Density-dependence is considered one of the most important regulators of population growth, and it has been documented across a wide variety of species. Typically, population growth rate and components thereof decline with increasing density (i.e., negative density-dependence); however, in species that exhibit high population densities and social behavior, positive density-dependence (i.e., Allee effect) may occur at low density. June sucker, a federally endangered lake sucker endemic to Utah Lake, Utah, USA, occurred historically at high density, and it exhibits coordinated feeding behavior. These characteristics indicate a potential for the existence of an Allee effect at current low population densities. To determine effects of density on growth, survival, and diet, I experimentally manipulated density of young June sucker in replicated enclosures in a natural environment. Larval June sucker were placed in enclosures at four different densities, and growth, survival, and diet of fish, and availability of prey (to determine selectivity) were measured at two time intervals. Both individual growth and survival were significantly lower at the lowest density compared to higher densities, indicative of a component Allee effect. Diets of individuals at low densities were more selective than diets of individuals at intermediate and high densities, suggesting a change in feeding strategy with density. Reduced growth and survival at low density suggests that corresponding, highly selective, feeding strategies may be less efficient than feeding strategies employed at higher densities. Allee effects appear to be an important consideration for recovery of this endangered species, and such effects may be common in historically abundant, but currently rare species.

Variational calculations have been performed using various internucleon interactions in an attempt to find an interaction which would reproduce the properties of the O-p shell nuclei. These interactions were derived by fitting procedures to the S-state phase shifts and to the properties of nuclear matter. A satisfactory interaction having been obtained, studies of isobaric nuclei have been undertaken. / Thesis / Doctor of Philosophy (PhD)

Os modelos de Daley-Kendall e Maki-Thompson são os dois modelos estocásticos para difusão de rumores mais citados até o momento. Em ambos, uma população finita fechada e totalmente misturada é subdividida em três classes de indivíduos denominados ignorantes, informantes e contidos. Depois de um rumor ser introduzido na população, difunde-se através desta seguindo determinadas regras que dependem da classe à qual a pessoa que sabe do rumor pertence. Tanto a proporção final de indivíduos que nunca chegam a conhecer o rumor quanto o tempo que este demora em ser difundido são variáveis de interesse para os modelos propostos. As técnicas encontradas na literatura para estudar modelos de rumores são o princípio de difusão de constantes arbitrárias; argumentos de martingais; o método de funções geradoras e a análise de versões determinísticas do processo. Neste trabalho apresentamos uma alternativa para essas técnicas baseando-nos na teoria de cadeias de Markov \"density dependent\'\'. O uso desta nova abordagem nos permite apresentar resultados assintóticos para um modelo geral que tem como casos particulares os famosos modelos de Daley-Kendall e Maki-Thompson, além de variações de modelos de rumores apresentados na literatura recentemente. / Daley-Kendall and Maki-Thompson models are the two most cited stochastic models for the spread of rumours phenomena, in scientific literature. In both, a closed homogeneously mixing population is subdivided into three classes of individuals called ignorants, spreaders and stiflers. After a rumor is introduced in the population, it spreads by following certain rules that depend on the class to which the individual who knows the rumor belongs. Both the final proportion of the population never hearing the rumor and the time it takes are variables of interest for the proposed models. The main tools used to study stochastic rumours have been the principle of the diffusion of arbitrary constants, martingale arguments, generating functions and the study of analogue deterministic versions. Relying on the theory of density dependent Markov chains, we present an alternative to these tools. This approach allows us to establish asymptotical results for a general model that has as particular cases the classical Daley-Kendall and Maki-Thompson models, and other variations for rumour models reported in the literature recently.

