Modeling of natural phenomena has been of particular interest in the graphics ommunity in recent years. This thesis will explore a method for creating and animating orb webs using a coupled spring-mass system. Using a spring-mass system for creating the orb web is ideal as we can represent each web strand using coupled spring-mass pairs. This allows the orb web simulator to be physically based, i.e., the simulation follows the laws that act on objects in the real world. This in turn simplifies the process of animating the web, as the animation emerges from the simulator without anyone having to set it up explicitly. Since this model is physically based, it would allow for realistic visualization of effects such as observing an orb web under a wind. In the children's book ``Charlotte's Web', the spider creates orb webs with words inscribed on them. Charlotte's web is used as an inspiration, in this thesis, to create webs which no real world spider could possibly create, while keeping the model physically based. This involves modifying the orb web such that the target text shows up on the orb web while keeping the web looking as natural as possible.

Modeling of natural phenomena has been of particular interest in the graphics ommunity in recent years. This thesis will explore a method for creating and animating orb webs using a coupled spring-mass system. Using a spring-mass system for creating the orb web is ideal as we can represent each web strand using coupled spring-mass pairs. This allows the orb web simulator to be physically based, i.e., the simulation follows the laws that act on objects in the real world. This in turn simplifies the process of animating the web, as the animation emerges from the simulator without anyone having to set it up explicitly. Since this model is physically based, it would allow for realistic visualization of effects such as observing an orb web under a wind. In the children's book ``Charlotte's Web', the spider creates orb webs with words inscribed on them. Charlotte's web is used as an inspiration, in this thesis, to create webs which no real world spider could possibly create, while keeping the model physically based. This involves modifying the orb web such that the target text shows up on the orb web while keeping the web looking as natural as possible.

The major aim of this thesis project was to determine the variables that most explain the elevated mercury concentrations in lake trout (<i>Salvelinus namaycush</i>), a predatory aquatic fish species in some lakes in northwestern Canada. High mercury concentrations in lake trout in other regions have been associated with the biological features of the fish and various chemical and physical aspects of their aquatic ecosystems. Data including lake trout age, length, weight, and stable isotope values, water chemistry, latitude, and lake and watershed area were collected, compiled and then included in statistical analyses of the factors affecting mercury concentration in the muscle of lake trout from a series of lakes from the Mackenzie River Basin (MRB) in the Northwest Territories (NT), Canada. These results are reported in Chapter 2. Fish age and lake surface area were the most important variables affecting mercury concentrations. However mercury concentration in muscle also was significantly (p < 0.05) related to: fish length, weight, and δ13C; watershed area to lake area ratio; and to total mercury concentration in zooplankton and water. These variables were run through best subsets analyses and multiple regressions in order to determine the regression equation most efficiently capable of predicting mercury concentration in lake trout in unstudied lakes in the MRB region. The resulting equation was: log Hg = 0.698 (0.0156 × latitude) + (0.0031 × age) + (0.000535 × length) (0.245 × log lake area) + (0.00675 × watershed area/lake area ratio), r2 = 0.73<p>Small lakes located in the southern NT and dominated by large and/or old lake trout are most likely to have lake trout whose mean mercury concentrations exceed 0.5 μg/g; the guideline for the commercial sale of fish. Latitude may be linked to mean annual temperature (and variables such as duration of ice cover, summer water temperature) while fish age and length may be related in part to fishing pressures and growth rates on these lake populations. In chapter 3, a more in-depth study was undertaken to investigate of role of feeding and relative tropic level in the bioaccumulation of mercury in lake trout. This was accomplished by comparing MRB lake trout population characteristics with those from a series of lakes in northern Alberta and Saskatchewan (NAS). The two population groups were compared with respect to size, age, growth rates, and mercury concentrations. In addition, trophic and mercury biomagnification relationships, as inferred from stable carbon and nitrogen isotope analyses, for the two lake trout populations were compared. Lake trout from the NT exhibited significantly higher mercury concentrations than those from the NAS lakes (p < 0.001). Mercury concentrations in biota (including lake trout, forage fish, benthic invertebrates and zooplankton) were positively and significantly correlated to δ15N values in all lakes in both of the study areas (p < 0.001). Mercury biomagnification in the NT lakes, as estimated from the slope of δ15N versus mercury concentration, was lower than in the NAS lakes. Thus, mercury biomagnifies more slowly in NT lake trout, but because of their greater mean age, reaches higher values than in NAS lakes. Northwest Territory lake trout generally exhibited more negative δ13C values, indicating more pelagic feeding habits than in NAS lakes: higher mercury concentrations previously have been associated with more pelagic feeding. <p>Finally, the relationship between mercury levels and growth rates in lake trout was investigated by comparing NAS and NT lake trout populations. These results are reported in chapter 4. Lake trout from the NT lakes grew at a slower rate (10.4 mm per year) than those from the NAS lakes (35.1 mm per year). Log mercury concentration was inversely correlated (p < 0.001) with growth rate for both lake trout populations; however, growth rate explained more of the variation in mercury level in the NT lakes than in the NAS lakes (NT, r2 = 0.11, p < 0.001; NAS, r2 = 0.03, p = 0.024). However, the correlation between mercury concentration and growth rate in the NAS study area improved when Reindeer Lake, possibly affected by anthropogenic inputs, was removed from the analyses (r = 0.13, p = 0.001). Therefore, lower mercury levels in lake trout are associated with higher growth rates through growth dilution. The higher mercury concentrations in NT lake trout are due not only to the old age of the fish, but to slower growth rates as well.

