Ecological studies of the Lactobacillus biota in the human digestive tract and adaptation of intestinal lactobacilli to the sourdough ecosystem

Laktobazillen haben unter den Bakterien, die den menschlichen Darm bewohnen, eine ansehnliche Beachtung aufgrund ihres positiven Einflusses auf das menschliche Wohlbefinden erlangt. Die Kultivierung dieser Bakterien gilt als zuverlässig, und so wurden zahlreiche Studien unter Anwendung von Kultivierungstechniken mit selektiven Medien durchgeführt, um die Laktobazillen in intestinalen Ökosystemen zu untersuchen (Tannock, 1995; Reuter, 2001). Vor kurzem führte die Anwendung der PCR-DGGE in Kombination mit Milchsäurebakterien (MSB)-spezifischen Primern zum Nachweis von Spezies, die nicht zu den klassischen intestinalen MSB gehören, sondern vielmehr Lebensmittel-assoziiert sind, z.B. Lactobacillus curvatus, Lactobacillus sakei, Leuconostoc mesenteroides and Pediococcus pentosaceus (Walter et al., 2001; Heilig et al., 2002). Interessanterweise konnten diese Spezies nicht durch Kultivierung auf Rogosa SL Agar erhalten werden (Walter et al., 2001). Das Kapitel III beschreibt die Anwendung unterschiedlicher Kultivierungsmedien und neuer Inkubationsbedingungen, um diese Schwierigkeiten zu überwinden. Menschliche Stuhlproben wurden auf selektive und nicht-selektive Agarplatten ausplattiert, und die Platten wurden unter den klassischen Bedingungen (37°C, anaerob) für intestinalen MSB sowie unter alternativen Bedingungen (30°C, 2% O2) inkubiert. Die Analyse von bakterieller Zellmasse, die von Agarplatten abgeschwemmt wurde, mittels PCR-DGGE brachte hervor, dass die Zusammensetzung der MSB-Spezies stärker von den angewandten Inkubationsbedingungen als von den Medien beeinflusst wurde. Es konnte beobachtet werden, dass Lebensmittel-assoziierte MSB wie L. sakei und Lc. mesenteroides, die bisher nicht als intestinale Bewohner beschrieben worden waren, leichter durch Einsatz der alternativen Inkubationsbedingungen kultiviert werden können. Eine Identifizierung zufällig ausgewählter Kolonien, die unter den alternativen Bedingungen auf Rogosa SL Agar gewachsen waren, zeigte, dass L. sakei einer der dominierenden Lebensmittel-assoziierten MSB in menschlichen Fäzesproben ist und dort in Keimzahlen von bis zu 106 KbE pro Gramm vorkommen kann. Ein Vergleich der kulturtechnischen Ergebnisse mit denen der PCR-DGGE-Analyse von Bakterienmassen auf Agarplatten zeigte außerdem, dass die Untersuchung der Bakterienmassen eine schnelle und zuverlässige Methode darstellt, um einen Einblick in die Spezieszusammensetzung der kultivierbaren MSB in Fäzes zu erhalten. Die Untersuchungen der intestinalen Laktobazillenpopulation in menschlichen Stuhlproben über einen längeren Zeitraum zeigte eine hohe Variabilität in der Komplexität und Stabilität der Spezieszusammensetzung (Vanhoutte et al., 2004; Walter et al., 2001). Ökologische Studien brachten hervor, dass die meisten Lactobacillus-Spezies im menschlichen Gastrointestinaltrakt (GIT) wahrscheinlich transient (allochthon) sind und entweder von Lebensmitteln oder aus der Mundhöhle stammen (Biblioni et al., 2004). Um zu untersuchen, inwieweit die oralen Laktobazillen einen Teil der fäkalen Laktobazillen ausmachen, wurde die Lactobacillus-Biota sowohl im Speichel als auch in Stuhlproben von drei Probanden untersucht und an zwei Zeitpunkten mit dreimonatigem Abstand verglichen (Kapitel IV). Die Zusammensetzung der Lactobacillus-Spezies im menschlichen Speichel und Fäzes war Individuum-spezifisch und fluktuierte in einem gewisse Maße, dennoch konnten die Spezies Lactobacillus gasseri, Lactobacillus paracasei, Lactobacillus rhamnosus und Lactobacillus vaginalis an beiden Zeitpunkten sowohl im Speichel als auch Fäzes der Probanden nachgewiesen werden. Durch RAPD-PCR-Analyse konnte gezeigt werden, dass mehrere Stämme dieser Spezies im Speichel und in Fäzes desselben Probanden vorhanden waren. Stämme von L. gasseri und L. vaginalis mit identischen RAPD-Mustern konnten aus beiden Speichelproben isoliert werden, was darauf hinweist, dass diese Spezies in der Mundhöhle autochthon sind. Die Ergebnisse dieses Kapitels gemeinsam mit kürzlich publizierten Daten stellen ein starkes Indiz dafür dar, dass einige Laktobazillen, die aus Stuhlproben isoliert werden können, aus der Mundhöhle stammen und somit im Intestinum allochthon sind. Laktobazillen sind in unterschiedlichen Ökosystemen gefunden worden und aufgrund ihrer kommerziellen Verwendung in der