Fundação de Amparo a Pesquisa no Estado do Rio Grande do Sul / In this work we propose a discrete predator-prey model with the purpose of analyzing the spatio-temporal dynamics of herbivorous and their predators. For that, we explicitly consider the dispersion of both species through Coupled Map Lattice models, that is, systems of difference equations coupled by dispersal. We suppose that the prey population presents density-dependent growth and predators, Holling type II functional response. In order to analyze the effects of prey-taxis showed by predators, which means, that predators direct their movement to regions of high prey densities, we computationally implemented our model for different movement schemes: difusion for both species, immobile prey and taxis for predators and, difusion for prey and taxis for predators. We conclude that the dispersal behavior of predators and preys plays a crucial role on their spatio-temporal dynamics and hence cannot be omitted when modeling predator-prey interactions. / Neste trabalho construímos um modelo presa-predador discreto com objetivo de analisar a dinâmica espaço-temporal de insetos herbívoros e seus predadores. Para tal, consideramos explicitamente a dispersão de ambas as espécies através de modelos de Rede de Mapas Acoplados, isto é, sistemas de equações a diferenças acopladas pela dispersão. Consideramos que as presas apresentam crescimento dependente da densidade e os predadores, resposta funcional Holling do tipo II. Para analisar os efeitos da movimentação de taxia dos predadores, isto é, o movimento direcionado às regiões de maiores densidades de presas, implementamos computacionalmente o modelo para diferentes esquemas de movimentação: difusão para ambas as espécies, presas imóveis e taxia para predadores e difusão para presas e taxia para predadores. Concluímos que o comportamento de movimentação de presas e predadores tem um papel relevante na sua dinâmica espaço-temporal e não pode ser ignorado na modelagem destes sistemas.

This thesis consists of four papers, three papers about modelling animal populations and one paper about an area integral estimate for solutions of partial differential equations on non-smooth domains. The papers are: I. Å. Brännström, Single species population models from first principles. II. Å. Brännström and D. J. T. Sumpter, Stochastic analogues of deterministic single species population models. III. Å. Brännström and D. J. T. Sumpter, Coupled map lattice approximations for spatially explicit individual-based models of ecology. IV. Å. Brännström, An area integral estimate for higher order parabolic equations. In the first paper we derive deterministic discrete single species population models with first order feedback, such as the Hassell and Beverton-Holt model, from first principles. The derivations build on the site based method of Sumpter & Broomhead (2001) and Johansson & Sumpter (2003). A three parameter generalisation of the Beverton-Holtmodel is also derived, and one of the parameters is shown to correspond directly to the underlying distribution of individuals. The second paper is about constructing stochastic population models that incorporate a given deterministic skeleton. Using the Ricker model as an example, we construct several stochastic analogues and fit them to data using the method of maximum likelihood. The results show that an accurate stochastic population model is most important when the dynamics are periodic or chaotic, and that the two most common ways of constructing stochastic analogues, using additive normally distributed noise or multiplicative lognormally distributed noise, give models that fit the data well. The latter is also motivated on theoretical grounds. In the third paper we approximate a spatially explicit individual-based model with a stochastic coupledmap lattice. The approximation effectively disentangles the deterministic and stochastic components of the model. Based on this approximation we argue that the stable population dynamics seen for short dispersal ranges is a consequence of increased stochasticity from local interactions and dispersal. Finally, the fourth paper contains a proof that for solutions of higher order real homogeneous constant coefficient parabolic operators on Lipschitz cylinders, the area integral dominates the maximal function in the L2-norm.