<p> I evaluated the efficacy of using woodland fire to alter vegetation composition in a manner that augments desert bighorn sheep (<i>Ovis canadensis nelsoni </i>) habitat in the Black Ridge Canyons Wilderness Area in western Colorado. I applied generalized linear mixed models to estimate pre&ndash;fire ewe habitat selection and then simulated a hypothetical widespread fire to spatially predict where fire would be most beneficial in expanding habitat. I found that ewes were avoiding habitats with high woodland canopy cover, the habitat most likely to be removed by fire. Given the removal of all woodlands, it is likely that habitat expansion would occur in areas near topographic escape terrain. Coupled with this analysis, I addressed concerns regarding potential negative effects of fire in this system by comparing vegetation composition of unburned habitats to burned habitats that were treated with a native seed mixture. I found that foliar cover in burned areas was on average two times greater than in unburned areas and that post-fire seeding efforts likely allowed for these differences to be proportionally similar between native and non-native grass species. My results provide an encompassing view on the effects of fire for a common management situation in which both land and wildlife values are of mutual interest.</p>

There is no abstract available for this thesis.

<p> Grasslands are known to have been an important ecosystem in the Illinois landscape prior to European settlement. They have been severely impacted by changes in land use such as the conversion of native grasslands to agricultural land for the production of crops and livestock. Grassland ecosystems are known to provide several essential ecosystem functions that are important for the maintenance of the ecosystem and for human survival. Some of the ecosystem functions associated with grasslands include: nutrient cycling, carbon sequestration, and the cleansing of environmental contaminants from water or soil. As grasslands are converted to agricultural use, their ability to perform these ecosystem functions are greatly impaired or lost completely. Due to their recognized importance, grassland restoration projects have been given high priority by conservationists and governmental agencies around the world. Some grassland restorations aim to restore the native vegetation including the great species richness that grasslands, and prairie ecosystems in particular, are known for. Other projects, like the Conservation Reserve Program (CRP), aim to restore one of the vital ecosystem functions that grasslands provide. The measure of success for a grassland restoration has largely been evaluated using species composition and indices of species richness and evenness. These types of measurements do not directly assess the ability of a restoration site to perform the ecosystem functions of a native grassland. The aim of this study is to determine if ecosystem function is recovered over time since restoration. This will be accomplished using a chronosequence of grassland restorations at the Nature Institute in Godfrey, IL ranging from 1 year to 25 years since restoration. Several indicators of ecosystem functioning will be assesses at each site including: soil bulk density, soil organic matter, and peak standing crop. The differences in these characteristics among the sites were analyzed by one-way ANOVA followd by Tukey&rsquo;s HSD test if significant. All properties were analyzed using linear regression to assess their fit to a linear model. Soil bulk density was found to moderately but significantly decrease in response to time since restoration (<i>p</i> = 0.0049) indicating a recovery from soil compaction and improved soil structure. Differences were detected in soil organic matter among the sites, but no linear trend in response to time since restoration was detected. Similarly with peak standing crop, differences were detected among the sites, but no linear trend with time since restoration. The lack of a predictable recovery in soil characteristics over time was attributed to differences in historical land use. In order to strengthen this study in the future, analysis of a remnant prairie and older restoration sites should be examined.</p>

This study developed a food preference survey to estimate adolescents willingness to consume energy-dense foods and sugar-sweetened beverages. Five focus group interviews with 13 to 19 year-old students were conducted, and items representing energy-dense foods, energy-dilute foods, sweetened beverages, and unsweetened beverages were determined (5 per category). The final survey was administered to 234 students. Willingness to consume items was assessed using a 7-point Likert Scale (1, representing Extremely Unwilling to 7, indicating Extremely Willing). Exploratory Factor Analysis using Principal Axis factoring with a Promax (oblique) rotation revealed two factors. Factor one included French fries, Kool-Aid, glazed donuts, cookies, lemonade, and pizza (23.9% of the variance). Factor 2 included nuts or peanut butter, low-fat or fat-free yogurt, grapes, and bananas (13.8% of the variance). Cronbachs alpha was 0.770 for factor 1 and 0.664 for factor 2.