Lebensmittelindustrie Gegenstand umfassender Forschung gewesen (Hammes und Hertel, 2003). Einige Lactobacillus-Spezies lassen sich häufig sowohl in fermentierten Lebensmitteln als auch im menschlichen GIT nachweisen, jedoch ist der genetische Hintergrund für diese ökologische Vielseitigkeit noch weitgehend unbekannt. Lactobacillus reuteri ist ein dominantes Mitglied in der Mikrobiota von Typ II Sauerteigfermentationen (Meroth et al., 2003) und gilt als einer der echten autochthonen Lactobacillus-Spezies bei Menschen (Reuter, 2001). In Kapitel V und VI wurde die von Walter et al. (2001) entwickelte "in vivo expression technology (IVET)" angewandt, um bei dem Sauerteigisolat L. reuteri LTH5531 Gene (sogenannte in vivo induzierte (ivi)-Gene) zu identifizieren, die während des Wachstums in einer Typ II Sauerteigfermentation (Kapitel V) bzw. während der Passage durch den GIT einer Maus (Kapitel VI) eine erhöhte Expression zeigen. Während der Sauerteigfermentation wurden 38 induzierte und stark exprimierte Genfusionen gefunden (Kapitel V), die auf der Basis der verfügbaren Sequenzen eine Identifizierung von 29 Genen erlaubten. Vier Gene kodierten für Stress-verwandte Funktionen (z.B. Säure- und allgemeine Stressantwort) und spiegeln somit die harschen Bedingungen in der Sauerteigfermentation wider. Weitere 8 Gene kodierten für Proteine, die in Transport und Synthese von Aminosäuren und Nukleotiden involviert sind, was eine limitierte Verfügbarkeit beider Komponenten während der Sauerteigfermentation anzeigte. Die restlichen Gene waren entweder Teil von Stoffwechselwegen, die in keiner Korrelation zum Ökosystem standen, oder kodierten für hypothetische Proteine. Die Identifizierung einer putativen Proteinase und einer Komponente des Argininedeiminase-Stoffwechsels ist von technologischer Bedeutung, da beide dahinter stehenden Systeme potenziell an der Bildung von Aromavorläufern beteiligt sein können. Bemerkenswerterweise wurden bei Anwendung der IVET mit der Genombibliothek, die bereits erfolgreich bei der Sauerteigstudie eingesetzt wurde (Kapitel V), keine ivi-Promotoren während der Passage von L. reuteri LTH5531 durch den GIT einer Maus identifiziert (Kapitel VI). Mit Hilfe der IVET werden durch die Expression eines "essentiellen Wachstumsfaktors" (in unserem System die Erythromycinresistenz vermittelt durch ErmGT) aktive Promotoren selektioniert, da diese Wachstum und/oder Kolonisierung des Organismus im Ökosystem erlauben (Rainey, 1999; Walter et al., 2001). Deshalb muss die Expression eines ivi-Promotors im Ökosystem permanent erfolgen und hoch genug sein, um ein vergleichbares Wachstum von ivi-Klonen und Klonen mit konstitutiven Promoter zu erhalten, insbesondere im GIT, wo langsam wachsende Bakterien sonst ausgewaschen werden. Die Ergebnisse aus Kapitel V und VI deuten darauf hin, dass L. reuteri LTH5531 keine stark exprimierten und "GIT induzierbaren" Gene besitzt, obwohl der Stamm 38 im Sauerteig spezifisch induzierbare Gene besitzt. Ivi-Gene sind wahrscheinlich eher für die Wettbewerbsfähigkeit bzw. das ökologische Verhalten eines Organismus in einem spezifischen Ökosystem verantwortlich, als Gene, die in unterschiedlichen Ökosystemen gleich stark exprimiert werden (Rainey, 1999; Gal et al., 2003; Walter et al., 2005). Somit sind Eigenschaften, die von ivi-Genen kodiert werden, eher für die Adaption verantwortlich und das Ausmaß ihrer Expression würde durch natürliche Selektion in der Art gestaltet werden, dass die ökologische Fitness verbessert wird. Die Identifizierung von 38 Sauerteig-spezifischen ivi-Genfusionen in L. reuteri LTH5531 spiegelt die lange Adaptation von LTH5531 an das Ökosystem Sauerteig wider, ebenso wie die ivi-Gene von L. reuteri 100-23, der aus Ratten isoliert wurde, die Adaption dieses Keim an den GIT von Ratten widerspiegelt (Walter et al., 2003). In der Tat wurde der Stamm LTH5531 aus einem Sauerteig isoliert, der mit einem industriellen Starter inokuliert wurde. Dieser industrielle Starter wurde über mehrere Jahre propagiert, so dass die enthaltenen Keime genug Zeit hatten sich zu adaptieren. In Übereinstimmung damit stehen die Ergebnisse von Meroth et al. (2003), die unter Anwendung der RAPD-PCR zeigten, dass der Stamm LTH5531 bereits in einem kommerziellen Typ II Sauerteigstarter enthalten war, der 10 Jahre vor der Isolierung des Stammes Gegenstand von Untersuchungen war. Das deutet darauf hin, dass sich der Stamm LTH5531 an das Ökosystem Sauerteig seit mindestens 