Dissertations / Theses on the topic 'Population dynamics'
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Koons, David Nelson Grand James Barry. "Transient population dynamics and population momentum in vertebrates." Auburn, Ala, 2005. http://repo.lib.auburn.edu/EtdRoot/2005/SPRING/Forestry_and_Wildlife_Sciences/Dissertation/KOONS_DAVID_55.pdf.
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Ruaro, Lorenzo. "Population dynamics of Ctenosaura bakeri." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/20747/.
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The Ctenosaura bakeri is an iguana species endemic to the island of Utila, a small island off the eastern coast of Honduras. It is currently one of the species of the genus Ctenosaura most threatened with extinction, having its conservation status labelled as "Critically Endangered" by the IUCN Red List. The goals of this paper are to give some insights on the intrinsic trend of the whole population and to analyse the influence of the greater threats to the survival of the species (such as sex dependent hunting and habitat destruction). We will use a transition matrix approach to investigate the intrinsic trend of the population and we will provide arguments for the estimation of the different parameters. For the influence of the threats we will take a deterministic approach using systems of ODEs and DDEs, investigating the stationary points and their stability and giving prediction through simulations for the evolution of the population. We will also introduce a model for the occurence of hybridization with another iguana species of the island. The achieved results are summarized and still open questions stated at the end.
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Agassiz, David J. L. "Population dynamics of invading insects." Thesis, Imperial College London, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.678691.
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Patra, Pintu. "Population dynamics of bacterial persistence." Phd thesis, Universität Potsdam, 2013. http://opus.kobv.de/ubp/volltexte/2014/6925/.
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The life of microorganisms is characterized by two main tasks, rapid growth under conditions permitting growth and survival under stressful conditions. The environments, in which microorganisms dwell, vary in space and time. The microorganisms innovate diverse strategies to readily adapt to the regularly fluctuating environments. Phenotypic heterogeneity is one such strategy, where an isogenic population splits into subpopulations that respond differently under identical environments. Bacterial persistence is a prime example of such phenotypic heterogeneity, whereby a population survives under an antibiotic attack, by keeping a fraction of population in a drug tolerant state, the persister state. Specifically, persister cells grow more slowly than normal cells under growth conditions, but survive longer under stress conditions such as the antibiotic administrations.
Bacterial persistence is identified experimentally by examining the population survival upon an antibiotic treatment and the population resuscitation in a growth medium. The underlying population dynamics is explained with a two state model for reversible phenotype switching in a cell within the population. We study this existing model with a new theoretical approach and present analytical expressions for the time scale observed in population growth and resuscitation, that can be easily used to extract underlying model parameters of bacterial persistence. In addition, we recapitulate previously known results on the evolution of such structured population under periodically fluctuating environment using our simple approximation method. Using our analysis, we determine model parameters for Staphylococcus aureus population under several antibiotics and interpret the outcome of cross-drug treatment.
Next, we consider the expansion of a population exhibiting phenotype switching in a spatially structured environment consisting of two growth permitting patches separated by an antibiotic patch. The dynamic interplay of growth, death and migration of cells in different patches leads to distinct regimes in population propagation speed as a function of migration rate. We map out the region in parameter space of phenotype switching and migration rate to observe the condition under which persistence is beneficial.
Furthermore, we present an extended model that allows mutation from the two phenotypic states to a resistant state. We find that the presence of persister cells may enhance the probability of resistant mutation in a population. Using this model, we explain the experimental results showing the emergence of antibiotic resistance in a Staphylococcus aureus population upon tobramycin treatment.
In summary, we identify several roles of bacterial persistence, such as help in spatial expansion, development of multidrug tolerance and emergence of antibiotic resistance. Our study provides a theoretical perspective on the dynamics of bacterial persistence in different environmental conditions. These results can be utilized to design further experiments, and to develop novel strategies to eradicate persistent infections.Das Leben von Mikroorganismen kann in zwei charakteristische Phasen unterteilt werde, schnelles Wachstum unter Wachstumsbedingungen und Überleben unter schwierigen Bedingungen. Die Bedingungen, in denen sich die Mikroorganismen aufhalten, verändern sich in Raum und Zeit. Um sich schnell an die ständig wechselnden Bedingungen anzupassen entwickeln die Mikroorganismen diverse Strategien. Phänotypische Heterogenität ist eine solche Strategie, bei der sich eine isogene Popolation in Untergruppen aufteilt, die unter identischen Bedingungen verschieden reagieren. Bakterielle Persistenz ist ein Paradebeispiel einer solchen phänotypischen Heterogenität. Hierbei überlebt eine Popolation die Behandlung mit einem Antibiotikum, indem sie einen Teil der Bevölkerung in einem, dem Antibiotikum gegenüber tolerant Zustand lässt, der sogenannte "persister Zustand". Persister-Zellen wachsen unter Wachstumsbedingungen langsamer als normale Zellen, jedoch überleben sie länger in Stress-Bedingungen, wie bei Antibiotikaapplikation. Bakterielle Persistenz wird experimentell erkannt indem man überprüft ob die Population eine Behandlung mit Antibiotika überlebt und sich in einem Wachstumsmedium reaktiviert. Die zugrunde liegende Popolationsdynamik kann mit einem Zwei-Zustands-Modell für reversibles Wechseln des Phänotyps einer Zelle in der Bevölkerung erklärt werden. Wir untersuchen das bestehende Modell mit einem neuen theoretischen Ansatz und präsentieren analytische Ausdrücke für die Zeitskalen die für das Bevölkerungswachstums und die Reaktivierung beobachtet werden. Diese können dann einfach benutzt werden um die Parameter des zugrunde liegenden bakteriellen Persistenz-Modells zu bestimmen. Darüber hinaus rekapitulieren wir bisher bekannten Ergebnisse über die Entwicklung solch strukturierter Bevölkerungen unter periodisch schwankenden Bedingungen mithilfe unseres einfachen Näherungsverfahrens. Mit unserer Analysemethode bestimmen wir Modellparameter für eine Staphylococcus aureus-Popolation unter dem Einfluss mehrerer Antibiotika und interpretieren die Ergebnisse der Behandlung mit zwei Antibiotika in Folge. Als nächstes betrachten wir die Ausbreitung einer Popolation mit Phänotypen-Wechsel in einer räumlich strukturierten Umgebung. Diese besteht aus zwei Bereichen, in denen Wachstum möglich ist und einem Bereich mit Antibiotikum der die beiden trennt. Das dynamische Zusammenspiel von Wachstum, Tod und Migration von Zellen in den verschiedenen Bereichen führt zu unterschiedlichen Regimen der Populationsausbreitungsgeschwindigkeit als Funktion der Migrationsrate. Wir bestimmen die Region im Parameterraum der Phänotyp Schalt-und Migrationsraten, in der die Bedingungen Persistenz begünstigen. Darüber hinaus präsentieren wir ein erweitertes Modell, das Mutation aus den beiden phänotypischen Zuständen zu einem resistenten Zustand erlaubt. Wir stellen fest, dass die Anwesenheit persistenter Zellen die Wahrscheinlichkeit von resistenten Mutationen in einer Population erhöht. Mit diesem Modell, erklären wir die experimentell beobachtete Entstehung von Antibiotika- Resistenz in einer Staphylococcus aureus Popolation infolge einer Tobramycin Behandlung. Wir finden also verschiedene Funktionen bakterieller Persistenz. Sie unterstützt die räumliche Ausbreitung der Bakterien, die Entwicklung von Toleranz gegenüber mehreren Medikamenten und Entwicklung von Resistenz gegenüber Antibiotika. Unsere Beschreibung liefert eine theoretische Betrachtungsweise der Dynamik bakterieller Persistenz bei verschiedenen Bedingungen. Die Resultate könnten als Grundlage neuer Experimente und der Entwicklung neuer Strategien zur Ausmerzung persistenter Infekte dienen.
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Guzmán, Alfredo. "Peru: population, dynamics and health." Universidad Peruana de Ciencias Aplicadas - UPC, 2007. http://hdl.handle.net/10757/272453.
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Milligan, Paul. "Population dynamics of African trypanosomiasis." Thesis, University of Salford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306017.
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Forrest, Michael Bruce. "Toxins and blowfly population dynamics." Thesis, University of Leicester, 1996. http://hdl.handle.net/2381/34346.
