Dissertations / Theses on the topic 'Biotic factors'

Many ecological communities show variation from place to place; understanding the causes of this variation is the goal of community ecology. Differences in community composition will be the result of both stochastic and deterministic processes. However, it is difficult to know to what degree deterministic processes will shape community composition. In this thesis I combined observational and experimental approaches to quantify deterministic processes within a particular ecological community -- they phytotelmata of bromeliad plants. In my thesis I describe three studies at different scales of organization: 1) do organisms of different size respond equally to changes in their environment 2) how do predators interact to influence prey survival 3) what mechanisms underly the response of similar species to the same environmental gradient, bromeliad size. In Chapter 1, I tested an hypothesis developed from previous observational data -- that smaller organisms respond less than larger ones to the same environmental gradient -- different bromeliad species that occur under different forest canopies. After removing variation caused by dispersal, I found that environmental variation explained little variation for bacteria, more for zooplankton and most of all for macroinvertebrates. In my second chapter, I examined ecological determinism on a smaller scale -- within a single trophic level (macroinvertebrate predators). I found that predators may interfere with each other, reducing predation rates and increasing prey survival. In Chapter 3, I examine macroinvertebrate responses to bromeliad volume. I use both null models and a field experiment to show that for at least one such pair, a difference in abiotic tolerances may be the plausible mechanism. Together these results illustrate when, and to what degree, bromeliad communities respond to deterministic factors. All three chapters first demonstrate a pattern, testing it against a suitable null distribution, before attempting to quantify possible mechanisms with a field experiment. This combination of observation and experiment is an approach which can contribute to our understanding of how ecological systems work.<br>Science, Faculty of<br>Graduate

Roots and their associated mycorrhizal fungi have long been recognised as major determinants of nutrient cycling. Their measurement has been limited because soil limits accessibility. The use of <I>in-situ</I> camera techniques in conjunction with minirhizotrons and image analysis software now make the acquisition of accurate root longevity data possible. The current literature was reviewed in relation to root longevity - both measurement techniques and available data. Four main experiments were employed to study the root longevity of a number of tree species, grass and clover subject to differing environmental conditions and grass and clover and poplar roots with and without colonisation by Arbuscular Mycorrhizal fungi. The data was analysed in a number of different ways including the use of the powerful statistical technique for censored data - survival analysis. This technique proved to be very useful for analysing temporal changes to root longevity. The data indicate that root longevity can be extremely short but is dependent upon environment and for some species, colonisation by Arbuscular Mycorrhizal fungi. Preliminary calculations were completed to determine the role of root death in nutrient cycling and these predict that large quantities of nitrogen, phosphorus and carbon are flowing from the live to the dead root pool on an annual basis.

Biological invasions are a major component of global environmental change and are increasing in frequency. Most community-level impact studies of invasions are concerned with interactions between exotic and native species. However, interactions among exotic species are becoming increasingly common, potentially altering their respective impacts on invaded ecosystems. This research identifies one possible outcome of such interactions: the growing phenomenon of 'exotic species replacement', whereby a newly arriving exotic species surpasses the abundance of a functionally similar incumbent exotic species. This phenomenon is explored here using two Eurasian dreissenid bivalves that invaded the St. Lawrence River in the early 1990s, the zebra mussel (Dreissena polymorpha) and quagga mussel (D. bugensis). I review the general replacement pattern of the zebra mussel by its congener, and examine environmental factors and life history traits that mediate this replacement in a navigational canal connected to the river. Since the 1990s, quagga mussels have replaced the zebra mussel as the dominant dreissenid mussel, but the contemporary adult distribution and abundance is spatially structured: quagga mussels dominate the deep zone, while zebra mussels remain common in the shallow margins of the canal. Field surveys and in situ field experiments are used to examine the relative importance of pre-settlement, settlement and post-settlement processes, in the context of life history trade-offs and environmental gradients, in determining patterns of adult mussel distribution and abundance. Despite the potential importance of larval supply and behavior, including substrate selection at settlement, none of these processes determined adult dreissenid distribution and abundance. Rather, the main determinants were post-recruitment processes involving condition-specific competition. Adult zebra mussels generally had lower body condition, growth, shell length, and survivorship than quagga mussels, and these differences were most pronounced in the deep zone of the canal. This case highlights the importance of subtle differences in life history and abiotic tolerances among closely-related species in understanding changing patterns of distribution and abundance in an invaded community.<br>Les invasions biologiques sont une composante majeure des changements environnementaux au niveau mondiale et leurs fréquences continuent à augmenter. La plupart des études sur l'impact des invasions à l'échelle communautaire s'intéressent principalement aux interactions entre les espèces exotiques et indigènes. Par contre, on observe de plus en plus des interactions entre des espèces exotiques, ce qui pourrait modifier leurs impacts respectifs sur les écosystèmes envahis. Cette recherche a pour but d'examiner le 'remplacement d'espèces exotiques', un phénomène par lequel l'abondance d'une espèce exotique nouvellement arrivée surpasse l'abondance d'une espèce exotique déjà présente et dominante, qui possède également une similarité fonctionnelle. Ce phénomène est exploré ici à l'aide de deux bivalves Eurasiennes de la famille des Dreissenidés qui ont envahi le fleuve Saint-Laurent au début des années 1990, la moule zébrée (Dreissena polymorpha) et la moule quagga (D. bugensis). J'examine le schéma général de remplacement de la moule zébrée par son congénère dans un canal de navigation relié au fleuve. J'examine également les facteurs environnementaux et les traits d'histoire de vie de ces moules qui peuvent influencer se remplacement. Depuis les années 1990, la moule quagga a remplacé la moule zébrée en tant que le dreissenidé dominant. Par contre, la distribution et l'abondance contemporaines des adultes sont structurées de façon spatiale: les moules quagga dominent la zone profonde, tandis que les moules zébrées demeurent communes dans la région peu profonde du canal. Des études sur le terrain et des expériences in situ ont été utilisées pour examiner l'importance relative des processus de pré-établissement, d'établissement et de post-établissement, sur la distribution et l'abondance des moules adultes. Malgré l'importance potentielle de l'approvisionnement et du comportement larvaire, y compris la sélection du substrat durant l'établissement, aucun de ces processus ne joue un rôle important dans la détermination de l'abondance et la distribution des dreissenidés adultes. Plutôt, les principaux facteurs déterminants étaient les processus de post-recrutement impliquant la compétition mediée par l'environnement. En générale, la condition, la croissance, la longueur de coquille et la survie des moules zébrées adultes étaient inférieures à celles des moules quagga, et ces différences étaient plus prononcées dans la zone profonde du canal. Cette étude met en valeur l'importance des différences subtiles des traits d'histoire de vie et des tolérances abiotiques d'espèces étroitement liées dans la compréhension des schémas changeants de distribution et d'abondance d'individus dans les communautés envahies.

CTMinimum and CTMaximum were measured in 620 goldfish to determine if biotic factors, in particular starvation, condition factor and size, affect temperature tolerance. Twenty-eight days of starvation adversely affected both upper and lower temperature tolerance. Condition factor was related to upper but not lower temperature tolerance.