Os modelos de Daley-Kendall e Maki-Thompson são os dois modelos estocásticos para difusão de rumores mais citados até o momento. Em ambos, uma população finita fechada e totalmente misturada é subdividida em três classes de indivíduos denominados ignorantes, informantes e contidos. Depois de um rumor ser introduzido na população, difunde-se através desta seguindo determinadas regras que dependem da classe à qual a pessoa que sabe do rumor pertence. Tanto a proporção final de indivíduos que nunca chegam a conhecer o rumor quanto o tempo que este demora em ser difundido são variáveis de interesse para os modelos propostos. As técnicas encontradas na literatura para estudar modelos de rumores são o princípio de difusão de constantes arbitrárias; argumentos de martingais; o método de funções geradoras e a análise de versões determinísticas do processo. Neste trabalho apresentamos uma alternativa para essas técnicas baseando-nos na teoria de cadeias de Markov \"density dependent\'\'. O uso desta nova abordagem nos permite apresentar resultados assintóticos para um modelo geral que tem como casos particulares os famosos modelos de Daley-Kendall e Maki-Thompson, além de variações de modelos de rumores apresentados na literatura recentemente. / Daley-Kendall and Maki-Thompson models are the two most cited stochastic models for the spread of rumours phenomena, in scientific literature. In both, a closed homogeneously mixing population is subdivided into three classes of individuals called ignorants, spreaders and stiflers. After a rumor is introduced in the population, it spreads by following certain rules that depend on the class to which the individual who knows the rumor belongs. Both the final proportion of the population never hearing the rumor and the time it takes are variables of interest for the proposed models. The main tools used to study stochastic rumours have been the principle of the diffusion of arbitrary constants, martingale arguments, generating functions and the study of analogue deterministic versions. Relying on the theory of density dependent Markov chains, we present an alternative to these tools. This approach allows us to establish asymptotical results for a general model that has as particular cases the classical Daley-Kendall and Maki-Thompson models, and other variations for rumour models reported in the literature recently.

Dispersal behavior plays an important role for the geographical distribution and population structure of any given species. Individual’s fitness, reproductive and competitive ability, and dispersal behavior can be determined by the age of the individual. Age-dependent as well as density-dependent dispersal patterns are common in many bird species. In this thesis, I first present age-dependent breeding ability and natal site fidelity in white storks (Ciconia ciconia); migratory birds breeding in large parts of Europe. I predicted that both the proportion of breeding birds and natal site fidelity increase with the age. After the seventies of the last century, following a steep population decline, a recovery of the white stork population has been observed in many regions in Europe. Increasing population density in the white stork population in Eastern Germany especially after 1983 allowed examining density- as well as age-dependent breeding dispersal patterns. Therefore second, I present whether: young birds show more often and longer breeding dispersal than old birds, and frequency of dispersal events increase with the population density increase, especially in the young storks. Third, I present age- and density-dependent dispersal direction preferences in the give population. I asked whether and how the major spring migration direction interacts with dispersal directions of white storks: in different age, and under different population densities. The proportion of breeding individuals increased in the first 22 years of life and then decreased suggesting, the senescent decay in aging storks. Young storks were more faithful to their natal sites than old storks probably due to their innate migratory direction and distance. Young storks dispersed more frequently than old storks in general, but not for longer distance. Proportion of dispersing individuals increased significantly with increasing population densities indicating, density- dependent dispersal behavior in white storks. Moreover, the finding of a significant interaction effects between the age of dispersing birds and year (1980–2006) suggesting, older birds dispersed more from their previous nest sites over time due to increased competition. Both young and old storks dispersed along their spring migration direction; however, directional preferences were different in young storks and old storks. Young storks tended to settle down before reaching their previous nest sites (leading to the south-eastward dispersal) while old birds tended to keep migrating along the migration direction after reaching their previous nest sites (leading to the north-westward dispersal). Cues triggering dispersal events may be