Diese Arbeit beschäftigt sich mit der Naturverjüngung von Traubeneiche (Quercus petraea (Matt.) Liebl.) unter Kiefernschirm. Eine erfolgreiche Verjüngung von Traubeneiche ist ohne menschliche Hilfe nur schwer umzusetzen. Als Ursache wird in der Literatur die Konkurrenzsituation von Begleitvegetation um die Ressource Wasser besonders hervorgehoben. Um künftige Managementmaßnahmen von Oberstand und Begleitvegetation bezüglich der Eichenverjüngung bewerten zu können, wurde das individuen-basierte Modell oak-lay entwickelt, das die Konkurrenz um Wasser explizit auf pflanzenphysiologischer Basis berücksichtigt. Die Kombination von individuen-basierten und prozess-basierten Ansätzen wird auch als Hybrid-Modell bezeichnet. In der Verjüngungsmodellierung ist bisher keine Anwendung eines Hybrid-Modells bekannt, so dass es sich vermutlich um das erste Modell seiner Art handelt. Die Arbeit ist in drei große Arbeitsschwerpunkte aufgeteilt. Im ersten Teil wird oak-lay detailliert vorgestellt und analysiert. Dabei kommen standardisierte Verfahren wie eine globale Sensitivitätsanalyse oder eine Analyse der Rechenzeit mittels Landau-Symbole zum Einsatz. Der zweite Teil analysiert mit Hilfe von Simulationsexperimenten eine neue Methode der Mortalitätsbeschreibung in individuen-basierten Modellen auf physiologischer Basis. Die prozess-basierte Wasserhaushaltsberechnung des oak-lay ermöglicht die Festsetzung einer Mortalitätsschwelle über das Druckpotential der Individuen. Für die Analysen wurde auf Ereigniszeitanalysen zurückgegriffen. Konkret angewandt wurden der Kaplan-Meier Schätzer und das semiparametrische Cox-Modell. Der dritte und letzte Teil wendet das Modell beispielhaft in einer Reihe von Simulationsexperimenten an. Dabei werden unterschiedliche Managementmaßnahmen am Oberstand und der Begleitvegetation simuliert und auf Unterschiede im Verjüngungserfolg und der räumlichen Verteilung getestet. Das Modell oak-lay konnte erfolgreich nachweisen, dass Hybrid-Modelle im Bereich der Verjüngungsmodellierung entwickelt und angewendet werden können. Die globale Sensitivitätsanalyse des Wasserhaushaltsmodells konnte die einflussreichsten Parameter identifizieren und das Laufzeitverhalten des Modells konnte ebenso analysiert werden. Die Einhaltung bestimmter Selbstdifferenzierungsmuster wurde über alle Simulationen geprüft. Dabei wurde erfolgreich die Mortalität über den Wassergehalt der Individuen bestimmt. Die Simulationsexperimente der verschiedenen Managementmaßnahmen haben gezeigt, dass eine Anwendung als Managementtool möglich ist. Die Entwicklung eines neuen Modelltyps bei der Verjüngungsmodellierung hat allerdings auch einigen neuen Forschungsbedarf generiert. Um oak-lay weiterzuentwickeln sind weitere Arbeiten nötig.