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This thesis studies the effects of toxins upon larvae of the blowfly Lucilia sericata. A field study of fly populations infesting carcasses showed aggregations in space and time of a number of fly species, although L, sericata was not common. The presence of cadmium or deltamethrin in the larval diet was shown to have deleterious effects upon the larvae. Development was slowed down and the resultant adults were smaller. When the diet contained cadmium, adults had a lower fecundity than those arising from larvae fed upon the control diet. These effects became more pronounced as larval population density was increased. Models were constructed that simulated the population dynamics of L. sericata under two conditions. In each population, the larval diet was limited to 20 g/day whilst in one the diet was contaminated with 50 mg Cd/kg diet. These models allowed the underlying dynamics and their driving forces to be identified. The control model predicted sustained population cycles with a period of 67 days, approximately twice the generation time calculated from cohort life-tables. The cadmium model predicted that these cycles would be dampened and the mass of individual pupae increased relative to those from the control simulation model. These theoretical results, which apparently contradict the predictions made by scope for growth theory, are consistent with results from a long-term population study and were due to the interaction of cadmium with the effects of population density.
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Siriwardena, Pathiranage Lochana Pabakara. "STOCHASTIC MODELS IN POPULATION DYNAMICS." OpenSIUC, 2014. https://opensiuc.lib.siu.edu/dissertations/908.
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This dissertation discusses the construction of some stochastic models for population dynamics with a variety of birth and death rate functions. A general model is constructed considering a fundamental growth rate function of the population while allowing random births and deaths in the population. Four stochastic discrete delay models and two non-delay models using the infinitesimal mean and variance given by birth and death rate functions have been produced and analyzed. In these constructions drift terms are in the form of logistic growth or logistic growth with delay. Logistic growth models are well known to biologists and economists. For each model, the existence and uniqueness of the global solution, non-negativeness of the solution is discussed, and for some models, boundedness of the path is also given. Persistence of the population and the boundary behavior have also been discussed through the hitting times. Here, a new method to analyze the hitting times for a specific class of stochastic delay models is presented. This work is related to and also extends the work of Edward Allen, Linda Allen and Bernt Oksendal in population dynamics.
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Choudhury, Md Abu Hasnat Zamil. "Population Dynamics of RNA viruses." Thesis, Queensland University of Technology, 2013. https://eprints.qut.edu.au/60866/1/Md._Choudhury_Thesis.pdf.
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Between 50 and 100 million people are infected with dengue viruses each year and more than 100,000 of these die. Dr Choudhury has demonstrated that populations of dengue viruses in individual patients are genetically and functionally very diverse and that this diversity changes significantly at the time of major outbreaks of disease. The results of his studies may inform strategies which will make dengue vaccines far more effective.
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Ward, Eric John. "Incorporating model selection and decision analysis into population dynamics modeling /." Thesis, Connect to this title online; UW restricted, 2006. http://hdl.handle.net/1773/5319.
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Klenzendorf, Sybille A. "Population dynamics of Virginia's hunted black bear (Ursus americanus) population." Diss., Connect to this title online, 2002. http://scholar.lib.vt.edu/theses/available/etd-02122002-160752/.
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Manokaran, N. "Population dynamics of tropical forest trees." Thesis, Available from the University of Aberdeen Library and Historic Collections Digital Resources, 1988. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?application=DIGITOOL-3&owner=resourcediscovery&custom_att_2=simple_viewer&pid=59678.
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Nickel, Anja Martina. "Population dynamics of Frankia in soil /." [S.l.] : [s.n.], 2000. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=13731.
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Bateman, Andrew Wade. "Population dynamics in meerkats, Suricata suricatta." Thesis, University of Cambridge, 2013. https://www.repository.cam.ac.uk/handle/1810/244662.
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Research on cooperatively breeding species has shown that their population dynamics can differ from those of conventional breeders. Populations of obligate cooperators are structured into social groups, the link between individual behaviour and population dynamics is mediated by group-level demography, and population dynamics can be strongly affected both by features of sociality per se and by resultant population structure. Notably, groups may be subject to inverse density dependence (Allee effects) that result from a dependence on conspecific helpers, but evidence for population-wide Allee effects is rare. To develop a mechanistic understanding of population dynamics in highly social species, we need to investigate how processes within groups, processes linking groups, and external drivers act and interact in space and time to produce observed patterns. Here, I consider these issues as they relate to meerkats, Suricata suricatta, obligate cooperative breeders that inhabit southern Africa. I use mathematical and statistical models, in conjunction with long-term data from a wild meerkat population, to explore population dynamics, group dynamics, group demography, Allee effects, and territory dynamics in this species. I start out by examining broad-scale patterns, and then examine some of the constituent processes. In Chapter Two, I assess the ability of phenomenological models, lacking explicit group structure, to describe population dynamics in meerkats, and I assess potential population-level Allee effects. I detect no Allee effect and conclude that explicit consideration of population structure will be key to understanding the mechanisms behind population dynamics in cooperatively breeding species. In Chapter Three, I focus on annual group-level dynamics. Using phenomenological population models, modified to incorporate environmental conditions and potential Allee effects, I first investigate overall patterns of group dynamics and find support for only conventional density dependence that increases after years of low rainfall. To explain the patterns, I examine demographic rates and assess their contributions to overall group dynamics. While per-capita meerkat mortality is subject to an Allee effect, it contributes relatively little to observed variation, and other (conventionally density dependent) demographic rates – especially emigration – govern group dynamics. In Chapter Four, I investigate group dynamics in more detail. I model demographic rates in different sex, age, and dominance classes on short timescales. Using these to build predictive and individual-based simulation models of group dynamics, I examine the demographic mechanisms responsible for declines in group size after dry years. Results reveal the delayed effect of environmental conditions, partially mediated by group structure. In Chapter Five, I explore meerkat territorial patterns. Using mechanistic home-range models, I examine group interactions, habitat selection, territory formation, and territory movement. I use meerkat data to test proposed improvements to these models, and I use the model results to start building a picture of spatial processes in meerkat population dynamics, laying the groundwork for future research. This thesis highlights the role of environment and social structure in characterizing population dynamics. I discuss the implications of my findings for the population dynamics of cooperative breeders and for population dynamics generally, noting the importance of sub-populations in drawing conclusions about socially complex systems.
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Wei, Hsin-Hua. "Population Dynamics of Central Place Foragers." Thesis, University of Ottawa (Canada), 2010. http://hdl.handle.net/10393/28661.
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In this thesis we use analysis and simulation to study the qualititative behavior of several mathematical models for consumer-resource interaction. While such models have been studied for several decades now, our approach to include a random-walk model for the foraging behavior of the consumer is novel. With this approach we are able to link individual movement rules to population-level patterns.
For every species, acquisition and assimilation of food is an important process that enables survival, growth, and reproduction. Different species have developed different strategies for this process. Individuals who depart from one location on foraging trips and return to the same location are called central place foragers. Examples include cave crickets, beavers, and colonial seabirds. Resources around central place foragers' habitats are the major source of food. In this thesis, we consider discrete-time consumer-resource models and examine the following questions: (1) Under what conditions can consumers and resources stabily coexist? (2) How does the distribution of consumers affect resource abundance spatially? (3) How does the abundance and distribution of resource affect the foraging behavior of consumers?
First, we study a non-spatial model by considering that consumers disperse evenly over the resource patch. We apply several different functions for resource growth (compensatory and overcompensatory), and we consider various foraging behaviors (random versus clumped). We analyze the stability behavior of steady states in each of these models and we summarize our results in bifurcation diagrams. Next, we study the spatial model by assuming that consumers tend to concentrate closer to the central place. We apply the Laplace distribution to describe consumers' dispersal. We focus on the compensatory dynamics for resource growth and consider both random search and clumped search for resources. In this section, we use a combination of analytical and numerical techniques to study the qualitative behavior of the system. Finally, we apply a random-walk framework to derive the distribution of consumers based on individual movement rules and the abundance of resources. That is, we have different consumer distributions depending on local resource abundance at different times. The analysis of this complex model is exclusively based on numerical simulation. For all consumer-resource models, we present one-parameter bifurcation diagrams for each parameter in the model to illustrate the qualitative behavior. We investigate the effects of parameters on the stability of steady states and limit cycles.
