Dissertations / Theses on the topic 'Population size'
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1
Inprasit, Utith 1956. "Equilibria in Size-Structured Population Models." Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/565549.
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Blayneh, Kbenesh W. "A hierarchical size-structured population model." Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/187505.
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A model is considered for the dynamics of a size-structured population in which the birth, death and growth rates of an individual of size s are functions of the total population biomass of all individuals of size larger or smaller than s. The dynamics of the size distribution is governed by the McKendrick equations. An existence/uniqueness theorem for this equation is proved using an equivalent pair of partial and ordinary differential equations. The asymptotic dynamics of the density function is studied and some applications of the model to intraspecific predation and certain types of intraspecific competitions are given.
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James, Jennifer E. "Investigating the effective population size of animals." Thesis, University of Sussex, 2018. http://sro.sussex.ac.uk/id/eprint/75023/.
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In this thesis I have investigated variation in the effective population size (Ne) between species, and the impact that this population genetics parameter has on molecular evolution. In Chapter 1 I review literature in order to outline our present understanding of variation in Ne, both between species and within a genome. In Chapter 2 I determine whether island species have lower effective population sizes than their mainland counterparts. I found that island species did not differ substantially from mainland species in terms of molecular evolution, despite their considerably smaller ranges. Chapter 3 examines the role of life history and demographic traits in shaping molecular evolution in mammals. Using mitochondrial DNA, I found significant correlations with species range for both genetic diversity (pS) and the efficiency of selection (pN/pS). Both latitude and body mass are also predictive of pS. However, these relationships are surprisingly weak. Additionally, no trait was predictive of nuclear molecular evolution. In Chapter 4 I determine whether there is adaptive evolution in animal mitochondrial DNA using McDonald-Kreitman style tests. While mitochondrial evolution is dominated by deleterious mutations, mitochondria also experience adaptive evolution, such that 26% of all nonsynonymous mutations are fixed by adaptive evolution. I also found evidence to suggest that the rate of adaptive evolution is correlated to Ne. In Chapter 5 I explore the relationship between pN/pS and pS, two variables that are expected to depend on Ne. I quantified the relationship between pS and pN/pS, after controlling for the statistical nonindependence between the two, to show that as πS doubles, πN/πS is reduced by 34%. I also investigated whether the slope of the regression between these variables is predicted by the shape parameter of the distribution of fitness effects. In Chapter 6 I give a general overview of my research, and bring together the key findings of this thesis.
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Crotti, Pablo. "Phenotypic variability, cell size and population fitness." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/43964.
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In all biological systems, phenotypes are quantitative measures of an organism's traits. To understand the relation between a genotype and phenotypes, the influence of genetic perturbations, such as gene deletions, on phenotypes is studied. Although it is common practice to look at the mean value of phenotypes to detect changes, it is less common to model such modifications by considering phenotypic variability. However, phenotypic variability could also contain important information about the phenotype-genotype map. Also, phenotypic variability is a determinant of an organism's robustness and fitness. This thesis is a collection of five studies devised to identify and analyse phenotypic variability in S. pombe, S. cerevisiae and E. coli. The first chapter determines the probabilistic nature of the dynamic transition from quiescence to proliferation in S. pombe. Based on the viability and the random nature of the quiescence of knockout genes, we demonstrate that two competing stochastic models explain the data equally well. The second and third chapters provide novel approaches to identifying mutant genes that increase/decrease phenotypic variability throughout the cell cycle of S. cerevisiae. Using machine learning algorithms, we observe that mutants divide in four categories acting positively and/or negatively on phenotypic variability. Additionally, we show that phenotypic robustness is inversely related to cell fitness. The fourth chapter builds morphological interaction networks in S. cerevisiae. By employing a Bayesian network framework, we show that cell size dictates nuclear size throughout most of the cell cycle. The fifth chapter investigates the growth rate of bacterial populations subject to fluctuations in the variance of their cell size distributions. By employing a population balance equation combined with an agent-based model, our results indicate that the cell size distribution affects the growth rate. Moreover, we show that cells possess a cell size regulator within their cycle.
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Chan, Kin-sun. "Statistical inference and designs for estimating population size /." Hong Kong : University of Hong Kong, 1998. http://sunzi.lib.hku.hk/hkuto/record.jsp?B20715468.
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Chan, Kin-sun, and 陳建新. "Statistical inference and designs for estimating population size." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B3122040X.
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O'Donoghue, Paul. "Reproductive success and effective population size in ungulates." Thesis, University of Sheffield, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.528893.
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Perry, R. J. O. "Shell size and population density in terrestrial molluscs." Thesis, University of Sunderland, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234753.
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Baalsrud, Helle Tessand. "Population characteristics and estimates of effective population size in a house sparrow metapopulation." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for biologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-15690.
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Effective population size (Ne) is a fundamental concept within biology and can be defined as the size of an ideal Wright-Fisher population in which the rate of genetic drift is the same as in the observed population. Natural populations are not ideal so that Ne is often < Nc. A low Ne can lead to inbreeding depression and less adaptability in a population, thus it is essential to know Ne for threatened populations. Ne can be estimated using genetic or demographic data. In this study four different genetic estimators (LDNE, ONeSAMP, MLNE and CoNe) and one demographic estimator were compared using data from a natural house sparrow metapopulation. How Ne related to Nc was also examined. All four genetic estimators seemed to be upwardly biased, however, LDNE often produced estimates in the expected range (Ne<N) and thus appeared to be less biased. To understand how characteristics of natural populations may affect the rate of genetic drift it is important to examine what influence the Ne/Nc-ratio. Thus, I investigated whether population characteristics such as population size, sex ratio, immigration rate, variance in population size and population growth rate explained the variation in the Ne/N ratio for the different genetic estimators. A general result was that the immigration rate had a positive effect on the Ne/Nc-ratio. The apparent upward bias of genetic Ne estimates and the positive effect of immigration rate on Ne/Nc-ratio suggest that gene flow between subpopulations within the study metapopulation was of significant importance for the rate of genetic drift. Genetic estimators of Ne seem like promising tools. However, if no knowledge of the ecology of the population in question exists, Ne should be interpreted cautiously. When assumptions underlying estimators are violated this can lead to erroneous conclusions about genetic processes in the population. 
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Meng, Vivian Yun. "Extensions to the multiplier method for inferring population size." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/50295.
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Estimating population size is an important task for epidemiologists and ecologists alike, for purposes of resource planning and policy making. One method is the "multiplier method" which uses information about a binary trait to infer the size of a population. The first half of this thesis presents a likelihood-based estimator which generalizes the multiplier method to accommodate multiple traits as well as any number of categories (strata) in a trait. The asymptotic variance of this likelihood-based estimator is obtained through the Fisher Information and its behaviour with varying study designs is determined. The statistical advantage of using additional traits is most pronounced when the traits are uncorrelated and of low prevalence, and diminishes when the number of traits becomes large. The use of highly stratified traits however, does not appear to provide much advantage over using binary traits. Finally, a Bayesian implementation of this method is applied to both simulated data and real data pertaining to an injection-drug user population. The second half of this thesis is a first systematic approach to quantifying the uncertainty in marginal count data that is an essential component of the multiplier method. A migration model that captures the stochastic mechanism giving rise to uncertainty is proposed. The migration model is applied, in conjunction with the multi-trait multiplier method, to real-data from the British Columbia Centre for Disease Control.Science, Faculty of
Statistics, Department of
Graduate
11
Bar-Ilan, Ittai. "How suspicion grows: effects of population size on cooperation." Thesis, Monterey, California: Naval Postgraduate School, 2014. http://hdl.handle.net/10945/43871.
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Approved for public release; distribution is unlimitedWe study the interaction between individuals in a population, where each individual encounters one another at random intervals, and in each encounter the two individuals play one round of the game of prisoner’s dilemma. By discounting future reward, and allowing for imperfect memory and mobility of the individuals, we study the evolutionary equilibrium strategy to identify situations where cooperation emerges. We find that cooperation among individuals typically emerges when future reward becomes more important, when individuals in the population have better memory, and when the individuals move in and out of the population less frequently. The findings help explain social loafing and free rider commonly seen in towns, corporations, and military units.
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Woolfit, Megan. "Effective population size and its effects on molecular evolution." Thesis, Lancaster University, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.420709.
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Uribe, Guillermo. "On the relationship between continuous and discrete models for size-structured population dynamics." Diss., The University of Arizona, 1993. http://hdl.handle.net/10150/186197.
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We address the problem of the consistency between discrete and continuous models for density-dependent size-structured populations. Some earlier works have discussed the consistency of density independent age and size-structured models. Although the issue of consistency between these models has raised interest in recent years, it has not been discussed in depth, perhaps because of the non-linear nature of the equations involved. We construct a numerical scheme of the continuous model and show that the transition matrix of this scheme has the form of the standard discrete model. The construction is based on the theory of Upwind Numerical Schemes for non-Linear Hyperbolic Conservation Laws with one important difference, that we do have a non-linear source at the boundary; interestingly, this case has not been explored in depth from the purely mathematical point of view. We prove the consistency, non-linear stability and hence convergence of the numerical scheme which guarantee that both models yield results that are completely consistent with each other. Several examples are worked out: a simple linear age-structured problem, a density-independent size-structured problem and a non-linear size-structured problem. These examples confirm the convergence just proven theoretically. An ample revision of relevant biological and computational literature is also presented and used to establish realistic restrictions on the objects under consideration and to prepare significant examples to illustrate our points.
