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Made available in DSpace on 2014-12-17T14:33:06Z (GMT). No. of bitstreams: 1 IgorGB_DISSERT.pdf: 695705 bytes, checksum: 0611f2165b1e05afa1e64ceaedeacebb (MD5) Previous issue date: 2012-08-27 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / High levels of local, regional, and global extinctions has progressively simplified communities in terms of both species and ecosystem functioning. Theoretical models demonstrated that the degree of functional redundancy determines the rates of functional group loss in response to species extinctions. Here, we improve the theoretical predictions by incorporating in the model interactions between species and between functional groups. In this study, we tested the effect of different scenarios of interspecific interactions and effects between functional groups on the resistance to loss of community functional groups. Virtual communities have been built with different distribution patterns of species in functional groups, both with high and low evenness. A matrix A was created to represent the net effect of interspecific interactions among all species, representing nesting patterns, modularity, sensitive species, and dominant species. Moreover, a second matrix B was created to represent the interactions between functional groups, also exhibiting different patterns. The extinction probability of each species was calculated based on community species richness and by the intensity of the interspecific interactions that act upon it and group to which it belongs. In the model, successive extinctions decrease the community species richness, the degree of functional redundancy and, consequently, the number of functional groups that remain in the system. For each scenario of functional redundancy, A, and B, we ran 1000 simulations to generate an average functional extinction curve. Different model assumptions were able to generate remarkable variation on functional extinction curves. More extreme variations occurred when the matrix A and B caused a higher heterogeneity in the species extinction probability. Scenarios with sensitive species, positive or negative, showed a greater variation than the scenarios with dominant species. Nested interactions showed greater variation than scenarios where the interactions were in modules. Communities with maximal functional evenness can only be destabilized by the interactions between species and functional groups. In contrast, communities with low functional evenness can have its resistance either increased or decreased by the interactions. The concentration of positive interactions in low redundancy groups or negative interactions in high redundancy groups was able to decrease the functional extinction rates. In contrast, the concentration of negative interactions in low redundancy groups or positive interactions in high redundancy groups was able to increase the functional extinction rates. This model shows results that are relevant for species priorization in ecosystem conservation and restoration / Os n?veis elevados de extin??es locais, regionais e globais t?m simplificado progressivamente comunidades em termos de esp?cies e funcionamento do ecossistema. Modelos te?ricos demonstraram que o grau de redund?ncia funcional determina as taxas de perda de grupos funcionais ? medida que as comunidades sofrem extin??o de esp?cies. Aqui n?s aprimoramos as predi??es te?ricas pela incorpora??o no modelo de intera??es entre esp?cies e entre grupos funcionais. Neste estudo, testamos o efeito de diferentes cen?rios de intera??es interespec?ficas e de efeitos entre grupos funcionais sobre a resist?ncia das comunidades ? perda de grupos funcionais. Comunidades virtuais foram constru?das com diferentes padr?es de distribui??o de esp?cies nos grupos funcionais, tanto com alta quanto com baixa equitabilidade. Uma matriz A foi criada para representar o efeito l?quido das intera??es interespec?ficas entre todas as esp?cies, representando padr?es de aninhamento, modularidade, esp?cies sens?veis ou dominantes. Al?m disto, uma segunda matriz B foi criada para representar as intera??es entre grupos funcionais, tendo tamb?m diferentes padr?es. A probabilidade de extin??o de cada esp?cie foi calculada com base na riqueza de esp?cie da comunidade e pela intensidade das intera??es interespec?ficas que atuam sobre ela e sobre o grupo funcional ao qual ela pertence. No modelo, extin??es de esp?cies sucessivas diminuem a riqueza da comunidade, o grau de redund?ncia funcional e consequentemente o n?mero de grupos funcionais que permanecem no sistema. Para cada cen?rio de redund?ncia funcional, A e B, n?s rodamos 1000 simula??es para gerar uma curva de extin??o funcional m?dia. Diferentes suposi??es do modelo foram capazes de gerar varia??es not?veis nas curvas de extin??o funcional. Varia??es mais extremas ocorreram quando as matrizes A e B definem um efeito diferencial acentuado na probabilidade de extin??o das esp?cies dos grupos funcionais. Cen?rios com esp?cies sens?veis, positivas ou negativas, apresentaram uma maior varia??o que os cen?rios com esp?cies dominantes. Intera??es aninhadas apresentaram maior varia??o do que cen?rios em que as intera??es s?o modulares. Comunidades com redund?ncia funcional m?xima podem somente ser fragilizadas pelas intera??es entre esp?cies e grupos funcionais. Em contraste, comunidades com baixa riqueza funcional pode ter sua resist?ncia aumentada ou diminu?da pelas intera??es. A concentra??o de intera??es positivas in grupos de baixa redund?ncia ou intera??es negativas em grupos de alta redund?ncia foi capaz de diminuir as taxas de extin??o funcional. Em contraste, a concentra??o de intera??es negativas em grupos de baixa redund?ncia ou de intera??es positivas em grupos de alta redund?ncia foi capaz de aumentar as taxas de extin??o funcional. Este modelo apresenta resultados relevantes para prioriza??o de esp?cies em trabalhos de conserva??o e restaura??o dos ecossistemas

Les invasions biologiques peuvent provoquer des pertes de biodiversité et ainsi de services écologiques. Cette thèse porte sur l'élaboration d'un modèle d'assemblage de réseau d'interactions, incluant tous les types d'interactions (trophiques et non trophiques), et respectant la conservation de la matière. Ce modèle montre un fort effet des interactions non trophiques sur les processus fonctionnels des écosystèmes (biomasse, production) et une diversité-dépendance des interactions interspécifiques; les mécanismes de la relation diversité-fonctionnement sont ainsi plus complexes dans les réseaux d'interactions que les réseaux trophiques. Le modèle prédit que les introductions d'espèces ont de forts impacts sur les propriétés des écosystèmes, que la résistance aux invasions et la robustesse vis-à-vis des extinctions d'espèces résidentes dues aux invasions augmentent avec la diversité spécifique, et sont maximales pour des interactions non trophiques de force et prévalence intermédiaires.