This thesis uses multiscale computational modelling to find the fundamental principles that govern defects forming during the operation of new electro-optical devices and the processing of spider silk fibers. The generalized approach developed in this thesis bridges engineering devices and biological processes based on liquid crystalline materials. / Three types of defects are encountered: inversion walls, lines and points. Inversion wall defects are found in the electro-optical device when a nematic thin film undergoes a temperature-induced surface anchoring transition. Point defects naturally occur in the tubular extrusion duct of spiders, while line defects present close topological connections with point defects and are widespread in many high-performance industrial fibers. Three models are used in this thesis and their usage is dependent on the characteristics of the defects studied. / In the case of inversion wall defects, computational modelling is used to verify, complement and analyze experimental measurements made with fluorescence confocal polarizing microscopy by our collaborator at the Georgia Institute of Technology. The various simulation results agree and explain very well experimental observations and provide a thorough understanding of the wall defects behavior. A computational technique is developed to enable the precise determination of the interaction between the liquid crystal and the device substrate. Understanding the behavior of wall defects and estimating interfacial properties are indispensable to the development and optimization of the electro-optical device as they affect properties like temperature of operation, switching voltages and response time. / Computational modelling is also used to investigate the behavior of nematic point defects confined in cylindrical cavities as observed along spiders' spinning apparatus, and to examined textural connections with other well know structures seen in industrial fibers. The various scenarios investigated include: interactions between point defects, topological transformations between point, line and ring defects as well as interactions between ring defects. The simulation results agree and complement previous investigations but also offer a new fundamental understanding on the nature and stability of defects in cylindrical cavities. Understanding the behavior of nematic point and line defects in cylindrical geometries is important as they play a fundamental role in the processing of natural and industrial high-performance fibers.

Biodiversity is a fundamental part of the functioning of ecosystems and their ability to provide ecosystem services. It has been shown that a high biodiversity increases the robustness of an ecosystem according to the insurance hypothesis. I propose that a similar effect can be seen on a higher scale, where a high diversity of ecosystem types might stabilize the ecological functionality of a region. By comparing eleven network characters in 70 tropical and temperate ecosystems, their diversity was measured as Euclidean distance between the systems in the 11-dimensional room defined by these characters.  The diversity of ecosystems was shown to be significantly higher in tropical latitudes than in temperate. A possible explanation to this result could be that the higher species diversity in the tropics allows for more types of ecosystems. A higher diversity of ecosystems in a region might indicate a larger amount and variation of possible ecosystem goods and services as well as provide the region with an increased robustness. The measurement of ecosystem diversity between regions might also be of importance in a conservation perspective, where unique and vulnerable ecosystems can be discovered and protected.