For models with fixed consumer distributions, we find that the clumped search for resources stabilizes the system. The resource and consumer populations can reach stable steady states if consumers aggregate intensively at the place with more abundant resources. We find that a resource-dependent distribution of consumers also stabilize the system as consumers settle at a more resource-rich location to forage. All parameters in our models have impacts on the population dynamics of resource and consumer. For the compensatory resource growth, we find that consumers can invade the system and both populations can reach a stable steady state for a higher value of resource growth rate or a lower value of consumer conversion efficiency. Other parameters can have different impacts on stability depending on different model structures.
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Bonsall, Michael B. "Temporal and spatial insect population dynamics." Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.406839.
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Yeates, G. "Microbial population dynamics of the rhizosphere." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334939.
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Greenberg, Daniel. "Population dynamics of a declining amphibian." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=121577.
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With concern rising over the global decline of amphibian populations, identifying the onset of declines and the factors driving them is paramount. Amphibian populations are naturally characterized by large fluctuations in abundance, which makes separating natural fluctuations from true declines very difficult. By improving our understanding of the natural dynamics of amphibian populations, we can separate normal fluctuations from altered dynamics associated with decline. I apply this principle to an endangered population of Fowler's toads (Anaxyrus [=Bufo] fowleri) in Long Point, Ontario which appears to have gradually declined in abundance. With over two decades of mark-recapture data, I investigate what factors, intrinsic and extrinsic, drive growth in this population. Over this same period, there have been considerable changes to the toads' habitat, as an invasive strain of the common reed, Phragmites australis, has overtaken the wetlands used by toads for breeding. I show that the expansion of this reed has altered the dynamics of the toad population, causing progressive decline due to breeding habitat loss. Prior to 2002, the population of toads was driven by density-dependent growth and overwinter mortality. After 2002, at which point the reeds had eliminated most of the open water habitat, the population of toads responded only to extrinsic factors, particularly the water level of Lake Erie. I then ask whether the expansion of invasive Phragmites has changed not just the quantity of larval habitat, but also its quality, through the release of secondary compounds. I hypothesize that Fowler's toad larvae, as obligate gill breathers, will experience reduced survival, growth, and development in the presence of gill damaging secondary compounds from the invasive Phragmites and native Typha. In contrast, the sympatric Northern leopard frog (Lithobates [=Rana] pipiens) should exhibit similar performance as tadpoles in the presence of secondary compounds, as a facultative gill breather. Contrary to my expectations, I found that Fowler's toad tadpoles had a similar performance across treatments, despite the presence of secondary compounds. Furthermore, the native plant, Typha, but not the invasive Phragmites, appeared to impede growth in Leopard frog tadpoles. Based on these results, I conclude that the expansion of invasive Phragmites has the potential to impact species through changes to available habitat, but not by reducing larval habitat quality. By incorporating population dynamics into the study of amphibian declines we can improve our ability to infer causal links between population declines and the mechanisms that drive them.Alors que le déclin de la population amphibienne mondiale est de plus en plus préoccupant, il est primordial d'identifier les facteurs qui en sont la cause. Puisqu'une certaine fluctuation de population est normale, il est difficile de déterminer si une variation donnée est naturelle ou symptomatique d'un déclin réel. Une meilleure compréhension des fluctuations de la population amphibienne pourrait servir à distinguer entre les facteurs naturels de variation et une altération de dynamique associée à un déclin. Voilà l'idée directrice de cette étude d'une espèce à risque, le crapaud de Fowler (Anaxyrus [=Bufo] fowleri) de Long Point en Ontario, dont la population semble diminuer graduellement. À partir de l'information recueillie sur deux décennies de marquage-recapture, j'ai examiné les facteurs, internes et externes, de variation de leur population. Au cours de la période, leur habitat de reproduction a été considérablement détérioré par la présence d'une espèce envahissante de roseau commun, le Phragmites australis. J'explore le lien entre cette altération de dynamique et le déclin progressif des crapauds de Fowler. Avant 2002, leur population était régulée par des facteurs internes comme la croissance en fonction de la densité et la mortalité hivernale. Depuis, les roseaux communs ont éliminé la plupart de l'habitat en eau libre des crapauds de Fowler, dont la population ne répond plus qu'à des facteurs externes d'influence, en particulier le niveau de l'eau du lac Érié. Ensuite, je cherche à voir si la présence de l'espèce envahissante a influencé, non seulement la quantité d'habitat de reproduction du crapaud de Fowler, mais aussi la qualité de ce qui reste, par la production de composés secondaires. L'hypothèse explorée est que les composés secondaires nuisibles aux branchies, produits autant par l'espèce envahissante Phragmites que par l'espèce native Typha, réduisent les chances de survie, la croissance et le développement des crapauds de Fowler, qui respirent nécessairement par leurs branchies. En toute logique, l'espèce sympatrique grenouille léopard du Nord (Lithobates [=Rana] pipiens), qui respire par ses branchies de façon facultative, devrait être affectée de façon similaire. Cependant, ce n'est pas le cas ; j'ai remarqué que les têtards de crapauds de Fowler n'étaient pas affectés par la présence de composés secondaires. De plus, c'est l'espèce native Typha qui semblait nuire à la croissance des crapauds de Fowler, plutôt que l'espèce envahissante Phragmites. J'en conclus que l'expansion de cette dernière peut influencer plusieurs espèces par une réduction de l'habitat disponible, mais pas par la détérioration de la qualité de son habitat larvaire. En étudiant le déclin amphibien à partir de la dynamique de population, nous pouvons améliorer notre capacité à établir des liens entre le déclin de populations d'espèces et les mécanismes qui y contribuent.
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O'Hara, Robert Brian. "Population dynamics of cereal powdery mildews." Thesis, University of East Anglia, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320775.
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COLOMBO, EDUARDO HENRIQUE FILIZZOLA. "SPATIAL PATTERN FORMATION IN POPULATION DYNAMICS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2014. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=24777@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
FUNDAÇÃO DE APOIO À PESQUISA DO ESTADO DO RIO DE JANEIRO
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO
BOLSA NOTA 10
Motivado pela riqueza de fenômenos produzidos pelos seres vivos, este trabalho busca estudar a formação de padrões espaciais de populações biológicas. De um ponto de vista mesoscópico, definimos os processos básicos que podem ocorrer na dinâmica, construindo uma equação diferencial parcial para a evolução da distribuição da população. Essa equação incorpora duas generalizações de um modelo pre-existente para a dinâmica de um espécie, que leva em conta interações de longo alcance (não locais). A primeira generalização consiste em considerar que a difusão é não linear, isto é, é afetada pela densidade local de tal modo que o coeficiente de difusão segue uma lei de potência. Por outro lado, visto a alta complexidade envolvida na natureza dos parâmetros do modelo, introduzimos como segunda generalização parâmetros que flutuam no tempo. Idealizamos estas flutuações como um ruído descorrelacionado temporalmente e que obedece uma distribuição gaussiana (ruído branco). Para estudar o modelo resultante, utilizamos uma abordagem analítica e numérica. As ferramentas analíticas se baseiam na linearização da equação de evolução e portanto são aproximadas. Todavia, complementadas com resultados numéricos, conseguimos extrair conclusões relevantes. A não localidade das interações induz a formação de padrões. O alcance dessas interações é o que determina o modo dominante presente nos padrões. Assim, para valores dos parâmetros acima de um limiar crítico, emergem padrões. Analiticamente, mostramos que, mesmo abaixo desse limiar, as flutuações nos parâmetros podem induzir a aparição de ordem espacial. Os efeitos da difusão não-linear são captados superficialmente pela análise linear. Numericamente, mostraremos que sua presença modifica a forma dos padrões. Observamos, especialmente, a existência de uma transição quando alternamos entre o caso em que a difusão é facilitada por altas densidades e o caso oposto. Para o primeiro caso, verificamos que os padrões se tornam fragmentados, ou seja, a população é agora composta de sub-grupos desconectados.
