Doctor of Philosophy / Department of Biology / Anthony Joern / Aboveground and belowground food webs are linked by plants, but their reciprocal influences are seldom studied. Because phosphorus (P) is the primary nutrient associated with arbuscular mycorrhizal (AM) symbiosis, and evidence suggests it may be more limiting than nitrogen (N) for some insect herbivores, assessing carbon (C):N:P stoichiometry will enhance my ability to discern trophic interactions. The objective of this research was to investigate functional linkages between aboveground and belowground invertebrate populations and communities and to identify potential mechanisms regulating these interactions using a C:N:P stoichiometric framework. Specifically, I examine (1) long-term grasshopper community responses to three large-scale drivers of grassland ecosystem dynamics, (2) food selection by the mixed-feeding grasshopper Melanoplus bivittatus, (3) the mechanisms for nutrient regulation by M. bivittatus, (4) food selection by fungivorous Collembola, and (5) the effects of C:N:P on invertebrate community composition and aboveground-belowground food web linkages. In my analysis of grasshopper community responses to fire, bison grazing, and weather over 25 years, I found that all three drivers affected grasshopper community dynamics, most likely acting indirectly through effects on plant community structure, composition and nutritional quality. In a field study, the diet of M. bivittatus was dominated by forbs with grasses constituting only a minor fraction of their diet under ambient soil conditions, but grass consumption approximately doubled as a result of changes in grass C:N:P. M. bivittatus was found to rely primarily on selective consumption of foods with varying nutritional quality, rather than compensatory feeding or altering post-ingestive processes, to maintain C:N homeostasis in a laboratory experiment. In a soil-based mesocosm study, I show that Collembola feed on both saprophytic and AM fungi, in some cases exhibiting a slight preference for AM fungi. In the final study, although I did not find the expected indirect relationship between soil Collembola and aboveground herbivory as mediated through host plant quality, there were significant effects of root C:N and AM colonization on Collembola density and of plant C:N on aboveground herbivory. Overall, this research shows that host plant C:N:P stoichiometry can influence both above- and belowground invertebrate population, community, and food web dynamics.

Master of Science / Department of Biology / Keith B. Gido / Stream networks provide complex habitats for fish assemblages that can vary gradually along a gradient of stream size or abruptly at transition zones between large rivers and their tributaries. We evaluated the relative importance of these gradual and abrupt habitat transitions in regulating stream fish assemblages by quantifying roles of stream size and spatial position within a drainage network as a determinant of fish assemblage structure within the Kansas River basin, KS. We predicted fish assemblage structure to generally be dependent on stream size and that smaller streams would be influenced by their connectance to larger mainstem rivers. Fishes in the Kansas River basin varied along a gradient of stream size and longitude, and after controlling for these effects, there was evidence that connectivity to a larger river influenced species richness and assemblage structure. In 1st order streams there was an increase in species richness with increasing distance from a mainstem confluence and species composition in larger tributaries (i.e., 4th order streams) varied with proximity to the mainstem river. We also found an increase in species richness at sites located on smaller tributaries connected to a larger downstream mainstem. Species composition in 1st and 4th order streams also varied with connectance to the mainstem river. Within three intensively sampled tributaries, there was an abrupt change in fish fauna between the Kansas River and sample sites above the confluence, but only gradual change in assemblage structure within each tributary with a high degree of seasonal variation. In the first 20 stream km of these three mainstem tributaries adult fishes were more structured along a gradient away from the mainstem river than juveniles, potentially suggesting more generalized habitat needs of juvenile fishes. At the spatial and temporal scale of our analysis, it appeared the effects of large rivers on tributary streams were generally localized. However, the documented influence of spatial position suggests movements between habitats could regulate community level dynamics as well as individual species over longer temporal scales.