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Jacobi, Frank. "Size and burden of mental disorders: A population based perspective." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1210771707872-94115.
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Die klinische Forschung zu Häufigkeit und Krankheitslast psychischer Störungen ist meist in mehrerer Hinsicht nicht repräsentativ. Insbesondere die Tatsache, dass die untersuchten Patienten sich von sich aus in Behandlung begeben, bedeutet eine gewisse Selektion (z.B. überdurchschnittlich motivierte). Mit wie vielen Fällen haben wir es aber zu tun, wenn man auch diejenigen berücksichtigt, die kein aktives Hilfesuch-Verhalten zeigen? Und wie hoch ist die in klinischen Stichproben offensichtliche individuelle Krankheitslast psychischer Störungen auf einer gesellschaftlichen Ebene – auch im Vergleich mit körperlichen Erkrankungen – einzuschätzen? Ansätze für solche Hochrechnungen und die Abschätzung von Häufigkeit, Störungskosten und Behandlungsbedarf psychischer Störungen müssen epidemiologisch anhand von Daten aus der Allgemeinbevölkerung geklärt werden. Die vorliegende Habilitationsschrift basiert auf Publikationen, die in meiner Arbeitsgruppe „Epidemiologie und Versorgungsforschung“ am Lehrstuhl für Klinische Psychologie und Psychotherapie zwischen 2001 und 2006 entstanden sind. Die entsprechenden Befunde und Implikationen wurden und werden nicht nur in der Klinischen Psychologie, sondern auch in Nachbardisziplinen (z.B. Psychiatrie, Epidemiologie, Occupational Health Psychology, Gesundheitsökonomie, Versorgungsforschung) sowie in der nicht-wissenschaftlichen Öffentlichkeit (z.B. Gesundheitsberichterstattung, Versorgungsplanung) zur Kenntnis genommen und zitiert. In den vorgestellten Arbeiten habe ich zunächst – erstmals für Deutschland – auf der Grundlage bevölkerungsbezogener Daten bundesrepräsentative Befunde zur Verbreitung psychischer Störungen herausgestellt (z.B. Jacobi, Wittchen et al., 2004; Jacobi, Hoyer & Wittchen, 2004; Jacobi, Klose & Wittchen, 2004). Zum zweiten beschäftigte ich mich mit der internationalen Befundlage, indem ich mich an der Koordination eines internationalen und multidisziplinären Forscher-Netzwerkes beteiligte, das eine umfassende Abschätzung der Größenordnung im Sinne von Verbreitung und Kosten für die EU vorgenommen hat (Wittchen & Jacobi, 2005). Vor diesem Hintergrund habe ich zum dritten ausgewählte Fragestellungen zum Zusammenhang zwischen psychischen Störungen und körperlichen Erkrankungen bzw. zur Stärke und zu Konsequenzen solcher Komorbidität verfolgt (z.B. Goodwin, Jacobi & Thefeld, 2003; Sareen, Jacobi et al., 2006). Die Habilitationsschrift verdeutlicht nicht nur die eminente Größenordnung und Krankheitslast psychischer Störungen (z.B. reduzierte Lebensqualität, Beeinträchtigungen, Krankheitskosten, Verschlechterung des gesundheitlichen Outcomes bei körperlichen Erkrankungen). Sie eröffnet auch neue wissenschaftliche Perspektiven ihrer Erforschung, z.B. im Hinblick auf Prävention und Behandlungsbedarf, oder hinsichtlich der Verschränkungen mit Prozessen körperlicher MorbiditätThis Habilitation-Thesis, based on 10 peer-reviewed publications (2001-2006), presents findings on size and burden of mental disorders in the community. First, following an introductory discussion of methodological aspects in epidemiological studies, an overview of the prevalence of mental disorders in Germany and Europe is given (Part A). As Examples for socio-economic determinants of mental disorders, some analyses on gender differences and a comparison between West and East Germany are presented (Part B). Further, it is shown that mental disorders are costly (in terms of disability adjusted life years as well as in terms of direct and indirect monetary burden) (Part C). This refers also to the interplay between mental disorders and somatic conditions: comorbid cases show significantly poorer outcomes (reduced health related quality of life, work loss and disability, help-seeking behaviour) (Part D)
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Brown, Malcolm. "Rats in an agricultural landscape : population size, movement and control." Thesis, University of Leicester, 2007. http://hdl.handle.net/2381/8193.
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This research investigated the effects of coordinating rodent control across areas up to 400 ha, using conventional and alternative strategies, to see if it was possible to reduce rat numbers and to keep them at a lower level compared with uncoordinated control. The aims were to reduce the rat numbers, reduce the amount of rodenticide used over time and to reduce the risk of secondary poisoning of non-target animals. Rodenticide loads in rat carcasses were investigated using historical and new samples from Berkshire, Leicestershire and Yorkshire in order to quantify risk to non-target predators of rats. Movement was also studied to see if rats were moving into farmyards in the autumn and out in the spring as is generally assumed. Analysis of radio-tracking data showed that the majority of rats tracked stayed within a small home range, two moved and stayed away from the trap site and only one moved into a farmyard. Analysis of the movement of the rats caught in traps showed that the movement towards and away from farms was in roughly equal numbers. The rodenticide analysis showed that rats from areas of rodenticide resistance carried a far greater body load of poison than those from non-resistance areas. Thus resistance increases the risk of a predator or scavenger of rats ingesting a lethal dose more quickly in areas of rodenticide resistance. The coordinated rat control was broadly successful over a period of two to three years. Rat numbers varied greatly between Yorkshire and Leicestershire, with Yorkshire having the larger numbers. Rat control in the coordinated areas showed a decreasing trend over the period. Bait take also generally showed a decline over the period. The results revealed an apparent delayed synchrony in rat numbers between coordinated and uncoordinated areas in Yorkshire that requires further investigation to explain.
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Jacobi, Frank. "Size and burden of mental disorders: A population based perspective." Doctoral thesis, Technische Universität Dresden, 2007. https://tud.qucosa.de/id/qucosa%3A23673.
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Die klinische Forschung zu Häufigkeit und Krankheitslast psychischer Störungen ist meist in mehrerer Hinsicht nicht repräsentativ. Insbesondere die Tatsache, dass die untersuchten Patienten sich von sich aus in Behandlung begeben, bedeutet eine gewisse Selektion (z.B. überdurchschnittlich motivierte). Mit wie vielen Fällen haben wir es aber zu tun, wenn man auch diejenigen berücksichtigt, die kein aktives Hilfesuch-Verhalten zeigen? Und wie hoch ist die in klinischen Stichproben offensichtliche individuelle Krankheitslast psychischer Störungen auf einer gesellschaftlichen Ebene – auch im Vergleich mit körperlichen Erkrankungen – einzuschätzen? Ansätze für solche Hochrechnungen und die Abschätzung von Häufigkeit, Störungskosten und Behandlungsbedarf psychischer Störungen müssen epidemiologisch anhand von Daten aus der Allgemeinbevölkerung geklärt werden. Die vorliegende Habilitationsschrift basiert auf Publikationen, die in meiner Arbeitsgruppe „Epidemiologie und Versorgungsforschung“ am Lehrstuhl für Klinische Psychologie und Psychotherapie zwischen 2001 und 2006 entstanden sind. Die entsprechenden Befunde und Implikationen wurden und werden nicht nur in der Klinischen Psychologie, sondern auch in Nachbardisziplinen (z.B. Psychiatrie, Epidemiologie, Occupational Health Psychology, Gesundheitsökonomie, Versorgungsforschung) sowie in der nicht-wissenschaftlichen Öffentlichkeit (z.B. Gesundheitsberichterstattung, Versorgungsplanung) zur Kenntnis genommen und zitiert. In den vorgestellten Arbeiten habe ich zunächst – erstmals für Deutschland – auf der Grundlage bevölkerungsbezogener Daten bundesrepräsentative Befunde zur Verbreitung psychischer Störungen herausgestellt (z.B. Jacobi, Wittchen et al., 2004; Jacobi, Hoyer & Wittchen, 2004; Jacobi, Klose & Wittchen, 2004). Zum zweiten beschäftigte ich mich mit der internationalen Befundlage, indem ich mich an der Koordination eines internationalen und multidisziplinären Forscher-Netzwerkes beteiligte, das eine umfassende Abschätzung der Größenordnung im Sinne von Verbreitung und Kosten für die EU vorgenommen hat (Wittchen & Jacobi, 2005). Vor diesem Hintergrund habe ich zum dritten ausgewählte Fragestellungen zum Zusammenhang zwischen psychischen Störungen und körperlichen Erkrankungen bzw. zur Stärke und zu Konsequenzen solcher Komorbidität verfolgt (z.B. Goodwin, Jacobi & Thefeld, 2003; Sareen, Jacobi et al., 2006). Die Habilitationsschrift verdeutlicht nicht nur die eminente Größenordnung und Krankheitslast psychischer Störungen (z.B. reduzierte Lebensqualität, Beeinträchtigungen, Krankheitskosten, Verschlechterung des gesundheitlichen Outcomes bei körperlichen Erkrankungen). Sie eröffnet auch neue wissenschaftliche Perspektiven ihrer Erforschung, z.B. im Hinblick auf Prävention und Behandlungsbedarf, oder hinsichtlich der Verschränkungen mit Prozessen körperlicher Morbidität.This Habilitation-Thesis, based on 10 peer-reviewed publications (2001-2006), presents findings on size and burden of mental disorders in the community. First, following an introductory discussion of methodological aspects in epidemiological studies, an overview of the prevalence of mental disorders in Germany and Europe is given (Part A). As Examples for socio-economic determinants of mental disorders, some analyses on gender differences and a comparison between West and East Germany are presented (Part B). Further, it is shown that mental disorders are costly (in terms of disability adjusted life years as well as in terms of direct and indirect monetary burden) (Part C). This refers also to the interplay between mental disorders and somatic conditions: comorbid cases show significantly poorer outcomes (reduced health related quality of life, work loss and disability, help-seeking behaviour) (Part D).