10 Jahren angepasst hat. Die Ergebnisse aus Kapitel V zeigen deutlich, dass die IVET eine geeignete Methode ist, die Erkenntnisse über die Genexpression und metabolische Aktivität von Bakterien während Lebensmittelfermentationen zu erweitern. Die gesammelten Ergebnisse stellen eine wichtige molekulare Grundlage dar, auf deren Basis verbesserte Starterorganismen für die Nutzung in der Lebensmittelindustrie entwickelt werden können. Darüber hinaus zeigen die Ergebnisse von Kapitel VI die Notwendigkeit in ökologischen Studien hoch-adaptierte, autochthone Stämme zu verwenden, um Kenntnisse über adaptive Wechselwirkungen zu erlangen, die für den ökologischen Erfolg dieser Bakterien in ihrem natürlichen Ökosystem sowie während der Lebensmittelfermentation verantwortlich sind.Among the bacteria inhabiting the human gut, lactobacilli have received considerable attention, due to their putative health promoting effects (Reid, 1999; Vaughan et al., 1999). Cultivation of lactobacilli is considered to be reliable and numerous studies using plating on selective media have been performed to investigate these bacteria in intestinal ecosystems (Tannock, 1995; Reuter, 2001). Recently, the application of PCR-DGGE in combination with primers specific for lactic acid bacteria (LAB) detected species which are not considered to be intestinal inhabitants but food-associated, such as Lactobacillus curvatus, Lactobacillus sakei, Leuconostoc mesenteroides and Pediococcus pentosaceus (Walter et al., 2001; Heilig et al., 2002). Remarkably, these species could not be recovered by traditional bacteriological culture on Rogosa SL agar (Walter et al., 2001). In Chapter III, different cultivation media, as well as new incubation conditions were applied to overcome these difficulties. Human faecal samples were plated on selective and non-selective media and incubated under standard condition (37°C, anaerobiosis) for faecal LAB as well as alternative condition (30°C, 2% O2). PCR-DGGE analyses of resuspended bacterial biomass (RBB) obtained from agar plates revealed that the species composition of the recovered LAB was affected stronger by the incubation condition than by the used medium. It was observed that food-associated LAB such as L. sakei and Lc. mesenteroides, hitherto not described as intestinal inhabitants, are more easily selected when the alternative incubation condition is used. Identification of randomly picked colonies grown under the alternative condition on Rogosa SL agar showed that L. sakei is one of the predominant food-associated LAB species in faecal samples, reaching counts of up to 106 CFU per gram faeces. Comparison of the results of bacteriological culture with those obtained by PCR-DGGE analysis of the RBB showed that investigation of RBB is a fast and reliable method to gain insight into the species composition of culturable LAB in faeces. Examination of the faecal Lactobacillus populations over longer periods has revealed marked variation in the complexity and stability of these populations among human subjects (Vanhoutte et al., 2004, Walter et al., 2001). Ecological studies indicate that most Lactobacillus species found in the human gastrointestinal tract (GIT) are likely to be transient (allochthonous), originating from either the oral cavity or food (reviewed in Bibiloni et al., 2004). In order to investigate if oral lactobacilli constitute a part of the faecal Lactobacillus biota, the Lactobacillus biota of saliva and faeces of three human subjects were investigated and compared at two time-points in a three months interval (Chapter IV). The species composition of the Lactobacillus biota of human saliva and faeces was found to be subject-specific and fluctuated to some degree, but the species Lactobacillus gasseri, Lactobacillus paracasei, Lactobacillus rhamnosus and Lactobacillus vaginalis were detected at both time-points in saliva and faecal samples of individual subjects. RAPD-PCR analysis indicated that several strains of these species were present both in the oral cavity and in the faecal samples of the same subject. Oral isolates of the species L. gasseri and L. vaginalis showing identical RAPD types were found to persist over time, suggesting that these species are autochthonous to the oral cavity. The results of Chapter IV, together with recently published data (reviewed in Bibiloni et al., 2004), give strong evidence that some lactobacilli found in human faeces are allochthonous to the