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Polychlorinated biphenyls (PCBs) are persistent organic pollutants that can bioaccumulate in organisms. PCBs are documented endocrine disrupting chemicals and are known to cause developmental, reproductive, and neurobiological disorders. This study examines the bioaccumulation of PCBs in the northern diamondback terrapin (Malaclemys terrapin terrapin), a species that is endemic to the brackish waters of the East Coast salt marshes of the United States. The two populations studied are located in Cape May County, NJ, a site with low levels of contamination and Jamaica Bay, NY, which is a highly contaminated site. While PCBs bioaccumulation has been extensively researched, many studies involve lethal sampling techniques. Such techniques can be detrimental to populations and may not be viable for long-term studies. This study examined the utility of the chorioallantoic membrane (CAM) as a non-lethal sampling technique for PCB analysis. In order to determine the viability of the CAM, maternal transfer of contaminants was also analyzed. Ten terrapin samples from each field location were analyzed. Egg and CAM samples were obtained from both field sites and liver samples were also collected from Cape May County terrapins. PCB levels and congener profiles were similar in both field locations. While PCB congeners were detected in liver, egg, and CAM samples, less chlorinated congeners preferentially partitioned in the CAM. Liver and egg sample PCB concentrations were strongly correlated, but the CAM concentrations were weakly correlated to liver and egg samples. Examination of homolog groups indicated a strong correlation between hexachlorinated biphenyls in all three sample types. Preliminary study results indicated that maternal transfer of PCB contaminants does occur with selective partitioning of congeners into the CAM. / Biology

In the Neotropical realm, little is yet known about the distribution, ecology, and biodiversity of limno-terrestrial tardigrades. Tardigrades are understudied micrometazoans and, in Chile, their biogeography and the variables that are associated with their diversity have never been recorded. This study proposes to examine the assemblages (composition and abundance) of tardigrades in forests throughout southern Chile and relate the patterns found to latitude, altitude, temperature, precipitation, primary productivity, and land use cover. This novel study shows basic information on the biogeographical distribution and diversity of forest Chilean tardigrades and examines the potential influence of landscape variables on the composition and abundance of this little-known phylum. Using univariate and direct gradient analysis, it was found that tardigrade alpha diversity was mainly effected by precipitation, mean monthly minimum, and maximum temperature; also, the combined effects of precipitation and mean monthly maximum temperature, precipitation, and mean monthly minimum temperature, had an interactive effect on tardigrade alpha diversity. The environmental and geographic variables explained the variation in the community structure of tardigrades. Overall, this study has given first insight into Chilean tardigrade ecology.

Lady Bird Lake and Lake Austin are adjacent reservoirs in Austin, Texas, with the primary functions of electrical power generation, flood control, and recreation. In 1999, the invasive submerged aquatic macrophyte (SAV), Hydrilla verticillata, was observed in Lake Austin where it established over the span of the lake, though never establishing in Lady Bird Lake. Management strategies to eradicate hydrilla included the stocking of sterile Asian grass carp, Ctenopharyngodon idella. This practice nearly eliminated hydrilla and resulted in the decline of native aquatic vegetation and increased shoreline erosion. Conservation efforts to reestablish the vegetation are underway. SAV, in addition to facilitating nutrient uptake and retention, enhancing water clarity, stabilizing substrate, and attenuating wave energy, provides food and refugia for aquatic fauna. My research aims to understand the biological implications of the restoration of various SAV assemblages by analyzing the macroinvertebrate communities present within bare, mixed, and monocultured habitat regimes. The data suggests that mixed-cultured SAVs, site disturbance, substrate composition, and macroinvertebrate taxonomic resolution are the primary determinants of macroinvertebrate richness, abundance, and diversity.

Leaf litter is a major nutrient source for aquatic detrital food webs, fueling the microbes and macroinvertebrates that colonize it. Litter is especially important as a nutrient source for macroinvertebrates in headwater streams that tend to have lower primary production than higher-order stream systems. Understanding how litter decomposition and macroinvertebrates interact at large scales facilitates predictions about how stream ecosystems will change over space and time with regards to allochthonous nutrient inputs. We utilized a subset of the National Ecological Observatory Network's wadeable stream sites to deploy a litter pack study across the United States and Puerto Rico to determine the controlling factors for litter decomposition and associated macroinvertebrate assemblages, abundances, and species richness at a national scale. We found that litter species was the most important contributing factor to litter decomposition, and despite litter decomposition differences from stream to stream, the relative differences in decomposition rate between litter types was very similar. Stream identity, temperature, and flow also played roles in affecting decomposition patterns. In contrast to litter decomposition, litter species did not significantly contribute to variation in macroinvertebrate assemblages, abundance, or species richness, though environmental variables did impact abundance and species richness. These results suggest that there is functional redundancy in aquatic detritivore communities at large scales, and that the assemblages colonizing different species of leaf litter–despite being similar–might be functioning differently.