Todo en la tierra es química. Esta afirmación tiene profundas implicaciones para las interacciones ecológicas. Los organismos vivos promueven y controlan flujos de materia y energía entre la atmosfera, hidrosfera y litosfera; modificando la composición química de la tierra de muchas maneras diferentes. La estequiometría ecológica estudia el balance y el papel de múltiples elementos químicos en las interacciones ecológicas y nos ayuda a entender patrones y procesos en la naturaleza. Representa el enlace entre la biogeoquímica y el funcionamiento de los ecosistemas, permitiéndonos describir procesos a todos los niveles de organización biológica, desde estructuras sub-celulares a ecosistemas. En esta Tesis he usado la estequiometría ecológica para describir procesos a nivel de organismo y ecosistema en tres condiciones ambientales terrestres diferentes. La estequiometría de los autótrofos se establece cuando estos usan luz para fijar carbono (C) y simultáneamente asimilan nutrientes. Las plantas son capaces de almacenar nutrientes en la vacuola intracelular y en diferentes órganos, lo que hace que su estequiometría sea muy flexible (baja homeostasis) y se adapten a diferentes ambientes, incluyendo condiciones del suelo limitantes para el desarrollo de las plantas. También, la interacción planta suelo se puede explorar a través de la estequiometría foliar, ya que se ha demostrado en todos los ecosistemas terrestres que el N:P foliar esta correlacionado positivamente con el N:P del suelo, sugiriendo que es un buen indicador de la disponibilidad de nutrientes. Las adaptaciones de las plantas a condiciones limitantes de nutrientes en el suelo son comunes en todos los ecosistemas terrestres, como es la fijación de nitrógeno, la asociación con micorrizas, producción de fosfatasas o la reabsorción de nutrientes desde las hojas senescentes para el reciclado interno de nutrientes. La composición elemental de las especies es afectada por esas interacciones abióticas y bióticas, y el intercambio de elementos químicos entre las especies y el espacio abiótico determinaran la composición elemental de las diferentes partes del ecosistema. En el Capítulo 2 exploramos el efecto biótico de la composición de las comunidades sobre la composición química foliar de distintas especies vegetales, a través del nicho biogeoquímico de cada especie. Encontramos que cada especie presenta su propio nicho biogeoquímico y fueron capaces de reajustar su composición química foliar en respuesta a las diferentes condiciones bióticas. Concluimos que las plantas pueden reajustar su composición elemental foliar cuando crecen en comunidades con diferente composición de plantas, a través del desplazamiento del nicho biogeoquímico, sugiriendo un uso diferencial de los recursos cuando los patrones de coexistencia cambian. En el Capítulo 3 hemos explorado el cambio en la composición química del sistema planta-suelo debido a la expansión de arbustos en los pastizales subalpinos del Pirineo. Esta expansión representa la transición desde pastizales puros a matorrales. Los pastizales son un ecosistema dominado por especies de ciclo de vida corto, rápido intercambio de nutrientes entre los compartimientos planta-suelo, altas concentraciones de nitrógeno (N), fósforo (P) y potasio (K) en el sistema planta-suelo, con alta productividad pero capacidad limitada de acumulación de biomasa. En cambio, los matorrales se caracterizan por ser un ecosistema dominado por especies de ciclo de vida largo, con estrategias más conservativas, con un intercambio de nutrientes más lento (relación de C:nutrientes altos en la biomasa aérea y baja concentración de N y P en el sistema planta-suelo) y mayor almacenamiento de nutrientes en la biomasa aérea de las plantas. La matorralización incrementa la dependencia de la adquisición de nutrientes como el N a través de micorrizas desde los pastizales puros a matorrales. Todos los cambios en el almacenamiento y composición elemental del sistema planta-suelo a lo largo de la sucesión desde pastizales a matorrales sugiere una desaceleración del ciclo biogeoquímico en las áreas montañosas donde la expansión de arbustos está presente. En el Capítulo 4, describimos la distribución de C y los nutrientes más importantes para el desarrollo de las plantas (N, P, K) en el sistema planta-suelo de bosques tropicales maduros en suelos pobres de la Guyana Francesa. También estudiamos el proceso de reabsorción de nutrientes desde las hojas senescentes, un mecanismo de nutrición de las plantas para evitar la perdida de nutrientes poco estudiado en este ecosistema. Nuestros resultados muestran que el P es el elemento más escaso presente en hojas, hojarasca y suelo. Las eficiencias de reabsorción de K y P fueron más altas que la de N y la estacionalidad solo afecto la reabsorción de K. La reabsorción de P fue la única que mostró una correlación, aunque débil, con el P en el suelo (total y disponible). Las relaciones entre la reabsorción de nutrientes y los rasgos funcionales de las especies (tasa de crecimiento, densidad de madera, diámetro a la altura del pecho y el área foliar específica) fueron débiles y variaron dependiendo del nutriente, en tanto que la relación filogenética no explica la variabilidad en las eficiencias de reabsorción de nutrientes de las especies. Nuestros resultados sugieren que la alta reabsorción de K y P desde las hojas senescentes es una estrategia adaptativa de las especies que les permite lidiar con la escasez de estos nutrientes en el suelo. Asimismo, el nivel de inmovilización de los nutrientes en los compuestos foliares (N > P > K) parece determinar significativamente el proceso de reabsorción. Concluimos que la reabsorción de nutrientes desde las hojas senescentes es un proceso clave de las plantas para la conservación de nutrientes en los bosques tropicales de la Guyana Francesa, especialmente para K y P, elementos que presentan una disponibilidad baja en el suelo, y esta depende principalmente del material parental y del proceso de lixiviación. En resumen, en esta Tesis hemos demostrado como la composición elemental del sistema planta-suelo refleja procesos e interacciones ecológicas, como son las interacciones intra e inter específica entre plantas (Capítulo 2), procesos fisiológicos poco estudiados en las plantas como la reabsorción de nutrientes (Capítulo 4) y la importancia de los estudios de estequiometría para describir cambios a nivel de ecosistema y predecir escenarios futuros (Capítulo 3). Estos estudios aportan nuevos conocimientos en el campo de la estequiometría ecológica y resaltan la importancia de este enfoque en los estudios ecológicos.<br>Everything on Earth is based on chemistry. This statement has profound implications for ecological interactions. Living organisms generate and control fluxes of energy and matter among the atmosphere, lithosphere and the hydrosphere, shaping the chemistry of the Earth in many different ways. Ecological stoichiometry aims to explore the balance and role of multiple chemical elements in ecological interactions and help us to understand patterns and processes in nature. It represents the link between the biogeochemistry and the ecosystems’ function and allows to describe processes across different levels of biological organization, from cellular structures to ecosystems. In this Thesis I use ecological stoichiometry to describe processes at organism and ecosystem levels in three contrasting terrestrial environment conditions. Autotrophs’ stoichiometry is established when these organism use light to fix carbon (C) and simultaneously assimilate nutrients. Plants are able to store nutrients in the cells’ vacuole and in different organs, which make them highly flexible (less homeostatic) in terms of their elemental composition. This feature explains the high adaptability of plants to different environments, including soil nutrient limitation conditions. Furthermore, plant-soil interaction could be explored through the foliar stoichiometry, because it has been shown that the foliar N:P is positive correlated with the N:P of soil in all terrestrial ecosystem, suggesting that foliar stoichiometry is a good indicator of the resource availability. Plant adaptations to soil nutrient limiting conditions are quite common in all terrestrial ecosystems, such as nitrogen fixation, mycorrhiza association, production of phosphatases and nutrient resorption before leave abscission. The species’ chemical composition is affected by all these abiotic and biotic interactions, and these exchange of chemical elements between the species and the abiotic part of the system determine the elemental composition of different components of the ecosystems. In Chapter 2, we explore the biotic effect of the community composition on the species foliar stoichiometry, taken as a proxy of the species’ biogeochemical niche. We found that each species has its own biogeochemical niche and is able to readjust its chemical composition in response to different biotic conditions. We conclude that plants can readjust their foliar element composition when they grow in communities with contrasting plant composition through the biogeochemical niche displacement, suggesting a differential use of the resources when the patterns of species coexistence change. In Chapter 3 we explore the plant-soil stoichiometry changes due the shrub expansion into the subalpine grassland in the Pyrenees. Shrub expansion had a clear impact on the plant-soil stoichiometry spectrum. This expansion represents the transition from pure grassland to shrubland. The grassland is an ecosystem dominated by short-lived species, fast nutrient turnover between the plant-soil compartments, high nitrogen (N), phosphorus (P) and potassium (K) concentrations in the plant-soil system, high productivity but low biomass stocks. The shrubland is an ecosystem characterized by long-lived species with more conservative strategy, slow nutrient turnover (low N and P concentrations in the plant-soil compartments, high C:nutrient ratios in the aboveground biomass) and high stocks of C and nutrients in the plant aboveground biomass. Shrub encroachment increase the acquisition of N through mycorrhizal associations. The changes in storage and elemental composition of the plant soil system along the succession from grassland to shrubland suggests that there is a slowdown of the biogeochemical cycle in the subalpine mountain areas where shrub encroachment occurred. In the Chapter 4, we describe the distribution of C and the most important nutrients for the plant development (N, P, K) in the plant and soil compartments in old-growth tropical forests growing in nutrient-poor soil in French Guiana. We also studied the nutrient resorption from senescent leaves, a poorly explored mechanism that plants use to avoid losing nutrients in this ecosystem. Our results showed that P was the scarcest nutrient in the leaf, leaf-litter and soil. Resorption efficiencies were higher for K and P than for N, and only K resorption efficiency was affected by seasonality. P resorption showed a negative and weak correlation with P in soil (total and available). Relationships between nutrient resorption and species functional characteristics (growth rate, wood density, diameter at breast height and specific leaf area) were weak and varied among the nutrients, and phylogenetic relatedness did not account for the variability in resorption efficiencies. Our results suggest that high K and P resorption from senescent leaves is an adaptive strategy allowing species to cope with soil nutrient scarcity. Furthermore, the level of nutrient immobilization in foliar compounds (N > P > K) seem to significantly determine the resorption process. We conclude that nutrient resorption from senescent leaves is a key process for plants to conserve nutrients in tropical forests of French Guiana, especially for K and P, where soil availabilities are low and depend mainly on soil parent material and leaching process. To sum up, in this Thesis we have demostrated how the elemental composition of the plant-soil system reflects ecological interactions and processes, such as intra and inter specific plant interactions (Chapter 2), poorly explored physiological processes such as nutrient resorption (Chapter 4) and the importance of stoichiometry studies for describing changes at ecosystem level and predicting future scenarios (Chapter 3). These studies add new knowledge to the ecological stoichiometry field and highlights the importance of this approach in the ecological studies.