European forests have experienced vitality loss and dieback due to increasing disturbances, temperatures, droughts, and forest management. Around 160 million cubic meters of woody biomass in Germany were damaged from 2018 to 2020. Protected areas can offer insights into the natural resilience of European forests after disturbances. However, they face conflicts such as mass outbreaks and the spread of insect pests that can threaten biodiversity and natural habitats. The European spruce bark beetle (Ips typographus) is among Europe’s most important and severe forest pest species and can act as an ecological disturbance. Due to ongoing climate change, no weakening is expected in the future. Forest management can directly influence important drivers of disturbance regimes. However, the response times are likely slow, requiring effective and adaptive risk-assessing management. Simulation models can play an important and influential role in such management as decision-making tools or for analysis of important drivers. Such models have been successfully applied in fishery management, disease control, and forest fire management. While there are many models published about Ips typographus, there is still no simulation tool that individually describes trees and beetles with their properties and decisions, tests the effectiveness of management measures, and uses spatially explicit data for natural landscapes. This approach would allow for investigating infestation patterns and development in natural landscapes based on individual beetle and tree traits. It could also be used to study the impact of climate change and forest protection management on all spatial scales - from individual beetles to entire landscapes. The main goal of the thesis is to predict the risk of bark beetle infestations and outbreaks in a national park region in Germany under different climate change and management scenarios as an emergent outcome of individual traits of the European spruce bark beetle and its host tree. To achieve this goal, a combination and improvement of existing models on the life history of Ips typographus and its host tree Picea abies is done to simulate infestations on an individual level. The results are then scaled to the landscape level using a Markov chain metamodel for 20 years into the future. It is shown how (i) management scenarios consisting of different sanitation felling intensities, and (ii) climate change scenarios representing increasing numbers of yearly beetle generations interact and affect the infestation spread. Chapter 2 discusses the creation, testing, and implementation of a new simulation model for the dispersal and infestation of Ips typographus in a natural European landscape. The IPS-SPREADS (Infestation Pattern Simulation Supporting PREdisposition Assessment DetailS) model is an innovative combination of existing models on beetle phenology (PHENIPS), spruce tree predisposition (PAS - predisposition assessment systems), and precise mechanistic dispersal flight in an artificial forest (IPS - Infestation Pattern Simulation). The model is used to study the effectiveness of sanitation felling in five different research areas at the border of a national park in Germany under varying annual beetle generation numbers. Chapter 3 explores the various purposes and types of metamodels used in agentbased modeling and attempts to identify and rank the most suited or efficient model types for each application. This assessment was accomplished through a systematic literature review of 27 scientific publications containing 40 different metamodel applications in an individual-based modeling context. A standardized rating instruction was created and used by the candidate and a group of other Ph.D. students and postdoctoral researchers to objectively rate different metamodel applications, such as upscaling agent-based models or conducting sensitivity analyses. In Chapter 4 of the dissertation, the IPS-SPREADS simulation model is used to predict the risk of bark beetle infestations in a national park region for 20 years into the future. A metamodel approach based on Markov chains is used to scale the computationally demanding IPS-SPREADS model to larger temporal and spatial scales. The metamodel is calibrated and validated using data on infested trees from 2015 to 2017. The model is then used to assess the effectiveness of sanitation felling