A synthetic analog of a spider silk protein (M4) was studied. Langmuir films were made and an inflexion in the isotherm indicated conformational changes upon compression. Deposition onto solid substrates was most successful using a hydrophobic substrate and the Langmuir-Schaeffer method. AFM was used to image the surface, which was mesh like and did not show any indication of order. / Gold nanoparticles were produced in the presence of the protein and protein solutions were added to read made nanoparticles for the purpose of displacing the weak ligands present. CD measurements were performed on the protein solutions to study its conformation. Nanoparticle size information was obtained from TEM images. DLS was used to determine if the protein was affected by the addition of the gold nanoparticles. Precipitation of the protein was shown not to affect the nanoparticles.

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 86-95). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 86-95). Also available on the Internet.

Trophic interactions within aquatic ecosystems are complex, with many different pathways facilitating transfer of energy and nutrients among trophic levels and many different mechanisms that influence energy and nutrient transfer. This is illustrated in the “top down” and “bottom up” regulatory effects on aquatic food webs, through which primary producer biomass and, therefore, herbivore and carnivore densities, are influenced by both nutrient availability (bottom up) and densities of consumers at higher trophic levels (top down). In an aquatic food web, planktivore presence can directly alter zooplankton density via consumption, while indirectly shaping phytoplankton biomass via reduced herbivore abundance and the release of nutrients due to excretion, egestion, and decomposition. Novel species introduced into an established food web may have important consequences. An invasive species may impact an invaded food web through competition, predation, alteration of nutrient cycling, or, potentially, through facilitation of native species or other invasives. For example, an invasive planktivore may shift zooplankton density or community composition, thereby facilitating phytoplankton blooms. Such a planktivore may also compete with and, potentially, replace native species. Moreover, an invasive species that reaches high densities within its invaded range may serve as an important nutrient sink as it consumes a high biomass of native species or a nutrient source via excretion or decomposition. Two such invasive species with the capacity to dramatically alter native food web dynamics are bighead (Hypophthalmichthys nobilis) and silver carp (H. molitrix; collectively, bigheaded carp). Bigheaded carp are large-bodied, planktivorous fishes that were introduced into the United States in the 1970s and have since spread throughout much of the Mississippi River and its tributaries. These species currently threaten the Great Lakes, where they may constitute a threat to native planktivores such as gizzard shad (Dorosoma cepedianum) and commercially important species such as walleye (Sander vitreus), although there remains a great deal of uncertainty surrounding their potential ecosystem impacts. Consumption of both zooplankton and phytoplankton has been observed in bigheaded carp, although their impact on primary producer biomass is not well understood. Although field observations suggest that condition and abundance of native planktivores, including gizzard shad and bigmouth buffalo (Ictiobus cyprinellus), as well as zooplankton density, have declined following the bigheaded carp invasion, there is little direct, experimental evidence of bigheaded carp food web impacts. Therefore, I sought to examine the effects of bigheaded carp on native ecosystems through a series of mesocosm experiments at the Southern Illinois University pond facility. My primary objectives were to 1) observe potential competition between bigheaded carp and the native gizzard shad, 2) evaluate effects of bigheaded carp predation on zooplankton and phytoplankton communities, 3) assess impacts of bigheaded carp decomposition on nitrogen and phosphorus availability, and 4) measure the rate at which bigheaded carp excrete nitrogen and phosphorus. In order to elucidate the impacts of bigheaded carp on gizzard shad growth and survival, zooplankton and phytoplankton densities, and nitrogen and phosphorus availability in the pelagic and benthic pools and to determine whether gizzard shad experience a diet shift in response to bigheaded carp presence, I performed two mesocosm experiments with three treatments: gizzard shad only, gizzard shad, bigheaded carp, and fishless control (Chapter 1). I predicted that bigheaded carp would reduce zooplankton densities but that gizzard shad, which are both detritivorous and planktivorous, would be unaffected due to their ability to use detritus as an alternative food source. Additionally, both predator release via zooplankton consumption and increased nutrient availability from bigheaded carp excretion would stimulate phytoplankton. I