sampling stream salamanders with multiple observers—time-constrained surveys, leaf-litter bags, and controlled-cobble added to the stream. I tested for differences among techniques, differences among habitats, and technique by habitat interactions. I also asked whether coefficients of variation across observers and sample dates differed among methods and habitats. For all species and life-stages, time-constrained surveys produced higher counts of stream salamanders and greater richness estimates than did leaf-litter bags or controlled-cobble surveys. However, interactions between techniques and habitat were never significant, indicating that all the methods detected similar patterns in counts among stream habitats. Coefficients of variation in single-species counts tended to be higher for time-constrained surveys, whereas CVs for species richness were significantly lower for time-constrained surveys. Overall, these results suggest that: (1) time-constrained surveys for stream salamanders work surprisingly well even with multiple observers, (2) leaf-litter bags may be quite useful for single-species studies, but are less effective for multi-species sampling, and (3) controlled-cobble added to streams is not particularly effective for sampling salamanders in rocky streams.

Invasive Plants in Wildlife Refuges: Coordinated Research with Undergraduate Ecology Courses

Answering large-scale questions in ecology can involve time-consuming data compilation. We show how networks of undergraduate classes can make these projects more manageable and provide an authentic research experience for students. With this approach, we examined the factors associated with plant species richness in US national wildlife refuges. We found that the richness of harmful invasive plants and the richness of native plants were positively correlated in mainland refuges but negatively correlated in island refuges. Nonnative richness and invasive richness were also positively correlated with colonization pressure as indicated by nonnative richness around each refuge. Associations between refuge characteristics and invasive plants varied substantially among regions, with refuge area and habitat diversity important predictors of invasion in some regions but not in others. Our results serve to identify the refuges that are most susceptible to plant invasion and demonstrate the potential value of a new model for education and research integration.