in preventing the spread of a bark beetle outbreak from the national park to adjacent forests until 2038. This work adds to a series of previous studies investigating several aspects of the Norway spruce (Picea abies) and European spruce bark beetle (Ips typographus) system, such as risk assessment, beetle development, beetle dispersal, and infestation patterns, the effectiveness of forest protection measures against the beetle spread or the impact of bark beetle disturbance on the forest as well as its interaction with other disturbances. The results of the studies presented as thesis chapters 2 to 4 indicate that regardless of the number of yearly beetle generations and the spatial or temporal scale, a sanitation felling intensity of 80 % and above seems to mitigate further mass outbreak propagation. It is also shown that habitat inter-connectivity and individual traits of beetles and host trees substantially affect the infestation patterns. In addition, commonly applied metamodel types and application purposes in an individual-based modeling context are revealed. The most promising model variant varies in regard to the chosen application aim. Further research directions based on the work presented in this thesis incorporate investigating spatial configurations of mixed forest stands and their effect on the dispersal and infestation risk of the European spruce bark beetle. Furthermore, it is discussed how applying and integrating open-access GIS data, such as the European Unions Copernicus program, could improve model validity and applicability. The effects and implications for implementing and analyzing further management measures, such as buffer zones around protected areas, terrestrial detection based on visual clues, and dispensers with anti-attractants in the proposed model framework, are discussed. / Europas Wälder haben aufgrund von zunehmenden Störungen, Temperaturen, Dürren und vergangener Managemententscheidungen an Vitalität verloren und zeigen großflächige Absterbeerscheinungen. Allein in Deutschland betrug das Schadvolumen von 2018 bis 2020 rund 160 Millionen Kubikmeter. Schutzgebiete können Einblicke in die natürliche Widerstandsfähigkeit der Wälder nach Störungen gewähren, bieten aber auch Potenzial für Konflikte wie Massenvermehrungen und Ausbreitung von Schädlingen, die die biologische Vielfalt und die natürlichen Lebensräume bedrohen können. Der Große Achtzähnige Fichtenborkenkäfer (Ips typographus) gehört zu den wichtigsten und schwerwiegendsten Waldschädlingen in Europa. Aufgrund des anhaltenden Klimawandels ist keine Gefährdungsabnahme der Waldbeständen zu erwarten. Während die Forstwirtschaft wichtige Treiber von Störungsregimen direkt oder indirekt beeinflussen kann, sind die Reaktionszeiten sehr langsam und verlangen ein wirksames und adaptives Risikomanagement. Simulationsmodelle können eine wichtige und effektive Rolle für das Management als Entscheidungshilfen oder zur Analyse wichtiger Treiber spielen. Beispiele für erfolgreiche Anwendungen im Entscheidungsprozess stellen Bereiche wie das Fischereimanagement, die Bekämpfung von Epidemien und das Waldbrandmanagement dar. Obwohl es bereits einige Simulationsmodelle für Ips typographus gibt, wurde bisher kein Ansatz untersucht, bei dem sowohl die Bäume als auch die Käfer als Individuen mit Eigenschaften, Wahrnehmung und Interaktionen abgebildet werden. Mit solch einem Modell könnte untersucht werden, wie sich die individuellen Eigenschaften der Käfer und der Bäume auf die Befallsmuster und die Wirksamkeit von Managementmaßnahmen in Abhängigkeit der betrachteten räumlichen oder zeitlichen Skala auswirken. Das Hauptziel der vorliegenden Dissertation besteht daher darin, das Risiko von Borkenkäferbefall und von Ausbrüchen unter verschiedenen Klimawandel- und Managementszenarien als emergentes Ergebnis individueller Eigenschaften des Großen Achtzähnigen Fichtenborkenkäfers und seines Wirtsbaums zu analysieren. Dies geschieht durch die Kombination, Verbesserung und Anwendung bestehender Modelle zur Lebensgeschichte von Ips typographus und dessen Wirtsbaum Picea abies am Beispiel einer Nationalparkregion in Deutschland. Die Ergebnisse des Individuenbasierten Modells werden anschließend auf die Landschaftsebene und für 20 Jahre in die Zukunft skaliert, indem ein auf Markov-Ketten basierendes Metamodel kreiert und validiert wird. Es wird gezeigt, wie (i) Managementszenarien