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Zhang, Xiao. "Confidence Intervals for Population Size in a Capture-Recapture Problem." Digital Commons @ East Tennessee State University, 2007. https://dc.etsu.edu/etd/2022.
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In a single capture-recapture problem, two new Wilson methods for interval estimation of population size are derived. Classical Chapman interval, Wilson and Wilson-cc intervals are examined and compared in terms of their expected interval width and exact coverage properties in two models. The new approach performs better than the Chapman in each model. Bayesian analysis also gives a different way to estimate population size.
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Tenesa-Prunyonosa, Albert. "Population-wide linkage disequilibrium and its uses in QTL mapping and estimation of ancestral population size." Thesis, University of Edinburgh, 2003. http://hdl.handle.net/1842/11451.
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The extent of LD was studied in two population, a dairy cattle population from the United Kingdom (UK) and a human isolated Sardinian population. For the dairy cattle population, data from 50 young bulls were available. These bulls were typed at 6 markers on chromosome 2 and 7 markers on chromosome 6, spanning 38 and 20 cM, respectively. LD extended to about 10 cM between pairs of loci in syntenic groups. Given the observed level of LD, mapping methods based upon population-wide association might provide better resolution than linkage methods in the UK dairy cattle population, as well as reduce the required sample sizes of the experiments. For the human population, 381 individuals typed at 22 markers on chromosome 19 were studied. High levels of disequilibrium were found that extended to 8 cM, when based on the LD measure D’, and 11 cM when based on the significance level of the allelic association. It was also shown, using bootstrapping, that small sample sizes can overestimate both the mean value of D’ and its variance by up to factors of about 3 and 23, respectively, when the sample size decreases from 381 to 25 individuals. Due to the high sampling variance of LD measures, the use of at least 200 unrelated individuals when characterizing the extent of LD is recommended. Three different strategies and study designs to map quantitative trait loci (QTL) using LD were studied using analytical methods and computer simulation. Finally, published data from human chromosomes 22 and 19 was used to infer past effective population size in a population of European ancestry. To do so, the extent of LD was first estimated using a multilocus measure of LD, the chromosome segment homozygosity (CSH). Results suggest that this population has had an average effective population size of around 4500 breeding individuals for approximately the last 4500 generations. This population had a relatively constant size (of between 3000 and 5000 individuals) from about 130000 years ago to about 2000 years ago, when it expanded to more than 10000 individuals.
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Asher, Allison Marie. "CONSERVATION GENETICS OF PADDLEFISH: GENETIC EFFECTIVE POPULATION SIZE AND RANGEWIDE GENETIC STRUCTURE." OpenSIUC, 2019. https://opensiuc.lib.siu.edu/dissertations/1693.
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Paddlefish (Polyodon spathula) is a commercially and recreationally important species, with a native range that extends over 22 US states. This is a large, long-lived, highly mobile riverine species that has been negatively impacted by habitat fragmentation, historic overharvest, and hatchery supplementation. Dams are the primary cause of habitat fragmentation, blocking migration routes, flooding spawning grounds, and isolating populations. A common management action to mitigate the impacts of habitat fragmentation and maintain harvestable populations is hatchery propagation and stocking. Reduction in stock size, isolation of populations, and stocking can all negatively impact the genetic integrity of Paddlefish. I evaluated the impacts of isolation and hatchery supplementation on the effective population size (Ne) of Paddlefish as well as the range-wide genetic structure of Paddlefish.
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Papkou, Andrei [Verfasser]. "The influence of population size on host-parasite coevolution / Andrei Papkou." Kiel : Universitätsbibliothek Kiel, 2017. http://d-nb.info/1138979643/34.
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Mortimer, Simon Richard. "The control of population size of sparse perennials in chalk grassland." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319820.
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Hua, Jianjun. "Confidence intervals for population size based on a capture-recapture design." Kansas State University, 2011. http://hdl.handle.net/2097/13103.
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Master of ScienceDepartment of Statistics
Paul I. Nelson
Capture-Recaputre (CR) experiments stemmed from the study of wildlife and are widely used in areas such as ecology, epidemiology, evaluation of census undercounts, and software testing, to estimate population size, survival rate, and other population parameters. The basic idea of the design is to use “overlapping” information contained in multiple samples from the population. In this report, we focus on the simplest form of Capture-Recapture experiments, namely, a two-sample Capture-Recapture design, which is conventionally called the “Petersen Method.” We study and compare the performance of three methods of constructing confidence intervals for the population size based on a Capture-Recapture design, asymptotic normality estimation, Chapman estimation, and “inverting a chi-square test” estimation, in terms of coverage rate and mean interval width. Simulation studies are carried out and analyzed using R and SAS. It turns out that the “inverting a chi-square test” estimation is better than the other two methods. A possible solution to the “zero recapture” problem is put forward. We find that if population size is at least a few thousand, two-sample CR estimation provides reasonable estimates of the population size.
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Sproul, John S. "Stoneflies of Unusual Size: Population Genetics and Systematics Within Pteronarcyidae (Plecoptera)." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3351.
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Chapter 1. The family Pteronarcyidae (Plecoptera) is a highly studied group of stoneflies and very important to a wide variety of aquatic studies. Several phylogenies have been proposed for this group recent decades, however there is little congruence between the various topologies. The present study revises the phylogeny of the group by combining molecular data from mitochondrial cytochrome oxidase subunit II, ribosomal subunit 12S, ribosomal subunit 16S, and nuclear loci ribosomal subinit 18S and Histone H3, with published morphological data in a parsimony-based total evidence analysis. The analysis produced a well-supported phylogeny with novel relationships within the genus Pteronarcys. Maximum Likelihood and Bayesian analyses produced topologies congruent with parsimony analysis. Character mapping revealed several homoplasious morphological characters that were previously thought to be homologous. Chapter 2. Phylogeographic studies in aquatic insects provide valuable insights into mechanisms that shape the genetic structure of aquatic communities. Yet studies that include broad geographic areas are uncommon for this group. We conducted a broad scale phylogeographic analysis of P. badia across western North America. In order to allow us to generate a larger mitochondrial data set, we used 454 seqeuncing to reconstruct the complete mitochondrial genome in the early stages of the project. Our analysis reveals what appears to be a complex history of isolation and multiple invasions among some lineages. The study provides evidence of multiple glacial refugia and suggests that historical climactic isolations have been important mechanisms in determining genetic structure of insects in western North America. Our ability to generate a large mitochondrial data set through mitochondrial genome reconstruction greatly improved nodal support of our mitochondrial gene tree, and allowed us to make stronger inference of relationships between lineages and timing of divergence events.
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Taglioni, Charlotte. "Bayesian hierarchical modelling for population size estimation: application to Italian data." Doctoral thesis, Università degli studi di Padova, 2019. http://hdl.handle.net/11577/3424971.
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Bayesian demography developments, global trends for substituting traditional censuses with cheaper methods able to use available information, and new technologies require investigating and providing new models to answer new requirements. In Italy in particular, during the last years Istat worked for launching in October 2018 the ``permanent census of population and housing''. After a first discussion on censuses, changes recommended by organisations such as the UN and the European Union to the National Statistical Institutes, and on new demographic models for population size estimation, the model proposed by Bryant and Graham (2013) is analysed. The model allows for integration of different data sources, for demographic series estimation, and it is very flexible and complex at the same time. Applications of this model to the Italian population are performed, highlighting its advantages and limits. Data for the period considered (2006-2015) and metadata come from Istat. Data are not always consistent, confirming the need of statistical methods able to integrate sources and reconstruct demographic series. As expected, census data and migration flows estimation caused most of the problems. The method still needs further experimentations, therefore applications aim to compare results when varying initial assumptions and to identify their pros and cons rather than provide actual results on the Italian population. Eventually a model extension, along with the first results of its application, is proposed using the Conway-Maxwell Poisson distribution Conway and Maxwell (1962), a flexible two parameters version of the Poisson distribution.
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Johnson, Linda Gail. "Effects of habitat patch size and isolation on the population structure of two siphonarian limpets." Thesis, Rhodes University, 2011. http://hdl.handle.net/10962/d1005364.