intestine and originate from the oral cavity. Lactobacilli have been detected in diverse environments and have been the subject of considerable research due to their commercial use in the food industry (reviewed in Hammes and Hertel, 2003). Several Lactobacillus species are commonly detected in both fermented food and the human GIT, but the genetic background for this ecological versatility is poorly understood. Lactobacillus reuteri is a dominant member of the microbiota of type II sourdough fermentations (Meroth et al., 2003) and is considered one of the truly autochthonous Lactobacillus species in humans (Reuter, 2001). The in vivo expression technology (IVET) developed by Walter et al. (2003) was used to identify genes (so-called ivi genes) of the sourdough isolate L. reuteri LTH5531 that show elevated levels of expression during growth of this organism in a type II sourdough fermentation (Chapter V) and during passage through the GIT of mice (Chapter VI). Thirty-eight induced fusions were found to be highly expressed during the sourdough fermentation (Chapter V), and 29 genes could be identified on the basis of the available sequence information. Four genes encoded stress-related functions (e.g. acid and general stress response) reflecting the harsh conditions prevailing during sourdough fermentation. Further eight genes were involved in acquisition and synthesis of amino acids and nucleotides, indicating their limited availability in sourdough. The remaining genes were either part of functionally unrelated pathways or encoded hypothetical proteins. The identification of a putative proteinase and a component of the arginine deiminase pathway are of technological interest, as they are potentially involved in the formation of aroma precursors. Remarkably, IVET with the genomic library that was successfully used in the sourdough study (Chapter V) did not detect ivi promoters when LTH5531 inhabited the GIT of mice (Chapter VI). With IVET, active promoters are selected by expression of an "essential growth factor" (in our system the erythromycin resistance mediated by ErmGT) that allows the organism to colonize and/ or grow in the ecosystem (Rainey, 1999, Walter et al., 2003). Expression of ivi promoters in particular ecosystems must therefore be permanent and strong in order to allow comparable growth rates of ivi clones and clones bearing constitutive promoters, especially in the GIT, where inactive bacteria are washed out. The findings of Chapter V and VI indicate that L. reuteri LTH5531 does not possess strongly expressed "GIT inducible" genes, while possessing 38 ones specifically induced in sourdough. Ivi genes are more likely to contribute to the ecological performance of an organism in a specific environment than genes expressed equally in a broad range of habitats (Rainey, 1999, Gal et al, 2003, Walter et al., 2005). Therefore, traits encoded by ivi genes are likely to be adaptive and the extent of their expression would be shaped by natural selection to improve ecological fitness. The presence of thirty-eight "sourdough specific" ivi fusions in L. reuteri LTH5531 probably reflects the long term adaptation of LTH5531 to the sourdough environment, just as ivi genes detected in strain 100-23 reflect adaptation of this GIT isolate to the rodent GIT (Walter et al., 2003). Indeed, LTH5531 was isolated from an experimental sourdough that had been inoculated with an industrial starter. This industrial starter has been propagated over several years, giving the organisms present sufficient time to adapt. In accordance with this, by using RAPD-PCR, Meroth et al. (2003) showed that strain LTH5531 was present in a commercial type II sourdough starter collected 10 years prior isolation of LTH5531, thus indicating that this strain has adapted to the sourdough environment for at least 10 years. The results of Chapter V clearly demonstrated that knowledge of gene expression and metabolic activities of bacteria during food fermentations can be obtained by applying IVET. The results collected provide an important molecular basis on which improved starter strains can be developed for industrial exploitation. Moreover, the results of Chapter VI show the importance of working with highly adapted, autochthonous strains in studies of microbial ecology in order to reveal the adaptive interactions responsible for the ecological success of these bacteria in their natural environment or during food fermentations

