Browsing by Author "Gorman, Thomas A."

Now showing 1 - 11 of 11
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    Does long-term fire suppression impact leaf litter breakdown and aquatic invertebrate colonization in pine flatwoods wetlands?
    Chandler, Houston C.; Colon-Gaud, J. Checo; Gorman, Thomas A.; Carson, Khalil; Haas, Carola A. (PeerJ, 2021-11-29)
    Ephemeral wetlands are commonly embedded within pine uplands of the southeastern United States. These wetlands support diverse communities but have often been degraded by a lack of growing-season fires that historically maintained the vegetation structure. In the absence of fire, wetlands develop a dense mid-story of woody vegetation that increases canopy cover and decreases the amount of herbaceous vegetation. To understand how reduced fire frequency impacts wetland processes, we measured leaf litter breakdown rates and invertebrate communities using three common plant species (Longleaf Pine (Pinus palustris), Pineland Threeawn Grass (Aristida stricta), and Black Gum (Nyssa sylvatica)) that occur in pine flatwoods wetlands located on Eglin Air Force Base, Florida. We also tested whether or not the overall habitat type within a wetland (fire maintained or fire suppressed) affected these processes. We placed leaf packs containing 15.0 g of dried leaf litter from each species in both fire-maintained and fire-suppressed sections of three wetlands, removing them after 103±104 days submerged in the wetland. The amount of leaf litter remaining at the end of the study varied across species (N. sylvatica D 7.97 ± 0.17 g, A. stricta D 11.84 ± 0.06 g, and P. palustris D 11.37 ± 0.07 g (mean ± SE)) and was greater in fire-maintained habitat (leaf type: F2,45 D 437.2, P < 0.001; habitat type: F1,45 D 4.6, P D 0.037). We identified an average of 260 ± 33.5 (SE) invertebrates per leaf pack (range: 19±1,283), and the most abundant taxonomic groups were Cladocera, Isopoda, Acariformes, and Diptera. Invertebrate relative abundance varied significantly among litter species (approximately 39.9 ± 9.4 invertebrates per gram of leaf litter remaining in N. sylvatica leaf packs, 27.2 ± 5.3 invertebrates per gram of A. stricta, and 14.6 ± 3.1 invertebrates per gram of P. palustris (mean ± SE)) but not habitat type. However, both habitat (pseudo-F1,49 D 4.30, P D 0.003) and leaf litter type (pseudo-F2,49 D 3.62, P D 0.001) had a significant effect on invertebrate community composition. Finally, this work was part of ongoing projects focusing on the conservation of the critically imperiled Reticulated Flatwoods Salamander (Ambystoma bishopi), which breeds exclusively in pine flatwoods wetlands, and we examined the results as they relate to potential prey items for larval flatwoods salamanders. Overall, our results suggest that the vegetation changes associated with a lack of growing-season fires can impact both invertebrate communities and leaf litter breakdown.
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    The Effects of Climate Change and Long-term Fire Suppression on Ephemeral Pond Communities in the Southeastern United States
    Chandler, Houston Cawthorn (Virginia Tech, 2015-01-15)
    In the southeastern United States, ephemeral wetlands in pine flatwoods provide important habitat for amphibians and aquatic invertebrates, but extensive deforestation has destroyed or isolated many wetlands and fire suppression has altered vegetation in others. My goals were to identify how wetland hydroperiods have changed through time and to examine the effects of long-term fire suppression on aquatic communities, including Reticulated Flatwoods Salamanders (Ambystoma bishopi) and Ornate Chorus Frogs (Pseudacris ornata). Chapter 1 used a modeling approach to relate wetland hydroperiods to current climate conditions and to hindcast historic conditions. Over the past 118 years, hydroperiods were often unfavorable for A. bishopi reproduction, and in recent years hydroperiods were shortened by persistent drought. Chapters 2 and 3 focused on identifying the effects of shifting from an open, grass dominated wetland to a wetland with high canopy cover and little herbaceous vegetation. In Chapter 2, I quantified amphibian and invertebrate communities in several wetlands. A. bishopi and P. ornata tended to occupy wetlands with lower canopy cover and higher herbaceous vegetation cover. Aquatic invertebrate abundance was generally higher in wetlands with lower shrub density and lower canopy cover. In Chapter 3, I examined how a reduction in herbaceous vegetation affected tadpoles when a predatory crayfish was present using two experiments. Crayfish were effective predators of both species across all vegetation treatments and often caused nonlethal tail injury. My results suggest that managers should focus on ensuring that wetland basins regularly burn, and wetlands with longer hydroperiods should be a management priority.