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Habitat fragmentation is a fundamental process that determines trends and patterns of distribution and density of organisms. These patterns and trends have been the focus of numerous terrestrial and marine studies and have led to the development of several explanatory hypotheses. Systems and organisms are dynamic and no single hypothesis has adequately accounted for these observed trends. It is therefore important to understand the interaction of these processes and patterns to explain the mechanisms controlling population dynamics. The main aim of this thesis was to test the effect of patch size and isolation on organisms with different modes of dispersal. Mode of dispersal has previously been examined as a factor influencing the effects that habitat fragmentation has on organisms. Very few studies have, however, examined the mode of dispersal of marine organisms because it has long been assumed that marine animals are not directly influenced by habitat fragmentation because of large-scale dispersal. I used two co-occurring species of siphonariid limpets with different modes of dispersal to highlight that not only are marine organisms affected by habitat fragmentation but that they are affected in different ways. The two species of limpet, Siphonaria serrata and Siphonaria concinna, are found within the same habitat and have the same geographic range along the South African coastline, however, they have different modes of dispersal and development. The effect of patch size on organism density has been examined to a great extent with varied results. This study investigated whether habitat patch size played a key role in determining population density and limpet body sizes. The two species are found on the eastern and southern coasts of South Africa were examined across this entire biogeographic range. Patch size was found to have a significant effect on population density of the pelagic developer, S. concinna, but not the direct developing S. serrata. Patch size did play a role in determining limpet body size for both species. S. concinna body size was proposed to be effected directly by patch size whilst S. serrata body size was proposed to be affected indirectly by the effects of the S. concinna densities. The same patterns and trends were observed at five of the seven examined regions across the biogeographic range. The trends observed for S. concinna with respect to patch size conform to the source-sink hypothesis with large habitat patches acting as the source populations whilst the small habitat patches acted as the sink populations. Many previous studies have focused on the effects of habitat patch size at one point in time or over one season. I tested the influence of habitat patch size on the two species of limpets over a period of twelve months to determine whether the trends observed were consistent over time or whether populations varied with time. S. concinna showed a consistently significant difference between small and large patches; whilst S. serrata did not follow a consistent pattern. The mode of dispersal for the two limpets was used to explain the different trends shown by the two species. This examination allowed for the determining of source and sink populations for S. concinna through the examination of fluctuations in limpet body sizes and population densities at small and large habitat patches over twelve months. The direct developing S. serrata trends could not be explained using source-sink theory, as populations were independent from one another. S. serrata demonstrated body size differences at small and large patches which, may be explained by interspecific and intraspecific competition. Habitat isolation is known to play an important role in determining the structure of assemblages and the densities of populations. In this study the population density of the pelagic developing S. concinna showed a weak influence of degree of isolation whilst that of the direct developing S. serrata did not, which may be because of habitat patches along the South African coastline not having great enough degrees of isolation. The population size-structure was influenced directly influenced by isolation for S. concinna, whilst the different population size structure for S. serrata may be explained by assemblage co-dependence. The mode of dispersal showed effects on the relationship of population density and population size-structure with habitat size and isolation. This study indicates the importance of investigating patterns and processes across a range of spatial and temporal scales to gain a comprehensive understanding of factors effecting intertidal organisms.
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Kupka, Kasper. "Effects of population size, density and local environment on the population dynamics of the fragrant orchid (Gymnadenia conopsea)." Thesis, Uppsala universitet, Institutionen för biologisk grundutbildning, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-447703.
Full textAbstract:
A wide majority of orchid populations are decreasing due to habitat fragmentation and to changes in land management. Population size, density and habitat quality are factors that are expected to be positively related to the viability and future growth of a population. We evaluated if population size, density and soil organic matter were good predictors of growth, survival, flowering, recruitment, and growth rate in 18 populations of the long-lived orchid Gymnadenia conopsea. We followed the populations for four years. Recruitment in 2020 increased with population size, and survival in 2018 was higher in denser populations. However, flowering probability and number of flowers both decreased with population size in 2018. Soil organic matter did not significantly influence any vital rate. In total, the studied population factors could explain very little of the variation in demography. The matrix modelling showed that 14 of the 18 populations had a positive stochastic growth rate, even with an increased probability of summer drought (scenario with 50% of the years equal to the dry summer of 2018). In the populations with negative growth rate, the probability of quasi-extinction in the next 50 years varied from 90 to 100%. Declining populations were characterized by low survival following the dry year. In sum, population size, density and soil organic matter did not convincingly explain variation in growth rate of G. conopsea, suggesting that other environmental factors are responsible of governing variation in vitals rates and population dynamics.
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Liu, Danping. "Semiparametric methods in generalized linear models for estimating population size and fatality rate." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B36164598.
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Nilsson, Karin. "Effects of size-dependent predation and competition on population and community dynamics." Doctoral thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-35686.
Full textAbstract:
Most animals grow substantially during their lifetime and change in competitive ability, predatory capacity and their susceptibility to predation as they grow. This thesis addresses the implications of this on regulation and dynamics within populations as well as between population interactions. In size-structured populations either reproduction or maturation may be more limiting. If juveniles are competitively superior, the competitive bottleneck will be in the adults and reproduction will be limiting. Mortality will in this case result in overcompensation in juvenile biomass through increased reproduction. Compensation in biomass was demonstrated in Daphnia pulex populations subjected to size-independent mortality, where juvenile biomass did not decrease when a substantial harvest was imposed due to increase per capita fecundity. This supported that juveniles were superior competitors and that population cycles seen in Daphnia are juvenile-driven. Compensatory responses in biomass may lead to that predators facilitate eachothers existence by feeding on a common prey, a phenomenon coined emergent facilitation. In an experimental test of the mechanism behind emergent facilitation it was demonstrated that the invertebrate predator Bythotrephes longimanus was favoured by thinning of its prey Holopedium gibberum. The thinning mimicked fish predation and targeted large individuals while Bythotrephes preferrs small prey. Size dependent predation also occurs within populations, i.e. cannibalism, were large individuals feed on smaller conspecifics. Two populations of the common guppy (Poecilia reticulata) originating from different environments were demonstrated to differ in cannibalistic degree. Cannibalism was also affected by the presence of refuges and females and juveniles from one population were better adapted to structural complexity than the other. The effects of these differences in cannibalism on population regulation and dynamics were studied in long term population experiments. Both populations were regulated by cannibalism in the absence of refuges, and displayed cannibal-driven cycles with suppression of recruitment and high population variability. The presence of refuges decreased density dependence and population variability and harvesting of large females in the absence of refuges led to population extinctions in the more cannibalistic population. The less cannibalistic population had higher population biomass and stronger density-dependence in the presence of refuges. When refuges were present, cohort competition increased and cycles with short periodicity were seen. Large individuals were not only cannibals, but could successfully prey on other species. Small and large guppies were allowed to invade resident populations of Heterandria formosa. Small invaders failed while large invaders succeeded as predation from large invaders broke up the competitive bottleneck that the resident population imposed on juveniles of the invader.
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Theunert, Christoph. "Approaches For Inferring Past Population Size Changes From Genome-wide Genetic Data." Doctoral thesis, Universitätsbibliothek Leipzig, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-150660.
Full textAbstract:
The history of populations or species is of fundamental importance in a variety of areas. Gaining details about demographic, cultural, climatic or political aspects of the past may provide insights that improve the understanding of how populations have evolved over time and how they may evolve in future. Different types of resources can be informative about different periods of time.
One especially important resource is genetic data, either from a single individual or a group of organisms. Environmental conditions and circumstances can directly affect the existence and success of a group of individuals. Since genetic material gets passed on from generation to generation, traces of past events can still be detected in today\'s genetic data. For many decades scientists have tried to understand the principles of how external influences can directly affect the appearance and features of populations, leading to theoretical models that can interpret modern day genetic variation in the light of past events.
Among other influencing factors like migration, natural selection etc., population size changes can have a great impact on the genetic diversity of a group of organisms. For example, in the field of conservation biology, gaining insights into how the size of a population evolves may assist in detecting past or ongoing temporal reductions of population size. This seems crucial since the reduction in size also correlates with a reduction in genetic diversity which in turn might negatively affect the evolutionary potential of a population. Using computational and population genetics methods, sequences from whole genomes can be scanned for traces of such events and therefore assist in new interpretations of historical details of populations or groups of interest.
This thesis focuses on the detection and interpretation of past population size changes. Two approaches to infer particular parameters from underlying demographic models are described. The first part of this thesis introduces two summary statistics which were designed to detect fluctuations in size from genome-wide Single Nucleotide Polymorphism (SNP) data. Demographic inferences from such data are inherently complicated due to recombination and ascertainment bias. Hence, two new statistics are introduced: allele frequency-identity by descent (AF-IBD) and allele frequency-identity by state (AF-IBS). Both make use of linkage disequilibrium information and exhibit defined relationships to the time of the underlying mathematical process. A fast and efficient Approximate Bayesian Computation framework based on AF-IBD and AF-IBS is constructed that can accurately estimate demographic parameters. These two statistics were tested for the biasing effects of hidden recombination events, ascertainment bias and phasing errors. The statistics were found to be robust to a variety of these tested biases. The inference approach was then applied to genome-wide SNP data to infer the demographic histories of two human populations: (i) Yoruba from Africa and (ii) French from Europe. Results suggest, that AF-IBD and AF-IBS are able to capture sufficient amounts of information from underlying data sets in order to accurately infer parameters of interest, such as the beginning, end and strength of periods of varying size. Additionally the results from empirical data suggest a rather stable ancestral population size with a mild recent expansion for Yoruba, whereas the French apparently experienced a rather long-lasting strong bottleneck followed by a drastic population growth.