Motivated by the richness of phenomena produced by living beings, this work aims to study the formation of spatial patterns in biological populations. From the mesoscopic point of view, we define the basic processes that may occur in the dynamics, building a partial differential equation for the evolution of the population distribution. This equation incorporates two generalizations of a pre-existing model for the dynamics of one species, which takes into account long-range (nonlocal) interactions. The first generalization is to consider that diffusion is nonlinear, i.e., it is affected by the local density such that the diffusion coeficient follows a power law. On the other hand, because of the high complexity involved in the nature of model parameters, we introduced as a second generalization time-fluctuating parameters. We idealize these fluctuations as Gaussian temporally uncorrelated (white) noises. To study the resulting model, we use an analytical and numerical approach. Analytical tools are based on the linearization of the evolution equation and are therefore approximate. However, as evidenced by numerical results, we draw important conclusions. The nonlocal feature of the interaction is the main mechanism which induces pattern formation. We show that the extent of these interactions is what characterizes the dominant mode. Thus, for parameter values above a critical threshold patterns emerge. Analytically, we also show that even below this threshold, fluctuations in the parameters can induce the appearance of spatial order. The effects of nonlinear diffusion are only superficially captured by the linear analysis. Numerically, we show that their presence modifies the patterns shape. We mainly observed the existence of a qualitative difference between the cases when diffusion is facilitated or not by high densities. In the first case, we note that the patterns become fragmented, that is, population becomes composed of disconnected clusters.
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Jatuviriyapornchai, Watthanan. "Population dynamics and stochastic particle systems." Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/99427/.
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Condensation is a special class of phase transition which has been observed throughout the natural and social sciences. The understanding of dynamics towards condensation on a mathematically rigorous level is currently a major research topic. Starting the system from homogeneous initial conditions, the time evolution of the condensed phase often exhibits an interesting coarsening phenomenon of mass transport between cluster sites. In this thesis, we study the coarsening dynamics in several condensing stochastic particle systems. First, we consider the single site dynamics in general stochastic particle systems of misanthrope type with bounded rates on a complete graph. In the limit of diverging system size, we establish convergence to a Markovian non-linear birth death chain, described by a mean-field equation also known from exchange-driven growth processes. Conservation of mass in the particle system leads to conservation of the first moment for the limiting dynamics, and to non-uniqueness of stationary measures. The proof is based on a coupling to branching processes via the graphical construction and establishing uniqueness of the solution for the limit dynamics. As particularly interesting examples we discuss the dynamics of two models that exhibit a condensation transition and their connection to exchange-driven growth processes. The first model is the zero-range process with bounded jump rates. It is well known that zero-range processes with decreasing jump rates exhibit a condensation transition under certain conditions. The mean-field limit of the single site dynamics leads to a non-linear birth death chain describing the coarsening behaviour. We introduce a size-biased version of the single site process, which provides an effective tool to analyse the dynamics of the condensed phase without finite size effects. The second model is the inclusion process, which has unbounded jump rates and also exhibits the condensation phenomenon. However, in this case, the mean-field equation is derived differently, and the single site process is in the form of a standard birth death chain. In addition to the site and size-biased processes, we derive some exact results on the system through duality. We compute the time dependent covariance using the self-duality of inclusion processes and a two-particle dual process. Our results are based on exact computations and are corroborated by detailed simulation data, which contribute to a rigorous understanding of the approach to stationarity in the thermodynamic limit of diverging system size and particle number.
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Fasiolo, Matteo. "Statistical methods for complex population dynamics." Thesis, University of Bath, 2016. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.687376.
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Dai, Lei Ph D. Massachusetts Institute of Technology. "Spatio-temporal dynamics before population collapse." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/95869.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references.
Theory predicts that the approach of catastrophic thresholds in natural systems may result in an increasingly slow recovery from small perturbations, a phenomenon called critical slowing down. In this thesis, we used replicate laboratory populations of the budding yeast Saccharomyces cerevisiae for direct observation of critical slowing down in spatio-temporal dynamics before population collapse. In the first project, we mapped the bifurcation diagram experimentally and found that the populations became more vulnerable to disturbance closer to the tipping point. Fluctuations of population density increased in size and timescale near the tipping point, in agreement with the theory. In the second project, we used spatially extended yeast populations to evaluate early warning signals based on spatio-temporal fluctuations. We found that indicators based on fluctuations increased before collapse of connected populations; however, the magnitude of increase was smaller than that observed in isolated populations, as local variation is reduced by dispersal. Furthermore, we propose a generic indicator based on deterministic spatial patterns, recovery length. In our experiments, recovery length increased substantially before population collapse, suggesting that the spatial scale of recovery can provide a warning signal before tipping points in spatially extended systems. In the third project, we characterized how different environmental drivers influence the dynamics of yeast populations. We compared the performance of early warning signals across multiple deteriorating environments. We found that the varying performance is determined by how a system responds to changes in a specific driver, which can be captured by a relation between stability and resilience. Furthermore, we demonstrated that the positive correlation between stability and resilience, as the essential assumption of indicators based on critical slowing down, can break down when multiple environmental drivers are changed simultaneously.
by Lei Dai.
Ph. D.
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Brett, Tobias Stefan. "Stochastic population dynamics with delay reactions." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/stochastic-population-dynamics-with-delay-reactions(61982a13-b969-4d8d-904b-21c289c813f2).html.
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All real-world populations are composed of a finite number of individuals. Due to the intrinsically random nature of interactions between individuals, the dynamics of finite-sized populations are stochastic processes. Additionally, for many types of interaction not all effects occur instantaneously. Instead there are delays before effects are felt. The centrepiece of this thesis is a method of analytically studying stochastic population dynamics with delay reactions. Dynamics with delay reactions are non-Markovian, meaning many of the widely used techniques to study stochastic processes break down. It is not always possible to formulate the master equation, which is a common starting point for analysis of stochastic effects in population dynamics. We follow an alternative method, and derive an exact functional integral approach which is capable of capturing the effects of both stochasticity and delay in the same modelling framework. Our work builds on previous techniques developed in statistical physics, in particular the Martin-Siggia-Rose-Janssen-de Dominicis functional integral. The functional integral approach does not rely on an particular constraints on the population dynamics, for example the choice of delay distribution. Functional integrals can not in general be solved exactly. We show how the functional integral can be used to derive the deterministic, chemical Langevin, and linear-noise approximations for stochastic dynamics with delay. In the later chapters we extend Gillespie’s approximate method of studying stochastic dynamics with delay reactions, which can be used to derive the chemical Langevin equation, by-pass the functional integral. We also derive an extension to the functional integral approach so that it also covers systems with interruptible delay reactions. To demonstrate the applicability of our results we consider various models of population dynamics, arising from ecology, epidemiology, developmental biology, and chemistry. Our analytical calculations are found to provide excellent agreement with exact numerical simulations.
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Constable, George William Albert. "Fast timescales in stochastic population dynamics." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/fast-timescales-in-stochastic-population-dynamics(2e9cace8-e615-44ec-818e-26b96aaa6459).html.
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In this thesis, I present two methods of fast variable elimination in stochastic systems. Their application to models of population dynamics from ecology, epidemiology and population genetics, is explored. In each application, care is taken to develop the models at the microscale, in terms of interactions between individuals. Such an approach leads to well-defined stochastic systems for finite population sizes. These systems are then approximated at the mesoscale, and expressed as stochastic differential equations. It is in this setting the elimination techniques are developed. In each model a deterministically stable state is assumed to exist, about which the system is linearised. The eigenvalues of the system's Jacobian are used to identify the existence of a separation of timescales. The fast and slow directions are then given locally by the associated eigenvectors. These are used as approximations for the fast and slow directions in the full non-linear system. The general aim is then to remove these fast degrees of freedom and thus arrive at an approximate, reduced-variable description of the dynamics on a slow subspace of the full system. In the first of the methods introduced, the conditioning method, the noise of the system is constrained so that it cannot leave the slow subspace. The technique is applied to an ecological model and a susceptible-exposed-infectious-recovered epidemiological model, in both instances providing a reduced system which preserves the behaviour of the full model to high precision. The second method is referred to as the projection matrix method. It isolates the components of the noise on the slow subspace to provide its reduced description. The method is applied to a generalised Moran model of population genetics on islands, between which there is migration. The model is successfully reduced from a system in as many variables as there are islands, to an effective description in a single variable. The same methodology is later applied to the Lotka-Volterra competition model, which is found under certain conditions to behave as a Moran model. In both cases the agreement between the reduced system and stochastic simulations of the full model is excellent. It is stressed that the ideas behind both the conditioning and projection matrix methods are simple, their application systematic, and the results in very good agreement with simulations for a range of parameter values. When the methods are compared however, the projection matrix method is found in general to provide better results.
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Sundell, Janne. "Vole population dynamics : experiments on predation." Helsinki : University of Helsinki, 2002. http://ethesis.helsinki.fi/julkaisut/mat/ekolo/vk/sundell/.
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Klaoudatos, D. "Reproductive ecology, population genetics and population dynamics of selected Decapod crustaceans." Thesis, Swansea University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637807.