age-dependent. Changes in the dispersal direction over time were observed. Dispersal direction became obscured during the second half of the observation period (1993–2006). Increase in competition may affect dispersal behavior in storks. I discuss the potential role of: age for the observed age-dependent dispersal behavior, and competition for the density dependent dispersal behavior. This Ph.D. thesis contributes significantly to the understanding of population structure and geographical distribution of white storks. Moreover, presented age- and density (competition)-dependent dispersal behavior helps understanding underpinning mechanisms of dispersal behavior in bird species. / Das Verständnis der Mechanismen, die dem Ausbreitungsverhalten und der Wahl des Neststandorts zugrunde liegen, gibt wichtige Einsichten in Strukturen und Dynamiken von Tierpopulationen. Der Gesundheitszustand, die Produktivität und Konkurrenzfähigkeit sowie das Ausbreitungsverhalten eines Individuums können über das Alter ermittelt werden. Alters- und dichteabhängige Veränderungen in Verbreitungsmustern kommen bei vielen Vogelarten vor. In der vorliegenden Studie untersuchten wir zunächst den Effekt des Alters auf die Reproduktivität, auf die Wahl des Neststandorts sowie auf die Geburtsorttreue des Weißstorchs (Ciconia ciconia). Wir fragten, ob sowohl der Anteil der brütenden Individuen als auch die Geburtsorttreue mit dem Alter zunimmt. Weißstörche sind Zugvögel, die während der Migration zumeist segelnd die Thermik nutzen und in weiten Teilen Europas brüten. Nach einem starken Bestandsrückgang konnte in vielen Regionen Europas ab den 1970er Jahren wieder ein positiver Trend in der Populationsentwicklung beobachtet werden. Die zunehmende Populationsdichte, besonders nach 1983 in der ostziehenden Subpopulation in den fünf Bundesländern der ehemaligen DDR, erlaubte die Analyse von dichte- und altersabhängigen Präferenzen in der Richtung der Brutstandorte sowie in der Verbreitungsfrequenz und -distanz. Wir untersuchten zudem die Alters- und Dichteabhängigkeit der Ausbreitungsrichtung einer Teilpopulation. Wir fragten, ob und wie die Hauptzugrichtung im Frühjahr mit der Verbreitungsrichtung interagiert: Beeinflussen Alter und Populationsdichte die Ausbreitungsrichtung? Der Anteil der brütenden Individuen, die älter als 22 Jahre sind, nahm innerhalb der beobachteten Teilpopulation ab, vermutlich aufgrund einer altersbedingten Abnahme des Gesundheitszustands. Junge Vögel zeigten eine starke Geburtsorttreue, was auf eine genetische Komponente in den Zugmustern junger Störche hinweist. Generell trat bei jungen Störchen häufiger Ausbreitungsverhalten auf als bei älteren Störchen. Eine signifikante Zunahme der Ausbreitungsdistanz von Individuen über die Zeit lässt auf eine dichteabhängige Komponente im Ausbreitungsverhalten der Weißstörche schließen. Weiterhin wurde eine signifikante Interaktion zwischen dem Alter sich ausbreitender Individuen und dem betrachteten Jahr gefunden. Demzufolge breiteten sich alte Vögel über die Zeit über größere Distanzen aus, vermutlich um der ansteigenden Konkurrenz, bedingt durch den wachsenden Bestandsdruck, zu entgehen.

Fluctuations in temperature and precipitation amounts due to climate change influence recharge rate of groundwater. Any variations in the amount of precipitation recharge and artificial discharge directly affect groundwater level and so the salt water intrusion rate in the aquifers, which are in contact with sea water. The purpose of this study is to determine the overall historical precipitation recharge trend in Sel&ccedil / uk sub-basin and to detect whether there is a decrease or increase in recharge amounts due to climate change since 1100 BC. Besides, it covers assessing the future position of the salt water-fresh groundwater interface as a result of possible fluctuations in climate and artificial discharge. For this purpose, numerical density dependent cross sectional groundwater flow with solute transport model was conducted using finite element approach. At first, current salt water-fresh water interface and artificial discharge related head changes in the aquifer were determined. Backward modeling was utilized to obtain concentration distribution in the year 1976 representing the last stage of the undisturbed period. Then, progradation of salt water-fresh water interface since 1100 BC to 1976 was modeled using calibrated parameters and current recharge value. As a result of sea-regression model simulations (1100 BC-1976) less degree of salt water intrusion than that of currently detected in the area was obtained. The result suggests that overall recharge amount in the last 3076 years must have been less than that of 1976. Moreover, future (2010-2099) position of the interface and head changes under the influence of both climate change and increasing water demand were determined. Future model simulations indicate that salt water-fresh water interface moves farther landward. However this movement is mostly due to increasing discharge amount rather than that of climatic changes.