bestehend aus verschiedenen Entnahmeintensitäten befallener Bäume sowie (ii) Klimawandelszenarien bestehend aus einer Zunahme der jährlichen Käfergenerationen interagieren und die Befallsausbreitung beeinflussen. In Kapitel 2 der Dissertation wird die Entwicklung, Überprüfung und Implementierung eines neuen Simulationsmodells für die Ausbreitung und den Befall von Ips typographus in einer realen Landschaft Europas diskutiert. Das IPS-SPREADS (Infestation Pattern Simulation Supporting REdisposition Assessment DetailS) Modell ist eine innovative Kombination bestehender Modelle zur Phänologie des Käfers (PHENIPS), der Prädisposition des Wirtsbaumes gegenüber Borkenkäferbefall (PAS - Prädispositionsabschätzsysteme) und der Individuen-basierten Simulation des Ausbreitungsflugs der Käfer in einem künstlichen Wald (IPS - Infestation Pattern Simulation). Das neue Modell IPS-SPREADS wird dann verwendet, um die Wirksamkeit der Entnahme befallener Bäume in fünf verschiedenen Probeflächen des Nationalparks Sächsische Schweiz während zunehmender jährlicher Käfergenerationen zu untersuchen. Darüber hinaus wird der Einfluss individueller Eigenschaften auf das Befallsgeschehen und auf die Wirksamkeit der Entnahme befallener Bäume analysiert. Kapitel 3 widmet sich der Anwendungsgebiete und Typen von Metamodellen, die für Agenten-basierten Modelle verwendet werden, und versucht, die vielversprechendsten Modelltypen je Anwendung zu identifizieren. Dies geschieht mittels einer systematischen Literaturanalyse, die 27 wissenschaftliche Veröffentlichungen mit insgesamt 40 verschiedenen Metamodellanwendungen für Individuen-basierte Modelle untersucht. Ein standardisiertes Bewertungsverfahen wird erstellt und vom Kandidaten zusammen mit einer Gruppe von Doktoranden und Postdoktoranden angewendet, um die Metamodelle im Bezug auf ihr Anwendungsziel objektiv zu bewerten. In Kapitel 4 der Dissertation wird das entwickelte IPS-SPREADS Modell verwendet, um das Risiko von Borkenkäferbefall in einer Nationalparkregion für 20 Jahre in die Zukunft vorherzusagen. Dafür wird ein Metamodell basierend auf Markov-Ketten entwickelt, welches das rechenintensive IPS-SPREADS Modell auf größere zeitliche und räumliche Skalen hebt. Dieses Metamodell wird mittels Befallsdaten aus der Nationalparkregion für die Jahre 2015 bis 2017 validiert. Im Anschluss wird das Metamodell dann verwendet, um die Wirksamkeit der Entnahme befallener Bäume für die Ausbreitungsbekämpfung eines Borkenkäfermassenbefalls vom Nationalpark in die angrenzenden Wälder während eines 20-jährigen Zeitraums zu untersuchen. Die vorliegende Arbeit baut auf einer Reihe von Studien auf, die verschiedene Aspekte des Systems von Großem Achtzähnigen Fichtenborkenkäfer (Ips typographus) und Gemeiner Fichte (Picea abies) untersuchen: Prädispositionsbewertung, Käferentwicklung, Ausbreitungs- und Befallsmuster sowie die Wirksamkeit von Waldschutzmaßnahmen gegen die Befallsausbreitung. Die Ergebnisse der als Kapitel zwei bis vier vorgestellten Studien zeigen, dass unabhängig von der Anzahl der jährlichen Käfergenerationen und der räumlichen oder zeitlichen Skala eine Entnahmeintensität befallener Bäume von 80 % und mehr die Ausbreitung eines Massenbefalls zu mindern scheint. Es wird auch gezeigt, dass die Habitatvernetzung und die individuellen Eigenschaften der Käfer und Wirtsbäume die Befallsmuster beeinflussen. Darüber hinaus werden häufig angewandte Metamodelltypen und Anwendungszwecke in einem Individuenbasierten Modellierungskontext zusammengetragen und die vielversprechendste Modellvariante je Anwendungsgebiet extrahiert. Zum Schluss werden weitere Forschungsrichtungen basierend auf den vorgestellten Studien diskutiert, wie zum Beispiel die Untersuchung der räumlichen Konfiguration von Mischwäldern und deren Auswirkungen auf das Befallsgeschehen des Großen Achtzähnigen Fichtenborkenkäfers. Des Weiteren wird diskutiert, wie die Anwendung und Integration von frei verfügbaren GIS-Daten, wie beispielsweise des Copernicus Programms der Europäischen Union, die Validität und Anwendbarkeit der entwickelten Modelle verbessern können. Am Ende werden potenzielle Implikationen für die Implementierung und Analyse weiterer Managementmaßnahmen wie Pufferzonen um Schutzgebiete, terrestrische Erkennung von Borkenkäferbefall sowie Dispenser mit Anti-Aggregationspheromonen im Rahmen der vorgestellten Modellstudien diskutiert.