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The reproductive ecology of three species of Decapod crabs, the shore crab (Carcinus maenas), the velvet crab (Necora puber) and the edible crab (Cancer pagurus), were studied in Swansea Bay and South Gower. Spawning occurs over winter and spring (shore crab), winter (edible crab), and summer (velvet crab). Berried females occur in spring and summer (shore crab), winter spring and summer (edible crab), summer and autumn (velvet crab). Eggs hatch in spring and summer (shore crab, edible crab), summer and winter (velvet crab). Copulation occurs in summer and autumn (shore crab), summer, autumn and winter (edible crab, velvet crab). Shore crabs from Swansea Queen’s Dock have a different reproductive cycle compared to the shore crabs from Tawe Barrage Impoundment and Mumbles Pier. More than one spawning periods or an extended spawning period was indicated for the shore crabs in the Docks. The genetic makeup of the shore crab populations present in Swansea Queen’s Dock and Mumbles Pier was compared using SSCP and cloning analysis of the 16S rRNA. Four different haplotypes were identified all of which were present in the Docks and one in the Pier, with low level of genetic divergence, and close relationship of the identified haplotypes with published shore crab haplotypes. AMOVA showed no significant difference between the study populations and published shore crab haplotypes. However, all identified haplotypes were different from published shore crab haplotypes, indicating a degree of reproductive isolation of the Swansea shore crab populations. Analysis of the permit return data for 1980-2002 of the edible and velvet crab fishery for the South Wales Sea Fisheries Committee District indicated that a combination of factors including overfishing, environmental conditions, and the “Sea Empress” oil spill in 1996 have contributed to a decline in landings that continues to date with limited signs of recovery.
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Hustin, Lucie. "Quantifying Haematopoietic Cell Dynamics." Electronic Thesis or Diss., Université Paris sciences et lettres, 2022. http://www.theses.fr/2022UPSLS065.
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L'hématopoïèse génère quotidiennement des milliards de cellules du sang. Au fil des ans, les chercheurs se sont concentrés sur l'étude de ce système et de sa structure dynamique en caractérisant la fonction des cellules souches et progéniteurs hématopoïétiques (CSPH), leur niche ainsi que leurs différentes lignées de différenciation. Alors que la dynamique du renouvèlement des cellules matures et de leurs CSPH a déjà été largement étudiée, notre compréhension de la cinétique globale de la production de cellules matures du sang à partir des CSPH reste approximative. Les mesures quantitatives font particulièrement défaut.Cette paucité d’études quantitatives de l'ensemble du système hématopoïétique peut s'expliquer par le manque d'outils expérimentaux, tels que les études de « traçage de lignée » et de « rétention de marqueurs », ainsi que par la difficulté d'établir des collaborations interdisciplinaires entre laboratoires, tels que les laboratoires d'hématologie, d'immunologie et de théorie dans ce contexte. Par conséquent, la plupart des études scientifiques se sont souvent concentrées sur le "haut" ou le "bas" de l'arbre hématopoïétiques, ou sur des modèles n’incluant pas ou peu de données expérimentales. Globalement, compte tenu de la complexité du système, des connaissances théoriques requises et de la rareté des protocoles expérimentaux adéquats, entreprendre de telles études quantitatives reste encore un défi.L'objectif de ce doctorat est donc de se concentrer sur les questions quantitatives concernant la cinétique de l'arbre hématopoïétique en combinant expériences et théorie. Tout d'abord, nous ferons une revue quantitative du système hématopoïétique et utiliserons ces résultats de travaux déjà publiés pour dériver des nombres sur le cinétique hématopoïétique. Ce travail servira à 1) faciliter notre compréhension de ce système dynamique et 2) fournir une base de données pour de futurs modèles mathématiques. Ensuite, nous utiliserons les outils actuellement disponibles, tels que les traceurs de génération cellulaire, pour étudier le lien entre la division cellulaire et les états de différenciation précoces des HSPC. Enfin, nous développerons un nouvel outil expérimental pour quantifier la division cellulaire, l'une des principales variables manquantes pour compléter notre compréhension quantitative de la dynamique de l'hématopoïèse, et l'utiliser pour étudier le nombre de divisions moyen réalisé par une population cellulaire au fil du temps et des processus de différentiations. En conclusion, en fournissant plusieurs quantifications de la cinétique des cellules hématopoïétiques, cette thèse vise à ouvrir la voie vers une compréhension plus globale et dynamique du paysage de différentiation cellulaire dans l'hématopoïèseHaematopoiesis generates billions of mature blood cells daily. Over the years researchers focussed on studying this dynamic system and its underlying structure by characterising haematopoietic stem and progenitor cell (HSPC) function, its niche as well as its various differentiation lineages. While dynamics of mature cell production and HSPC turnover is extensively studied, less is known about the overall kinetic of cell production from HSPC to mature cells in health and diseases, in particular quantitative information are lacking.This sparsity in quantitative studies of the complete haematopoietic system can be explained by a lack of experimental tools as well as the challenge of establishing collaborations between labs with different expertise, such as haematology, immunology and theoretical labs in this context. Most studies often focussed either on the “top” or the “bottom” of the tree, or on models independent of experimental data. Overall, with the complexity of the system, the required theoretical knowledge and the paucity of experimental setups, undertaking such quantitative studies still remains challenging.The aim of this PhD is therefore to focus on quantitative questions about the haematopoietic tree kinetics combining both experimental and theoretical work. First of all, we will quantitatively review the hematopoietic system and derive quantities linked to haematopoiesis dynamics using published data. This work will 1) ease our understanding of this dynamic system and 2) provide a database of numbers to be used in future mathematical models. Second of all, we will use the current tools available such as cell tracer dyes, to describe the early differentiation fates of HSPCs and its link to cell division. Finally, we aim to develop a new experimental tool to quantify cell division, one of the major variables that is lacking to complete our quantitative understanding of haematopoiesis dynamics, and use it to study the average division of a cell population over time and fate decisions. In providing several quantifications of hematopoietic cell kinetics, this thesis aims to pave the way toward a more global and dynamical understanding of the cell fate landscape in hematopoiesis
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黃道全 and Richard Huang. "Spatial variation in Cellana grata populations: the interplay of population dynamics and foodavailability." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B31243125.
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Hindle, Bethan J. "Unravelling the effects of environmental variation on the population dynamics of structured populations." Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/19466/.
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Complex environmental effects, combined with little temporal replication in most data sets, make investigating the ecological consequences of rapid climate change difficult with current tools. Structured population models are widely used to explore population responses to environmental variation. I develop and apply new statistical methods to parameterise such models. First I describe a structural equation model (SEM) approach for capturing temporal covariation among demographic rates via latent variable(s). When rates are positively correlated the latent variable(s) act as axes of ‘environmental quality’. This provides a simpler target for identifying the drivers of variation, than treating each process independently. Where drivers cannot be identified perturbing the latent variable(s) may represent the best alternative for exploring population-level responses to environmental change. Quantifying the effects of underlying drivers allows population viability under different management strategies to be predicted. Such studies frequently assume a stationary environment, despite rapid climate change. Where climatic drivers are included, single temporal windows of influence are typically chosen a priori. I show forecasted climate change alters predicted population viability under different management regimes in a rare fire-adapted herb. I illustrate that the effect of a single climatic variable may differ over time, suggesting a priori selection of single temporal windows can decrease predictive performance. I use the SEM approach to show that most (co)variation in survival and fecundity across different age-sex classes in a Soay sheep population is driven by a single environmental axis. I show climatic conditions during the energetically expensive autumn rut are nearly as important for overwinter mortality as the winter periods focused on in previous studies. I explore how density dependence, a temporal trend, population structure, and environmental variation interact to drive dynamics in this population. Throughout this thesis I apply novel methods that increase our ability to accurately forecast population dynamics under environmental change.
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Bishop, Jonathan R. B. "Embedding population dynamics in mark-recapture models." Thesis, St Andrews, 2009. http://hdl.handle.net/10023/718.
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Gross, Thilo. "Population dynamics general results from local analysis /." [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972885455.
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Rodríguez, Amor Daniel. "Population and evolutionary dynamics in spatial systems." Doctoral thesis, Universitat de Girona, 2013. http://hdl.handle.net/10803/128501.