Density-dependent groundwater flow in the Floridan aquifer system (FAS) depends on chloride concentrations and fluid temperature. Previous studies addressing the role of chloride concentration and temperatures on groundwater flow in the FAS have relied on observation data or simplified two-dimensional numerical models. A three-dimensional hydrologic analysis of FAS in peninsular Florida was performed using a modified version of SUTRA (SUTRA-MS) capable of simulating multi-species solute and heat transport. SUTRA-MS was developed during this investigation and is capable of reproducing results for several problems with known solutions.The model was developed using available geometric and hydraulic parameter data and calibrated using hydraulic head, chloride concentrations, and temperatures representative of conditions prior to significant groundwater pumpage from the FAS. The calibrated model is capable of reproducing observed pressures and temperatures but in general ov er-simulates chloride concentrations. The inability of the model to simulate observed chloride concentrations suggests chloride concentrations in the FAS are not in equilibrium with current sea level. Previous hydrologic studies of the FAS have attributed anomalous chloride concentrations to incomplete flushing of relict seawater that entered the aquifer during previous sea-level highstands.Three hypothetical, sinusoidal sea-level changes occurring over 100,000-years were used to evaluate how the aquifer responds to sea-level fluctuations. Model results indicate pressure equilibrates most rapidly and is followed by temperatures and then chloride concentrations. Confining unit thicknesses directly affect response times of pressure, temperature, and chloride concentrations in the FAS.Simulation of the system with ("geothermal case") and without ("isothermal case") the geothermal component reveals that the inflow of seawater from the Florida Straits would be similar without the heat f low but the distribution would differ significantly. The addition of heat flow also reduces the asymmetry of the circulation. Simulations evaluating aquifer responses to sea-level fluctuations and the thermal component indicate that the complicated three-dimensional setting of the FAS is a key component of the groundwater flow system and steady state conditions may not exist for relatively thick coastal aquifers that have experienced multiple sea-level cycles.

Habitat loss and predation are threatening many shorebird populations worldwide. While habitat preservation often is preferable, sometimes habitat needs to be restored or created in order to stave off immediate declines. The Great Plains population of piping plovers (Charadrius melodus) was listed as threatened in 1986, and habitat loss and predation appear to be limiting the growth of this population. On the Missouri River, piping plovers nest on sandbars, but the damming of the mainstem of the Missouri in the mid-twentieth century reduced the natural capacity of the Missouri River to create sandbar habitat. In 2004, the United States Army Corps of Engineers (USACE) implemented a habitat creation project on the Gavins Point Reach of the Missouri River (stretch of river immediately downriver from the Gavins Point Dam) in an effort to promote recovery of piping plovers and the endangered least tern (Sternula antillarum). The USACE built 3 sandbars in 2004 – 2005 and built another sandbar on Lewis and Clark Lake in 2007. We studied the population dynamics of piping plovers in relationship to this newly engineered habitat. We monitored 623 nests on 16 sandbar complexes, to evaluate habitat selection, determine the factors affecting nesting success, and compare nesting success between natural and engineered habitat. From these 623 nests, we banded 357 adults and 685 chicks to investigate the factors affecting adult and juvenile survival. We used a logistic-exposure model to calculate nest survival. Adult and juvenile survival was calculated using Cormack-Jolly-Seber based models in Program MARK. We used the estimates from these studies to create a matrix population model for piping plovers nesting on the Gavins Point Reach. We used this model to predict the effects of engineered habitat on the population growth rate. Piping plovers selected for engineered sandbars and against natural and natural/modified habitats. Daily survival rate (DSR) on engineered habitats was significantly higher than on natural or natural modified habitats (log odds: 2.71, 95% CI: 1.20 – 6.08). Predator exclosures around nests did not affect DSR after controlling for the effects of date, nest age, and clutch size. Piping plover juvenile survival to recruitment was negatively related to nesting density on the relatively densely populated engineered sandbars. On the less dense natural sandbars, survival to recruitment was positively correlated with density. Adult survival did not appear to be related to density within our study. Movement within the study area was related also to density. Juveniles from densely populated engineered sandbars were more likely to leave engineered habitat to nest on natural sandbars than were juveniles hatched on less densely populated engineered sandbars. Movements among sandbars by breeding adults suggested that adults preferred engineered habitat. It is possible that juveniles moved to natural habitats because they were unable to compete with adults for the more desirable engineered habitats. Adults and juveniles emigrated from the study area at a higher rate after the 2006 breeding season, a year when water discharge was higher, nesting densities were higher, and reproductive success was lower (as a result of predation) than in the other years. Deterministic modeling suggested that engineered habitat significantly increased population growth. Decreased productivity over time and associated predicted negative population growth suggest that the amount of engineered habitat created was inadequate to sustain population growth, and/or that relatively high water discharge and nesting densities coupled with low reproductive rates and high emigration rates could lead to rapid declines in the plover population. Continued research is needed to determine the effects of these factors on long-term population growth. Our results suggest that habitat creation could be a viable short-term solution to population declines in shorebird populations limited by habitat loss, but high densities and increased predation associated with habitat creation indicate that other, long-term solutions may be required. / Ph. D.