The City of Denton, located in a semi-arid region of Texas, has over 200 manmade ponds within its city limits. Many of these ponds, located in densely populated areas, are engineered to control storm water runoff. There is a general lack of recognition of the value these waters contribute to regional biodiversity and as greenspaces. This study, conducted in Denton, is monitoring habitat variables and macroinvertebrate diversity in a series of ponds selected to represent a gradient of urban influences. The objective of this study is to identify the variables associated with the highest diversity. Using drone imagery and a meter square box sampler, the quantitative approach allowed for delineation of three habitat types and area. The macroinvertebrates where identified to the genus level which allowed for higher resolution and resulted in stronger comparisons of the communities and conditions of the ponds. Taxa richness was positively correlated to pond size and trees along shoreline and negatively associated with average depth. Overall, submerged vegetation supported highest diversity and abundance, especially genera of Chironomidae (Diptera). Conductivity was associated with urban influences and the most urban influenced pond had the lowest taxa richness, but also reduced habitat area. Results of this study conclude that these stormwater ponds benefit to the ecology of the city and provide beautiful, green spaces. If managed correctly, these systems can be incorporated into sustainable development in the future of the City of Denton.

Master of Science / Department of Biology / Jesse B. Nippert / The Konza Prairie in northern Kansas, USA contains over 550 vascular plant species; of which, few have been closely studied. These species are adapted to environmental stress as imposed by variable temperature, precipitation, fire, and grazing. Understanding which plant traits relate to drought responses will allow us to both predict drought tolerance and potential future shifts in plant community composition from changes in local climate. Morphological and physiological measurements were taken on 121 species of herbaceous tallgrass prairie plants grown from seed in a growth chamber. Gas exchange measurements including maximum photosynthetic rate, stomatal conductance to water vapor, and intercellular CO[subscript]2 concentration were measured. All plants were exposed to a drought treatment and were monitored daily until stomatal conductance was zero. At this point, critical leaf water potential (Ψ[subscript]crit), an indicator of physiological drought tolerance was assessed. Other measurements include root length, diameter, volume, and mass, leaf area, leaf tissue density, root tissue density, and root to shoot ratio. Traits were compared using pair-wise bivariate analysis and principal component analysis (PCA). A dichotomy was found between dry-adapted plants with thin, dense leaves and roots, high leaf angle, and highly negative Ψ[subscript]crit and hydrophiles which have the opposite profile. A second axis offers more separation based on high photosynthetic rate, high conductance rate, and leaf angle, but fails to provide a distinction between C[subscript]3 and C[subscript]4 species. When tested independently, grasses and forbs both showed drought tolerance strategies similar to the primary analysis. Matching up these axes with long term abundance data suggests that species with drought tolerance traits have increased abundance on Konza, especially in upland habitats. However, traits that relate to drought tolerance mirror relationships with nutrient stress, confounding separation of low water versus low nutrient strategies. My results not only illustrate the utility of morphological and physiological plant traits in classifying drought responses across a range of species, but as functional traits in predicting both drought tolerance in individual species and relative abundance across environmental gradients of water availability.

Master of Science / Department of Biology / John M. Blair / Climate change predictions for the Great Plains region of North America include increased temperatures, changes to annual precipitation, and reduced growing season precipitation, which will likely alter grassland soil systems. To date, few studies have examined belowground community responses to predicted climate change scenarios, with fewer assessing long-term changes. My research focused on the impacts of long-term changes in precipitation and associated soil water content on belowground grassland systems (belowground plant biomass, soil carbon (C) and nitrogen (N) pools, microbial biomass C and N, and invertebrate communities) using recently collected samples from a long-term (16-yr) reciprocal core transplant between Konza Prairie Biological Station (MAP = 850 mm) and Kansas State Agricultural Research Center at Hays (MAP = 580 mm), with the Hays site having a long-term average annual precipitation amount that is ~30% less than the Konza site. Results from the experiment indicate that either increases or decreases in annual precipitation can have profound effects on belowground grassland systems. Belowground plant biomass, microbial biomass, and potential C mineralization rates were greater at the wetter Konza site regardless of soil origin. Total C stored in soils incubated at Konza was significantly greater as well, likely due to greater root inputs. The effects of precipitation were most apparent in the surface soil layers (0-20 cm), while soil origin impacted soil properties to a greater extent with increasing depth. This contrasted with results for the soil mesofauna, where total microarthropods responded negatively and nematodes responded positively to increased annual precipitation. Results of this study indicate important changes in soil C and N pools, belowground plant biomass, and soil mesofauna within grassland systems subject to changing precipitation regimes, and suggest more mesic prairie systems are more sensitive to changes in soil water availability than those in more arid grassland systems.