This thesis aims at improving our knowledge on swirl combustors. The work presented here is based on Large Eddy Simulations (LES) coupled to an advanced combustion model: the Conditional Moment Closure (CMC). Numerical predictions have been systematically compared and validated with detailed experimental datasets. In order to analyze further the physics underlying the large numerical datasets, Proper Orthogonal Decomposition (POD) has also been used throughout the thesis. Various aspects of the aerodynamics of swirling flames are investigated, such as precession or vortex formation caused by flow oscillations, as well as various combustion aspects such as localized extinctions and flame lift-off. All the above affect flame stabilization in different ways and are explored through focused simulations. The first study investigates isothermal air flows behind an enclosed bluff body, with the incoming flow being pulsated. These flows have strong similarities to flows found in combustors experiencing self-excited oscillations and can therefore be considered as canonical problems. At high enough forcing frequencies, double ring vortices are shed from the air pipe exit. Various harmonics of the pulsating frequency are observed in the spectra and their relation with the vortex shedding is investigated through POD. The second study explores the structure of the Delft III piloted turbulent non-premixed flame. The simple configuration allows to analyze further key combustion aspects of combustors, with further insights provided on the dynamics of localized extinctions and re-ignition, as well as the pollutants emissions. The third study presents a comprehensive analysis of the aerodynamics of swirl flows based on the TECFLAM confined non-premixed S09c configuration. A periodic component inside the air inlet pipe and around the central bluff body is observed, for both the inert and reactive flows. POD shows that these flow oscillations are due to single and double helical vortices, similar to Precessing Vortex Cores (PVC), that develop inside the air inlet pipe and whose axes rotate around the burner. The combustion process is found to affect the swirl flow aerodynamics. Finally, the fourth study investigates the TECFLAM configuration again, but here attention is given to the flame lift-off evident in experiments and reproduced by the LES-CMC formulation. The stabilization process and the pollutants emission of the flame are investigated in detail.

Humans evolved in a world of giant creatures. Current evidence suggests that most ice age megafauna went extinct around the transition to our current Holocene epoch. The ecological reverberations associated with the loss of over 65% of Earth’s largest terrestrial animals transformed ecosystems and human lifeways forever thereafter. However, there is still substantial debate as to the cause of this mass extinction. Evidence variously supports climate change and anthropogenic factors as primary drivers in the restructuring of the terrestrial biosphere. Much of the ongoing debate is driven by the insufficient resolution accessible via macro-remains. To help fill in the gaps in our understandings of the Pleistocene-Holocene transition, I utilized the growing power of sedimentary ancient DNA (sedaDNA) to reconstruct shifting signals of plants and animals in central Yukon. To date, sedaDNA has typically been analyzed by amplifying small, taxonomically informative regions. However, this approach is not ideally suited to the degraded characteristics of sedaDNA and ignores most of the potential data. Means of isolating sedaDNA have also suffered from the use of overly aggressive purification techniques resulting in substantial loss. To address these limitations, I first experimentally developed a novel means of releasing and isolating sedaDNA. Secondly, I developed a novel environmental bait-set designed to simultaneously capture DNA informative of macro-scale ecosystems. When combined, we identify a substantial improvement in the quantity and breadth of biomolecules recovered. These optimizations facilitated the unexpected discovery of horse and mammoth surviving thousands of years after their supposed extirpation. I followed up these results by extracting DNA from multiple permafrost cores where we confirm the late survival signal and identify a far more complex and high-resolution dataset beyond those identifiable by complementary methods. I was also able to reconstruct mitochondrial genomes from multiple megafauna simultaneously solely from sediment, demonstrating the information potential of sedaDNA. / Dissertation / Doctor of Philosophy (PhD) / A new addition to the rapidly growing field of palaeogenetics is environmental DNA (eDNA) with its immense wealth of biomolecules preserved over millennia outside of biological tissues. Organisms are constantly shedding cells, and while most of this DNA is metabolized or otherwise degraded, some small fraction is preserved through sedimentary mineral-binding. I experimentally developed new ancient eDNA methods for recovery, isolation, and analysis to maximize our access to these biomolecules and demonstrate that this novel approach outperforms alternative protocols. Thereafter, I used these methods to extract DNA from ice age permafrost samples dating between 30,000–6,000 years before present. These data demonstrate the power of ancient eDNA for reconstructing ecosystem change through time, as well as identifying evidence for the Holocene survival of caballine horse and woolly mammoth in continental North America. This late persistence of Pleistocene fauna has implications for understanding the human ecological and climatological factors involved in the Late Pleistocene mass extinction event. This effort is paralleled with megafaunal mitogenomic assembly and phylogenetics solely from sediment. This thesis demonstrates that environmental DNA can significantly augment macro-scale buried records in palaeoecology.