The second part of this thesis introduces a new way of summarizing information from the site frequency spectrum. Commonly applied site frequency spectrum based inference methods make use of allele frequency information from individual segregating sites. Our newly developed method, the 2 point spectrum, summarizes allele frequency information from all possible pairs of segregating sites, thereby increasing the number of potentially informative values from the same underlying data set. These additional information are then incorporated into a Markov Chain Monte Carlo framework. This allows for a high degree of flexibility and implements an efficient method to infer population size trajectories over time. We tested the method on a variety of different simulated data sets from underlying demographic models. Furthermore, we compared the performance and accuracy of our method to already established methods like PSMC and diCal. Results indicate that this non-parametric 2 point spectrum method can accurately infer the extent and times of past population size changes and therefore correctly estimates the history of temporal size fluctuations. Furthermore, the initial results suggest that the amount of required data and the accuracy of the final results are comparable with other publicly available non-parametric methods. An easy to use command line program was implemented and will be made publicly available.
In summary, we introduced three highly sensitive summary statistics and proposed different approaches to infer parameters from demographic models of interest. Both methods provide powerful frameworks for accurate parameter inference from genome-wide genetic data. They were tested for a variety of demographic models and provide highly accurate results. They may be used in the settings as described above or incorporated into already existing inference frameworks. Nevertheless, the statistics should prove useful for new insights into populations, especially those with complex demographic histories.
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HOSKINSON, JOSHUA SCOTT. "AN ESTIMATION OF COYOTE POPULATION SIZE FOR EVIDENCE OF A TROPHIC CASCADE." Thesis, The University of Arizona, 2016. http://hdl.handle.net/10150/618748.
Full textAbstract:
Following the re-introduction of gray wolves (Canis lupus occidentalis) into Yellowstone National Park in 1998, a dramatic influence of the wolves on the landscape of Yellowstone ecosystem was observed over the following x decades, termed a trophic cascade. Trophic cascade is defined as the reciprocal predator-prey effects that alter the abundance, biomass, or productivity of a population, community, or trophic level across more than one link in a food web, and this effect was has been well-documented from reintroduction efforts of apex predators in the United States. In the Yellowstone wolf example, the wolves have initiated both a traditional trophic cascade, which spans across trophic levels (predator-prey-vegetation), and a carnivore cascade, which spans across a predator guild (wolf-coyote-fox). A goal of the present study was to determine whether or not the Mexican gray wolf (Canis lupus baileyi) can initiate a carnivore cascade in Arizona and New Mexico, assessed by estimation of a coyote minimum population size on the White Mountain Apache Reservation in Arizona. This was accomplished by genotyping scats collected in 2008 and 2009 for polymorphic microsatellite DNA loci, to estimate the population size through a simple genetic minimum population size using all unique individuals. Sixty-one individual coyotes were estimated using minimum population estimate in 2008 and 28 individual coyotes in 2009, on the study plot, however, the estimate did not include the influence of Mexican gray wolves on coyotes population size, due to carnivore cascades in this region.
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Forest, Marie. "Simultaneous estimation of population size changes and splits times using importance sampling." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:8c067a3d-44d5-468a-beb5-34c5830998c4.
Full textAbstract:
The genome is a treasure trove of information about the history of an individual, his population, and his species. For as long as genomic data have been available, methods have been developed to retrieve this information and learn about population history. Over the last decade, large international genomic projects (e.g. the HapMap Project and the 1000 Genomes Project) have offered access to high quality data collected from thousands of individuals from a vast number of populations. Freely available to all, these databases offer the possibility to develop new methods to uncover the history of the peopling of the world by modern humans. Due to the complexity of the problem and the large amount of available data, all developed methods either simplify the model with strong assumptions or use an approximation; they also dramatically down-sample their data by either using fewer individuals or only portions of the genome. In this thesis, we present a novel method to jointly estimate the time of divergence of a pair of populations and their variable sizes, a previously unsolved problem. The method uses multiple regions of the genome with low recombination rate. For each region, we use an importance sampler to build a large number of possible genealogies, and from those we estimate the likelihood function of parameters of interest. By modelling the population sizes as piecewise constant within fixed time intervals, we aim to capture population size variation through time. We show via simulation studies that the method performs well in many situations, even when the model assumptions are not totally met. We apply the method to five populations from the 1000 Genomes Project, obtaining estimates of split times between European groups and among Europe, Africa and Asia. We also infer shared and non-shared bottlenecks in out-of- Africa groups, expansions following population separations, and the sizes of ancestral populations further back in time.
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Lucas, T. C. D. "The role of population structure and size in determining bat pathogen richness." Thesis, University College London (University of London), 2016. http://discovery.ucl.ac.uk/1531925/.
Full textAbstract:
Pathogens acquired from animals make up the majority of emerging human diseases, are often highly virulent and can have large effects on public health and economic development. Identifying species with high pathogen species richness enables efficient sampling and monitoring of potentially dangerous pathogens. I examine the role of host population structure and size in maintaining pathogen species richness in an important reservoir host for zoonotic viruses, bats (Order, Chiroptera). Firstly I test whether population structure is associated with high viral richness across bat species with a comparative, phylogenetic analysis. I find evidence that bat species with more structured populations have more virus species. As this type of study cannot distinguish between specific mechanisms, I then formulate epidemiological models to test whether more structured host populations may allow invading pathogens to avoid competition. However, these models show that increasing population structure decreases the rate of pathogen invasion. As both global host population structure and local group size appear to be important for disease invasion, I use the same modelling framework to compare the importance of host density, group size and number of groups. I find that host group size has a stronger effect than density or number of groups. There are few bat population size estimates to empirically test the importance of host population size on pathogen richness. Therefore, to assist future research, I develop a method for estimating bat population sizes from acoustic surveys. Overall in this thesis, I show that the structure and size of host bat populations can affect their ability to maintain many pathogen species and I provide a method to measure population sizes of bats. These findings increase our understanding of the ecological process of pathogen community construction and can help optimise surveillance for zoonotic pathogens.
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Silva, Cibele Queiroz da. "Capture-recapture estimation of bowhead whale population size using photo-identification data /." Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/8954.
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Vivarelli, Daniele <1978>. "Consequences of plant population size for pollinator visitation and plant reproductive success." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/324/1/complete_for_web_def.pdf.
Full textAbstract:
Habitat loss and fragmentation have a prominent role in determining the size of plant populations,
and can affect plant-pollinator interactions. It is hypothesized that in small plant populations the
ability to set seeds can be reduced due to limited pollination services, since individuals in small
populations can receive less quantity or quality of visits. In this study, I investigated the effect of
population size on plant reproductive success and insect visitation in 8 populations of two common
species in the island of Lesvos, Greece (Mediterranean Sea), Echium plantagineum and Ballota
acetabulosa, and of a rare perennial shrub endemic to north-central Italy, Ononis masquillierii.
All the three species depended on insect pollinators for sexual reproduction. For each species,
pollen limitation was present in all or nearly all populations, but the relationship between pollen
limitation and population size was only present in Ononis masquillierii. However, in Echium
plantagineum, significant relationships between both open-pollinated and handcrossed-pollinated
seed sets and population size were found, being small populations comparatively less productive
than large ones. Additionally, for this species, livestock grazing intensity was greater for small
populations and for sparse patches, and had a negative influence on productivity of the remnant
plants. Both Echium plantagineum and Ballota acetabulosa attracted a great number of insects,
representing a wide spectrum of pollinators, thereby can be considered as generalist species. For
Ballota acetabulosa, the most important pollinators were megachilid female bees, and insect
diversity didn’t decrease with decreasing plant population size. By contrast, Ononis masquillierii
plants generally received few visits, with flowers specialized on small bees (Lasioglossum spp.),
representing the most important insect guild. In Echium plantagineum and Ballota acetabulosa,
plants in small and large populations received the same amount of visits per flower, and no
differences in the number of intraplant visited flowers were detected. On the contrary, large Ononis
populations supported higher amounts of pollinators than small ones. At patch level, high Echium
flower density was associated with more and higher quality pollinators.
My results indicate that small populations were not subject to reduced pollination services than
large ones in Echium plantagineum and Ballota acetabulosa, and suggest that grazing and resource
limitation could have a major impact on population fitness in Echium plantagineum. The absence of any size effects in these two species can be explained in the light of their high local abundance,
wide habitat specificity, and ability to compete with other co-flowering species for pollinators. By
contrast, size represents a key characteristic for both pollination and reproduction in Ononis
masquillierii populations, as an increase in size could mitigate the negative effects coming from the
disadvantageous reproductive traits of the species. Finally, the widespread occurrence of pollen
limitation in the three species may be the result of 1) an ongoing weakening or disruption of plantpollinator
interactions derived from ecological perturbations, 2) an adaptive equilibrium in response
to stochastic processes, and 3) the presence of unfavourable reproductive traits (for Ononis
masquillierii).