No description available.

Collective cell migration is an important process during biological development and tissue repair but may turn malignant during tumor invasion. Mathematical and computational models are essential to unravel the mechanisms of self-organization that underlie the emergence of collective migration from the interactions among individual cells. Recently, guidance-by-followers was identified as one such underlying mechanism of collective cell migration in the embryo of the zebrafish. This poses the question of how the guidance stimuli are integrated when multiple cells interact simultaneously. In this study, we extend a recent individual-based model by an integration step of the vectorial guidance stimuli and compare model predictions obtained for different variants of the mechanism (arithmetic mean of stimuli, dominance of stimulus with largest transmission interface, and dominance of most head-on stimulus). Simulations are carried out and quantified within the modeling and simulation framework Morpheus. Collective cell migration is found to be robust and qualitatively identical for all considered variants of stimulus integration. Moreover, this study highlights the role of individual-based modeling approaches for understanding collective phenomena at the population scale that emerge from cell-cell interactions.

No description available.

Nos estudos de populações pesqueiras é comum o uso de modelos hidrodinâmicos acoplados a modelos biológicos e, um tipo de modelo merece destaque: o baseado no indivíduo (IBM). A Plataforma Continental do Atlântico Sudoeste comporta uma importante atividade pesqueira e, a influência da circulação na distribuição de ovos/larvas nessa região é pouco entendida. Estudos anteriores sugerem que o transporte de Ekman em direção à costa e o deságue de água fluvial impedem a perda de ovos e larvas da área costeira. Este trabalho apresenta resultados de um estudo englobando os padrões de circulação e de transporte de larvas nessa área, realizado através do desenvolvimento de um IBM para os estágios iniciais da Engraulis anchoita e o acoplamento deste a dois campos de velocidade superficial: a de Ekman, e a saída de um modelo hidrodinâmico 3D. Os resultados mostram que somente a deriva de Ekman não é suficiente para explicar o padrão de retenção larval observado na região. Os valores de retenção encontrados com a utilização da saída do modelo estão próximos aos observados. Maiores concentrações larvais foram obtidas no outono/inverno e menores na primavera/verão. Estes resultados estão diretamente relacionados à combinação dos efeitos dos padrões de vento da área com a influência das Correntes do Brasil e das Malvinas e do deságue continental na circulação sobre a plataforma. / Recruitment of pelagic fishes is the net result a series of continuous events in their life cycle. Most of the variability in natural mortality is thought to occur during the early stages of development and is related to environmental factors. The use of coupled physical-biological modeling in the study of fisheries populations is very common and a particular type of model deserves special mention: the Individual Based Model (IBM). The Atlantic Southwestern Continental Shelf is one of the most productive fishing sites in the Western South Atlantic, but the processes involving the circulation in this area and its influence on eggs/larvae transport and retention are still poorly understood. Recent studies describe the spawning activity of anchovy and its relationship to oceanographic processes and suggest that predominant onshore Ekman transport, during the austral winter/spring, keeps the eggs and larvae in coastal areas. According to these studies, the river runoff contributes to the formation of a retention zone for planktonic organisms over the area. This work presents results of a study that considers both the circulation pattern and larval transport, throught the development of an IBM for the early stages of anchovy Engraulis anchoita. The model is coupled to two surface velocity fields: the Ekman drift, and the output of a 3D hydrographic model. The results show that just Ekman surface velocities are not able to explain the larval dispersion observed in this region. Retention values obtained with the model output are much closer to observed values. Autumn and winter seasons present the highest values of retention. These results are due to the combined effect of the wind patterns registered in the area with the influence of the river runoff and the Brazil-Malvinas shelf circulation.