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    Evaluating Methods to Restore Amphibian Habitat in Fire-Suppressed Pine Flatwoods Wetlands
    Gorman, Thomas A.; Haas, Carola A.; Himes, John G. (2013-04-01)
    Although fire is recognized as an important disturbance in longleaf pine uplands of the southeastern US, less is known about the importance of fire or other disturbances in the wetlands embedded within this ecosystem. The reticulated flatwoods salamander (Ambystoma bishopi), a federally endangered species, and other rare and declining amphibians, are less likely to breed in low-quality wetlands with high canopy cover and low herbaceous groundcover that typically occur from fire exclusion. Fire rarely carries through these wetlands during winter because of the presence of standing water at this time of year. Our objective was to evaluate whether mechanical removal of the woody midstory could serve as a surrogate for fire, and create high-quality wetlands with moderate canopy cover and high herbaceous groundcover. We chose a series of high-quality (n = 4) and low-quality (n = 21) ephemeral wetlands for study. A subset of the low-quality wetlands were then treated mechanically and with herbicide (n = 8), burned (n = 4), or retained in a low-quality state (n = 7). Mechanical treatments reduced canopy cover (from 55.7 % to 41.4 %) to similar levels as high-quality sites (36.7 %); however, herbaceous groundcover did not increase (17.2 % post-treatment compared to 37.3 % at high-quality sites). Fire reduced the canopy cover (from 41.3 % to 33.0 %), and herbaceous groundcover was similar (33.2 % post treatment) to high-quality sites as of four months post burn. More time will be required to assess the response of herbaceous groundcover and whether mechanical methods can be used as a surrogate for fire to restore amphibian breeding habitat. Identifying surrogates for fire could add an important technique to our management toolbox.
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    Feral swine Sus scrofa: a new threat to the remaining breeding wetlands of the Vulnerable reticulated flatwoods salamander Ambystoma bishopi
    Jones, Kelly C.; Gorman, Thomas A.; Rincon, Brandon K.; Allen, John; Haas, Carola A.; Engeman, Richard M. (2018-10)
    Feral swine Sus scrofa have been implicated as a major threat to sensitive habitats and ecosystems as well as threatened wildlife. Nevertheless, direct and indirect impacts on threatened species (especially small, fossorial species) are not well documented. The decline of the U.S. federally endangered reticulated flatwoods salamander Ambystoma bishopi, categorized as Vulnerable on the IUCN Red List, has been rapid and there are few remaining breeding locations for this species. The flatwoods salamander depends on complex herbaceous vegetation in all life stages, including eggs, larvae and adults. Historically sets of hog tracks have been observed only occasionally in the vicinity of monitored reticulated flatwoods salamander breeding wetlands, and damage to the wetlands had never been recorded. However, during the autumn-winter breeding season of 2013-2014 we observed a large increase in hog sign, including extensive rooting damage, in known flatwoods salamander breeding wetlands. Our objective was to assess the amount of hog sign and damage in these wetlands and to take corrective management actions to curb additional impacts. Of 28 wetlands surveyed for hog sign, presence was recorded at 68%, and damage at 54%. Of the 11 sites known to be occupied by flatwoods salamanders in 2013-2014, 64% had presence, and 55% had damage. We found that regular monitoring of disturbance in wetland habitats was a valuable tool to determine when intervention was needed and to assess the effectiveness of intervention. Habitat damage caused by feral hogs poses a potentially serious threat to the salamanders, which needs to be mitigated using methods to control and exclude hogs from this sensitive habitat.