Paulownia is a newly developed industry in Western Australia. Relying on high levels of fertiliser and irrigation to attain maximum growth, Paulownia often has nitrogen levels of 4.5 to 5 %. Alternaria, a pathogen with the potential to defoliate trees, has been isolated from blighted leaves of Paulownia for the first time in the literature. It was hypothesised that luxury fertiliser treatments may predispose Paulownia fortunei to disease. To test for the influence of luxury fertiliser regimes on Alternaria blight of Paulownia fortunei, clonal trees were grown in a glasshouse and fertilised using a nil, low, medium and high fertiliser regime. Plants were measured for height, stem diameter, gas exchange, chlorophyll, soluble protein and inorganic nutrient concentrations in the leaves. It was found that rising fertiliser supply resulted in all measures increasing, then plateauing at the two highest fertiliser rates. The only exceptions to this trend were leaf sodium and stem boron and potassium concentrations which dropped with increasing fertiliser. Photosynthesis and leaf nitrate were the only measures which were significantly higher in the highest fertiliser treatment. Thus, concluding that additional N, up to 46%, is of limited benefit to plant growth and function. Three inoculation treatments were conducted, leaf disc, excised leaf and in-situ. Each infection trial only produced lesions where leaves were wounded prior to infection. Fertiliser treatments had no effect on disease development in the leaf disc and excised leaf inoculation treatments. However, the in-situ inoculation trial had significantly (p < 0.01) larger lesions in the nil fertiliser treatment than all other fertiliser treatments. Unfortunately, there was no significant difference between the inoculated and control leaves within the nil fertiliser treatment. A systemic fungicidal influence on Paulownia by VAM was also examined. Seedlings inoculated with VAM were measured by the same methods as the nutrition trial with the exception of gas exchange. The presence of VAM increased plant height, root weight and approximately half of the nutrients analysed. Fertiliser treatment significantly increased the majority of plant biomass and function measurements. However, the inorganic nutrient analysis of the leaves revealed that the soil sterilisation process resulted in more nutrients becoming available to the plants. The infection of the VAM trial with Alternaria resulted in no lesions on the leaves and stems. There is no evidence to suggest that the luxurious fertiliser applied to field grown Paulownia predisposes them to infection by Alternaria. However, there is evidence that this pathogen may be opportunistic as only wounded leaves produced lesions during all nutrient infection trials. The impact of VAM on Paulownia growth is limited and needs further research.

Les interaccions basades en la mida individual dels organismes tenen un paper important en la dinàmica de la comunitat i en els processos dels ecosistemes aquàtics, ja que la mida d’un individu és un tret clau dels organismes molt vinculat a la seva taxa metabòlica. El canvi climàtic i les pertorbacions afecten a les xarxes tròfiques planctòniques d'aigua dolça, debilitant les interaccions basades en la mida dels individus. En aquesta tesi es van desenvolupar quatre estudis relacionats però independents per obtenir una comprensió més profunda de les interaccions tròfiques basades en la mida individual dels organismes. L’objectiu era demostrar com els factors biòtics i ambientals afecten les interaccions basades en la mida dels individus de xarxes tròfiques planctòniques utilitzant aproximacions observacionals i experimentals en diferents localitats a Europa. Generalitzant, les nostres troballes clau d'aquesta tesi ressalten la importància d’integrar les relacions basades en la mida dels organismes i la resiliència de les comunitats amb la variació intraespecífica dels organismes a l’hora d’estudiar les interaccions tròfiques entre els organismes d’un ecosistema aquàtic. La comprensió d'aquestes interaccions ens permetrà gestionar i restaurar millor els ecosistemes aquàtics davant el canvi climàtic i altres pertorbacions induïdes per l'home.<br>Individual size-based interactions play a significant role in the community dynamics and ecosystem processes of aquatic ecosystems, because body size is a key trait of organisms that is highly linked to metabolic rates. Climate change and disturbances influence freshwater planktonic food webs, weakening the strength of size-based interactions. In this thesis, we conducted four related but independent studies to obtain a deeper understanding of the size-based trophic interactions. We aimed to demonstrate biotic and environmental factors influencing size-based interactions in planktonic food webs using observational and experimental approaches at different locations in Europe. Overall, our key findings from this thesis suggest that integrating size-based relationships and resilience of communities together with intraspecific variation is important while studying trophic interactions. Understanding these interactions will allow us to better manage and restore aquatic ecosystems in the face of climate change and other human-induced disturbances.

