473 research outputs found

    MARINE ECOSYSTEMS THROUGH THE LENS OF SOUNDSCAPE ECOLOGY: HOW BIOLOGICAL PROCESSES, LANDSCAPE STRUCTURE, AND ANTHROPOGENIC ACTIVITY AFFECT SPATIOTEMPORAL SOUNDSCAPE PATTERNS

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    Marine soundscapes, or the collection of all sounds across a landscape, consist of dynamic patterns resulting from natural and anthropogenic sound-producing processes. Soundscape ecology is focused on understanding how these processes interact with environmental variables and landscape structure to create dynamic soundscape patterns across space and time. As the field develops, there has been rising interest in using soundscapes as a tool to assess biodiversity and inform conservation and management decisions. However, understanding spatiotemporal soundscape patterns and their associations with ecological and environmental covariates is needed for passive acoustic monitoring to be informative. My dissertation addresses this need through two focal questions: (1) how do soundscapes vary across marine landscapes and is this variation explained by ecological metrics; and (2) how can soundscapes, or passive acoustic monitoring, be used to inform conservation and management priorities? To understand soundscape variation, I first compared the soundscapes of natural and artificial offshore reefs, finding that their temporal patterns were similar but spectral content differed. Following these results, I evaluated soundscape spatial variation across a range of estuarine habitat mosaics to explore whether soundscape differences between habitat types were associated with environmental metrics. I observed four distinct soundscape types that were associated with patch- and landscape-scale habitat metrics. Variation in all soundscape metrics summarized was explained by landscape-scale habitat metrics, while patch-scale metrics also explained sound levels, and abiotic metrics explained species-specific call rates. To evaluate how passive acoustic monitoring can be applied to conservation and management questions, I assessed whether soundscape monitoring was a useful complement to traditional video monitoring for tracking community development following deployment of an artificial reef. Comparing the soundscape of a newly deployed artificial reef to that of a nearby established reef revealed the colonization of multiple cryptic species that were not available from video monitoring. Lastly, I used multiple passive acoustic monitoring technologies to assess the spawning-associated grunt dynamics of Atlantic cod in a region with imminent offshore wind energy development. Elucidating the peak spawning period and aggregation site revealed that interactions between Atlantic cod spawning and offshore wind energy construction are likely. This dissertation advances understanding of soundscape variability in multiple ecosystems and demonstrates the benefit of passive acoustic monitoring for addressing applied ecological questions. By focusing on periods of peak acoustic activity and exploring variation across marine landscapes, my research explained previously undescribed soundscape variation and identified the relevance of landscape context in understanding marine soundscape variability. In applied contexts, my findings demonstrate that species-specific results are the most ecologically informative, but the current application of passive acoustic monitoring is limited by a lack of reliable identification of species-specific call types and associated call detectors. Advances in call detection will facilitate more nuanced ecological questions to be asked of marine soundscape and expand its relevance for addressing conservation and management priorities.Doctor of Philosoph

    Prehistoric pathways to Anthropocene adaptation: Evidence from the Red River Delta, Vietnam

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    Over the past twenty years, government advisory bodies have placed increasing emphasis on the need for adaptive measures in response to the effects of human-induced climate change. Integrated Assessment Models (IAMs), which incorporate macroeconomic and climate variables, feature prominently in advisory content, though they rarely draw on data from outside strictly constrained hypothetical systems. This has led to assertions that they are not well-suited to approximate complex systemic human-environment processes. Modular, interdisciplinary approaches have offered a way to address this shortcoming; however, beyond climate records, prehistoric data continue to be under-utilised in developing such models. In this paper we highlight the contribution that archaeology and palaeoecology can make to the development of the next generation IAMs that are expected to enhance provision for more local and pro-active adaptations to future climate change. We present data from one of Southeast Asia’s most heavily developed river deltas: the Red River (Song Hong) Delta, in Vietnam and localised analysis from the Tràng An Landscape Complex World Heritage Site, on the delta’s southern margin. Comparison is made between Shared Socio-economic Pathways (SSP) 5–8.5 and SSP2–4.5 emission projection models and the Mid-Holocene inundation of the Red River Basin. We highlight the value to taking a scientific long view of coastal evolution through an illustrative set of eight research foci where palaeo-data can bring new and localised empirical data to bear on future risk management planning. We proceed to demonstrate the applicability of palaeoenvironmental, zooarchaeological and historical evidence to management and the development of sustainable conservation strategies using Tràng An as a case study. In so doing, we further highlight the importance of knowledge exchange between scientific, corporate, non-governmental, local, and state stakeholders to achieve tangible results on the ground

    Molecular clouds and stellar feedback: an investigation of synthetic line and continuum emission maps