Globally, riparian ecosystems are in decline due to anthropogenic modifications including damming, channelization and the conversion of the floodplain for human use. These changes can profoundly affect riparian species as many have adapted to the historical dynamism of these ecosystems. On the managed Missouri River, an imperiled shorebird, the piping plover (Charadrius melodus) uses riverine sandbars to breed. From 2004 to 2009, due to limited breeding habitat and low population numbers, the U.S. Army Corps of Engineers constructed 255 ha of sandbar habitat to benefit piping plovers and least terns (Sternula antillarum). During the breeding seasons of 2010 and 2011, historically high flows resulted in the creation of 1,887 ha of suitable sandbar habitat. Our study compared the demographic response and the condition of piping plovers to these anthropogenic and natural habitat creation events. From 2005–2014 we monitored 1,071 nests, and from those nests we uniquely banded 968 adults and 2,021 piping plover chicks. We obtained 405 egg (clutch) mass measurements, 1,285 mass measurements from 633 adults, and 7,093 mass measurements from 1,996 plover chicks resulting in 3,175 mass measurements from 654 broods of chicks. We also collected 3,347 invertebrate prey samples. We used a random effects logistic exposure model to estimate nest success, a random effects Cormack-Jolly-Seber model in RMARK to estimate pre-fledge chick survival and the Barker model in RMARK to estimate hatch-year (HY) and after hatch-year (AHY) survival and fidelity to our study area. We then used estimates from these analyses to calculate reproductive output, reproductive output necessary for a stationary population, and population growth (λ). For adult condition and egg (clutch) mass we used generalized linear mixed regression, and for pre-fledge chick growth rates we used a modified Richard's model to estimate the effects of habitat type (pre- vs. post-flood). We also tested for differences in invertebrate prey abundance between habitat types using negative binomial regression. Our results indicated that AHY survival varied throughout our study and was lowest during the flood (2010 and 2011). We found that nest success, pre-fledge chick survival, reproductive output, and HY survival and fidelity were consistently higher on the flood-created habitat than engineered habitat, leading to sustained population growth after the flooding, as compared to just one year of population growth prior to the flood. Unlike pre-flood engineered habitat, the demographic parameters we measured did not decrease as the post-flood habitat aged. These differences were related to increased sandbar habitat, low nesting densities, and decreased nest and chick predation on the post-flood habitat. Although we hypothesized that increased demographic rates would be reflected by increased piping plover condition following the flood, we found that our measured condition variables (adult mass, clutch mass, and pre-fledge chick growth rates) remained unchanged following the flood. We also found evidence that clutch mass, chick growth rates and invertebrate prey abundance decreased as the post-flood sandbar habitat aged. As the condition of individuals did not appear to contribute directly to the increased demographic rates following the flood, we suggest that the change in density-dependent predation pressure may explain the discrepancy. As many ecosystems have previously been altered, it's rare that ecologists have the opportunity to compare management practices with natural ecosystem processes. Results from this study suggest that management intervention may not be an equivalent substitute for natural ecosystem processes and provide insight on future management of riparian ecosystem. / Master of Science / Worldwide, riverine ecosystems are declining, which has had a negative effect on many species. On the managed Missouri River, a threatened shorebird, the piping plover (<i>Charadrius melodus</i>), likes to nest on unvegetated sandbars with saturated, or ‘muddy’ areas where they, and their chicks can feed on insects. Historically, flooding of the river created new sandbar habitat and scoured vegetation off of existing sandbars. However, the current river management regime, including dams and channelization, means that the river floods less, and over time sandbars become vegetated and eventually erode away. From 2004 to 2009 the U.S. Army Corps of Engineers built sandbars for piping plovers to use for nesting and raising their chicks. In 2011, the Missouri River flooded as a result of increased mountain snow and spring precipitation. Although devastating at the time, the flood created an abundance of new sandbar habitat for piping plovers to use, nearly ten times more habitat than was available before. To understand what effect the flood and the newly created sandbars had on piping plovers, we collected data on the Missouri River from 2005–2014. We monitored nests to figure out how many hatched, and used color bands on both adults and chicks to see how many survived throughout the season and over the years. We also weighed piping plover eggs, chicks, and adults and collected insect prey samples. Following the flood, more nests hatched, more chicks survived to fledging, and more chicks survived from one year to the next than during any of the years prior. This success led to the population of piping plovers nearly doubling each year. Because the flood created so much habitat, piping plovers were still able to successfully hatch nests and raise their chicks, even with the sandbars eroding and vegetating over time. Although we thought that the increase in rates such as survival and population growth, would be reflected by increased egg masses, adult masses, and chick masses, we found that they remained unchanged following the flood. We also found evidence that egg masses and chick masses were related to the amount of insect prey. Following the flood, less nests and chicks were eaten by predators such as, mink, crow, and great-horned owls, and we think this is a result of decreases in nesting densities which may have made nests and chicks harder to locate. These results indicate that the amount of habitat available to nesting piping plovers is an incredibly important factor in the population growth of this imperiled species.