Les flors emeten compostos orgànics volàtils (VOCs) per tal d’atreure pol·linitzadors i estimular la fecundació creuada. Alguns volàtils florals però juguen altres funcions, com ara la defensa contra els herbívors. Aquesta dualitat de rols que tenen les olors florals les converteix en complexes mescles de compostos amb múltiples efectes sobre diferents organismes. La complexitat de comprendre i caracteritzar les emissions florals augmenta quan considerem que són variables en el temps i l’espai. A aquestes fonts de variabilitat cal afegir diversos factors ambientals biòtics i abiòtics que modifiquen les emissions de COVs florals de diverses maneres. L’objectiu principal d’aquesta tesi és esclarir quins són els factors que determinen les emissions florals de volàtils, i veure de quina manera les afecten a elles i a les seves funcions ecològiques. En el primer capítol de la tesi hem revisat el coneixement actual sobre les emissions florals de VOCs i hem identificat les qüestions que necessitaven ser investigades en aquest camp de recerca. Les emissions florals estan determinades en primer lloc per la diversitat de compostos que les espècies són capaces de produir, els seu potencial biosintètic i la seva capacitat d’emissió, que estan fortament lligades a la biologia de l’espècie. Hem testat i demostrat que les plantes pol·linitzades per insectes solen presentar major diversitat de volàtils florals i emeten una major quantitat d’aquests que les plantes pol·linitzades pel vent, que no necessiten volàtils florals per funcions d’atracció. Hem testat si els patrons estacionals de disminució de la competència que ocorren cada any entre plantes d’una mateixa comunitat vegetal han donat lloc a la selecció d’un patró de disminució de les emissions i les recompenses florals al llarg del període de floració de cada espècie. També hem observat que les plantes adapten la seva fisiologia per optimitzar les seves emissions florals sota les condicions climàtiques de la seva època de floració. Les emissions florals de COVs es veuen afectades per factors ambientals al nivell d’organisme o de teixit. Hi ha diversos estats fisiològics de la planta que poden modificar substancialment la composició i la quantitat de les emissions florals de COVs. Els nostres experiments han demostrat que la microbiota floral pot jugar un rol crucial sobre la quantitat i composició de les emissions florals de COVs. També hem mostrat que l’herbivoria de flors per part d’erugues de Pieris brassicae sobre plantes de Diplotaxis erucoides indueixen augments immediats de les emissions de compostos amb funcions defensives. A més, l’herbivoria de flors i fulles combinada va mostrar un efecte sinèrgic que augmenta la resposta defensiva. La recerca sobre els canvis que poden experimentar les emissions florals en resposta a diversos agents del Canvi Global són de gran interès degut als diversos efectes que aquests canvis poden tenir sobre les interaccions que s’estableixen mitjançant els COVs florals. Els nostres resultats revelen que els augments de temperatura previstos per al segle següent deguts a l’Escalfament Global poden conduir a augments significatius de les emissions totals de COVs i també a canvis importants en la composició relativa de les olors florals. També hem observat que l’ozó causa una degradació significativa dels compostos florals i provoca canvis en la composició relativa de les olors. Els testos de resposta indiquen que els canvis observats en les olors florals exposades a ozó resulten en la pèrdua de l’atracció de pol·linitzadors. Aquesta tesi proporciona una nova visió sobre els factors que determinen les emissions florals de volàtils i les seves repercussions sobre les interaccions planta-pol·linitzador, i garanteix una major consideració dels factors biòtics i abiòtics que afecten la química i l’ecologia de les olors florals en un ambient contínuament canviant.<br>Flowers emit volatile organic compounds (VOCs) to attract pollinators and stimulate reproductive outcrossing. Some floral volatiles can play roles other than attraction, such as defense against herbivores. This duality of roles of flower emissions converts floral scents into complex mixtures of compounds with multiple effects on different organisms. The complexity of understanding and characterising floral emissions increases when considering that they are variable in time and space. To all these sources of variability we can add diverse biotic and abiotic environmental factors that modify floral VOC emissions in many different ways. The main objective of this thesis was to shed light on which are the factors that determine floral volatile emissions, and how do they affect these emissions and their ecological functions. In the first chapter of this thesis we reviewed the current knowledge on floral VOC emissions. We identified the open questions that still needed to be addressed or investigated in more detail in the research field of floral VOC emissions. Floral emissions are first determined by the array of compounds that the species are able to produce and their potential biosynthetic and emission capacities, which are strongly related to the species biology. We tested and demonstrated that flowering plants pollinated by insects usually present higher diversities of floral volatiles and emit higher amounts of them, than do plants pollinated by wind which do not need floral volatiles for attractive purposes. We tested whether well-known seasonal patterns of decreasing competition occurring every year in a community among co-flowering plants for pollinators led to the selection of a pattern of decreasing emission of floral volatiles and decreasing production of floral rewards along the flowering period of each species. We also observed that plants adapt their physiology to optimize their floral emissions under the climatic conditions of the flowering period. Floral VOC emissions of the species are affected by environmental factors at the individual (organism) or tissular level. There are diverse physiological states of the plant that can substantially modify the emission profiles and amounts of floral VOCs. Our experiments demonstrated that floral microbiota can play a crucial role in the quantity and quality of floral VOC emissions. We also showed that flower herbivory by Pieris brassicae caterpillars on Diplotaxis erucoides plants induced immediate increases in floral emission rates of few compounds with known defensive functions. Leaf herbivory caused no changes in the emissions of intact flowers, but the combination of leaf herbivory with flower herbivory showed a synergistic effect with enhanced defensive response. The research on the potential changes that floral emissions could experience in response to diverse drivers of Global Change are of critical interest because of the diverse effects that such changes can have on the interactions that floral VOCs mediate. Our results revealed that temperature increases as those predicted for the next century as a result of Global Warming can lead to significant total increases in floral VOC emissions and also to important changes in floral scent relative composition. We also detected that ozone caused significant degradation of floral compounds and changes in their relative composition. Behavioural tests indicated that all the changes observed in floral chemical cues when exposed to ozone resulted in the loss of attraction effect on pollinators. This thesis thus provides new insights on the factors that determine floral volatile emissions and their repercussions on plant-pollinator interactions and warrant deep consideration of both biotic and abiotic factors driving floral scent chemistry and floral scent ecology in a continuously changing environment.

Thesis (Ph.D.)--Kent State University, 2009.<br>Title from PDF t.p. (viewed Nov. 16, 2009). Advisor: Mark Kershner. Keywords: crayfish; stream; predation; current velocity; water depth; grain size; resource competition. Includes bibliographical references.

Over the last two decades, Ostreopsis cf. ovata blooms have been reported with increased frequency, intensity and areal distribution in the Mediterranean Sea. The epiphytic/benthic dinoflagellate proliferates under low hydrodinamism, and produces toxins (palytoxin-like compounds) causing human health problems and massive mortalities of benthic invertebrate communities. While several studies have assessed some effects of abiotic factors like hydrodynamics, water temperature and inorganic nutrients on O. cf. ovata bloom dynamics, biotic factors have been barely addressed. In an effort to provide insights about competition with other microalgal species and microalgal-bacterial interactions in affecting O. cf. ovata growth, physiology and ultimately bloom dynamics, this thesis investigated: (i) the inorganic nutrients uptake and organic phosphorus utilization by O. cf. ovata; (ii) the phylogenetic structure of bacterial assemblages co-occurring with O. cf. ovata bloom in situ; (iii) the microbial (bacteria and viruses) dynamics and toxin production along the O. cf. ovata growth in batch cultures. Data collected show the high efficiency of O. cf. ovata in both inorganic and organic phosphate acquisition, an aspect that could confer advantages towards competing species co-occurring in the microphytobenthos. Recurrent functional associations between O. cf. ovata and Alphaproteobacteria have been evidenced both in situ and in batch cultures, and indicate the latter as a reliable tool for future investigations on O. cf. ovata-bacteria interactions. The ability of some O. cf. ovata-associated Roseobacters (i.e. Ruegeria, Jannaschia, Dinoroseobacter, Roseovarius) to switch from mutualistic to antagonistic relationships depending on algal physiological status suggests an important role of dinoflagellate-bacterial interactions in bloom dynamics. Furthermore, while the vast majority of studies on harmful algal blooms to date have focused on macronutrients’ dynamics, data in this thesis pave the way for further investigations on the role of allochthonous vitamins in O. cf. ovata bloom development and maintenance.

Over the last two decades, Ostreopsis cf. ovata blooms have been reported with increased frequency, intensity and areal distribution in the Mediterranean Sea. The epiphytic/benthic dinoflagellate proliferates under low hydrodinamism, and produces toxins (palytoxin-like compounds) causing human health problems and massive mortalities of benthic invertebrate communities. While several studies have assessed some effects of abiotic factors like hydrodynamics, water temperature and inorganic nutrients on O. cf. ovata bloom dynamics, biotic factors have been barely addressed. In an effort to provide insights about competition with other microalgal species and microalgal-bacterial interactions in affecting O. cf. ovata growth, physiology and ultimately bloom dynamics, this thesis investigated: (i) the inorganic nutrients uptake and organic phosphorus utilization by O. cf. ovata; (ii) the phylogenetic structure of bacterial assemblages co-occurring with O. cf. ovata bloom in situ; (iii) the microbial (bacteria and viruses) dynamics and toxin production along the O. cf. ovata growth in batch cultures. Data collected show the high efficiency of O. cf. ovata in both inorganic and organic phosphate acquisition, an aspect that could confer advantages towards competing species co-occurring in the microphytobenthos. Recurrent functional associations between O. cf. ovata and Alphaproteobacteria have been evidenced both in situ and in batch cultures, and indicate the latter as a reliable tool for future investigations on O. cf. ovata-bacteria interactions. The ability of some O. cf. ovata-associated Roseobacters (i.e. Ruegeria, Jannaschia, Dinoroseobacter, Roseovarius) to switch from mutualistic to antagonistic relationships depending on algal physiological status suggests an important role of dinoflagellate-bacterial interactions in bloom dynamics. Furthermore, while the vast majority of studies on harmful algal blooms to date have focused on macronutrients’ dynamics, data in this thesis pave the way for further investigations on the role of allochthonous vitamins in O. cf. ovata bloom development and maintenance.