Nos estudos de populações pesqueiras é comum o uso de modelos hidrodinâmicos acoplados a modelos biológicos e, um tipo de modelo merece destaque: o baseado no indivíduo (IBM). A Plataforma Continental do Atlântico Sudoeste comporta uma importante atividade pesqueira e, a influência da circulação na distribuição de ovos/larvas nessa região é pouco entendida. Estudos anteriores sugerem que o transporte de Ekman em direção à costa e o deságue de água fluvial impedem a perda de ovos e larvas da área costeira. Este trabalho apresenta resultados de um estudo englobando os padrões de circulação e de transporte de larvas nessa área, realizado através do desenvolvimento de um IBM para os estágios iniciais da Engraulis anchoita e o acoplamento deste a dois campos de velocidade superficial: a de Ekman, e a saída de um modelo hidrodinâmico 3D. Os resultados mostram que somente a deriva de Ekman não é suficiente para explicar o padrão de retenção larval observado na região. Os valores de retenção encontrados com a utilização da saída do modelo estão próximos aos observados. Maiores concentrações larvais foram obtidas no outono/inverno e menores na primavera/verão. Estes resultados estão diretamente relacionados à combinação dos efeitos dos padrões de vento da área com a influência das Correntes do Brasil e das Malvinas e do deságue continental na circulação sobre a plataforma. / Recruitment of pelagic fishes is the net result a series of continuous events in their life cycle. Most of the variability in natural mortality is thought to occur during the early stages of development and is related to environmental factors. The use of coupled physical-biological modeling in the study of fisheries populations is very common and a particular type of model deserves special mention: the Individual Based Model (IBM). The Atlantic Southwestern Continental Shelf is one of the most productive fishing sites in the Western South Atlantic, but the processes involving the circulation in this area and its influence on eggs/larvae transport and retention are still poorly understood. Recent studies describe the spawning activity of anchovy and its relationship to oceanographic processes and suggest that predominant onshore Ekman transport, during the austral winter/spring, keeps the eggs and larvae in coastal areas. According to these studies, the river runoff contributes to the formation of a retention zone for planktonic organisms over the area. This work presents results of a study that considers both the circulation pattern and larval transport, throught the development of an IBM for the early stages of anchovy Engraulis anchoita. The model is coupled to two surface velocity fields: the Ekman drift, and the output of a 3D hydrographic model. The results show that just Ekman surface velocities are not able to explain the larval dispersion observed in this region. Retention values obtained with the model output are much closer to observed values. Autumn and winter seasons present the highest values of retention. These results are due to the combined effect of the wind patterns registered in the area with the influence of the river runoff and the Brazil-Malvinas shelf circulation.

Nous connaissons depuis plus d’un siècle des bouleversements climatiques, socio-économiques et sociétaux de plus en plus fréquents et intenses. L’adaptation à ce contexte incertain, pour envisager l’avenir de façon durable, est un défi particulièrement important. L’agriculture est au cœur de ce défi et de la réflexion sur les modes d’adaptation. Les anthropologues ont récemment identifié deux types de changements de l’agriculteur: le changement mineur (en accord avec le comportement normatif de référence), et le changement majeur (changement profond, remise en cause des normes majoritaires permettant l’adoption de comportements innovants). Ces deux types de changement sont très proches de l’adaptation incrémentale et de l’adaptation transformationnelle qui sont définis tant pour des individus que pour des institutions locales, nationales ou internationales … Nous proposons un modèle individu-centré de l’adaptation des agriculteurs qui intègre dynamiquement changements mineurs et majeurs, en nous focalisant sur la dimension psycho-sociale de ces changements. Nous appliquons notre modèle à la question, de la conversion à l’agriculture biologique des éleveurs laitiers français. Cette transition a en effet été généralement caractérisée comme un changement majeur, ou une adaptation transformationnelle, et s’avère donc pertinente pour tester