Between 2002 and 2005, I examined spatial and temporal patterns in the hydrology, water chemistry, and algal nutrient-limitation status (N and/or P) in Delta Marsh, a 18,500-ha coastal lacustrine freshwater marsh on the south shore of Lake Manitoba, to determine the influence of surface water exchange with Lake Manitoba on these properties. Daily and annual marsh water level changes were found to be highly correlated with those of the lake, during some of the highest and lowest long-term water levels in recorded history. The average magnitude of water level changes in the marsh ranged from to a few centimeters to half a meter, which is significant in shallow coastal wetlands systems like Delta Marsh where the average depths are ≤ 1 m. In general, marsh sites located closest to the lake were influenced to the greatest degree by the flushing and dilution effect of the lake. Spatially, in connected sections of the marsh concentrations of dissolved inorganic and total N (DIN-N and TN), total reactive and total phosphorus (TRP-P and TP), dissolved organic carbon (DOC), chloride (Cl-), sulfate (SO4-), alkalinity and conductivity decreased with decreasing distance to Lake Manitoba. Regardless of east and west location and the distance of connected marsh sites from Lake Manitoba, annual variation in water level was the most significant predictor of differences in several water chemistry characteristics between sample sites including DIN-N, TN, TRP-P, TP, alkalinity, DOC, Cl-, SO4-, and conductivity. Annually, concentrations of DIN-N, TN, alkalinity, DOC, Cl-, SO4- and conductivity were negatively correlated with increasing water depth, and the spatial variation in the concentration of these water chemistry parameters also decreased with increasing water level. Results of nutrient diffusing substrata bioassay experiments indicated that periphyton biomass in the marsh was predominately limited by N. The predominance of N limitation in Delta Marsh was found to be significantly negatively correlated with water column N concentrations, but not correlated with P concentrations. Collectively, this study illustrates the important role of lake connection and hydrological influence on the structure and function of adjoining coastal freshwater wetlands.

In Manitoba, moose are the preferred prey species, and occupy similar landscapes to caribou. To reduce predation, caribou separate themselves from moose by selecting habitat less suitable to moose. Corridors linking caribou and moose habitat can facilitate access to caribou. The relationship between species and linear features was assessed through radio telemetry and surveys along natural and anthropogenic corridors. Surveys were used to determine distribution of all species relative to each other, and their proximity to linear features. Wolf scat was used to determine diet. Corridor surveys showed an even distribution of use between natural and anthropogenic corridors. Surveys showed association between moose and wolves, but not caribou. Wolves and moose were closer to river and road features and farther from lakes than caribou. Wolf diet included moose and beaver, not caribou. Caribou demonstrated partitioning from moose. Anthropogenic corridors appear to be additive, contributing to an overall wolf travel network.

Since northern mixed prairies evolved under the influence of bison, grazing may be an important process maintaining diversity in these ecosystems. However, it is unclear whether grazing by cattle has the same ecological consequences as grazing by bison. I surveyed plant communities that were grazed at a range of intensities by bison or cattle, or were mechanically mowed. I used generalized linear mixed models and geostatistical techniques to evaluate the effects of grazing intensity and species of grazer on structural and floristic responses, and analysis of variance to evaluate the effects of mowing. I found that both grazing and mowing increased diversity and reduced evenness of the plant community. Spatial patterns of grazing were similar for bison and cattle, although bison created more discrete patches at the highest intensities of grazing. My results suggest that despite some differences in their selective preferences, the two species may have similar ecological effects.