Abstract Deciduous shrubs form the tallest type of vegetation in arctic-alpine areas and are important for ecosystem function. In the southern part of the Eurasian tundra zone, willows (Salix spp.) are the most common species in the shrub layer. In the alpine areas of Northern Fennoscandia, willow shrubs are characteristic to areas between tree line and treeless tundra heaths. Vertical structure and composition of willow-characterized tundra vegetation is affected by a variety of ecological factors including climate and herbivory. In turn, the abundance of the willow canopy affects understory species in several ways that still remain inadequately understood. In this PhD work I describe compositional differentiation of willow-characterized vegetation by using a large data set spanning from north-western Fennoscandia to the Yamal Peninsula in north-western Siberia. I studied environmental factors affecting willow-characterized vegetation and willow growth by using correlative analyses. The factors under investigation were latitude, distance from the sea, depth of thaw, position in the slope, industrial disturbance and reindeer grazing. In addition, I examined the relationships between the shrub biomass estimate and composition and species richness of understory vegetation. The effects of reindeer grazing on vegetation in an alpine forest-tundra ecotone were studied experimentally using reindeer-proof exclosures. I found that willow-characterized vegetation is floristically variable and comprises at least eight vegetation types. The most abundant willow thickets typically have a forb-rich understory. The growth of willow increased along with increasing summer temperatures. However the height of willow was more determined by distance from the sea, thaw depth and slope position. Reindeer grazing decreased the abundance of willow and changed the composition of understory vegetation. In addition, industrial activities were detected to have destructed shrub vegetation and turned it into graminoid-dominated vegetation. Shrub canopies facilitated forbs but decreased the cover of all the other groups including dwarf shrubs, bryophytes and lichens. The species richness of vegetation decreased along with increasing shrub abundance. My study shows that arctic-alpine willow vegetation is more diverse than previously thought. There is a predictable relationship between summer temperatures and willow growth. However, the results also show that there are many factors, both physical and anthropogenic, that are likely to complicate this pattern. Most important of these counteracting effects are industrial activities and reindeer grazing. In the areas where shrubs grow in abundance, the species richness of understory vegetation is likely to decrease and forbs are likely to replace other tundra species.

Submitted by Aelson Maciera (aelsoncm@terra.com.br) on 2017-04-25T19:44:33Z No. of bitstreams: 1 DissVSK.pdf: 2947181 bytes, checksum: 3c3bd8a24247cda4927887b3e6e3218b (MD5)<br>Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-05-02T13:09:55Z (GMT) No. of bitstreams: 1 DissVSK.pdf: 2947181 bytes, checksum: 3c3bd8a24247cda4927887b3e6e3218b (MD5)<br>Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-05-02T13:10:02Z (GMT) No. of bitstreams: 1 DissVSK.pdf: 2947181 bytes, checksum: 3c3bd8a24247cda4927887b3e6e3218b (MD5)<br>Made available in DSpace on 2017-05-02T13:14:36Z (GMT). No. of bitstreams: 1 DissVSK.pdf: 2947181 bytes, checksum: 3c3bd8a24247cda4927887b3e6e3218b (MD5) Previous issue date: 2016-09-01<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)<br>The relationship between latitude and microbial diversity in the ocean is controversial. Niche models predict higher richness at high latitudes in winter, while snapshot field-sampling point towards higher richness at intermediate latitudes, with lower values both towards equatorial and Polar Regions. However, given the dynamic nature of ocean’s ecosystem it is difficult to account for temporal variations in empirical assessments of microbial biodiversity. Here, we compared the components of diversity (richness and evenness) and microbial population stability (coefficient of variation) in two coastal ocean observatories with similar trophic state located in contrasting latitudes, one located in the Equatorial Atlantic Ocean, and one temperate located in the Northwestern Mediterranean Sea, to evaluate which factors drive the dynamics of microbial communities in each site. Our observations support the view that, as animals and plants, microbial communities exhibit higher (or at least similar) richness towards the equator, at least in the coastal ocean. We also found evidence of increasing stability with increasing evenness in tropical microbial communities when compared to the temperate ones. Temperature and silicates drove temperate free-living prokaryotic communities, while tropical ones were driven by stochastic factors such as biotic interactions with eukaryotes. We propose a conceptual framework where microbial community composition would be driven by deterministic factors in higher latitudes and once the factor temperature is removed moving towards the equator, more stochastic factors such as biotic interactions would emerge as the main factors shaping microbial communities. This study highlights the importance of comparative studies on Eulerian time-series distributed at different latitudes to fully understand the diversity patterns of microbial communities in the ocean.<br>A relação entre a latitude e diversidade microbiana no oceano é controversa. Modelos de nicho preveem maior riqueza em altas latitudes no inverno, enquanto amostragens pontuais indicam uma maior riqueza em latitudes intermediárias, com valores mais baixos para regiões equatoriais e polares. No entanto, dada a natureza dinâmica do ecossistema oceânico, é difícil explicar variações temporais da biodiversidade microbiana nas avaliações empíricas. Nesse trabalho comparamos os componentes da diversidade (riqueza e equitabilidade) e estabilidade das populações microbianas (coeficiente de variação) em dois observatórios oceânicos costeiros com estados tróficos semelhantes, localizados em latitudes contrastantes: um localizado no Oceano Atlântico Equatorial e um em clima temperado localizado no noroeste do Mar Mediterrâneo, a fim de avaliar quais fatores estruturam a dinâmica das comunidades microbianas em cada local. Observamos que tal como animais e plantas, as comunidades microbianas exibem maior (ou pelo menos similar) riqueza no equador pelo menos em águas costeiras. Também encontramos evidências de aumento da estabilidade com o aumento da uniformidade nas comunidades microbianas tropicais, quando comparadas com as de clima temperado. De modo geral, temperatura e silicatos foram as variáveis que condicionaram as comunidades procariotas de vida livre no observatório da região temperada, enquanto que no observatório tropical, fatores estocásticos tais como interações bióticas com eucariotos, foram os fatores que mais influenciaram as comunidades bacterianas. Assim, propomos um quadro conceitual onde a composição da comunidade microbiana seria impulsionada por fatores determinísticos em latitudes mais elevadas, enquanto que em latitudes menores, seriam determinados por fatores mais estocásticos, como interações bióticas. Nosso estudo destaca a importância de estudos comparativos utilizando series temporais Eulerianas em diferentes latitudes para entender os padrões de diversidade das comunidades microbianas no oceano.

Les basses mediterrànies són ecosistemes amb un alt valor ecològic, que pateixen una forta regressió per les pressions antròpiques. No obstant això, l'atenció científica rebuda sempre ha estat molt escassa, i la majoria dels estudis ecològics s'han centrat en la seva biodiversitat, més que l'estructura de la mida corporal de les seves comunitats. Les comunitats planctòniques i les poblacions del peix endèmic i amenaçat Aphanius iberus (Valenciennes, 1846) es van analitzar en basses costaneres permanents salobres (Capítol 1 i 2) i en basses temporànies d'aigua dolça (Capítol 3). L'estructura de la mida es va estudiar mitjançant diferents mètriques de mida (índex de diversitat de mida, espectre de mida, longitud corporal mitjana) i es va aplicar a diferents escales ecològiques (grups funcionals, nivell de població, considerant més d'un nivell tròfic a la vegada), per esbrinar els principals factors ambientals i biòtics que determinaven l'estructura de mides de les comunitats i poblacions aquàtiques a les basses mediterrànies.<br>Mediterranean ponds are ecosystems with a high ecological value, suffering a strong regression due to anthropogenic pressures. Notwithstanding, the received scientific attention has always been far lesser than other larger water bodies. Most ecological studies on Mediterranean ponds have focused on their biodiversity, but only to a lesser extent they have paid attention to the body size structure of their communities. Planktonic communities and populations of the endemic and threatened fish Aphanius iberus (Valenciennes, 1846) were analyzed in brackish permanent coastal ponds (Chapter 1 and 2) and in temporary freshwater ponds (Chapter 3). Size structure was studied using different size metrics (e.g., size diversity index, size spectrum, mean body length, etc.) and applied at different ecological scales (i.e., functional groups, population level, more than one trophic level together), to unravel which were the main environmental and biotic drivers shaping the size structure of aquatic communities and populations in Mediterranean ponds.