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Physical and mathematical models are extremely useful to understand key processes in population and evolutionary dynamics. Such models allow the study of many diverse features in spatial systems such as front propagation, the evolution of the population number density, interactions between species (or individuals), the evolution of strategies, etc. This thesis is devoted to several physical models describing spatial systems. The first model focuses on the effects of the population structure in two-dimensional invasive fronts. An expression for the front speed is derived from the equations for structured populations. The second model is devoted to the study of Vesicular Stomatitis Virus infections. In this case, reaction-diffusion equations are used to describe the interactions between uninfected cells, infected cells and virus populations. In the last model, the Prisoner's Dilemma game is used to study the evolution of cooperation and defection strategiesEls models físics i matemàtics són de gran utilitat a l'hora d'entendre processos clau en la dinàmica poblacional i evolutiva. Aquests models permeten l'estudi de característiques molt diverses dels sistemes espacials, com són la propagació de fronts, l'evolució de la densitat de població, les interaccions entre espècies (o individus), l'evolució d'estratègies, etc. Aquesta tesi presenta diversos models físics que descriuen sistemes espacials. El primer model estudia els efectes de l'estructura de la població en fronts invasius bidimensionals. Una expressió per la velocitat del front és derivada de les equacions per a poblacions estructurades. El segon model es consagra a l’estudi d’infeccions del Vesicular Stomatitis Virus. En aquest cas, s’utilitzen equacions de reacció-difusió per descriure les interaccions entre les poblacions de cèl·lules no infectades, cèl·lules infectades i virus. A l’últim model, el joc del Dilema del Presoner s'utilitza per estudiar l'evolució d'estratègies de cooperació i deserció
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Arugaslan, Cincin Duygu. "Differential Equations With Discontinuities And Population Dynamics." Phd thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/3/12610574/index.pdf.
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In this thesis, both theoretical and application oriented results are obtained for differential equations with discontinuities of different types: impulsive differential equations, differential equations with piecewise constant argument of generalized type and differential equations with discontinuous right-hand sides. Several qualitative problems such as stability, Hopf bifurcation, center manifold reduction, permanence and
persistence are addressed for these equations and also for Lotka-Volterra predator-prey models with variable time of impulses, ratio-dependent predator-prey systems and logistic equation with piecewise constant argument of generalized type.
For the first time, by means of Lyapunov functions coupled with the Razumikhin method, sufficient conditions are established for stability of the trivial solution of differential
equations with piecewise constant argument of generalized type. Appropriate examples are worked out to illustrate the applicability of the method. Moreover, stability analysis is performed for the logistic equation, which is one of the most
widely used population dynamics models.
The behaviour of solutions for a 2-dimensional system of differential equations with discontinuous right-hand side, also called a Filippov system, is studied. Discontinuity sets intersect at a vertex, and are of the quasilinear nature. Through the B−
equivalence of that system to an impulsive differential equation, Hopf bifurcation is investigated. Finally, the obtained results are extended to a 3-dimensional discontinuous system of Filippov type. After the existence of a center manifold is proved for the 3-dimensional system, a theorem on the bifurcation of periodic solutions is provided in the critical case. Illustrative examples and numerical simulations are presented to verify the theoretical results.
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Kjellander, Petter. "Density dependence in roe deer population dynamics /." Uppsala : Swedish Univ. of Agricultural Sciences (Sveriges lantbruksuniv.), 2000. http://epsilon.slu.se/avh/2000/91-576-5888-9.pdf.
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Naundorf, Björn. "Dynamics of Population Coding in the Cortex /." [S.l.] : [s.n.], 2005. http://www.gbv.de/dms/goettingen/502262788.pdf.
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Daukšte, Liene. "Mathematical Modelling of Cancer Cell Population Dynamics." Thesis, University of Canterbury. Mathematics and Statistics, 2012. http://hdl.handle.net/10092/9356.
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Mathematical models, that depict the dynamics of a cancer cell population growing out of the human body (in vitro) in unconstrained microenvironment conditions, are considered in this thesis. Cancer cells in vitro grow and divide much faster than cancer cells in the human body, therefore, the effects of various cancer treatments applied to them can be identified much faster. These cell populations, when not exposed to any cancer treatment, exhibit exponential growth that we refer to as the balanced exponential growth (BEG) state. This observation has led to several effective methods of estimating parameters that thereafter are not required to be determined experimentally. We present derivation of the age-structured model and its theoretical analysis of the existence of the solution. Furthermore, we have obtained the condition for BEG existence using the Perron- Frobenius theorem. Amathematical description of the cell-cycle control is shown for one-compartment and two-compartment populations, where a compartment refers to a cell population consisting of cells that exhibit similar kinetic properties. We have incorporated into our mathematical model the required growing/aging times in each phase of the cell cycle for the biological viability. Moreover, we have derived analytical formulae for vital parameters in cancer research, such as population doubling time, the average cell-cycle age, and the average removal age from all phases, which we argue is the average cell-cycle time of the population. An estimate of the average cell-cycle time is of a particular interest for biologists and clinicians, and for patient survival prognoses as it is considered that short cell-cycle times correlate with poor survival prognoses for patients. Applications of our mathematical model to experimental data have been shown. First, we have derived algebraic expressions to determine the population doubling time from single experimental observation as an alternative to empirically constructed growth curve. This result is applicable to various types of cancer cell lines. One option to extend this model would be to derive the cellcycle time from a single experimental measurement. Second, we have applied our mathematical model to interpret and derive dynamic-depicting parameters of five melanoma cell lines exposed to radiotherapy. The mathematical result suggests there are shortcomings in the experimental methods and provides an insight into the cancer cell population dynamics during post radiotherapy. Finally, a mathematical model depicting a theoretical cancer cell population that comprises two sub-populations with different kinetic properties is presented to describe the transition of a primary culture to a cell line cell population.
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Daukste, Liene. "Mathematical Modelling of Cancer Cell Population Dynamics." Thesis, University of Canterbury. Department of Mathematics and Statistics, 2012. http://hdl.handle.net/10092/10057.
Full textAbstract:
Mathematical models, that depict the dynamics of a cancer cell population growing out of the human body (in vitro) in unconstrained microenvironment conditions, are considered in this thesis. Cancer cells in vitro grow and divide much faster than cancer cells in the human body, therefore, the effects of various cancer treatments applied to them can be identified much faster. These cell populations, when not exposed to any cancer treatment, exhibit exponential growth that we refer to as the balanced exponential growth (BEG) state. This observation has led to several effective methods of estimating parameters that thereafter are not required to be determined experimentally.
We present derivation of the age-structured model and its theoretical analysis of the existence of the solution. Furthermore, we have obtained the condition for BEG existence using the Perron-Frobenius theorem. A mathematical description of the cell-cycle control is shown for one-compartment and two-compartment populations, where a compartment refers to a cell population consisting of cells that exhibit similar kinetic properties. We have incorporated into our mathematical model the required growing/aging times in each phase of the cell cycle for the biological viability. Moreover, we have derived analytical formulae for vital parameters in cancer research, such as population doubling time, the average cell-cycle age, and the average removal age from all phases, which we argue is the average cell-cycle time of the population. An estimate of the average cell-cycle time is of a particular interest for biologists and clinicians, and for patient survival prognoses as it is considered that short cell-cycle times correlate with poor survival prognoses for patients.
Applications of our mathematical model to experimental data have been shown. First, we have derived algebraic expressions to determine the population doubling time from single experimental observation as an alternative to empirically constructed growth curve. This result is applicable to various types of cancer cell lines. One option to extend this model would be to derive the cell cycle time from a single experimental measurement. Second, we have applied our mathematical model to interpret and derive dynamic-depicting parameters of five melanoma cell lines exposed to radiotherapy. The mathematical result suggests there are shortcomings in the experimental methods and provides an insight into the cancer cell population dynamics during post radiotherapy. Finally, a mathematical model depicting a theoretical cancer cell population that comprises two sub-populations with different kinetic properties is presented to describe the transition of a primary culture to a cell line cell population.
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Soja, Rachel Halina. "Dynamics of the Solar System Meteoroid Population." Thesis, University of Canterbury. Department of Physics and Astronomy, 2010. http://hdl.handle.net/10092/4305.