notre modèle. Le modèle d’agriculteur est en général dans un régime stable durant lequel seuls des changements mineurs sont opérés. Ces changements sont menés en imitant des comportements adoptés par les agriculteurs les plus crédibles. La crédibilité d’un agriculteur pour un autre est d’autant plus forte que son volume produit est supérieur à celui de cet agriculteur. Ces changements se traduisent concrètement par des modifications des volumes produits qui correspondent à des choix de pratiques plus ou moins intensifs.Le modèle peut passer d’un régime stable à un autre en transitant par un changement majeur impliquant de changer la hiérarchie des importances, accordées aux dimensions « productiviste » et « environnementale », qui pondèrent son évaluation des résultats de son mode de production (par exemple : conventionnel ou biologique). Le calcul de son évaluation utilise la théorie de l’action raisonnée. Il permet à l’agriculteur de déterminer sa satisfaction, à partir de ses résultats précédents, et de ses résultats comparés à ceux de ses pairs crédibles, en tenant compte de l’importance accordées à chaque dimension d’évaluation. Lorsqu’un agriculteur est insatisfait de son mode de production courant, il évalue sa satisfaction potentielle pour un autre mode de production, et adopte ce dernier si son gain de satisfaction est supérieur à un seuil. Il change alors la hiérarchie des importances accordées à ses dimensions d’évaluation pour être en accord avec le mode adopté. Un agriculteur biologique accordera ainsi par exemple une importance plus forte à la dimension environnementale qu’à la dimension productiviste. Ce changement implique alors une réévaluation tant de la crédibilité de ses pairs que de leurs pratiques. (...) / For more than a century, climatic, socio-economic and societal changes are more and more frequent and intense. Adapting to this uncertain context to envisage a sustainable future is a particularly important challenge. Agriculture is at the heart of this challenge and the reflection on the modes of adaptation. Anthropologists have recently identified two types of farmer changes: minor change (consistent with normative behavior), and major change (deep change, challenge the majority norms allowing adoption of innovative behaviors). These two types of change are very close to the incremental adaptation and the transformational adaptation that are defined for individuals as well as for local, national or international institutions.We propose an individual-based model to study farmers’ adaptations that dynamically integrates minor and major changes. We focus on the social-psychological dimension of these changes. Our model is applied to the question of French dairy farmers’ conversions to organic farming. This transition has been characterized as a major change, or a transformational adaptation, and is therefore relevant to test our model.A farmer stays generally in a stable regime doing only minor changes. These changes are carried out by imitating the practices of the most credible farmers. The credibility of one farmer given to another is larger if his (her) produced volume is greater than that of this farmer. These changes are shown by concrete changes of produced volumes, which correspond to more or less intensive choices of practice.In the model, a farmer passes from one stable regime to another through a major change involving a change of his (her) hierarchy of importance over the "productivist" and "environmental" evaluative dimensions. The importance weights his (her) evaluation of the results according to the mode of production (for example: conventional or organic). The computation of the evaluation is based on the theory of reasoned action. This evaluation shows a farmer’s satisfaction that is based on his (her) previous results and his (her) results compared to those of his (her) credible peers, taking into account the importance given to each dimension of evaluation. When a farmer is dissatisfied with his (her) current mode of production, he (she) evaluates his (her) potential satisfaction with another mode of production, and adopts the latter if his (her) satisfaction gain is above a threshold. He (she) then changes the importance hierarchy given to the evaluation dimensions to be in agreement with the adopted mode. For example, an organic farmer will given more importance to the environmental dimension than to the productivist dimension. This change implies a reassessment of both the credibility given to his (her) peers and their practices. (...)