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    Molecular clouds are complex systems and the search of adequate observational measurements to trace their evolution is still an open problem. In this thesis, we use produce synthetic emission maps of the 12CO 1-0, 13CO 1-0, [CI] 1-0, and [CII] lines, as well as of the FIR continuum emission, to test to which extent these emission measurements can be used as tracers of the evolutionary stage of molecular clouds. We use numerical simulations of molecular clouds performed within the SILCC-Zoom project. These simulations include detailed stellar feedback due to ionizing radiation, external magnetic fields, and a chemical network evolved on-the-fly. We compare two different chemical networks, NL97 and NL99, and we find that NL97, even though it does not include neutral carbon, more accurately reproduces the abundances of CO and C+. We then use NL97 in the rest of the work. We introduce a novel post-processing procedure for the C+ abundance using CLOUDY, essential in HII regions to account for the higher ionization states due to stellar radiation. Furthermore, we show that assuming chemical equilibrium results in H and H2 being underestimated and overestimated, respectively, by up to a factor of 2. The abundances of C+ and CO are also, respectively, underestimated and overestimated. This is reflected and amplified in the estimation of the CO and [CII] luminosity as well. We also investigate the capability of the L_CO/L_[CII] luminosity ratio to trace the H2 mass fraction in the clouds, but find no clear trend. We then investigate the [CII]/FIR ratio in HII regions and in entire clouds with stellar feedback. In young HII regions the drop of the [CII]/FIR intensity ratio is mainly due to the strong FIR emission produced by hot and dense dust, and the contemporary saturation of the [CII] line. In more evolved HII regions, the second ionization of carbon is the main reason for the low [CII]/FIR ratio. The evolution of this ratio is reflected in the evolution of the L_[CII]/L_FIR luminosity ratio in the entire clouds. This evolution can be schematized in three phases. Overall, L_[CII]/L_FIR is well correlated with the total stellar luminosity L_*tot. The relation between L_[CII]/L_FIR andL_*tot can be fitted with a power-law. When L_*tot is large, i.e., in evolved clouds which formed many massive stars, L_[CII]/L_FIR is particularly low, determining an observable [CII]-deficit in these clouds. However, this relation breaks when the total FIR luminosity stars decreasing as a consequence of the cloud dispersal caused by the stellar feedback. The aspect of HII regions in molecular clouds strongly depends on the geometry of the cloud, and on the line of sight. Indeed, a certain HII region can have different properties when observed from different LOS, and apparent HII regions, which are actually only the result of projection effects, can be observed

    Comparing real and synthetic observations of protostellar disks

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    Nascent envelope disk structures around protostars play a crucial role in the process of star and planet formation. As ALMA reveals unprecedented details of the envelope, disk, and outflow structures in nearby protostellar systems, a consistent interpretation for these observations remains absent, instead, highly simplified models are often adopted to partially fit the observed features. In this project, we aim to generate more realistic synthetic observations of the nascent protostellar disk and envelope system, using existing radiation and non-ideal magnetohydrodynamic simulations of protostellar collapse and disk formation. The main goal of the project is to provide multi-facet interpretation of the current continuum and polarization observations of protostellar sources at their earliest stages, and offer more realistic constraints on the dust growth in the early protoplanetary disks