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The purpose of this study is to develop an understanding of the observability of small-scale dynamical Solar System features in meteor orbit radar data, particularly with reference to mean motion resonance effects. Particular focus is placed on the presence of `resonant swarms' in meteoroid streams: the resonant swarm at the 7:2 Jovian mean-motion resonance is used as an example, as it best satisfies radar observability criterion. Furthermore, evidence for this structure exists in visual meteor data. The radar dataset used for this study is that of the Canadian Meteor Orbit Radar (CMOR) as this dataset contains the largest number of meteoroid stream particles. The aim here is to determine whether the Taurid resonant swarm is observable in datasets produced by radars such as CMOR, or what improvements in individual orbital uncertainties are necessary for positive detection to be possible.
The observability of the Taurid swarm in radar data depends on the limitations of the radar data (in terms of the individual measurement uncertainties); and on the properties of the resonance itself. Both aspects are investigated in this thesis. A statistical study is first conducted to assess whether evidence for the swarm exists in a dataset containing CMOR Northern and Southern Taurids from the years 2002 to 2007. It is found that the level of variations present is consistent with that expected due to random fluctuations: there is no evidence for a statistically significant resonant feature at the location of the 7:2 Jovian resonance. Additionally, the observability of various sizes of resonant peak for different sizes of dataset and for different levels of measurement uncertainties is investigated by addition of a modelled resonant feature to the data, followed by replacement of individual meteors by Gaussian profiles to simulate the effect of orbital uncertainties. It is clear that the level of broadening resulting from the uncertainties of the CMOR data used will not allow the observation of a resonant peak of the expected size. Detection is expected to be more likely in a `swarm encounter year' (a year in which the geometry between the resonant swarm and Earth is favourable to detection). The velocity uncertainties of a meteor orbit radar (similar to CMOR) need to be improved by a factor of 5 to 10 (relative to the CMOR uncertainties) in order to detect a resonant swarm that is composed of ~30% to ~5% (respectively) of the total number of observed Taurids in a swarm encounter year. An improvement significantly greater than a factor of ~10 is unlikely to result in a significant improvement in the ability to detect the resonant swarm. It is expected that a factor of 10 improvement in radar measurement uncertainties is achievable with the current techniques of radar systems and signal processing.
These statistical tests require knowledge of the resonant width of the 7:2 Jovian resonance in semi-major axis, as this provides the size of the resonant feature of interest. Such resonant or libration widths can be determined analytically for orbits with low eccentricities. As Taurid orbits have high eccentricities (e~0.83), a hierarchical N-body integrator is used to examine the dynamics in the region of the 7:2 resonance, and determine a resonant width of (0.047±0.005) AU. To verify this method the standard analytic equations and a semi-analytic method are compared (at low eccentricities) with the numerical resonant width values: the agreement is within 10% for eccentricities below 0.4.
It is important to know what proportion of radar Taurids are expected to be resonant in a swarm year in order to evaluate the observability of the swarm in radar data. One important factor that may affect this is the mass distribution of particles in the swarm. This is investigated by ejecting particles in multiple directions from three model comets: the first with a mass and orbit in agreement with those of the current 2P/Encke; the second with 2P/Encke mass and an orbit matching that of the proposed proto-Encke object; and a third with the mass and orbit of proto-Encke. The resulting orbits are examined to determine what proportion will land within the 7:2 resonance, for a range of particle masses and densities. The instantaneous effect of radiation pressure on the orbits of ejected particles is also considered. However, it is difficult to determine accurate capture percentage values due to the uncertainty surrounding cometary ejection mechanisms. Nevertheless, it is found that capture of Taurids into the 7:2 resonance by all comets is possible. Using comparisons between the percentages of visual-sized and radar-sized particles captured, it is determined that in weak swarm years (in which only 20% of visual meteoroids detected are resonant) only 4% to 5% of observed visual Taurids are expected to be resonant. Such a swarm would be on the edge of observability. However, in stronger swarm years (such as 2005), the resonant proportion will exceed that required for detection with a reduction in CMOR measurement uncertainties of a factor of ten.
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Sarafoglou, Nikias. "A contribution to population dynamics in space." Doctoral thesis, Umeå universitet, Institutionen för nationalekonomi, 1987. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-99835.
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Population models are very often used and considered useful in the policy-making process and for planning purposes. In this research I have tried to illuminate the problem of analysing population evolution in space by using three models which cover a wide spectrum of complementary methodologies: a The Hotell.ing-Puu model b A multiregional demographic model c A synergetic model Hotelling's work and Puu's later generalization have produced theoretical continuous models treating population growth and dispersal in a combined logistic growth and diffusion equation. The multiregional model is a discrete model based on the Markovian assumption which simulates the population evolution disaggregated by age and region. It is further assumed that this population is governed by a given pattern of growth and interregional mobility. The synergetic model is also a discrete model based on the Markovian assumption incorporating a probabilistic framework with causal structure. The quantitative description of the population dynamics is treated in terms of trend parameters, which are correlated in turn with demo-economic factors.Diss. Umeå : Umeå universitet, 1988
Digitalisering@umu
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Lindh, Markus V. "Bacterioplankton population dynamics in a changing ocean." Doctoral thesis, Linnéuniversitetet, Institutionen för biologi och miljö (BOM), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-38712.
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Bacterioplankton is characterized by high diversity, short generation times and rapid turnover. Despite their small size, these numerous microorganisms are a fundamental piece of aquatic ecosystems by channeling carbon to higher trophic levels through dissolved organic matter utilization. Yet, several gaps remain in our knowledge and understanding of bacterioplankton populations regarding detailed temporal dynamics, and mechanisms determining biogeographical patterns and potential responses to climate change. The aim of this thesis was to examine responses in bacterioplankton community composition and function when challenged by natural and anthropogenically-induced change in environmental conditions. High temporal resolution analysis of bacterioplankton population dynamics in the Baltic Sea indicated detailed seasonal responses. It also showed a similar but wide spectrum of niche differentiation patterns within several major bacterial groups. Analysis of geographic distributions of marine bacterial populations revealed bimodal occupancy-frequency patterns in bacterial communities, indicating that the presence of many locally rare taxa along with a few locally abundant taxa were explained by stochastic variation in colonization and extinction rates. Experimental manipulations with natural marine bacterioplankton assemblages revealed both specialist and generalist strategies in utilizing specific dissolved organic carbon compounds. When subjected to experimentally increased sea surface temperatures, lowered pH and additions of terrigenous carbon, some populations decreased in relative abundance while others were stable; concomitantly, many populations increased in relative abundance. Shifts in bacterial community composition were shown to correlate with changes in community functioning, but detection of such correlations depended largely on the detail of phylogenetic analysis and successional stage of the communities. The results in this thesis suggest that both natural and anthropogenically-induced changes in environmental conditions promote simultaneous adjustment and replacement of bacterial populations tightly linked with metabolic plasticity. These trade-offs play a significant role for understanding the relationship between bacterioplankton population dynamics and potential shifts in carbon cycling properties. We also show the importance of regional effects in shaping bacterial community composition, crucial for interpreting bacterioplankton distribution patterns. In conclusion, this thesis emphasizes the critical importance of connecting analysis of bacterioplankton population dynamics with examination of ecological mechanisms to improve our understanding of factors that regulate the distribution and activity of distinct bacterioplankton populations.Hälften av all fotosyntes på vår planet utförs av växtplankton. De producerar organiskt material som utgör grunden för näringskedjan i havet. Ungefär hälften av det organiska material som produceras av växtplankton utnyttjas inte direkt, utan omsätts istället av bakterieplankton som lever och växer fritt i vattenmassan eller på olika partiklar. Bakterieplankton spelar därmed en nyckelroll i ekosystemet genom sin konsumtion av organiskt kol som för energi högre upp i näringskedjan. Trots deras nyckelroll i akvatiska miljöer vet vi fortfarande mycket lite om bakteriernas detaljerade säsongsmönster, mekanismer bakom rumsliga mönster och hur olika populationer kan komma att svara på klimatförändringar. Målet med denna avhandling var att undersöka hur specifika populationers dynamik och ekosystemfunktion påverkas av naturliga eller klimatorsakade förändringar i havsmiljön. Våra resultat av högupplöst säsongsbunden dynamik i Östersjöns bakteriesamhälle avslöjar en liknande bred uppdelning av ekologiska strategier inom varje större grupp av bakterier, både i relativ abundans och temporal fördelning. Utbredning i rum och tid av många lokalt ovanliga populationer jämfört med få lokalt vanliga populationer förklarades genom stokastisk variation i kolonisations- och utdöendehastigheter. Vidare tyder experimentella studier med tillsatser av olika kolkällor på att marina bakterier har olika ekologiska strategier, där populationer är specialister eller generalister i utnyttjandet av enskilda kolkällor. Med hjälp av experiment med naturliga bakteriesamhällen bekräftade vi tydliga temperatureffekter på bakteriesamhällets sammansättning, och en mindre effekt av lägre pH - som dock tillsammans med förhöjd temperatur bidrog till en tydlig synergistisk effekt på artsammansättningen. Ökad temperatur tillsammans med tillsats av terrestert kol gav också en stor effekt på bakteriesamhällets struktur och ekosystemfunktion och pekar på en potentiellt viktig påverkan av ökad framtida nederbörd och avrinning från vattendrag till havet. Samtliga tre experiment med fokus på klimatpåverkan bekräftade förekomsten av populationer som försvann eller minskade i relativ abundans vid klimatpåverkan (känslighet), medan andra var stabila (resistens). Samtidigt svarade många populationer positivt på klimatorsakade förändringar i havsmiljön och ökade i relativ abundans (respons) samtidigt som bakteriernas ekosystemfunktion påverkades positivt. Sammanfattningsvis visar denna avhandling att vissa nya bakteriepopulationer kan etablera sig och ersätta andra samtidigt som vissa befintliga populationer anpassar sin livsstrategi och ekologi till förändringar i havsmiljön. Vi visar också vikten av regionala effekter, d.v.s. kolonisation och utdöende, för bakteriesamhällets struktur, viktigt för tolkningen av biogeografiska mönster och den genomiska potentialen hos specifika populationer. Denna avhandling poängterar därmed betydelsen av att koppla studier av ekologiska mekanismer till både rumsliga och temporala spridningsmönster hos bakterier och till populationers kapacitet att svara på och anpassa sig till förändringar i havsmiljön.