Extending and integrating ecological concepts and theories can provide new solutions for difficult ecological problems. The ecosystem concept and ecosystem ecology theory have seen important developments through the elaborations of metaecosystem theory, which extends the ecosystem concept through spatial flows of energy, materials and organisms between interconnected ecosystems, and ecological stoichiometry, which extends ecological energetics by examining multiple chemical balances of substances in ecological interactions. However, these two extensions of ecosystem ecology theory have not been brought together in any form. In this thesis, I first extend both ecological stoichiometry and metaecosystem theory, and then integrate them in order to clarify difficult ecological concepts and to provide new solutions to ecological problems.My overall approach is to develop mathematical models to formally articulate ecological concepts such as nutrient colimitation, stoichiometric imbalances and metaecosystem connectivity within the frameworks of ecological stoichiometry and metaecosystem theory. First, I present a parameterized stoichiometric ecosystem model that examines the relationship between mechanisms and phenomenology of nutrient colimitation, and how the mechanisms may interact with stoichiometrically imbalanced trophic interactions. I show that there are no clear relationships between mechanisms and phenomena, and that the mechanisms of colimitation are key in determining ecological dynamics and functioning.I then examine in a spatially-explicit model how the connectivity of a metaecosystem and the relative movement rates of nutrients and organisms can drive dynamics of spatially perturbed metaecosystems. I show that the eigenvalues of the matrix that describes metaecosystem connectivity can be used to predict the spatial dynamics of a metaecosystem and the kinds of dynamics present depends heavily on relative movement rates. Lastly, I bring metaecosystem theory and ecological stoichiometry together in a spatially-explicit stoichiometric metaecosystem model to examine how spatial flows of nutrients and organisms can act as a mechanism to cause nutrient colimitation at local and regional scales. The model indicates that nutrient colimitation can be caused by spatial flows and this mechanism can be used to explain many confounding patterns in colimited growth responses found in the empirical literature. / L'extension et l'intégration des théories et des concepts écologiques peuvent nous aider a trouver de nouvelles solutions pour des problèmes ecologiques difficiles. Le concept de l'écosystème et la théorie des écosystèmes ont survécu a d'importants changements par l'élaboration de la théorie des métaécosystèmes, qui ajoute au concept de l'écosystème des flux d'énergie, de matériaux et d'organismes entre des écosystèmes liés ensemble, et la stoechiometrie ecologique, qui étend la théorie énergétique des écosystèmes par l'inclusion de l'équilibre de plusieurs substances chimiques dans les interactions écologiques. Pourtant, ces deux extensions de la théorie des écosystèmes ne sont pas encore reunies. Dans ma thèse, j'étends la théorie des métaécosystèmes et la stoechiométire écologique, et par la suite je les unis ensemble pour adresser des conceptsécologiques difficiles et pour trouver des solutions aux probeèmes écologiques.La méthodologie pour aborder ces sujets consiste à développer des modèles mathématiques pour l'articulation des concepts ́écologiques comme la limitation du croissance par plusieurs nutriments, les déséquilibres stoechiométriques et la connectivité des métaécosystèmes dans le cadre de la théorie des métaécosystèmes et la stoechiométrie écologique. Premièrement, je presente un modèle stoechiométrique d'un écosystème avec des paramètres pris d'un écosystème réel qui a pour but d'examiner les relations entre les mécanismes et les phénomènes de la limitation de la croissance par plusieurs nutriments. En plus, j'examine comment cette limitation peut intéagir avec les déséquilibres stoechiométriques entre les autotrophes et les herbivores.Deuxièment, j'étudie avec un modèle spatial comment la connectivité d'un métaécosystème et les taux relatifs de mouvement des nutriments et des organismes peuvent diriger les dynamiques des métaécosystèmes perturbés. Je montre que les valeurs charactéristiques de la matrice qui décrit la connectivité du métaécosystème peuvent être utilisées pour prédire les dynamiques spatiales du métaécosystème et les types de dynamiques dépendent des taux relatifs de mouvement.Finalement, j'unis la théorie des métaécosystèmes avec la stoechiométrie écologique dans un modèle qui contient un métaécosystème stoechiométrique. J'utilise ce modèle pour examiner si les flux de nutriments et des organismes peuvent agir comme un mécanisme de limitation de la croissance par plusieurs nutriments dans les écosystèmes locaux et les métaécosystèmes. Le modèle indique que la limitation de la croissance par plusieurs nutriments peut être causée par les flux spatiaux et ce mécanisme à la capacité d'expliquer plusieurs phénomèmes empiriques dans le domaine de la limitation par plusieurs nutriments.