Exploration of the Lean Limit in a Split-Cycle Engine

With increasing focus on efficiency and reduction of greenhouse gases, combustion processes need to be improve. Whether through use of alternative fuel or alternative combustion cycles, improvements to the combustion process are desired. Natural gas composed primarily of methane is an alternative fuel for internal combustion engines that has a potential to meet these goals. It has a high octane number, reduced CO2 output and lower emissions than other gases. Natural gas has a low laminar flame speed, making its implementation in internal combustion engines challenging. A split-cycle engine has been constructed at the University of Windsor to address issues typical of natural gas combustion. The architecture promotes intense turbulence leading to improved burn rates. Testing on the split-cycle has shown burn durations under 30°CA, amongst the fastest for natural gas engines presented in literature. This work will address two issues with the split-cycle engine, the high lean limit of operation and the low loads achieved by the engine. The lean limit of operation is extended using a dual coil ignition strategy, increasing energy input to the kernel, thereby increasing stability. Secondly, it has been shown that early exhaust valve closure results in excessive combustion products being in-cylinder, resulting in 15-25% charge dilution. A change in exhaust valve timing is shown to effect the lean limit of operation. Low loads are attempted to be addressed with a change of valve timing. The valve timing change results in improved combustion parameters yet poorer indicated output. This cause of this issue is determined using a mass balance analysis which shows that the mass ow rate through the system is partially dependent on the mass transfer from the crossover passage, which should be optimized for the best performance for this type of engine. A new parameter that is used to characterize split-cycle engine performance, the mass compressed ratio, is defined in this work

Nuclear prompt gamma spectroscopy for range verification in ion-beam therapy

Proton and heavier ions have a characteristic energy deposition profile presenting the maximum at the end of range of the primary particles. This feature potentially allows delivering highly conformal radiation therapy, depositing most of the dose in the target volume and sparing the healthy tissue surrounding it. Despite its expanding clinical application, several limitations still affect this technique and there are great opportunities for further improvement. This thesis addresses the issue of range uncertainties. Many factors influence the range of the primary particles. Due to the sharp spatial gradients of the dose distribution, even a small shift can lead to severe changes in the treatment quality. Countermeasures are usually adopted in clinical practice to make the dose delivery robust to such shifts at the price of obtaining sub-optimal treatment plans. This thesis aims to develop a preclinical prototype to measure on-line and in-vivo the position of the dose deposition. The technique is based on nuclear prompt gamma spectroscopy. In this work, we first proposed the use of a novel detector type. Then, we optimized through simulations and experimentally characterized the detector system. Finally, we experimentally demonstrated the measurement of the particles range with millimetric precision in clinically relevant conditions

Geometric Shape Recognition algorithm from coaxial vision system images for 3D reconstruction

openGeometric Shape Recognition algorithm from 2D images provided by a coaxial vision system for the reconstruction of the 3D model of objects and related UV mappings.Geometric Shape Recognition algorithm from 2D images provided by a coaxial vision system for the reconstruction of the 3D model of objects and related UV mappings