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    Hindcasting Historical Breeding Conditions for an Endangered Salamander in Ephemeral Wetlands of the Southeastern USA: Implications of Climate Change
    Chandler, Houston C.; Rypel, Andrew L.; Jiao, Yan; Haas, Carola A.; Gorman, Thomas A. (PLOS, 2016-02-24)
    The hydroperiod of ephemeral wetlands is often the most important characteristic determining amphibian breeding success, especially for species with long development times. In mesic and wet pine flatwoods of the southeastern United States, ephemeral wetlands were a common landscape feature. Reticulated flatwoods salamanders (Ambystoma bishopi), a federally endangered species, depend exclusively on ephemeral wetlands and require at least 11 weeks to successfully metamorphose into terrestrial adults. We empirically modeled hydroperiod of 17 A. bishopi breeding wetlands by combining downscaled historical climate-model data with a recent 9-year record (2006–2014) of observed water levels. Empirical models were subsequently used to reconstruct wetland hydrologic conditions from 1896–2014 using the downscaled historical climate datasets. Reconstructed hydroperiods for the 17 wetlands were highly variable through time but were frequently unfavorable for A. bishopi reproduction (e.g., only 61% of years, using a conservative estimate of development time [12 weeks], were conducive to larval development and metamorphosis). Using change-point analysis, we identified significant shifts in average hydroperiod over the last century in all 17 wetlands. Mean hydroperiods were shorter in recent years than at any other point since 1896, and thus less suitable for A. bishopi reproduction. We suggest that climate change will continue to impact the reproductive success of flatwoods salamanders and other ephemeral wetland breeders by reducing the number of years these wetlands have suitable hydroperiods. Consequently, we emphasize the importance of conservation and management for mitigating other forms of habitat degradation, especially maintenance of high quality breeding sites where reproduction can occur during appropriate environmental conditions.
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    Modeling Driver Intent in Potential Right Turning Scenarios
    Gorman, Thomas A. (National Surface Transportation Safety Center for Excellence, 2020-04-20)
    The objective of this work was to build predictive models of driver intent at T-intersections based on vehicle speed, acceleration, brake pedal state, and speed limit data from the Second Strategic Highway Research Program. The generated models predict if the driver will go straight or turn right at the intersection. The models show promise in predictive ability and could be incorporated into an automated driving system to help inform the system when more conservative driving might be beneficial. However, the derived models should not be used as the only source for safety decision-making because the risk of a crash would be too high.
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    Partner PhDs: dual careers in grad school and beyond
    Homyack, J. A.; Gorman, Thomas A. (Ecological Society of America, 2009-04)
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    Quantifying climate sensitivity and climate-driven change in North American amphibian communities
    Miller, David A. W.; Grant, Evan H. Campbell; Muths, Erin; Amburgey, Staci M.; Adams, Michael J.; Joseph, Maxwell B.; Waddle, J. Hardin; Johnson, Pieter T. J.; Ryan, Maureen E.; Schmidt, Benedikt R.; Calhoun, Daniel L.; Davis, Courtney L.; Fisher, Robert N.; Green, David M.; Hossack, Blake R.; Rittenhouse, Tracy A. G.; Walls, Susan C.; Bailey, Larissa L.; Cruickshank, Sam S.; Fellers, Gary M.; Gorman, Thomas A.; Haas, Carola A.; Hughson, Ward; Pilliod, David S.; Price, Steven J.; Ray, Andrew M.; Sadinski, Walt; Saenz, Daniel; Barichivich, William J.; Brand, Adrianne; Brehme, Cheryl S.; Dagit, Rosi; Delaney, Katy S.; Glorioso, Brad M.; Kats, Lee B.; Kleeman, Patrick M.; Pearl, Christopher A.; Rochester, Carlton J.; Riley, Seth P. D.; Roth, Mark; Sigafus, Brent H. (2018-09-25)
    Changing climate will impact species' ranges only when environmental variability directly impacts the demography of local populations. However, measurement of demographic responses to climate change has largely been limited to single species and locations. Here we show that amphibian communities are responsive to climatic variability, using >500,000 time-series observations for 81 species across 86 North American study areas. The effect of climate on local colonization and persistence probabilities varies among eco-regions and depends on local climate, species life-histories, and taxonomic classification. We found that local species richness is most sensitive to changes in water availability during breeding and changes in winter conditions. Based on the relationships we measure, recent changes in climate cannot explain why local species richness of North American amphibians has rapidly declined. However, changing climate does explain why some populations are declining faster than others. Our results provide important insights into how amphibians respond to climate and a general framework for measuring climate impacts on species richness.
