Effects of Agriculture on Species and Habitats


Agricultural tile drain, Roberts Co., South Dakota

Throughout the Midwest, agricultural contaminants are present in wetlands and may be responsible in part for regional amphibian declines. A local factor contributing to elevated levels of contaminants in these wetlands is the presence of agricultural tile drains. These tile drains promote crop growth by removing excess water and salts from fields; however, it can also transport contaminants (e.g., pesticides, fertilizers, metals) directly into nearby wetlands at concentrations above benchmarks for the protection of aquatic life. Much of my dissertation aims to examine the effects of this tile drain effluent on water quality, wetland habitat quality, and wetland-dependent taxa (i.e., amphibians, aquatic invertebrates).

Interactive Effects of Multiple Stressors


Reference wetland in Minnehaha County, South Dakota

Due to increasing levels of anthropogenic disturbance, it is important to understand how these disturbances act as stressors. These anthropogenic disturbances such as habitat modification, contaminants, introduced species, and pathogens are all recognized as stressors that act on individuals and act in combination with natural stressors. The combinations of multiple stressors can have additive, synergistic, or antagonistic effects on organisms. Even if the effects of a particular stressor are known, it may be difficult to anticipate its effects when additional stressors are present. I am currently investigating the interactions of contaminants, habitat degradation, pathogens, and stress hormones in populations of larval Western Tiger Salamanders.

Amphibian Diseases


Plains Spadefoot (Spea bombifrons) tadpole infected with ranavirus

Emerging infectious diseases such as chytridiomycosis (caused by the fungus Batrachochytrium dendrobatidis) and ranavirosis are well-known factors which are contributing to global amphibian declines. I am interested in the both lethal and sub-lethal effects (i.e., behavioral changes, reduced growth, delayed development) of these pathogens on amphibians as well as the effects of infection on the stress hormone response of individuals. I am currently surveying for these pathogens in the Northern Great Plains, and am using both field-based and experimental studies to better understand their effects on amphibians. Additionally, I have expanded my involvement in efforts to screen amphibians for these pathogens in Oklahoma, West Virginia, and in southeast Asia.

Stress Physiology


Collecting water-borne hormones from larval Western Tiger Salamanders (Ambystoma mavortium)

Both natural and anthropogenic stressors are known to affect stress hormone production in amphibians. Traditionally, hormones have been measured via plasma collection or whole-body assays, but alternatives such as urinary collection have been developed. For a portion of my thesis work, I helped to develop novel methods to collect water-borne hormones from small aquatic salamanders. I am interested in using these methods to assess stress in individuals from both experimental laboratory comparing individual responses to stressors, and field settings to compare population level responses to large-scale habitat disturbance. I am currently involved in projects examining the role of urbanization, agricultural development, predators, contaminants, and disease play in influencing stress hormone levels.

Predator-Prey Interactions


San Marcos Salamander (Eurycea nana)

Predation is a dominant element of ecological communities. The introduction of novel predatory fish into environments has been particularly problematic and has lead to significant declines in amphibian populations. I am broadly interested in how amphibians respond to novel predators and the sensory modalities mediating these interactions. Additionally, I am interested in the role of innate and learned predator recognition as well as predator generalization play in the recognition of novel predators. The majority of my work investigating these topics has involved fully-aquatic Eurycea salamanders of central Texas, most of which are highly endemic and are state and federally protected.

Mud Turtle ecology in the Chihuahuan desert

Yellow Mud Turtle (Kinosternon flavescens) near an ephemeral pool.

In 2007 I became involved in several research projects examining different aspects of the ecology of the Yellow Mud Turtle (Kinosternon flavescens) in the Chihuahuan Desert of west Texas. We have been studying population demographics, growth, movement, phenology, and a novel shell disease in a population of these turtles on C. E. Miller Ranch in Jeff Davis County. Historically, these turtles solely relied on ephemeral pools that filled for short periods of time after summer rains and once these sites dried out, these turtles move back to upland terrestrial habitats. However, the presence of permanent, well-filled cattle ponds has allowed these turtles to remain in these habitats for prolonged periods of times, influencing growth their growth and subsequently the progression of an algae-mediated shell disease.

Morphological and Genetic Variation Among Populations of Plethodon albagula

Western Slimy Salamander (Plethodon albagula)

The Western Slimy Salamander (Plethodon albagula) is recognized as having two disjunct ranges, one on the Edwards Plateau of Central Texas and the other within the Interior Highlands of Missouri, Oklahoma, and Arkansas. Morphological and genetic variation has been found within the Edwards Plateau among several different lineages, though less is known about the Interior Highlands population. Currently, I am currently examining both morphological and genetic variation within the Interior Highlands populations and between these two broadly distributed populations, and plan to expand these studies to include ecological perspectives.

Distributions of Amphibians and Reptiles in South Dakota


Map of South Dakota showing amphibian and reptile specimens collected pre-2000 (black) and post-2000 (blue).

Current understanding of the distributions of amphibians and reptiles in South Dakota is limited compared to that of many other vertebrate groups in the state. Continuing increases in human population, conversion of grasslands to agriculture, and habitat degradation all likely have strong negative impacts South Dakota’s amphibian and reptile species, but their effects are difficult to track because of limited historic and modern sampling. I am currently working to update the known distributions of all South Dakota amphibian and reptile species and have compiled a database of over 11,700 specimens to better map these distributions. For additional information on this project visit:

Philippine Amphibian and Reptile Diversity

Pseudogekko phylogeny

The Philippines is home to a remarkable diversity of amphibians and reptiles, the majority (~75%) of which are endemic to this island archipelago. Recent studies of the archipelago’s terrestrial biodiversity have dramatically increased the number of recognized species, often as the result of identification of unique genetic lineages. Species once recognized to have wide distributions that spanned multiple faunal regions have more recently been revealed to constitute complexes of multiple species, each of which is typically restricted to a specific faunal region, island group, or complex geographic regions. I have been collaborating with researchers to help describe this incredible species diversity and resolve taxonomic issues with newly collected morphological and molecular datasets. Two focal genera that I have been working with are limb-reduced Brachymeles (Scincidae) and secretive Pseudogekko (Gekkonidae).

Natural History of Reptiles and Amphibians

Big Bend Patch-nosed Snake (Salvadora deserticola)

Another avenue of research which I have a particular interest in is natural history. While many people favor ‘hypothesis-driven’ studies, there is a paucity of information about a vast number of amphibian and reptile species. Particularly, little is known about species which have limited geographic ranges, are infrequently encountered, or are of conservation concern. Further, many ecological questions can only be fully understood with an intimate knowledge about the species involved and often, this information is lacking. As we increase our understanding of particular aspects of natural history, we can better manage populations and species which are of interest.