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This research is inserted in the Biomathematics Research Group of the Programa de Pós-Graduação em Matemática of the Universidade Federal de Santa Maria-RS. It consists in the study of a discrete model for a prey-predator-insecticide system based on the Coupled Map Lattice as basic tool for its formulation. Due to the serious problems that crop pests represent to agriculture, we aproached the Integrated Pest Management (IPM), which is a pest control system that seeks to preserve and enhance the natural mortality factors of pests by integrated use of control methods selected based on technical, economic, ecological and sociological parameters. The objective of this work is to build a model as simple as possible to study the effects of different pests management strategies. These strategies are divided into different treatments which take into account the number of measurements of pest population, establishing control levels (CL) and different control measures (pesticide and biological control). For comparison and to point where the treatment is more efficient to compute the total density of the pest population without any control measure and when each treatment is applied over a certain period of time. The difference between these values is converted into a decreasing percentage of the population of pests. The same is done to obtain the percentage decrease in the number of treated sites. It was found that the sooner you apply the insecticide in the system, the more effective the treatment. Furthermore, it was observed that the presence of predators (biological control) decreases the amount of treated sites and, in some instances, is less effective in controlling pest. / Esta pesquisa está inserida na Linha de Pesquisa Biomatemática, do Programa de Pós-Graduação em Matemática da Universidade Federal de Santa Maria-RS. Configura-se como um estudo sobre um modelo discreto para um sistema praga-predador-inseticida tendo como ferramenta básica para sua formulação a Rede de Mapas Acoplados. Devido aos sérios problemas que pragas de lavoura representam para agricultura, abordou-se o Manejo Integrado de Pragas (MIP), que é um sistema de controle de pragas que busca preservar e aumentar os fatores de mortalidade natural de pragas pelo uso integrado de métodos de controle selecionados com base em parâmetros técnicos, econômicos, ecológicos e sociológicos. O objetivo deste trabalho é construir um modelo tão simples quanto possível, para estudar as consequências de diferentes estratégias de manejos de pragas. Essas estratégias são divididas em tratamentos diferentes nos quais leva-se em consideração o número de medições da população de pragas, estabelecimento de níveis de controle (NC) e diferentes medidas de controle aplicadas (inseticida e controle biológico). Para comparar e apontar qual dos tratamentos é mais eficiente, computou-se a densidade total da população de pragas sem nenhuma medida de controle e quando cada um dos tratamentos é aplicado ao longo de um determinado período de tempo. A diferença entre esses valores é convertida em um percentual de decrescimento da população de pragas. O mesmo é feito para se obter o percentual de decrescimento do número de sítios tratados. Foi possível constatar que quanto mais cedo se aplica o inseticida no sistema, mais efetivo é o tratamento. Além disso, observou-se que a presença dos predadores (controle biológico) diminui a quantidade de sítios tratados e, em alguns momentos, é menos eficiente no controle da praga.

The aim of this thesis is to investigate the dynamical behaviors of spatially extended systems with fluctuating time delays. In recent years, the study of spatially extended systems and systems with fluctuating delays has experienced a fast growth. In ubiquitous natural and laboratory situations, understanding the action of time-delayed signals is a crucial for understanding the dynamical behavior of these systems. Frequently, the length of the delay is found to change with time. Spatially extended systems are widely studied in many fields, such as chemistry, ecology, and biology. Self-organization, turbulence, and related nonlinear dynamic phenomena in spatially extended systems have developed into one of the most exciting topics in modern science. The first part of this thesis considers the discrete system. Diffusively coupled map lattices with a fluctuating delay are used in the study. The uncoupled local dynamics of the considered system are represented by the delayed logistic map. In particular, the influences of diffusive coupling and fluctuating delay are studied. To observe and understand the influences, the results for the considered system are compared with coupled map lattices without delay and with a constant delay as well as with the uncoupled logistic map with fluctuating delays. Identifying different patterns, determining the existence of traveling wave solutions, and specifying the fully synchronized stable state are the focus of this part of the study. The Lyapunov exponent, the master stability function, spectrum analysis, and the structure factor are used to characterize the different states and the transitions between them. The second part examines the continuous system. The delay is introduced into the reactionterm of the Fisher-KPP equation. The focus of this part of study is the time-delay-induced Turing instability in one-component reaction-diffusion systems. Turing instability has previously only been found in multiple-component reaction-diffusion systems. However, this work demonstrates