Master of Science / Department of Biology / Brett K. Sandercock / Monitoring programs indicate that numerous shorebird populations are subject to on-going declines. The U.S. Shorebird Conservation Plan lists twenty-seven shorebird species as species of high concern and seven as highly imperiled, including the Buff-breasted Sandpiper (Tryngites subruficollis). One hypothesis for ongoing population declines is exposure to toxic chemicals and pollutants. The purpose of this project was to characterize plasma cholinesterases (ChEs) of migratory shorebirds and address potential exposure to organophosphorus (OP) and carbamate (CB) pesticides. Consumption or contact with these pesticides can cause mortality and a variety of sub-lethal effects. Buff-breasted Sandpipers and other upland shorebirds are particularly likely to encounter agrochemicals due to their habitat use at the non-breeding grounds. I sampled migratory shorebirds over three seasons, during north- and southbound migration in 2006 and 2007 in Texas, Kansas, and Nebraska and during the non-breeding season in 2007 in Argentina, Uruguay, and Paraguay. I collected blood samples and footwashings from reference sites, where OP and CB pesticides were not used, and agricultural sites, where these two insecticides were recommended for control of crop pests. I assessed several variables known to affect plasma ChE activity including body size, date of capture, time of capture, condition, sex, and region. Small-bodied species had higher levels of ChE activity in plasma than large-bodied species. Plasma ChE activities varied with date of capture in 3 of 5 species sampled in North America. Sex differences were significant in 1 of 4 species tested. Plasma acetylcholinesterase (AChE) activity was higher among White-rumped Sandpipers sampled in North America but there was no difference between regions among Buff-breasted Sandpipers. Time of capture and individual condition did not affect plasma ChE activity. Estimates of exposure to ChE inhibitors were addressed in five species. Plasma AChE and butyrylcholinesterase (BChE) activities of Buff-breasted Sandpipers were lower at agricultural sites in South America but BChE activity was higher at agricultural sites in North America. There were no differences between sites in four other species tested. A meta-analysis across all species indicated that in 4 of 6 comparisons habitat type had a negative effect on AChE activity consistent with exposure to ChE inhibitors but there was a regional positive effect of agricultural habitat on BChE activity in North America. Comparison of body mass between sites suggested that use of habitats with potential pesticide application did not affect mass gain. Project results suggest that 1 of 5 shorebird species tested was exposed to ChE-inhibiting pesticides at the non-breeding grounds and future monitoring is necessary to assess potential effects at the population level. This study highlights the importance of complete sampling and addressing variability in plasma ChEs before making estimates of exposure to OP and CB pesticides. It provides the first estimates of migratory shorebird exposure to OP and CB pesticides, a potential conservation issue. Future research should include continued monitoring of Buff-breasted Sandpiper ChE levels and habitat use. Other sources of anthropogenic declines such as habitat loss and illegal hunting should be investigated for species that did not show evidence of exposure.

Doctor of Philosophy / Department of Biology / John M. Blair / Approximately 96% of native tallgrass prairie in North America has been lost, which accentuates the need for effective methods to restore the structure and function of these degraded ecosystems. Many prairie restorations aim to restore grass and forb species in proportions reflecting plant species diversity in native prairie. A target grass-forb species mixture is typically chosen at the onset of restoration, but often, grasses become excessively dominant and forbs are underrepresented as the community develops. Several studies have examined the potential for increasing forb cover and diversity in newly restored grasslands, but few studies have assessed factors limiting forb cover and diversity in well-established grass-dominated prairie restorations. The primary objective of this research was to assess the potential for enhancing plant species diversity and productivity in an established grass-dominated prairie restoration by selective removals of dominant grass species, and by manipulating resources (soil nutrients, light availability) or mycorrhizal interactions. A 7-year old grass-dominated restoration was used to evaluate plant and soil responses to manipulations in three separate studies. The first study examined the potential suppressive effects of dominant grasses on plant diversity by reducing the cover and biomass of two dominant grass species, Andropogon gerardii and Panicum virgatum. After 3 years, the removal of A. gerardii increased species richness and diversity, which was correlated with increased light availability, but not changes in soil resources. The second study examined the responses of restored grassland communities to long-term manipulation of soil resources (nutrient availability or soil depth), and to aboveground biomass removal via mowing. The long-term manipulation of soil resources did not alter plant species diversity, but nitrogen and light availability were important factors regulating plant productivity. The third study assessed the effects of manipulating arbuscular mycorrhizal (AM) fungi, through the use of either commercial inoculum or fungicide, on plant communities in restored prairie. Mycorrhizal suppression reduced grass productivity, suggesting that fungicide may be useful for enhancing diversity of restored prairies that are dominated by obligate mycotrophic grasses. In total, these studies suggest that competition between dominant grasses and subordinate forbs limits plant diversity in restored tallgrass prairie.

In the scientific literature pertaining to the world's loss of biodiversity, an extensive amount of research has been undertaken to describe the local biological processes involved in the loss of endangered habitats. However, the social mechanisms that infringe upon these habitats and perpetuate human activities that destroy rare and endangered species has largely been ignored. This thesis is an attempt to discover the social, political and economic causes of habitat loss in the particular case of New Caledonia. Specifically, the extraction of nickel in New Caledonia was examined as a resource that has been central to the island's development history and which has been the cause of the most forest damage. Globalization theory and World-Systems theory have been used in a complementary way to provide a framework for how the integration of New Caledonia into the global economic system over the past 150 years has impacted the island's rare forest systems. Periods of globalization prior to the 1970's were found to have had the most destructive impact on forest habitat than the years following 1975. Greater ecological protections implemented as a result of pressures on France from both global and local environmental groups were found to have increased protection measures for the various forest habitats. However, the destruction of the forests of New Caledonia continues and strong ecological protections that would guarantee the forest's long-term health are still missing.