Orientador: Luciana Lasry Benchimol Reis<br>Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia<br>Made available in DSpace on 2018-08-23T21:57:40Z (GMT). No. of bitstreams: 1 Perseguini_JulianaMoriniKupperCardoso_D.pdf: 12546958 bytes, checksum: 39944eda3d8791dd247ca42277bb68df (MD5) Previous issue date: 2013<br>Resumo: O resumo poderá ser visualizado no texto completo da tese digital<br>Abstract: The abstract is available with the full electronic document<br>Doutorado<br>Genetica Vegetal e Melhoramento<br>Doutora em Genética e Biologia Molecular

In June 2009 I conducted a study of the habitat associated with Broadleaf Barbara's Buttons (Marshallia trinervia) along Bird's Creek in Vernon Parish, LA. Twenty two plots were sampled for all vascular plants. Of these, 17 samples were from the area where M. trinervia was present and 5 samples were from the area where M. trinervia was absent. From each sampling plot a soil sample was collected and analyzed. There were significant differences in the species richness of all plant groups (p=0.0075), herbaceous plants (p=0.056), and woody vines (p=0.083) between the two locations. The soil texture was also significantly different in the percentage of sand (p=0.021), silt (p=0.029), and clay (p=0.089) between the study locations. The study found that the samples associated with M. trinervia were higher in species richness for all plant groups and the soils from these locations had a higher mean percentage of silt and clay particles.

The diversity-invasion relationship states that more diverse communities are more resistant to invasion. Listeria monocytogenes ? a gram-positive facultative anaerobe, soil saprotroph, and opportunistic human pathogen ? is capable of surviving in a diverse range of habitats, including soil, and several recent studies have shown that the prevalence of L. monocytogenes in soil increases with proximity to surface water. In addition, L. monocytogenes resides frequently in the guts of ruminants and poultry, creating many opportunities for deposition in soil. However, little work has been done to examine the effects of native soil microbiota on the survival of the pathogen. This thesis builds on previous work by examining microbial community diversity in the prairie pothole ecosystem and how it impacts the survival of L. monocytogenes. Results indicate that survival of L. monocytogenes does not seem to differ greatly as an effect of community diversity.

Double-cropping of corn (Zea mays L.) for grain following the harvest of a small grain crop has been under evaluation in Virginia as an alternative cropping strategy (Brann and Pitman, 1997). To assess the potential constraints on late planted corn imposed by insects and diseases, double-cropped corn was evaluated in field experiments in Montgomery County, Virginia from 1998 to 2000. Factors included two near-isoline hybrids (NK4640 and NK4640Bt), insecticides at planting (tefluthrin in all years, 1998-2000; and imidacloprid in 1999 and 2000), and fungicide treatments (azoxystrobin or propiconazole). Response variables included yield, moisture at harvest, grain test weight, damage by European corn borer (Ostrinia nubilalis), damage by corn earworm (Heliothis zea), disease progress curves for gray leaf spot Cercospora zeae-maydis), and number of plants exhibiting virus symptoms. The Bt hybrid performed significantly better than the non-Bt hybrid for yield and test weight in double-cropped corn in 1998 and 2000, but not in 1999. A spatially referenced site suitability analysis was performed for full season and double-cropped corn in Virginia using weighted abiotic factors and constraints. Thornthwaite potential evapotranspiration (PET) and PET minus precipitation were used to identify areas of the state having a lower average moisture deficit during the silking months for double-cropped corn compared to full-season corn. It is concluded that double-cropped corn production is a viable option in Virginia where abiotic factors are not constraining, particularly growing season length and moisture availability during the sensitive stages of development.<br>Master of Science

Species ranges, which are manifestations of species ecological niches in space, are generally determined by gradients of abiotic and biotic factors. In group-living organisms, not only the properties of individuals, but also those of their groups, should interact with environmental challenges and opportunities to determine a species range. Social and subsocial spiders are well known for having distinct geographical distributions. Intriguingly, subsocial species in the genus Anelosimus are absent from the lowland tropical rainforest where social congeners thrive. Previous studies have attributed this absence to increasing rain intensity and predation, particularly by ants, closer to the rainforest. After confirming that these factors do indeed increase in intensity approaching the lowland tropical rainforest, I test these hypotheses by transplanting nests of the subsocial Anelosimus elegans from its native lower montane cloud forest (1000m) to the lowland tropical rainforest (400m). At both locations I performed a fully factorial ant and rain exclusion experiment and monitored colony survival over time. I found that survival was lower in the lowlands, but improved by the exclusion of rain and ants. At the native higher elevation habitat, in contrast, colony survival did not differ between treatments and controls, confirming that neither intense rains nor predation are factors that negatively impact colony survival in the native habitat. At both locations, large colonies were able to build more webbing, suggesting that larger groups with limited dispersal may benefit from reduced per capita web maintenance in addition to increased predator protection. These findings would explain why subsocial Anelosimus, with small single-family groups and dense webs, have been unable to colonize the lowland tropical rainforest where their social congeners thrive.<br>Science, Faculty of<br>Zoology, Department of<br>Graduate

La mida corporal és potser la mesura més senzilla per quantificar en un organisme però amb un rerefons potent en el camp de l’ecologia. La tesi doctoral es va centrar en l’estudi de l’estructura de mides corporal amb els peixos del llac i a diferents escales ecològiques i espacials. Els objectius generals van ser estudiar com l’estructura de mides dels peixos responia a les variacions de les interaccions tròfiques així com integrar altres aproximacions taxonòmiques i funcionals que poden ajudar a entendre aquests canvis. Es va concloure que l’estructura de mides dels peixos respon a les variacions de les interaccions tròfiques com també a les variables ambientals i a les pressions antropogèniques. Les aproximacions basades en la taxonomia i altres trets funcionals poden ajudar en l’estudi de l’estructura de mides dels peixos. L’estructura de mides dels peixos es pot utilitzar com a una mesura bioindicadora per la gestió dels sistemes aquàtics continentals sempre i quan primer es controli la variació de les interaccions tròfiques i de les variables ambientals que poden influir significativament en ella.<br>Body size is perhaps the simplest metric to quantify in an organism but with a powerful background in the ecological framework. The thesis focused on the study fish body size structure at different ecological and spatial scales. The general objectives were to study the fish size structure to understand the trophic interactions in fish as well as the effect of environmental and anthropogenic factors in the lake systems; and to expand the focus on the fish size structure and integrate taxonomic indices as well as other functional approaches. Trophic interactions can be considered as one of the most important key predictors of the variation in the fish size structure in lakes. Furthermore, the taxonomic-based approaches and other functional traits can be integrated in the study of the fish size structure to increase the accuracy of the understanding of ecological processes. The fish size structure may be used as a bioindicator for the management of freshwater ecosystems, after controlling for trophic interactions and natural variation that may significantly modify the size structure.