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Feakes, Karl Anthony. "The distribution and population dynamics of Corixidae." Thesis, University of Salford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308132.
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Calver, Andrew Robert. "Oligodendrocyte population dynamics : insights from transgenic mice." Thesis, University College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322239.
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Reade, Brian. "The population dynamics of mixed pathogen infections." Thesis, University of Liverpool, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264017.
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Purves, Drew William. "Local spatial structure and plant population dynamics." Thesis, University of York, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251813.
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Hoitzing, Hanne. "Controlling mitochondrial dynamics : population genetics and networks." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/58020.
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Mitochondria form an essential component of nearly all eukaryotic cells, are implicated in numerous diseases and may play important roles in ageing. Mitochondrial populations are dynamic, controlled and heterogeneous, with different types -- both mutant and wildtype -- potentially coexisting in single cells. This thesis will study the dynamics of both mitochondria and their genetic material (mtDNA) to improve our understanding of the role of these dynamics in pathology and ageing. This study suggests, as well as critically evaluates, reasons for the existence of complex continuous mitochondrial networks using coarse-grained mathematical models, underlining a nonlinear relation between functionality and network structure. Understanding the link between morphology and function is important as disruption of the former is directly implicated in cellular dysfunction. We perform experiments in which we measure the influence of mitochondrial fusion and division events on integrated mitochondrial membrane potential, an indicator of functionality, and find evidence for its conservation. The cellular homeostatic control acting on a mitochondrial population is poorly understood; to address this, we study the influence of general feedback control strategies on mutant and wildtype mtDNA dynamics. We introduce a simple linear control mechanism that captures a wide variety of biologically observed dynamics, and study optimal parameterisations through the construction of an energy-based mitochondrial cost function. Not only cellular control, but also gene-therapeutic control of mtDNA is studied, allowing us to investigate optimal treatment strategies to reduce mutant loads. The cellular proportion of mutant mtDNA molecules, known as heteroplasmy, is crucial in mitochondrial disease and we study the influence of cellular mtDNA exchange on heteroplasmy dynamics and mutant expansion during ageing. We find that this exchange of genetic material can induce preferential mutant expansion during ageing (even in the face of selection against mutants) through a stochastically driven increase in cellular mean heteroplasmy levels.
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Stringell, Thomas Brian. "Population dynamics of marine turtles under harvest." Thesis, University of Exeter, 2013. http://hdl.handle.net/10871/14521.
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Understanding the ecology and life history of marine turtle populations is fundamental for their effective conservation, especially for those that are harvested for food. This thesis presents a collection of six chapters that progress from the applied to the pure; conservation and management in the first chapters through to animal ecology in the latter. A variety of contemporary and multidisciplinary techniques are utilised to explore the structure, populations dynamics and ecology of two marine turtle species, the green turtle (Chelonia mydas) and the hawksbill turtle (Eretmochelys imbricata), under harvest in the Turks and Caicos Islands (TCI), Caribbean. The work first focuses on the structure of TCI’s small-scale fishery and the demographics of turtles landed and incorporates nesting seasonality, adult take, satellite tracking and genetic structure to suggest evidence-based legislative amendments. As part of the study of this fishery, this work reports on how the harvest might increase prevalence of disease in green turtles. As an exploration into the ecology of turtle stocks found in TCI, the work then describes and compares in- water immature and adult sex ratios, genetic differentiation and sex biased dispersal. Finally, stomach content and habitat matching, and stable isotope analyses provide insights into the foraging ecology and suggested keystone roles of sympatric green and hawksbill turtles.
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Ying, Killian Ping-Hung. "Small area population dynamics in Hong Kong /." The Ohio State University, 1985. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487262825075016.
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Bierman, Stijn Martinus. "Spatio-temporal models in animal population dynamics." Thesis, University of Aberdeen, 2004. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU195633.
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Population dynamics is the study of how and why populations of animals change in distribution and abundance. Thus, the aims of the science of population dynamics are twofold: to document the empirical patterns of population distribution and change, and to determine the mechanisms underlying those observed patterns. Population dynamics data typically have rich and complex spatio-temporal patterns. Modern and flexible statistical methods are needed to describe these patterns, and for the sound estimation of parameters in realistic mathematical models of spatio-temporal population dynamics. Of particular importance has been the development over the past decade of modern computational statistical methods, such as Markov chain Monte Carlo (McMC), that enable rigorous parameter estimation for more realistic models. The work as reported in this thesis has evolved around three case studies, each involving a long-term data set of estimated abundance's of a species at different locations over time, and a specific set of questions of interest: 1) Linking the spatio-temporal variation in recruitment of the Atlantic puffin (Fractercula arctica) to the spatio-temporal variation in densities of nesting herring gulls (Larus argentatus ) and lesser black-backed gulls (Larus fuscus) within the Isle of May natural nature reserve. 2) The use of flexible statistical tools to investigate coincident changes in the spatial and temporal dynamics of cyclic populations of field voles (Microtus agrestis). 3) Investigating the metapopulation dynamics of water voles (Arvicola terrestris) in the Scottish uplands using stochastic patch occupancy models. In each case study, the central aim was to formulate mathematical models that describe the spatio-temporal dynamics of the animal populations, and to develop and investigate the uses of flexible statistical methods that can be used to inform these models using the data.
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Chotibut, Thiparat. "Statistical Fluctuations in Evolutionary and Population Dynamics." Thesis, Harvard University, 2016. http://nrs.harvard.edu/urn-3:HUL.InstRepos:33493257.
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In this thesis, we study collective phenomena that arise from microscopic fluctuations at the individual level of two different living populations. First, we study evolutionary dynamics of two-species competitions in a well-mixed environment subject to population size fluctuations. We demonstrate a mechanism for neutral evolution such that population size fluctuations favor a fixation of one species over the other. An effective evolutionary dynamics for fluctuation-induced selection is derived. We then investigate strong mutualism, in a limit where a varying population size can strongly influence the evolutionary dynamics. We determine fixation probabilities as well as mean fixation times taking into account the population size degree of freedom. The results elucidate the interplay between population size fluctuations and evolutionary dynamics in well-mixed systems. Second, we investigate single species marine population subject to a constant flow field and quenched random spatially fluctuating growth rates. We show that the non-equilibrium steady-state population density of a generalized Fisher-Kolmogorov-Petrovsky-Piscounov (FKPP) equation develops a flow-driven striation pattern. The striations are highly asymmetric with a longitudinal correlation length that diverges linearly with the flow speed and a transverse correlation length that approaches a finite velocity-independent value. The findings suggest that, although the growth disorder can be spatially uncorrelated, correlated population structures with striations emerge naturally at sufficiently strong advection.Physics