A magnesium refining facility in Quebec was a known point source of persistent organic pollutants namely polychlorinated biphenyls, dioxins and furans, and hexachlorobenzene. Contaminants concentrations were measured in the fat tissue of local white-tailed deer with the assistance of the local community and hunters. Concentrations in the deer from 1999, one year before the smelter opened, were compared with deer from 2002. Results showed a significant increase in PCBs from 1999 to 2002, and total PCB concentrations showed significant decreases with distance from the smelter. Many of the mid-range PCB homologues that bioconcentrate sharply in deer showed similar relationships. Sigmacoplanar PCBs and Cytochrome P450 1A expression in liver also showed a significant inverse relationship with distance in 2002. Results of a human health risk assessment indicated that the number of deer meal portions required to exceed safe consumption levels for PCDD/Fs and coplanar PCBs increased with the distance from the smelter.

Penguin colonies from permanently cold environments have a strong impact on their surrounding ecosystem because their excrements provide ample nutrients to the soils and sediments. The high phosphate content of the penguin guano directly affects primary productivity. However, phosphate solubility is dependent on the presence of iron and other metals, which can form stable PO4-rich minerals. Phosphate can also be sorbed onto minerals, including iron oxides. The present study investigated the biogeochemistry of phosphorus in a 42 cm-deep soil profile on Gardiner Island in Antarctica in order to assess the effect of penguin excrements on P partitioning in the solid and aqueous phases. The results indicate that the porewaters were slightly acidic (pH 5-6) and contained extremely high levels of dissolved organic carbon (DOC; 120 mM), PO4 (120 mM), SO4 (27 mM), NO3 (18 mM), Cl (320 mM), F (2 mM), Sr (0.10 mM), Ca (18 mM) and Mg (150 mM) at the top of the soil profile. Dissolved iron concentrations were generally low (< 0.04 mM) and increased at a depth of 15-20 cm and at the bottom of the profile. Chemical extraction revealed the presence of two zones of reactive phosphorus (P-ascorbate extractable fraction) in the soil profile, i.e., at the surface and between 16 and 20 cm. Enriched reactive and crystalline iron fractions were also present at a depth of 16-20 cm, but fluctuated throughout the profile. The Fe(II)/Fe(III) molar ratio of the soil was greater than 1 at the surface of the profile and declined with depth. X-ray diffraction analysis showed that the soil likely contained berlinite, strengite and vivianite, along with silicates and quartz. Saturation index calculations also indicated that Ca and Mg-rich phosphate minerals were likely present in the soil. Based on the above results, the presence of penguin colonies on Gardiner Island strongly impacted the geochemical and mineralogical composition of the soil, as observed in other studies on bird guano impacted (ornithogenic) soils. In addition, the presence of both Fe(II) and Fe(III) points to the fact that the soil undergos redox changes, likely as a result of seasonal water table fluctuations. Microcosm experiments with selected samples from the soil profile and an iron-reducing bacterium indeed showed that iron and phosphorus were released into solution as a result of microbial iron reduction. However, abiotic systems also showed a release of phosphorus indicating that non Fe-rich phosphate minerals are soluble under the conditions prevailing in the growth medium.

The Bayou LaBranche wetland system, located 22 miles west of New Orleans, LA, received wastewaters from Norco oil refinery from 1920 to 1995. In 1989, the sediment of one of the waterways, Bayou Trepagnier, was designated contaminated with Pb, Cr, Zn, and polycyclic aromatic hydrocarbons. In 1995, the wastewaters were diverted to the Mississippi River, taking with them the main source of fresh water for the system. After seven years of diversion, it is unclear whether contaminants or a loss of significant freshwater input has been more harmful to organisms in this system, or if the organisms have been impacted at all. The stomach contents of two top predators, spotted gar and largemouth bass, were analyzed to determine if there are seasonal variations in dietary preferences and if these variations are due to contaminants in the water and sediment or changes in water quality. The results indicate that the fish collected in Bayou Trepagnier are eating better and are in better condition than those in the other two waterways / acase@tulane.edu

No description available.

No description available.