Browsing by Author "Chandler, Houston Cawthorn"

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    Amphibian and reptile conservation in a changing environment: Case studies from the southeastern United States
    Chandler, Houston Cawthorn (Virginia Tech, 2023-05-22)
    The southeastern United States is a global biodiversity hotspot but has experienced severe declines of natural ecosystems. The southeast is currently facing widespread change, particularly from an increasing human population and climate change, that is likely to impact all remaining natural areas to some degree. In this work, I examine some of the challenges currently facing imperiled species of reptiles and amphibians in this region. The work is focused on two species, the Reticulated Flatwoods Salamander (Ambystoma bishopi) and the Eastern Indigo Snake (Drymarchon couperi) both of which are listed on the U.S. Endangered Species List. Chapter 1 used Light Detection and Ranging (LiDAR) data to measure wetland bathymetry (basin shape) in flatwoods salamander breeding wetlands. Bathymetry data were used to construct stage–area relationships for each wetland, and a history of water level monitoring data were applied to these relationships to build multi-year time series of flooded area metrics. These metrics were then combined with an assessment of vegetation characteristics to map potentially suitable habitat for flatwoods salamander breeding within each wetland. Chapter 2 focused on flatwoods salamander phenology (the timing of life history events) in response to climate change. I quantified flatwoods salamander movements into and out of breeding wetlands over a 10-year period (2010–2020), identifying temperature and precipitation patterns that were conducive to salamander movements. I then used future climate projections to forecast movement opportunities for flatwoods salamander from 2030–2099 and used an existing hydrologic model built on the same climate data to understand how phenology may interact with hydrology. Overall, only a small number of years are likely to have an ideal intersection of phenology and hydrology as has been observed during recent breeding seasons. Chapter 3 described the construction of a stochastic Integral Projection Model for flatwoods salamanders. I integrated the projections from Chapter 2 with the population model to estimate the viability of two flatwoods salamander populations from 2030–2099 under multiple climate change scenarios. The results indicated that approximately half of the examined scenarios resulted in a high probability (>0.5) of extinction when considering both wetland hydrology and salamander phenology. In Chapter 4, I described the creation of a stochastic Integral Projection Model for indigo snakes. I then demonstrated the utility of this model by examining the effects of initial population size, road density, and removal of individuals to support a captive colony on indigo snake populations. I found that high road densities and high collection rates would likely lead to population declines, although the rate of declines and extinction risk varied across scenarios. Taken together, these projects highlight some of the challenges currently facing herpetofauna in the southeastern United States, demonstrate the difficulty in conserving these often-overlooked species, and provide useful tools for ongoing conservation efforts focusing on these two imperiled species.
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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.