Temperature is a primary physical constraint on the distribution and abundance of aquatic organisms. Increasingly, human activities modify natural thermal regimes of aquatic systems, thereby altering the composition and structure of the organismal community. For decades, the Gentilly-2 Nuclear Power Plant (G2NPP) in Bécancour, QC, has discharged coolant water into the St. Lawrence River at temperatures more than 10ºC above ambient. My study aimed to quantify how the diversity, composition, and abundance of the St. Lawrence benthic macroinvertebrate community has been altered by G2NPP thermal effluent. Benthic samples were collected at sites along the thermal gradient downstream of G2NPP in May and September 2012. Environmental predictors varying with distance downstream of G2NPP (e.g., temperature, depth, flow rate) were recorded at each station. Macroinvertebrate diversity and abundance were measured for each site and analyzed in relation to local environmental variables. Taxonomic richness and abundance (density and biomass) were elevated close to the power plant, but these patterns were best explained by environmental variables such as depth and sediment type. Taxonomic evenness was reduced in the warmest sites, and this pattern was driven by a few highly tolerant taxa, including thermophilic invasive species like the Asian clam, Corbicula fluminea, which was amongst the most dominant species in terms of abundance and biomass. Despite the strong thermal gradient at G2NPP, diversity indices and characteristics of community composition primarily reflected abiotic habitat characteristics other than temperature, whereas temperature was an important predictor only for a minority of taxa, like C. fluminea. With the closure of G2NPP in December 2012, and the subsequent eradication of cold-sensitive C. fluminea, these results provide a baseline for monitoring the succession of the benthic community in future years. / La température de l'eau est une composante principale dans la distribution et l'abondance des organismes aquatiques. Aussi, l'essor des activités anthropogeniques modifient les régimes thermiques des écosystèmes aquatiques et changent par le fait même la composition et la structure des communautés d'organismes. Pendant des décennies, la centrale nucléaire Gentilly-2 (CNG-2) à Bécancour, QC, a déchargé ses eaux de refroidissment dans le Fleuve St- Laurent à des températures supérieures à 10ºC la température ambiante du cours d'eau. L'objectif de mon étude a été de quantifier les patrons de diversité, de composition, et d'abondance de la communauté benthique de macroinvertébrés du Fleuve St-Laurent affectée par l'effluent thermique de la CNG-2. Des échantillons benthiques ont été récoltés à différentes stations le long du gradient thermique en aval de la CNG-2 en mai et septembre 2012. Les variables environnementales qui variaient en fonction de la distance par rapport à la source de l'effluent thermique (e.g., température, profondeur, courant) ont été enregistrés à chaque station. La diversité et l'abondance des macroinvertébrés ont été mesurées à chaque station et analysées par rapport aux variables environnementales locales. La richesse taxonomique et l'abondance (densité et biomasse) étaient élévées près de la centrale nucléaire, mais ces observations étaient davantage liées à des variables environnementales comme la profondeur et le type de sédiments. La regularité taxonomique était réduite aux stations les plus chaudes expliquée par la présence de quelques taxa seulement tolérant aux températures élevées, dont des éspèces envahissants thermophiles comme la petite corbeille d'Asie, Corbicula fluminea, qui était parmi les plus dominantes en termes d'abondance et de biomasse. Malgré le gradient thermique prononcé à la CNG-2, les indices de diversité et les caractéristiques de la composition de la communauté benthique reflètent essentiellement l'importance de caractéristiques abiotiques de l'habitat autres que la température, une componsante importante pour une minorité d'espèces seulement, telle C. fluminea. Avec la fermature de la CNG-2 en décembre 2012, et l'éradication de C. fluminea, les resultats présentés seront une référence au cours des prochaines années quant au suivi de la succession de la communauté benthique.