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Vivarelli, Daniele <1978>. "Consequences of plant population size for pollinator visitation and plant reproductive success." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/324/.
Full textAbstract:
Habitat loss and fragmentation have a prominent role in determining the size of plant populations,
and can affect plant-pollinator interactions. It is hypothesized that in small plant populations the
ability to set seeds can be reduced due to limited pollination services, since individuals in small
populations can receive less quantity or quality of visits. In this study, I investigated the effect of
population size on plant reproductive success and insect visitation in 8 populations of two common
species in the island of Lesvos, Greece (Mediterranean Sea), Echium plantagineum and Ballota
acetabulosa, and of a rare perennial shrub endemic to north-central Italy, Ononis masquillierii.
All the three species depended on insect pollinators for sexual reproduction. For each species,
pollen limitation was present in all or nearly all populations, but the relationship between pollen
limitation and population size was only present in Ononis masquillierii. However, in Echium
plantagineum, significant relationships between both open-pollinated and handcrossed-pollinated
seed sets and population size were found, being small populations comparatively less productive
than large ones. Additionally, for this species, livestock grazing intensity was greater for small
populations and for sparse patches, and had a negative influence on productivity of the remnant
plants. Both Echium plantagineum and Ballota acetabulosa attracted a great number of insects,
representing a wide spectrum of pollinators, thereby can be considered as generalist species. For
Ballota acetabulosa, the most important pollinators were megachilid female bees, and insect
diversity didn’t decrease with decreasing plant population size. By contrast, Ononis masquillierii
plants generally received few visits, with flowers specialized on small bees (Lasioglossum spp.),
representing the most important insect guild. In Echium plantagineum and Ballota acetabulosa,
plants in small and large populations received the same amount of visits per flower, and no
differences in the number of intraplant visited flowers were detected. On the contrary, large Ononis
populations supported higher amounts of pollinators than small ones. At patch level, high Echium
flower density was associated with more and higher quality pollinators.
My results indicate that small populations were not subject to reduced pollination services than
large ones in Echium plantagineum and Ballota acetabulosa, and suggest that grazing and resource
limitation could have a major impact on population fitness in Echium plantagineum. The absence of any size effects in these two species can be explained in the light of their high local abundance,
wide habitat specificity, and ability to compete with other co-flowering species for pollinators. By
contrast, size represents a key characteristic for both pollination and reproduction in Ononis
masquillierii populations, as an increase in size could mitigate the negative effects coming from the
disadvantageous reproductive traits of the species. Finally, the widespread occurrence of pollen
limitation in the three species may be the result of 1) an ongoing weakening or disruption of plantpollinator
interactions derived from ecological perturbations, 2) an adaptive equilibrium in response
to stochastic processes, and 3) the presence of unfavourable reproductive traits (for Ononis
masquillierii).
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Timm, Anne Louise. "Brook Trout Population Genetic Tools for Natural Barriers in Fragmented Subwatersheds." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/77044.
Full textAbstract:
Barriers to fish movement can cause aquatic habitat fragmentation by reducing the amount of available habitat. The primary goal of my research was to investigate applications of population genetic analysis tools as indicators of barrier effects on brook trout populations in fragmented subwatersheds.
In chapter1, I tested the hypothesis that brook trout population genetic differentiation (FST) above and below barriers will differ in relation to barrier height and gradient. I also tested the hypothesis that average gene diversity per locus (H) and the numbers of alleles (A) differed between samples below and above each barrier. There was no significant difference in average number of alleles (A) or average gene diversity per locus (H) between the above- and below-barrier samples, but linear regression identified a statistically significant relationship between barrier height and FST values. Unrooted neighbor-joining consensus trees of Cavalli-Sforza and Edwards (1967) chord distances provided evidence of genetic differentiation between samples of resident brook trout above and below natural barriers. Additionally, average total allelic diversity (A), average gene diversity per locus (H), average number of private alleles per locus per sample, and total alleles per sample differed between Level III Ecoregions.
In chapter 2 I tested the hypothesis that the presence of a barrier, total habitat potentially isolated above a barrier (km), road density, and percent forest cover within a subwatershed (USGS 6th-level Hydrologic Units) were significant habitat fragmentation factors affecting the effective population size (Ne) of brook trout in the Blue Ridge Level III Ecoregion. Multivariable linear regression indicated that total habitat above the barrier (km) and road density were significant variables retained in the model to predict Ne.
In chapter 3, the objective of the study was to infer relationships between barriers and family structure in brook trout populations. Maximum likelihood analysis of pairwise kinship relationships between above- and below-barrier individuals indicated the presence of parent-offspring relationships between above- and below-barrier individuals at six sites in the Blue Ridge Level III Ecoregion and five sites in the Northern Lakes and Forests Level III Ecoregion, which indicated movement of individuals between the above- and below-barrier locations.Ph. D.
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Xi, Liqun, and 奚李群. "Estimating population size for capture-recapture/removal models with heterogeneity and auxiliary information." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B29957783.
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Ozbahar, Ilker. "Breeding Biology, Population Size And Spatial Distribution Of A Common Nightingale (luscinia Megarhynchos Brehm, 1831) Population At Yalincak (ankara)." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606981/index.pdf.
Full textAbstract:
Many bird populations are known to show strong territoriality as well as high site fidelity during breeding. The Common Nightingale (Luscinia megarhynchos) is one of many such migratory species that annually occupies the same favourable habitat. Especially dominant males prefer to breed in the same area every year, and high fidelity probably assures high breeding success. This study aims to investigate breeding biology, population size and spatial distribution of nightingales at a small area in Yalincak within the METU campus grounds (Ankara, Turkey).
From 2003 to 2005, birds were captured and marked with metal or colour rings or radio tags for monitoring. Analyses were carried out on 77 individuals, including ringing data from the previous two years.
Phenology of the study population was characterized by early arrival of males in late April, followed one week later by females. Nesting immediately followed and the first young fledged in early June. Second broods were also recorded. Most birds apparently left for the south within August.
The population in the 2.65 ha large area was estimated to be about 20-25 individuals. However, only 2-4 breeding territories were present and a large proportion of floaters existed. Territory sizes were smaller than reported elsewhere. Annual survival rate was 0.424 
0.121. Contrary to previous knowledge, taxonomically the Yalincak population belonged to subspecies africana although more westerly subspecies could be recorded during migration. This study revealed the importance of small but productive biotopes as important breeding habitats for passerines. It also showed that a few highly successful individuals may contribute out of proportion to the next generation.
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O'Neill, Deborah M. "Estimating Black Bear Population Size, Growth Rate, and Minimum Viable Population Using Bait Station Surveys and Mark-Recapture Methods." Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/34140.
Full textAbstract:
We initiated bait station surveys for black bears in southwestern Virginia in 1999. Bait station surveys are intended to be used as an index to follow bear population trend over time. We compared the bait station visitation (black bear visitation) to black bear harvest and mast surveys 1999 = 2002. The mean bait station visitation rate during 1999 - 2002 was 15.3% (SE = 2.89, n = 4). The number of bears harvested in the 3 counties that also had bait station surveys was 48 (31 males, 17 females), 59 (44 males, 15 females), 45 (32 males, 13 females), and 43 (26 males, 17 females) in 1999, 2000, 2001, and 2002, respectively. Harvest of males and females differed (n = 2, F = 19.44, df = 1, P = 0.0045). Bait station visitation and female harvest had a strong functional relationship with a negative slope (n = 4, r = -0.78, P = 0.22). The strongest relationship was between male harvest and total harvest (n = 4, r = 0.97, P = 0.03). Mean index to mast production for 1999 - 2002 was 2.3 (range 1.5 - 3.1), 2.7 (range 1.8 - 3.4), 2.3 (range 1.6 - 3.6), and 1.6 (range 1.2 - 2.4), respectively. The overall summary for mast production for the same years was described as fair, good, fair, and poor to fair. Mast production was significantly different between years (n = 4, F = 3.44, df = 3, P = 0.0326), and soft and hard mast production appeared to be above average in 2000. This corresponded with the lowest visitation (10.2%) of the 4 years. There was no correlation between bait station visitation and mast production (n = 4, r = 0.11, P = 0.87).
Since 1998, the annual bear harvest in Virginia has exceeded 900 individuals (with the exception of 824 in 2001), and peaked in 2000 when 1,000 bears were harvested. Though harvest rates were high, a reliable population estimate did not exist for black bears in Virginia. We estimated population size, growth rate, and minimum viable population size using data collected between 1995-2000. We used Jolly-Seber, direct recovery, and minimum population size methods to estimate population size. The Jolly-Seber method estimate of adult female density was 0.23-0.64 bears/km2, and 0.01 bears/km2 for adult males. We estimated a density of 0.09-0.23 bears/km2 for all sex and age classes using direct recovery data. Using minimum population size, we found adult female density was higher than any other sex or age class (n = 6, t = 2.02, df = 40, P < 0.0001) with an average density of 0.055 adult females/km2.