with the help of the stability exponent that fluctuating delay can result in Turing instability in one-component reaction-diffusion systems as well. / Ziel der vorliegenden Arbeit ist die Untersuchung der Einflüsse der zeitlich fluktuierenden Verzögerungen in räumlich ausgedehnten diffusiven Systemen. Durch den Vergleich von Systemen mit konstanter Verzögerung bzw. Systemen ohne räumliche Kopplung erhält man ein tieferes Verständnis und eine bessere Beschreibungsweise der Dynamik des räumlich ausgedehnten diffusiven Systems mit fluktuierenden Verzögerungen. Im ersten Teil werden diskrete Systeme in Form von diffusiven Coupled Map Lattices untersucht. Als die lokale iterierte Abbildung des betrachteten Systems wird die logistische Abbildung mit Verzögerung gewählt. In diesem Teil liegt der Fokus auf Musterbildung, Existenz von Multiattraktoren und laufenden Wellen sowie der Möglichkeit der vollen Synchronisation. Masterstabilitätsfunktion, Lyapunov Exponent und Spektrumsanalyse werden benutzt, um das dynamische Verhalten zu verstehen. Im zweiten Teil betrachten wir kontinuierliche Systeme. Hier wird die Fisher-KPP Gleichung mit Verzögerungen im Reaktionsteil untersucht. In diesem Teil liegt der Fokus auf der Existenz der Turing Instabilität. Mit Hilfe von analytischen und numerischen Berechnungen wird gezeigt, dass bei fluktuierenden Verzögerungen eine Turing Instabilität auch in 1-Komponenten-Reaktions-Diffusionsgleichungen gefunden werden kann

The aim of this thesis is to investigate the dynamical behaviors of spatially extended systems with fluctuating time delays. In recent years, the study of spatially extended systems and systems with fluctuating delays has experienced a fast growth. In ubiquitous natural and laboratory situations, understanding the action of time-delayed signals is a crucial for understanding the dynamical behavior of these systems. Frequently, the length of the delay is found to change with time. Spatially extended systems are widely studied in many fields, such as chemistry, ecology, and biology. Self-organization, turbulence, and related nonlinear dynamic phenomena in spatially extended systems have developed into one of the most exciting topics in modern science. The first part of this thesis considers the discrete system. Diffusively coupled map lattices with a fluctuating delay are used in the study. The uncoupled local dynamics of the considered system are represented by the delayed logistic map. In particular, the influences of diffusive coupling and fluctuating delay are studied. To observe and understand the influences, the results for the considered system are compared with coupled map lattices without delay and with a constant delay as well as with the uncoupled logistic map with fluctuating delays. Identifying different patterns, determining the existence of traveling wave solutions, and specifying the fully synchronized stable state are the focus of this part of the study. The Lyapunov exponent, the master stability function, spectrum analysis, and the structure factor are used to characterize the different states and the transitions between them. The second part examines the continuous system. The delay is introduced into the reactionterm of the Fisher-KPP equation. The focus of this part of study is the time-delay-induced Turing instability in one-component reaction-diffusion systems. Turing instability has previously only been found in multiple-component reaction-diffusion systems. However, this work demonstrates with the help of the stability exponent that fluctuating delay can result in Turing instability in one-component reaction-diffusion systems as well. / Ziel der vorliegenden Arbeit ist die Untersuchung der Einflüsse der zeitlich fluktuierenden Verzögerungen in räumlich ausgedehnten diffusiven Systemen. Durch den Vergleich von Systemen mit konstanter Verzögerung bzw. Systemen ohne räumliche Kopplung erhält man ein tieferes Verständnis und eine bessere Beschreibungsweise der Dynamik des räumlich ausgedehnten diffusiven Systems mit fluktuierenden Verzögerungen. Im ersten Teil werden diskrete Systeme in Form von diffusiven Coupled Map Lattices untersucht. Als die lokale iterierte Abbildung des betrachteten Systems wird die logistische Abbildung mit Verzögerung gewählt. In diesem Teil liegt der Fokus auf Musterbildung, Existenz von Multiattraktoren und laufenden Wellen sowie der Möglichkeit der vollen Synchronisation. Masterstabilitätsfunktion, Lyapunov Exponent und Spektrumsanalyse werden benutzt, um das dynamische Verhalten zu verstehen. Im zweiten Teil betrachten wir kontinuierliche Systeme. Hier wird die Fisher-KPP Gleichung mit Verzögerungen im Reaktionsteil untersucht. In diesem Teil liegt der Fokus auf der Existenz der Turing Instabilität. Mit Hilfe von analytischen und numerischen Berechnungen wird gezeigt, dass bei fluktuierenden Verzögerungen eine Turing Instabilität auch in 1-Komponenten-Reaktions-Diffusionsgleichungen gefunden werden kann