This thesis deals with important factors that affect the temporal organization of emergence and early survival of Baltic salmon (Salmo salar L.). The study population was obtained from the Norrfors hatchery (63°50'N,20°05'E), Umeälven (Ume river) in Northern Sweden. The main objectives of the thesis has been to study; a: the effect of female and egg characteristics on embryonic survival, b: the effect of egg size, temperature and photoperiod on the emergence pattern and c: the impact of early or late emergence on survival in relation to predation and limited territorial space. The main results are summarized as follows: (1) Fecundity and egg size increased with increasing weight of females. No effect of female size were found on egg colour. Longer impoundment and later stripping increase egg colour. Egg mortality was not correlated with egg colour. Stripping date was found to have the strongest effect on mortality. (2) Egg size had no effect on the timing of emergence but fry of different egg size emerged synchronously. Fry from large eggs left the gravel as heavier fry and with a larger proportion of yolk left compared to fry from small eggs. (3) The number of days and number of degree days from hatching to 50% emergence decreased exponentially with increasing temperature. Synchronization of emergence increased with increasing temperature. Fry emerged with more yolk at 12 °C compared to 6 °C. (4) Eggs kept in a LD 16:8 light regime hatched mainly during the light period, while eggs kept in constant darkness hatched continously over a 24 hour period. Alevins kept at different light regimes (light&gt;4h) from hatching until emergence left the gravel during the dark period. Daylength had no effect on the annual onset of emergence. (5) In a laboratory stream channel, predator presence at emergence increased mortality especially in early emerging fry. If the predator was introduced after completed emergence high mortality was noted among late emerging fry. The presence of fish predators and a limited territorial space for fry seemed to make early and late emergence hazardous and to favour a "peak" emergence. In the presence of a predator the fry changed their behaviour by reducing their swimming activity.<br>digitalisering@umu.se

Temperature is commonly suggested to be the most important regulating factor for the position of the treeline. But also other abiotic and biotic processes may influence. To understand treeline shifts, it is necessary to improve the knowledge about the treeline forming species and their establishment, growth and survival. What are the drivers behind the shifts? The abundance of other vegetation is previously reported to facilitate growth of seedlings above treeline and also warmer temperatures are commonly observed to improve growth.   This study observed growth of mountain birch seedlings during one growing season. The relative importance of environmental factors in relation to the amount of growth and abundance was investigated. The study was conducted in the area of Abisko, Northern Sweden, using 4 sites, where transects were established just above the treeline. The sites differed in the amount of mean precipitation and aspect of the slopes. The vegetation composition around the seedlings and at the average treeline was observed, soil temperatures measured and the aspect of the slope estimated   Seedling growth was observed at all sites, with the highest amount in the sites with most precipitation, Pålnoviken and Katterjåkk. The observed soil mean and maximum temperatures were consistently highest in the southern facing slopes of Jiebrenjåkk and Pålnoviken. The vegetation was mostly dominated by dwarf shrubs, herbaceous plant cover, mosses and bare ground, and did not differ between the seedlings and the average treeline. The best model for growth was found to be the combination of the factors site, herbaceous plant cover, litter and soil mean temperature. Herbaceous plant cover was observed to improve the amount of growth in the drier sites of Pålnoviken and Jiebrenjåkk.   The finding of mountain birch seedlings growing in all vegetation types along the treeline, indicates that they have no preference of vegetation type for establishment. However, the negative influence of bare ground on growth supports the theory that abundance of vegetation facilitates growth of seedlings. The highest amount of growth was found in the sites with most precipitation, suggesting this to be an important factor for growth. In contrast to the expectations, warmer soil temperatures and the south facing slopes did not affect growth positively. This could be explained by the extremely high temperatures of the summer that may have induced drought. Finally, the improved growth by herbaceous plant cover in the drier sites may be because of their preference of moisture and nutrient rich soils, that could also support the growth of mountain birch seedlings.

Tomato production was an important economic activity in the Limpopo Province of South Africa. A clear tomato yield gap existed between South Africa and the other countries in Southern Africa. Understanding the reasons behind tomato crop failures and successes in South Africa could increase tomato production in the fast-growing tomato markets of Angola, Mozambique and Zimbabwe, thereby improving food and nutrition security for smallholders and the population in general. In this study, the i) economics of tomato production in South Africa was investigated and compared to similar production systems in the USA, Turkey and India, ii) the interactions between biotic and abiotic factors that limited tomato yield and quality within three climatically distinct planting windows in the Limpopo Province of South Africa were examined, and iii) the correlations between three commercially available soil health metrics (i.e., a microscope-based method for estimating the biomass of soil bacteria, fungi and protozoans; nematode community profiling based on counts and trophic group classifications and related indices; polyphasic soil health testing based on soil biological, physical and chemical variables) and tomato yield were assessed. Meta-analysis was used to explore yield variation in open field production systems in the international context. The main yield-limiting factors were identified as planting times, planting density, soil-water relations, and synthetic/organic nitrogen fertilization. The focus of the study shifted to commercial tomato production in the Limpopo Province of South Africa. Since 2003, these tomato producers practiced intensive open field tomato production using a combination of synthetic and organic soil, crop and pest management technologies. A review of tomato production economics revealed that within a period of six years, South African tomato production cost per hectare more than doubled but the profit margin halved. The importance of tomato quality as an economic factor was demonstrated. Economic pressures forced these tomato producers to intensify production, which underscored the need for the continued development of sustainable tomato production systems. To achieve this strategic goal, the primary biotic and abiotic factors that limited tomato production were identified. The results indicated that complex interactions between biotic and abiotic factors explained yield and quality variation. Climate variation dominated crop productivity, especially in unsuitable planting windows. Soil and crop management variables, notably synthetic fertilizer and pesticide usage, ensured high quality yield. Soil biology management was an important aspect of sustainable agriculture and the use of appropriate soil biology metrics facilitated soil biology management at field scale. All three soil biology metrics were sensitive to distinguish between three types of disturbed soils commonly encountered in the open field tomato production context: natural, disturbed and cultivated soils. The microscope-based method used for quantifying bacterial, fungal and protozoan biomass and numbers was unsuitable for explaining yield variation. Nematode community profiling, in conjunction with polyphasic soil health testing, was very useful for explaining yield variation. In particular, soil pH, boron, aggregate stability, Paratrichodorus spp. and the balance among soil cations (especially exchangeable K and Mg) explained yield variation. In conclusion, sustainable open field tomato production depends on the integrated use of synthetic and organic crop nutrition and protection technologies, optimum planting times, disease-resistant genetic material, and cultivation on healthy soils. The findings of this study will benefit policy development in support of sustainable vegetable production in the rural areas of Southern Africa.<br>Thesis (PhD)--University of Pretoria, 2016.<br>tm2016<br>Plant Production and Soil Science<br>PhD<br>Unrestricted