Petiole rot caused by Fusarium monoliforme, a new disease or Areca palm

Chez le palmier Areca (Chrysalidocarpus lutescens), cultivé dans une serre à La Plata (Buenos Aires, Argentine), on a observé des symptômes d'une maladie qui n'avait pas été décrite précédemment. Les jeunes pétioles du bas pourrissaient d'abord, puis la feuille ensuite. Chez les pétioles malades, on a observé un mycélium aérien qui a donné une espèce de Fusarium en culture. D'après les caractéristiques morphologiques et culturales, tous les isolats ont été identifiés comme appartenant au F. moniliforme. Le pouvoir pathogène du champignon isolé a été démontré par inoculation sur des palmiers Areca. F. moniliforme a été ré-isolé à partir des palmiers inoculés et devenus infectés, selon les exigences du postulat de Koch.Symptoms of a previously undescribed disease were observed on greenhouse-planted Areca palms (Chrysalidocarpus lutescens), grown in La Plata (Buenos Aires, Argentina). Lower young petioles were rotted with the decay extending to the entire leaves. White mycelium was observed on diseased petioles from which a Fusarium sp. was recovered. Based on morphological and cultural criteria all isolates were identified as F. moniliforme. Pathogenicity was demonstrated on Areca plants inoculated with the fungus. F. moniliforme was reisolated from the inoculated palms to complete Koch's postulates

Performance docente: a sala de aula de teatro como espaço de criação

This text introduces the concept of inner creative state based on the work of the Russian director and pedagogue Konstantin Stanislavski, describing and analyzing it within the original context in which it appeared in the Actor's Pedagogy. This notion is used as a tool to think the work of theater teachers in classrooms. This work, considered as a teacher's performance, where the body has a leading role, is analyzed within the student/teacher relationships. The research was based on the observation of the classes of ten teachers, at different educational levels, complemented by semi-structured interviews with them. The teachers were chosen based on their experiences as actors, in parallel to their work as theater teachers. This choice aimed at identifying traces of artistic performances in their activities. The notion of performance articulates, in this research, different dimensions of teacher/student relationships, emphasizing the body as the locus for those relationships. Therefore, the idea of an inner creative state raises, in the work of those teachers, relationships conducive to education. We highlight two inner creative states that are central to their work. The first one refers to the collective character of the relationships, revealing how the roles of teacher and student are not performed based on hierarchies. The second one shows how the transformation, either in the actual theatrical task of transforming oneself, or in the educational tasks of teaching and learning, is a constant in the classrooms of those teachers, producing a specific ethic. This transformation as a condition for theatrical work in the classroom and as an assumption, presupposes an overflow of the work beyond the professional dimension. The inner creative state is presented, thus, as the construction of a collective ethics that transforms the subjects beyond the professional dimension.Este texto apresenta o conceito de condição criativa a partir da obra do diretor e pedagogo russo Konstantin Stanislavski, descrevendo-o e analisando-o no contexto original de sua aparição na Pedagogia do Ator. Essa noção é utilizada como ferramenta para pensar o trabalho do professor de teatro em sala de aula. Esse trabalho, pensado como performance docente, na qual o corpo tem papel preponderante, é analisado no interior das relações entre alunos e professores. Tal investigação partiu da observação das aulas de dez professores, em diferentes níveis de ensino, complementadas por entrevistas semiestruturadas com os professores. Os professores foram escolhidos a partir de suas experiências como atores, paralelas ao trabalho como professores de teatro. Essa escolha visou verificar os traços da performance artística contidos na performance docente. A noção de performance articula, nesta investigação, diferentes dimensões das relações entre professores e alunos, enfatizando o corpo como lócus das relações. A ideia de condição criativa faz emergir, portanto, no trabalho desses professores, as relações propícias para ensinar e aprender. Enfatizam-se duas condições criativas centrais no trabalho desses professores. A primeira diz respeito ao caráter coletivo das relações, mostrando como os papéis de professor e de aluno não são performados a partir de hierarquias. A segunda mostra como a transformação, seja na tarefa propriamente teatral de transformar-se, seja na tarefa docente de ensinar e aprender é uma constante na sala de aula desses professores, produzindo uma ética específica. Tal transformação como condição do trabalho teatral da sala de aula e como pressuposto, supõe um transbordamento do trabalho para além da dimensão profissional. A condição criativa é apresentada, assim, como construção de uma ética coletiva que transforma os sujeitos partícipes para além da dimensão profissional

Influenza dell'eterogeneità ambientale nella valutazione dell'effetto riserva: il caso dei popolamenti ittici dell'Arcipelago Toscano.