We used mark-recapture data collected from 148 individual bears (96 males:52 females) captured 270 times in program MARK to estimate survival using recapture, dead recovery, and Burnham's combined models. Adult females had the highest survival rate of 0.84-0.86, while yearling males had the lowest with 0.35. Using direct recovery data, adult females again had the highest survival rate with 0.93 (0.83-1.0) and 3-year old males had the lowest with 0.59 (0.35-0.83). We estimated growth rate using population estimates from Jolly-Seber, direct recoveries, and minimum population size methods. The lowest growth rate estimated was for all females (ages lumped) using minimum population size data (λ=0.82). Direct recovery data for all bears (sex and age lumped) during 1995 - 2000 showed the highest positive annual growth rate (λ = 1.24).
We developed a population model using Mathcad 8 Professional to determine population growth rate, MVP, and harvest effects for an exploited black bear population in southwestern Virginia. We used data collected during the CABS study (1995 - 2000) in the model including population estimates derived from direct recovery data, age and sex specific survival rates, and cub sex ratios. When we used actual population values in the model, the bear population in southwestern Virginia did not go extinct in 100 years (l = 1.03, r = 0.03). When we reduced adult female survival from 0.94 to 0.89, the probability of extinction in 100 years was 3.0% and l = 0.99 (r = -0.01; Table 3.2). When the survival was reduced by an additional 0.01 to 0.88, the probability of extinction increased to 13.0% (l = 0.99, r = -0.01). Growth rate and extinction probabilities were very sensitive to adult female survival rates. Two-year old and 3-year old females did not impact extinction probabilities and growth rates as much as adult females. Their survival could be decreased by 44.0%, and still be less than the 5.0% extinction probability.Master of Science
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Xu, Zhiqing. "Bayesian Inference of a Finite Population under Selection Bias." Digital WPI, 2014. https://digitalcommons.wpi.edu/etd-theses/621.
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Length-biased sampling method gives the samples from a weighted distribution. With the underlying distribution of the population, one can estimate the attributes of the population by converting the weighted samples. In this thesis, generalized gamma distribution is considered as the underlying distribution of the population and the inference of the weighted distribution is made. Both the models with known and unknown finite population size are considered. In the modes with known finite population size, maximum likelihood estimation and bootstrapping methods are attempted to derive the distributions of the parameters and population mean. For the sake of comparison, both the models with and without the selection bias are built. The computer simulation results show the model with selection bias gives better prediction for the population mean. In the model with unknown finite population size, the distributions of the population size as well as the sample complements are derived. Bayesian analysis is performed using numerical methods. Both the Gibbs sampler and random sampling method are employed to generate the parameters from their joint posterior distribution. The fitness of the size-biased samples are checked by utilizing conditional predictive ordinate.
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Williams, Clair. "Metapopulation dynamics of the crested newt, Triturus cristatus." Thesis, University of Kent, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314265.
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Ballard, Grant. "Biotic and physical forces as determinants of Adélie penguin population location and size." Thesis, University of Auckland, 2010. http://hdl.handle.net/2292/5621.
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Adélie penguins (Pygoscelis adeliae) are among the most thoroughly studied wild animals, which is remarkable considering they are sea-ice obligates, living only in the Antarctic, one of the most remote regions on Earth. Building on several decades of research on the Ross and Beaufort Island metapopulation, I have focused on understanding the underlying mechanisms related to colony size and growth patterns. I have found that life for a penguin at a large colony is extremely competitive, and that the ultimate size of these colonies is determined by the trade-off between the needs of parents and chicks, with penguins at large colonies approaching an energetic limit not reached at smaller colonies. However, some individuals are consistently able to utilize the available resources within these limits more efficiently than others by diving more deeply and recovering more quickly, especially when environmental conditions are less favorable. It is likely that these individuals thereby exhibit increased fitness in terms of their genetic contribution to the population. At smaller colonies, this kind of advantage does not necessarily translate to increased fitness, since there appear to be ample resources for all, or for none, depending more closely on simple yet extreme physical environmental stochasticity. Finally, in the larger context of Adélie penguin life-history throughout the annual cycle, they are confronting large scale changes in their environment that have been occurring for millennia, but which are currently in an unusual state of flux. Ultimately a lack of sufficient daylight overlapping the region of sea ice that is accessible to them during the inter-breeding period may constrain their populations.
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Liu, Danping, and 劉丹平. "Semiparametric methods in generalized linear models for estimating population size and fatality rate." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B36164598.
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Hui, Tin-Yu Jonathan. "Estimating effective population size from genetic data : the past, present, and the future." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/49250.
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Effective population size (Ne) is an important statistic in conservation science and in the broader topics of evolutionary genetics. Ne is often used to quantify the rate of evolutionary events such as losses in genetic diversity. Estimating and interpreting such quantity can however be challenging. Chapter 2 focuses on the change in allele frequency between two or more time points due to genetic drift. A new likelihood-based estimator N̂_B for contemporary Ne estimation is proposed by adopting a hidden Markov algorithm and continuous approximations. N̂_B is found to be several-fold faster than the existing methods without sacrificing accuracy. It also relaxes the upper bound of Ne to several million and which is currently limited to about 50000 due to computing limitations. Chapter 3 extends N̂_B to handle multialleleic loci through using Dirichlet-multinomial distributions. An R package is also provided and available for download. Chapter 4 explores the signatures of linkage disequilibrium (LD) between a pair of loci induced by genetic drift as a function of recombination rate and historical population sizes. E[r²] can be expressed as the weighted sum of the probability of coalescent at different time points of which information about Ne is contained. This relationship is verified by computer simulation and then applied to historical Ne estimation as illustrated in an example of Anopheles coluzzii population. A new likelihood-based routine Constrained ML is suggested in chapter 5 to estimate haplotype frequencies and r² from genotypes under Hardy-Weinberg Equilibrium. It is shown to be identical to existing EM algorithm under normal conditions but far less sensitive to initial conditions. A new “unbiased” sample size correction is also proposed to estimate r². To summarise, this work pushes the Ne estimation to its current boundary and more importantly provides suitable tools to analyse the ever-growing datasets.
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Jeffery, Douglas John. "The effects of population size on agathosma collina (rutaceae) and its conservation implications." Master's thesis, University of Cape Town, 1997. http://hdl.handle.net/11427/19422.
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Agathosma collina is a relatively typical widespread, outcrossing shrub species, endemic to the coastal vegetation between the Agulhas Plain and Heidelberg in the Southern Cape. Although not a rare species, its endemism makes it a suitable candidate for a study of population size effects and the conservation implications for similar outbreeding species. Theory predicts that we should expect demographic problems to arise, for ecological or genetic reasons, when population size becomes too small. Initially, therefore, a study was carried out to assess if there was any discernible effect of population size on the population structure. As predicted by theory, the demographic status of small populations was worse than larger ones, measured in terms of seedling recruitment with small populations having relatively fewer seedlings than large. This effect was quite small and far from dramatic. Demographic aspects such as length of flowering, predation and seed set per capsule in different sized populations were studied. Inflorescence predation rates were found to increase to a peak during the peak flowering time of A. collina and medium sized populations showed the highest predation rate while lower predation percentages in large and small populations were probably a result of predator satiation (large populations) and crypsis (small populations). Seed set per capsule varied from mostly one seed per capsule in small and medium populations to two seeds per capsule in large populations in 1988. However, 1989 data showed an almost identical spread in the numbers of seeds per capsule in the different sized populations. None of the above results seemed sufficiently consistent over time or population size to be of importance regarding population structure differences between different sized populations. In order to obtain an indication of the amount of genetic exchange between populations, gene flow studies were carried out using pollen dispersal and seed dispersal. Although direct estimates of gene flow proved difficult to obtain, these studies indicated that gene flow was limited. Neighbourhood area resulting from estimates of pollen dispersal distances was only 2.12m² compared to ballistic seed dispersal neighbourhood area of 3.05m2, while that resulting from possible myrrnecochorous seed dispersal was 41.97m². Neighbourhood size proved to be heavily dependent on population density and was very specific to a population and care should be taken when extrapolating results to different populations or plant species. Cross pollination experiments were carried out to attempt to identify an optimal outbreeding distance. Although pollen from 7km away produced the highest capsule set of all the treatments this could have resulted from heterosis. The species is self-compatible but geitonogamous matings produced lower capsule set than outcrossed matings. Of the pollination distances which could be expected under natural circumstances the nearest neighbour crosses produced the most capsules. This corroborates the results of the gene flow studies which indicate that gene flow may be over very short distances. Inbreeding depression in small populations of A. collina seems likely since neighbourhood size is very small resulting in a low probability of pollen transfer from any great distance and since A. collina is self-compatible allowing geitonogamous matings in very small populations. Electrophoresis was then attempted to confirm the above results from a genetic aspect. Unfortunately this was not successful. This study provided some empirical support for theoretical predictions of the effects of population size on plants but suggests that the main problems may be genetic rather than ecological. The magnitude of the population size effects were small and then only in very small populations and are therefore probably only of concern under rare circumstances.
Bibliography: pages 100-111.
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Munson, Susannah. "Genetic Admixture and Tooth Size in an Enslaved Population from Newton Plantation, Barbados." OpenSIUC, 2012. https://opensiuc.lib.siu.edu/theses/958.