found that gizzard shad survival was reduced by bigheaded carp presence but that surviving gizzard shad did not experience a decline in growth in the bigheaded carp plus gizzard shad treatments. This may have been due to the ability of gizzard shad to consume detritus, as foreguts of sampled gizzard shad in Experiment 2 contained mostly detritus. Moreover, phytoplankton density declined in the presence of silver carp in Experiment 2, suggesting silver carp herbivory. In addition, nitrogen and phosphorus availability in either the pelagic or benthic pools did not appear to be impacted by bigheaded carp presence. After demonstrating experimentally the overall negative impact of bigheaded planktivory on native food webs, I focused my remaining two chapters on the effects of silver carp on nutrient availability. In Chapter 2, I outline a decomposition experiment testing for potential changes in pelagic and benthic nitrogen and phosphorus availability and, in turn, phytoplankton, zooplankton, and macroinvertebrate densities in response to silver carp decomposition. Although silver carp die offs have been reported throughout the Midwest, little is known about the magnitude of those die offs and their consequences for the ecosystem. In this study, silver carp decomposition did not appear to alter nutrient availability or densities of phytoplankton or invertebrates. However, in comparison to northern streams in which salmon spawning and decomposition provide an important nutrient subsidy, the mesocosms used in this study have relatively higher background nutrient concentrations. Thus, silver carp decomposition, at least at the densities studied, may have little importance to in-stream nutrient availability. Lastly, because I am interested in how bigheaded carp, particularly silver carp, alter nutrient dynamics in invaded food webs, it is necessary to calculate silver carp nitrogen and phosphorus excretion rates, as well as body nitrogen and phosphorus content (Chapter 3). Nutrient stoichiometry theory predicts a balance between the relative consumption of nutrients by an organism and the extent to which the organism retains nutrients in its tissues or excretes them. Thus, it is a useful tool in determining how an invasive species may alter nutrient availability via consumption and excretion. In Chapter 3, I describe the body and excretion N:P ratios for silver carp, which exhibit a lower body N:P ratio than excretion N:P, suggesting that these organisms may serve as a sink for phosphorus. Moreover, silver carp body excretion N:P ratios were higher than those reported for gizzard shad, suggesting that, in regions where silver carp may replace gizzard shad or lower gizzard shad population density via competition (Chapter 1), silver carp may alter nutrient cycling processes in aquatic ecosystems by shifting the overall available N:P ratio. Bigheaded carp may pose a significant threat to invaded ecosystems through their potential to compete with native species, reduce plankton densities, and alter nutrient availability. However, although bigheaded carp are expanding in range and approaching the Great Lakes, the full extent of their ecosystem impacts remain uncertain. Through my work on bigheaded carp food web impacts, particularly the influence of silver carp on native species and nutrient cycling processes, I have found that bigheaded carp have the capacity to negatively impact invaded ecosystems overall by reducing zooplankton, phytoplankton, and forage fish densities. Moreover, as bigheaded carp in particular continue to reach high densities as they expand in range, their capacity to alter relative nitrogen and phosphorus availabilities must be monitored to understand the extent of their influence. Due to their ability to disrupt top down and bottom up processes in freshwater ecosystems, bigheaded carp constitute a critical environmental issue in the Great Lakes area and throughout the Midwest and, thus, it is imperative to continue to experimentally assess how bigheaded carp interact with native species to the detriment or benefit of U.S. freshwater communities.

This thesis deals with the role of species traits in predator-prey interactions and food web structure. I conducted laboratory experiments with predatory aquatic insects and their prey to reveal the traits determining who eats whom in small standing waters. I also focused on the possibility of incorporating the observed dependence of predator-prey interactions on body mass into existing food web models. Further, I developed a simple simulation model to explore the consequences of body mass dependent feeding and dispersal for food web assembly. Last, I show that four common methods for sampling aquatic insects differ in their selectivity, especially on the basis of body mass of sampled insects. In conclusion, I combined laboratory experiments, field work and mathematical models to evaluate the importance of body mass and other species traits, such as foraging behaviour and microhabitat selectivity, in predator-prey interactions and explored selected food web level consequences.