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    Quantitative evidence for the effects of multiple drivers on continental-scale amphibian declines
    Grant, Evan H. Campbell; Miller, David A. W.; Schmidt, Benedikt R.; Adams, Michael J.; Amburgey, Staci M.; Chambert, Thierry; Cruickshank, Sam S.; Fisher, Robert N.; Green, David M.; Hossack, Blake R.; Johnson, Pieter T. J.; Joseph, Maxwell B.; Rittenhouse, Tracy A. G.; Ryan, Maureen E.; Waddle, J. Hardin; Walls, Susan C.; Bailey, Larissa L.; Fellers, Gary M.; Gorman, Thomas A.; Ray, Andrew M.; Pilliod, David S.; Price, Steven J.; Saenz, Daniel; Sadinski, Walt; Muths, Erin (Springer Nature, 2016-05-23)
    Since amphibian declines were first proposed as a global phenomenon over a quarter century ago, the conservation community has made little progress in halting or reversing these trends. The early search for a "smoking gun" was replaced with the expectation that declines are caused by multiple drivers. While field observations and experiments have identified factors leading to increased local extinction risk, evidence for effects of these drivers is lacking at large spatial scales. Here, we use observations of 389 time-series of 83 species and complexes from 61 study areas across North America to test the effects of 4 of the major hypothesized drivers of declines. While we find that local amphibian populations are being lost from metapopulations at an average rate of 3.79% per year, these declines are not related to any particular threat at the continental scale; likewise the effect of each stressor is variable at regional scales. This result - that exposure to threats varies spatially, and populations vary in their response - provides little generality in the development of conservation strategies. Greater emphasis on local solutions to this globally shared phenomenon is needed.
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    Radar-Based Over-the-Air Message Generator for Accelerating Connected Vehicle Deployment
    Viray, Reginald; Gorman, Thomas A.; Doerzaph, Zachary R. (Connected Vehicle/Infrastructure University Transportation Center (CVI-UTC), 2016-10-15)
    The market penetration levels needed to realize the full safety, economic, and environmental benefits of connected vehicle (CV) systems will not be met for some time. During the transition, it would be beneficial if data on non-CVs could be measured and included within the real-time CV data stream. Conceptually, a connected vehicle with advanced sensors, such as radar, could measure the dynamics of adjacent vehicles and, in addition to broadcasting its own Basic Safety Message (BSM), broadcast a pseudo BSM representing the non-connected vehicles. This project investigated the use of radar sensors to compute the position, speed, and heading of a non-connected vehicle (non-CV) for packaging into a pseudo BSM. An algorithm was developed to estimate the speed, position, and heading of a nearby non-CV via speed, Global Positioning System (GPS) coordinates, and radar data from the CV. Field tests were conducted with two vehicles on the Virginia Smart Road and on public roads in the New River Valley of Virginia. The field tests were designed to cover a variety of vehicle formations, traffic densities, velocities, and roadway environments. The final results showed that 67.9% of the position estimates were within 3 m of the measured position along the x-axis (longitudinal) and within 1.5 m of the measured position along the y-axis (lateral). Heading and speed estimates were generally excellent. Although the estimated position accuracy was lower than desired, the data that were collected and analyzed were sufficient to suggest ways to improve the system, such as fusing the radar data with camera-based vision data or using a more accurate GPS.
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    Reconciling larval and adult sampling methods to model growth across life-stages
    Brooks, George C.; Gorman, Thomas A.; Jiao, Yan; Haas, Carola A. (2020-08-21)
    Individual growth rates are intrinsically related to survival and lifetime reproductive success and hence, are key determinants of population growth. Efforts to quantify age-size relationships are hampered by difficulties in aging individuals in wild populations. In addition, species with complex life-histories often show distinct shifts in growth that cannot be readily accommodated by traditional modelling techniques. Amphibians are often characterized by rapid larval growth, cessation of growth prior to metamorphosis, and resumption of growth in the adult stage. Compounding issues of non-linear growth, amphibian monitoring programs typically sample larval and adult populations using dissimilar methods. Here we present the first multistage growth model that combines disparate data collected across life-history stages. We model the growth of the endangered Reticulated Flatwoods Salamander,Ambystoma bishopi, in a Bayesian framework, that accounts for unknown ages, individual heterogeneity, and reconciles dip-net and drift fence sampling designs. Flatwoods salamanders achieve 60% of growth in the first 3 months of life but can survive for up to 13 years as a terrestrial adult. We find evidence for marked variability in growth rate, the timing and age at metamorphosis, and maximum size, within populations. Average size of metamorphs in a given year appeared strongly dependent on hydroperiod, and differed by >10mm across years with successful recruitment. In contrast, variation in the sizes of emerging metamorphs appeared relatively constant across years. An understanding of growth will contribute to the development of population viability analyses for flatwoods salamanders, will guide management actions, and will ultimately aid the recovery of the species. Our model formulation has broad applicability to amphibians, and likely any stage-structured organism in which homogenous data cannot be collected across life-stages. The tendency to ignore stage-structure or omit non-conforming data in growth analyses can no longer be afforded given the high stakes of management decisions, particularly for endangered or at-risk populations.