Ceratitis capitata Wiedemann (Diptera: Tephritidae) is a cosmopolitan pest, originary from West-Africa, that has invaded almost all the temperate and tropical countries by the unwanted aid of the men. During its adaptation to these new environments, C. capitata has widened its host plant portfolio, being nowadays a key pest for more than 400 plant species of economic importance. Due to this importance, many importing countries had established quarantine measures and borders against fruit world-wide trade, which had directly impacted on the plant protection policies of producer countries. Spain and Tunisia are located in the Mediterranean basin; the first known world-wide dispersal point of C. capitata. In these two countries, C. capitata is considered a key pest mainly for citrus species and other soft-fruits. From a historical point of view, Plant Protection policies in Spain were switched from a nearly ecological management (with great losses) to mainly chemical-based treatments with the spread of organosphosphate compounds early on XX century. With the development of European Union, national Plant Protection plans were modified, introducing the Integrated Pest Management programs (IPM), on which environment and human-friendly methods should be selected instead of the most damaging chemical treatments. Following these steps, Tunisia is integrating the use of biorrational methods while keeping the use of chemicals as low as possible. To this end, in the present thesis dissertation, I would focus on the use of natural enemies as the best and sustainable control method, coming back to the Biological Control programs that were successful in the past against other pests in both countries. More precisely, this dissertation is presenting the results on the implementation of Classical Biological Control against C. capitata in citrus, by the importation, evaluation and release of the parasitoid species Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae) in both countries. This parasitoid species, native from East Asia, is currently used against other tephritid pest species, key species for other countries and commodities. In the First Chapter I will present a literature review on the Plant protection policies against this key pest, and what is know about the performance and success of this parasitoid species. At the Second Chaper, I will present the results of the implementation of laboratory rearings of both insects to achieve all the remaining objectives, along with the determination of life parameters of the specie that will determine its success as natural enemy. In this second chapter I will also present the determination of biotic (host densities and availability) and abiotic (temperature, RH, rainfall) factors affecting the performance of D. longicaudata over C. capitata. During the Third Chapter, I will demonstrate that D. longicaudata is able to exhert control of C. capitata under natural Mediterranean climatic conditions when either challenging the parasitoid with hosts directly from the laboratory rearing or in a more natural condition, within the fruits, a forestep required to determine its inclusion in the national Plant Protection Policies. Results show that D. longicaudata exhert up to 30% of medfly population reduction by means of induced mortality along the provisioning of new parasitoid offspring that would propagate and establish in the country. Along these results I showed that D. longicaudata was able to control medfly infestation foci at a rate that depend on climatic conditions and on the number of released females. At the Fourth Chapter, I will reveal the results of D. longicaudata dispersion abilities along its capability to exhert control of C. capitata populations while applied joinly with SIT, by means of open-field test trials, with a new developed sentinel fruits methodology. In this chapter, I consider also the abiotic factors that could determine its naturalization in other Mediterranean countries with similar climatic conditions. The results of this chapter highlight the need of such dispersal studies at the corresponding local climatic conditions to establish the release procedures. At the Fifth Chapter, I will expose the results of importation and naturalization of D. longicaudata in Tunisia, with the required studies on the presence of native enemies and the identification of a new parasitoid Pachycrepoideus vindemmiae Rondani (Hymenoptera: Pteromalidae)., the establishment of laboratory rearings for the release trials, and the side-effects of the available control measures that will face D. longicaudata in Tunisian citrus orchards which will determine the procedure in tempo and form for the releases. At the end of this dissertation, I will present the main conclusions achieved that can be summarized in: (i) D. longicaudata is a viable natural enemy that can be successfully released in Mediterranean countries against C. capitata; (ii) Its biotic potential under the mild climatic conditions identified will help in the naturalization of this species, and in the establishment of release protocols, but also, (iii) its climatic requirements highlight the need of switching from Classical Biological Control to Inoculative Biological control, that means that both countries require mass-rearing facilities to provide these insects, along the involvement of growers in the application of IPM measures including the augmentoriums to facilitate the naturalization of the introduced species along the preservation of the native ones.

Thesis (Ph. D.)--University of California, San Diego, 2007.<br>Title from first page of PDF file (viewed June 21, 2007). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.

Philosophiae Doctor - PhD<br>As a consequence of various cellar activities the wine industry produces copious volumes of potentially hazardous wastewater each year. South Africa is one of the top ten wine-producing countries, making the successful treatment of cellar effluent an important environmental obligation in this country. Constructed wetlands (CWs) are resilient to the seasonal input fluxes associated with agri-industrial waste and are ideal systems for the in-situ treatment of cellar effluent in small to medium-sized wineries not connected to municipal reticulation systems. In a project sponsored by the Water Research Commission of South Africa, a number of studies were undertaken to assess the remediation of winery wastewater and common components of winery wastewater in sand-filled pilot-scale constructed wetlands operated in batch mode. This thesis contains the results of three studies. The first study evaluated the temporal aspects of CW equilibration as a basis for future studies of system response to amendment. Microbial biomass and hydraulic conductivity values were monitored and microbial community fingerprints were obtained using denaturing gradient gel electrophoresis. The study showed that microbial community fingerprinting provides a valuable tool to assess the time-scales of microbial equilibration, which was found to be in the order of 100 days. In the second study, the biodegradation and mineralization of ethanol by acclimated and non-acclimated microbial populations in CWs were compared. By increasing the influent ethanol concentration at incremental intervals (incremental priming), the biodegradative capacity was significantly enhanced. At an influent COD concentration of 15 800 mg/L, no volatile fatty acids were detected in the effluent of an incrementally primed system and the maximum effluent COD measured was 180 mg/L. In contrast, an identical, unprimed system, amended with a lower concentration of COD (7587 mg/L), exhibited a maximum effluent COD concentration of 1 400 mg/L, with the metabolites butyrate and propionate accounting for up to 83% of the effluent COD. It was conclusively demonstrated that the use of incremental priming, together with the batch mode of operation enhanced long-term function of the CWs. In the third study, the removal of the phenolic component of winery wastewater was evaluated in CWs, as well as in sand columns and microcosms. It was found that at low influent phenolic concentrations in CWs, complete organic removal was accomplished, but at high concentrations, there was incomplete substrate removal and an accumulation of potentially toxic metabolites, including catechol. The sand provided a suitable substrate for the treatment of phenolic-laden waste, and both biotic (48%) and abiotic (52%) removal mechanisms effected the removal of model phenolics. Prior acclimation of microbial communities increased the biodegradation rate of phenolic acids significantly.

Species’ distributions are influenced by abiotic and biotic factors but direct comparison of their relative importance is difficult, particularly when working with complex, multi-species datasets. Here, we present a flexible method to compare abiotic and biotic influences at common scales. First, data representing abiotic and biotic factors are collected using a combination of geographic information system, remotely sensed, and species’ functional trait data. Next, the relative influences of each predictor variable on the occurrence of a focal species are compared. Specifically, ‘sample’ data from sites of known occurrence are compared with ‘background’ data (i.e. pseudo-absence data collected at sites where occurrence is unknown, combined with sample data). Predictor variables that may have the strongest influence on the focal species are identified as those where sample data are clearly distinct from the corresponding background distribution. To demonstrate the method, effects of hydrology, physical habitat, and co-occurring fish functional traits are assessed relative to the contemporary (1950 – 1990) distribution of the American Eel (Anguilla rostrata) in six Mid-Atlantic (USA) rivers. We find that Eel distribution has likely been influenced by the functional characteristics of co-occurring fishes and by local dam density, but not by other physical habitat or hydrologic factors.

Enteric viruses are responsible for a significant amount of foodborne disease in the United States. Foodborne disease associated with enteric viruses has been increasing within the last few years due to technological advances and raised awareness. Salads and salad crops are the principal vector for transmission of enteric viruses. The objective of this study was to determine if viruses are able to attach non-specifically to the surface of lettuce and to determine the forces responsible for non-specific viral adsorption to lettuce. Additionally, the impact of the microbial flora on viral persistence was studied to determine the effect on viruses. The four viruses studied were echovirus 11, feline calicivirus, MS2 and φX174. The viruses were chosen based on their varying isoelectric points and similar physicochemical attributes. The isoelectric point was not the main factor determining virus attachment to lettuce. Viruses had varying attachment efficiencies, with echovirus 11 having the highest affinity to lettuce and φX174 the least. Viral adsorption to lettuce was mediated by electrostatic forces due to the removal of virus adsorption at pH 7 and 8 with the addition of 1 M NaCl to the buffer solutions. Microcosm studies indicated that the microbial flora did not have a negative impact on virus survival. The bacteriophages had the highest survival rate. Virus survival in the microcosm studies was not indicative of virus survival on the surface of the lettuce. The animal viruses exhibited survival rates greater than or equal to the survival of bacteriophages at 4° C, but at room temperature viable animal viruses rapidly declined compared to the bacteriophages. Additional studies also indicated that the microbial flora was not able to degrade the viruses for aerobic microbial growth. Overall, these results indicate that viruses are able to attach to the surface of lettuce, providing a possible explanation for the high incidence of virus associated disease involving salads and fresh produce. More importantly the use of surrogates for virus studies involving fresh produce must be re-evaluated, because of the lack of correlation between animal viruses and bacteriophages. Appropriate viral surrogates, if used, have to be carefully chosen based on viral physicochemical properties as well as the infectious route of the virus.