Lakes are among the most susceptible ecosystems to anthropogenic modification as humans are drawn to freshwaters for the multitude of ecosystems services they provide. The littoral habitat structure of lakes, both in the form of aquatic vegetation (macrophytes) and coarse woody debris (CWD), is often negatively altered by direct and indirect human activities. Little is known about the effect that loss of littoral structure might have on whole lake food webs with respect to energy flow and trophic transfers. The maximum number of trophic transfers within a food web is referred to as food chain length and can control community composition through trophic cascades. Therefore, detectable changes in food chain length likely have impacts on the lake food web. I predicted that loss of littoral structure would result in reduced food chain length due to loss of refuge for intermediate consumers. I used a field study and a simulation model to (1) determine if there was a significant relationship between food chain length and littoral structure in the form of macrophytes and (2) assess the support for two different potential mechanisms (i.e. for changes in refuge or productivity) through which macrophytes and coarse woody debris could alter food chain length. The field study showed that food chain length was positively related to macrophyte abundance. The simulation model shed further insight and showed that refuge provided by macrophytes and CWD may account for observed food chain length increases due to preservation of predatory invertebrates. From these results, we can infer that the loss of littoral habitat structure likely results in a shortening of the lake food chain, which can have implications for community composition, energy flow and whole ecosystem responses to change. / Les lacs sont parmi les écosystèmes les plus sensibles aux modifications d'origine anthropique car les humains sont attirés par les eaux douces et elles fournissent une multitude de services écosystémiques. La structure de l'habitat dans la zone littorale des lacs, représentée par la végétation aquatique (macrophytes) et les débris ligneux grossiers (DLG), est souvent altérée négativement par les activités anthropiques directes et indirectes. Nous avons très peu d'évidence sur les effets qu'une perte de la structure d'habitat en zone littorale pourrait avoir sur les réseaux trophiques des lacs, plus particulièrement en ce qui concerne les flux d'énergies et les transferts trophiques. Le nombre maximum de transferts trophiques au sein d'un réseau trophique, appelée longueur de la chaîne trophique, peut contrôler la structure des communautés par le biais de cascades trophiques. Par conséquent, des changements significatifs dans la longueur de la chaîne trophique ont fort probablement des répercussions sur la chaîne trophique d'un lac. Dans ma thèse de maîtrise, j'ai prédit qu'une perte de la structure d'habitat dans la zone littorale entraînerait une réduction de la longueur de la chaîne trophique en raison d'une perte de refuges pour les consommateurs intermédiaires. J'ai utilisé des données récoltées sur le terrain et un modèle de simulation pour (1) déterminer s'il y a une relation significative entre la longueur de la chaîne trophique et la structure d'habitat de la zone littorale en utilisant l'abondance des macrophytes et pour (2) évaluer comment les macrophytes et les DLG peuvent modifier la longueur de la chaîne trophique en explorant la plausibilité de deux mécanismes potentiels différents, c'est-à-dire un changement dans la disponibilité des refuges ou un changement de la productivité. Les données de terrain ont démontré que la longueur de la chaîne trophique est positivement reliée à l'abondance de macrophytes. Le modèle de simulation a stimulé le développement de nouvelles idées et a démontré que les refuges fournis par les macrophytes et les DLG peuvent expliquer l'augmentation de la longueur de la chaîne trophique observée par la préservation des invertébrés prédateurs. Mes résultats me permettent de conclure qu'une perte de la structure de l'habitat en zone littorale résulte en un raccourcissement de la chaîne trophique d'un lac, ce qui peut avoir des répercussions importantes sur la structure des communautés, le flux d'énergie et les réponses des écosystèmes face aux changements d'origine anthropique.