Biological invasions are major threats to any nation’s economy and biodiversity. To detect new biological incursions of some species biosecurity agencies deploy pheromone sentinel traps for targeted species at high risk sites such as airports, seaports and transitional facilities. A good example is the gypsy moth surveillance program in New Zealand. Following the detection of an incursion by an unwanted organism, ground-based searches to locate the source can be very expensive, but are essential to identify the introduction pathway and to increase the chances of success eradicating the unwanted organism. In such circumstances, the possibility of better targeting the search for the source of the incursion using a modelling approach is worthy of investigation A stochastic mechanistic model to hindcast moth flight from a recapture location to the release location was developed based on insect behaviour in response to wind and pheromones. The model was composed of two main processes, 1) downwind dispersal, assumed to result from an appetitive behaviour, indicated by an analysis of a previous mark-release-recapture experiment on painted apple moth (Teia anartoides, Walker) and, 2) anemotaxic dispersal inspired by pheromone anemotaxis theory but up-scaled from a fine-scaled behaviour model to a 2 m scale. A genetic algorithm was used to fit some model parameters. A specialised fitness function was developed to allow the genetic algorithm to identify parameters that resulted in models that reflected both the spread and density patterns in the trapping data. The resulting function allowed the stochastic model results to be compared with the inherently stochastic trapping data. The resulting individual based model simulates the spatio-temporal dispersal pattern of painted apple moth recorded during a previous mark-release-recapture experiment. While the proposed model is shown to have limitations with respect to accuracy and precision it is also demonstrated to greatly improve biosecurity incursion response capability, by more efficient targeting of search effort for the proximal source of an incursion.

This dissertation analyses the effects of current fisheries practices and management regulations of the green spiny lobster (Panulirus gracilis) in the Eastern Tropical Pacific Region (ETP). P. gracilis has reached a critical state in the ETP. Country-based studies report that between 60 and 98% of lobsters caught in the wild are under the minimum landing size (MLS). This means that spiny lobsters are being extracted before reproducing and contributing to the replenishment of interconnected populations. The recovery of green spiny lobster populations in the ETP and the future maintenance of a sustainable fishery will depend on effective management decisions and on taking in account environmental factors that influence the population dynamics of the lobsters. In the first study (Chapter 2), the B52 Spiny Lobster individual based simulation model was used for conducting a population viability analysis to quantify the effect of current fishing practices and the effect of varying management regulations on minimum landing size (MLS) and fishing effort. The best suit of regulations to maintain the highest abundance, production of offspring and catch is to protect juveniles and egged females, and to establish a MLS that assures the reproduction of individuals before being extracted. This study revealed regional variations, however the patterns and the causes for variation were not yet clear. This led to the next chapters in this dissertation. In Chapter 3, I used a meta-analysis to explore regional lobster variability by comparing published studies from the ETP. The objective was to identify patterns of variation related to geographic and environmental factors of the region that can inform the establishment and evaluation of coordinated regulations. Morphological relationships showed to be more variable at northern latitudes, where the mean annual sea surface temperatures are higher than at lower temperatures at the Equator. In terms of management, MLS regulations should be adapted accounting for the effect of sea surface temperature and its variation. Additionally, it was observed that monitoring methodologies are not standardized within the region and even in some cases, neither within countries. Furthermore, in most places monitoring of the spiny lobster fishery happens sporadically, only in Galapagos takes place every year. Identifying patterns of variations can improve the accuracy of prediction models which can help to explore, design, and apply more effective management measures, as well as promote regional coordination to support the recovery and maintenance of spiny lobsters. In Chapter 4, I contrast current Ecuadorian minimum landing size (MLS) regulation to lobster empirical measurements within Ecuador in order to recognize potential pitfalls for management enforcement. I used linear regression and multiple regression models with the objective of identifying potential relative size variations of the individuals caught in the wild over time and in the different fishing areas in Ecuador, as well as to analyse the effect of locality, sex, age and mean SST on the tail length/total length ratio. Morphological relations were significantly different among sexes, in time and by all sites. Most importantly, this study shows that current minimum size regulations are not applicable to all sites. Additionally, I found that water temperature has a significant effect on morphological relationship variations. However, it was not the main site-specific variable responsible for explaining such variations. In general, this work emphasizes the need for length data collection standardization and the consideration of temporal and spatial variation implications in national and regional fishery management planning, enforcement and evaluation.