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This study examined the amount of European genetic admixture in the enslaved African population from Newton Plantation, Barbados. Newton Plantation was a British sugar plantation from the 17th to 19th centuries. Approximately 150 individuals were recovered from an unmarked slave cemetery during archaeological investigations in the 1970s and 1990s. Using maximum mesiodistal and buccolingual tooth measurements of the available teeth from the individuals in the cemetery, Newton was compared to nineteen comparative samples of African, European, African American and European American populations that date from the time of British colonization to the 20th century. Previous European admixture estimations in the Newton Plantation cemetery sample were 5-10% (Corruccini et al., 1982; Ritter, 1991); this study found similar rates of admixture in the population (5.38-10.25%). Because of social practices in the Caribbean during the time of slavery, European admixture could have resulted in preferential treatment of slaves with such genetic background.
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Johnson, Kelly Singleton. "Quantitative Poverty: Relationship Between Poverty Level and Population Size, GDP, and Gini Coefficient." ScholarWorks, 2017. https://scholarworks.waldenu.edu/dissertations/4455.
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This research examines why poverty has been persistent in all regimes that have tried to use public policy to eradicate it with no success. This research begins to examine the economic, fiscal, and current Federal Reserve monetary policy for an understanding of why poverty persists. The purpose of this experimental, cross-sectional design is to test the relationship between poverty level, population size, gross domestic product and the Gini coefficient. The most important outcome of the research is to understand if poverty is an unintended consequence of economic activity and not individual circumstance. In the dissertation, 5 U.S. states are examined in the year 2014. The data were collected using the U.S. Census Bureau and American Community Surveys. Using multiple regression, this research aimed to establish the minimum amount of expected poverty in the sample's population and gross domestic product (GDP). Using the results and further research, a predictive model could be created to understand how poverty, population, and GDP intersect to create stable economies. The key results yielded the Gini coefficient has no effect in predicting expected poverty levels. As determined by the model, Arizona would have a poverty decrease of 17.1% and Illinois' poverty would decrease by 7.7%. Georgia and Washington would increase by 9.4% and 21.8%, respectively. New York's levels would remain the same. One of the recommendations is continuing research to understand other quantitative factors that reduce or increase poverty numbers. These results help promote social change by possibly informing monetary policymakers more targeted solutions to mitigating poverty levels.
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Wiff, Rodrigo. "Predicting food consumption and production in fish populations : allometric scaling and size-structured models." Thesis, University of St Andrews, 2010. http://hdl.handle.net/10023/935.
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Life-history traits in fish populations are highly correlated. A subset of these correlations are called allometric scaling, they refer to biological processes which can be described using body size as independent variable. Particularly, allometric scaling related with food consumption (Q) and biomass production (P) has gained the attention of ecologists for several decades. This thesis proposes a quantitative framework for food consumption, which allows both the identification of the mechanisms underlying the allometric scaling for Q and the development of a predictive model for consumption to biomass ratio (Q/B) in fish populations. This thesis is based on the fact that food consumption can be inferred from first principles underlying the von Bertalanffy growth model. In addition, it has been noticed in the literature that biomass production and food consumption show similar allometric scaling dependence, therefore, both can be derived from these first principles. Thus, a similar quantitative framework was used to produce models for P/B in fish populations. Once functional forms for production and food consumption were identified, a third model was developed for the ratio between production and consumption (P/Q). This ratio is usually named ecological efficiency because it determines how efficiently a population can transform ingested food into biomass. Several authors have noticed that P/Q remains invariant (independent of body size) across species. From a theoretical point of view, the results presented here allow the first quantitative explanation for the existence of the allometric scaling for Q/B and the invariance of P/Q across fish species. These results, together with the explanation for allometry in P/B reported in the literature, suggest that the regular across-species pattern for the trio {P/B,Q/B,P/Q} can be explained by basic principles that underpin life-history in fish populations. This quantitative framework for the trio {P/B,Q/B,P/Q} is based on an explicit dependence with body size, which simplifies the estimation of these quantities. Model complexity depends, in part, on which data are available. Models were applied to real data from commercially important species fished in Chile. Statistical properties of the new models were evaluated by an intensive resampling approach. The simplest possible model for the trio {P/B,Q/B,P/Q} rests on the assumption of a stable age distribution. These quantities have a key importance in ecosystem modelling because they determine population energetics in terms of food intake by predation and the transformation of this energy into population biomass of predators. Application of the new models produces results which were comparable to those given by standard methods. This thesis is a result of multidisciplinary research which attempts to make a contribution to the understanding of the mechanisms underlying the allometric scaling of food consumption and production in fish populations. It proposes models for the trio {P/B,Q/B,P/Q} and thus, has the potential to be widely applicable in fisheries science.
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Abu, Awad Diala. "Death and sterility with a side of evolutionary suicide : the interplay of deleterious mutations and population size and the evolution of self-fertilisation." Thesis, Lille 1, 2014. http://www.theses.fr/2014LIL10134/document.
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La présence des mutations délétères a favorisé l'évolution de mécanismes, au niveau cellulaire et au niveau des organismes (e.g. les régimes de reproduction), permettant de diminuer leurs effets négatifs. Au cours de cette thèse nous avons étudié leur impact sur la taille des populations à travers des modèles tenant compte de l'interaction entre la démographie et la sélection, cette interaction étant souvent mise de coté dans les modèles conventionnels de génétique des populations. Dans un contexte déterministe à un seul locus des mutations somatiques et gamétiques influencent la taille et le fardeau génétique des populations (ces derniers étant dépendants du moment d’expression des mutations dans le cycle de vie). Nos modèles stochastiques avec un grand nombre de locus indiquent que la viabilité des populations dépend des paramètres démographiques et génétiques (taux de mutation, effet délétère des mutations). L'autofécondation est généralement avantageuse, augmentant la taille et la viabilité des populations, mais lorsque les mutations sont de faible effet un régime d'autogamie stricte mène à l'extinction par fonte mutationelle. En permettant l'évolution de l'autofécondation à partir d'une population allogame nous observons des cas de suicide évolutif où les populations évoluent vers l'autogamie stricte et s'éteignent, ce qui pourrait expliquer les taux d’extinctions élevés des espèces auto-fécondantes comparées aux allo-fécondantes. Ces modèles prédisent que la taille des populations pourrait être une conséquence et non une cause de leurs propriétés génétiques, appuyant sur l’importance de prendre en compte leur interaction dans l'étude de l'évolution des populationsAs the ultimate source of genetic variation, mutation has the inconvenience of introducing deleterious mutations. These mutations shape the evolution of species, from genetic mechanisms on the cellular level to reproductive systems, which lessen their effects on fitness. In this thesis we explore how these mutations influence population size by allowing the interaction between population size and selection, which has been little explored in conventional population genetics models. In a deterministic context with a single locus, germ-line and somatic mutations influence population size and the mutation load, both which depend on the timing of the expression of these mutations. Multi-locus individual based models show that population viability depends on the demographic properties and on the rate of introduction and impact of mutations. Though self-fertilisation generally increases population viability, strictly self-fertilising populations go extinct due to mutational meltdown when mutations are of small effect. When selfing is allowed to evolve from an outcrossing reproductive regime, there are cases of evolutionary suicide where strict selfing evolves and leads to extinction. We predict that the genetic properties of populations may not be a consequence but a cause of population size. We have emphasized the importance of taking the demographic consequences of deleterious mutations into account when studying the evolution of populations, as in the case of the evolution of self-fertilisation where the previously undetected evolutionary suicide was observed. This result may explain the observed higher extinction rates in selfing compared to outcrossing species
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Gattepaille, Lucie. "Population Genetic Methods and Applications to Human Genomes." Doctoral thesis, Uppsala universitet, Evolutionsbiologi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-260998.
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Population Genetics has led to countless numbers of fruitful studies of evolution, due to its abilities for prediction and description of the most important evolutionary processes such as mutation, genetic drift and selection. The field is still growing today, with new methods and models being developed to answer questions of evolutionary relevance and to lift the veil on the past of all life forms. In this thesis, I present a modest contribution to the growth of population genetics. I investigate different questions related to the dynamics of populations, with particular focus on studying human evolution. I derive an upper bound and a lower bound for FST, a classical measure of population differentiation, as functions of the homozygosity in each of the two studied populations, and apply the result to discuss observed differentiation levels between human populations. I introduce a new criterion, the Gain of Informativeness for Assignment, to help us decide whether two genetic markers should be combined into a haplotype marker and improve the assignment of individuals to a panel of reference populations. Applying the method on SNP data for French, German and Swiss individuals, I show how haplotypes can lead to better assignment results when they are supervised by GIA. I also derive the population size over time as a function of the densities of cumulative coalescent times, show the robustness of this result to the number of loci as well as the sample size, and together with a simple algorithm of gene-genealogy inference, apply the method on low recombining regions of the human genome for four worldwide populations. I recover previously observed population size shapes, as well as uncover an early divergence of the Yoruba population from the non-African populations, suggesting ancient population structure on the African continent prior to the Out-of-Africa event. Finally, I present a case study of human adaptation to an arsenic-rich environment.