Áreas como política, economia e marketing sofrem grandes influências no que diz respeito à difusão de informação. Por este motivo, diversos ramos da ciência tem estudado tais fenômenos a fim de simulá-los e compreendê-los por meio de modelos matemáticos e/ou estocásticos. Em virtude disto, este trabalho de doutorado tem como objetivo generalizar modelos de difusão de inovação já existentes na literatura. O primeiro modelo utiliza o mecanismo de social reinforcement para difusão de inovação e o qual foi construído para o grafo completo. Neste caso, consideramos uma população finita, fechada, totalmente misturada e subdividida em quatro classes de indivíduos denominados ignorantes, conscientes, adotadores e abandonadores da inovação. Assim, será apresentado uma Lei Fraca dos Grandes Números e um Teorema Central do Limite para a proporção final da população que nunca escutou sobre a inovação e aqueles que já conhecem sobre ela mas ainda não adotaram. Ademais, também será apresentado um resultado de convergência para o máximo de adotadores em um intervalo estocástico, assim como o instante de tempo em que o processo atinge esse estado. Para esse estudo, foram utilizados resultados da teoria de cadeias de Markov dependentes da densidade. Ademais, formulamos um modelo estocástico com estrutura de estágios para descrever o fenômeno da difusão de inovação em uma população estruturada. Mais precisamente, propomos uma cadeia de Markov a tempo contínuo definida na rede hipercúbica d-dimensional. Cada indivíduo da população deve estar em algum dos M+1 estados pertencentes ao conjunto {0;1;2; ::;M}. Nesse sentido, 0 representa um ignorante, i para i &isin; {1; :::;M - 1} um consciente no estágio i e M um adotador. Dessa forma, são estudados argumentos que permitem encontrar condições suficientes nas quais a inovação se espalha ou não com probabilidade positiva. / Areas such as politics, economics and marketing are heavily influential in terms of information diffusion. For this reason, several branches of science have studied such phenomena in order to simulate and understand them by mathematical and/or stochastic models. In this context, this phd project aims to generalize innovation diffusion models that there is in the literature. The first model uses the social reinforcement mechanism for diffusion of innovation and which was built for the complete graph. In this case, we consider a finite population, closed, totally mixed and subdivided into four classes of individuals called ignorants, aware, adopters and abandoner of innovation. We prove a Law of Large Numbers and a Central Limit Theorem for the proportion of the population who have never heard about the innovation and those who know about ir but they have not adopted it yet. In addition, we also obtain result for the convergence of the maximum of adopter in a stochastic interval, as well as the instant of time that the process reaches that state. For this study, we used results of the theory of density dependent Markov chains. Furthermore, we formulated a stochastic model with structure stages to describe the phenomenon of innovation diffusion in a structured population. More precisely, we proposed a continuous time Markov chain defined in a population represented by the d-dimensional integer lattice. Each individual of the population must be in some of the M +1 states belonging to the set {0;1;2; :::;M}. In this sense, 0 stands for ignorant, i for i &isin; {1; :::;M - 1} for aware in stage i and M for adopter. The arguments, that allow to obtain sufficient conditions under which the innovation either becomes extinct or survives with positive probability, are studied.