In un pianeta in rapida crescita demografica ed economica la presa di coscienza del progressivo deterioramento degli ecosistemi marini, da un lato, e il crescente interesse per la biodiversità degli ambienti marini ed i processi ecologici ad essi associati, dall’altro, hanno messo in luce l’incapacità dell’uomo di gestire l’immenso patrimonio custodito negli oceani e la totale mancanza di un approccio lungimirante, teso a quantificare l’impatto provocato dall’uso indiscriminato delle risorse marine. Una corretta tutela e una gestione sostenibile dell’ambiente, in particolare quello marino, vengono oggi avvertite, sia dai governi, sia dall’opinione pubblica come una necessità per il presente e un dovere verso le generazioni future. Le Aree Marine Protette (AMP), ad oggi, sono globalmente riconosciute come uno dei migliori strumenti volti alla protezione della biodiversità, la conservazione degli ecosistemi marini e la gestione degli stock ittici. All’interno delle AMP si riscontra, infatti, un generale aumento di densità, taglia e biomassa corporea per specie target della pesca, nonché un notevole miglioramento dell’output riproduttivo di tali specie. Tutto ciò si traduce spesso in un incremento di biodiversità dell’area soggetta a protezione. Le specie maggiormente soggette a prelievo, infatti, occupano spesso i livelli più alti delle reti trofiche e il loro sovrasfruttamento può determinare gravi conseguenze sull’intera comunità attraverso le cosiddette cascate trofiche con una riduzione della diversità complessiva. Le AMP hanno dimostrato di essere in grado di ristabilire le interazioni predatorie perdute e di promuovere il recupero a livello delle comunità. Nonostante i risultati ottimistici ottenuti in molti studi, le risposte dei popolamenti ittici alla protezione variano sia in direzione, che entità e le basi di questa eterogeneità negli effetti delle AMP sono tuttora in gran parte sconosciuti. Le principali sorgenti di eterogeneità nell’efficacia delle AMP sono: taglia ed età (cioè il tempo trascorso dall’istituzione) della riserva, possibile inclusione in una rete di riserve, ciclo vitale e caratteristiche ecologiche delle diverse specie soggette a protezione ed eterogeneità spaziale nella distribuzione dei popolamenti protetti. In particolare, la frammentazione degli habitat naturali rappresenta un importante fattore di confusione che dovrebbe essere sempre considerato se si vogliono esaminare gli effetti di una AMP; tuttavia, raramente figura negli studi presenti in letteratura. Il presente lavoro di tesi si inserisce in questo contesto e si propone valutare gli effetti di confusione che processi spaziali legati all’eterogeneità ambientale (riassunti negli indici di eterogeneità del substrato e della costa e dalle coordinate geografiche) possono introdurre nella valutazione dell’effetto riserva, presso alcune isole del Parco Nazionale dell’Arcipelago Toscano (Capraia, Giannutri, Montecristo e Pianosa), attraverso un campionamento della fauna ittica (effettuato tramite tecniche non distruttive di visual census) appropriato per comparare la struttura dei popolamenti ittici, le densità e le distribuzioni di taglia di singole specie target all’interno ed all’esterno delle AMP. L’analisi è stata condotta avvalendosi di GAMM (Generalized Additive Mixed Models), che permettono di modellizzare in maniera flessibile gli effetti delle covariate (in questo caso le variabili predittive relative ai processi spaziali e ambientali) utilizzando come predittore lineare una combinazione additiva di funzioni non parametriche delle covariate ed effetti di fattori casuali (qui il tempo). I risultati relativi alle modalità di distribuzione delle abbondanze delle specie censite non hanno mostrato significative differenze tra le aree protette e le località esterne alle AMP, mentre è emersa l’importanza degli effetti relativi alle coordinate spaziali e all’indice di eterogeneità della costa. Nonostante i fattori da considerare siano molteplici, dalle caratteristiche del ciclo vitale proprie di ciascuna specie all’efficacia delle misure di controllo e tutela dell’area, i risultati ottenuti col presente studio suggeriscono l’importanza di includere, negli studi sulla valutazione dell’effetto riserva, indici relativi a processi spaziali legati all’eterogeneità ambientale