    Merging, fragmentation and collapse of interstellar filaments

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    Sterne haben die Menschen schon seit jeher fasziniert und Beobachtungen zeigten bereits vor Jahrzehnten, dass leichte Sterne filamentartigen Strukturen entspringen. Dennoch ist der Entstehungsprozess dieser Filamente sowie deren Entwicklung und Fragmentierung in einzelne Kerne bislang nicht hinreichend verstanden. Wie ich in der vorliegenden Arbeit, die neue Erkenntnisse zur Dynamik, Fragmentierung und zum Kollaps von Filamenten ermöglicht, zeige, spielt das Aufstellen, Verstehen und Vergleichen von Zeitskalen hierbei eine wesentliche Rolle. Von zentraler Bedeutung hierbei ist die Zeitskala, auf der Filamente kollabieren, denn diese bestimmt ihre Lebensdauer und somit den zeitlichen Rahmen in dem physikalische Prozesse innerhalb des Filaments ablaufen können. Da es keine hydrostatische Lösung entlang der Hauptachse eines Filaments gibt, sind diese nicht stabil. Aus theoretischer Sicht müssen somit alle Filamente einem longitudinalen Kollaps unterliegen, wobei sich durch das Profil der Beschleunigung eine Verdichtung an jedem Ende des Filaments bildet. Dies ist der sogenannte „Edge Effect“. Die vorliegende Arbeit zeigt, dass der Filament-Kollaps in einem zweistufigen Prozess abläuft. Die erste Phase ist dominiert durch Eigengravitation, die zu einem beschleunigten Kollaps führt. In der zweiten Phase erfährt die Verdichtung am Ende des Filaments einen Staudruck durch das Material im Inneren des Filaments, was zu einer gleichförmigen Bewegung führt. Ausgehend von diesen Erkenntnissen lässt sich der Kollaps analytisch beschreiben und eine Kollapszeit berechnen, welche mit empirischen Betrachtungen übereinstimmt. Unsere Studien zeigen, dass die Zeitskala, auf denen Filamente kollabieren, und somit auch der Edge Effect stark vom Dichtegradienten in der Endregion abhängt. Auch wenn er den Kollaps nicht aufhalten kann, so kann er diesen verlangsamen. Wird der Kollaps hinreichend verlangsamt, können Störungen schneller anwachsen, was zur Fragmentation entlang des Filaments führt. Das erklärt, weshalb der Edge Effect seltener beobachtet wird, als bisher theoretisch erwartet. Auf Basis unserer Ergebnisse ist zu erwarten, dass die meisten Filamente Dichtegradienten am Ende besitzen, die größer sind als der kritische Gradient, bei dem der Edge Effect und das Anwachsen der Störungen gleich schnell sind. Eine Verlangsamung des Filament Kollaps ermöglicht den Ablauf von Prozessen, welche auf ähnlichen Zeitskalen stattfinden, wie zum Beispiel das Verschmelzen von Filamenten. Ich zeige in dieser Arbeit, dass es ohne die Verlangsamung des Kollapses bestimmte Rahmenbedingungen braucht, unter denen eine Verschmelzung überhaupt möglich ist. Die notwendigen Grenzwerte verschieben sich durch die Verlangsamung und machen eine Verschmelzung deutlich wahrscheinlicher. Durch die Verschmelzung unterliegen Filamente einer langanhaltenden Oszillation, die auch in der Geschwindigkeitsdispersion und der Säulendichte beobachtbar ist. In beispielhaften Filamenten der Orion-Region haben wir Hinweise auf ähnliche Strukturen gefunden. Schlussendlich gebe ich noch einen Ausblick, wie maschinelles Lernen Simulationen von Filamenten beschleunigen kann. Wir haben ein Netzwerk entwickelt, das die Abschwächungskoeffizienten von interstellarer ultravioletter Strahlung bei bekannter Dichteverteilung bestimmt, was rechnerisch deutlich effizienter ist als herkömmliche Methoden. Große Strukturen werden gut reproduziert, jedoch ist die Reproduktion von kleinen und dichten Strukturen noch nicht hinreichend akkurat.Stars have always fascinated people and already decades ago observations showed that low-mass stars originate from filamentary structures. Nevertheless, the formation process of these filaments, as well as their evolution and fragmentation into individual cores, is not yet sufficiently understood. As I will show in this thesis, which provides new insights into the dynamics, fragmentation and collapse of filaments, determining, understanding and comparing timescales plays a crucial role, in this regard. The timescale on which filaments collapse is of key importance because it determines their lifetime and therefore the timeframe in which physical processes can take place within the filament. Since there is no hydrostatic solution, filaments are not stable along their main axis. From a theoretical point of view, all filaments must therefore collapse in longitudinal direction with a compression forming at each end of the filament due to the profile of the acceleration. This is the so-called ‘edge effect’. The present thesis demonstrates that the filament collapse is a two-phase process. The first phase is dominated by the self-gravity of the filament, leading to an accelerated collapse. In the second phase, the condensations at the end of the filament experience the ram pressure of the material inside the filament, leading to a uniform movement. With these findings, the collapse can be described analytically and a collapse timescale can be determined which agrees well with empirical results. Our studies show that the timescale on which filaments collapse, and therefore also the edge effect, strongly depends on the density gradient in the end region. Although a density gradient cannot stop the edge effect, it can slow it down. If the slow-down is sufficiently large, perturbations can grow faster than the edge, leading to fragmentation along the filament. This explains why the edge effect is observed less than theoretically expected. Our results suggest that most of the filaments are required to have density gradients shallower than the critical gradient, for which the edge effect and the perturbations grow on the same timescale. The slow down of the filament collapse allows processes to occur that happen on similar timescales as, for example, filament mergers. In this work, I show that without slowing down the collapse, special initial conditions have to be met in order to make filament mergers possible. The necessary thresholds are shifted due to the slow-down, making a filament merger much more probable. The merger induces long-lived oscillations which can be observed in velocity dispersion and column density. We found evidence of similar signatures in exemplary filaments in the Orion region. Finally, I will give an outlook on how machine learning can speed up simulations of filaments. We developed a network that predicts attenuation coefficients of interstellar ultraviolet radiation given a certain density distribution and which is computationally much more efficient than traditional methods. The overall structure is well reproduced, whereas the determination of small and dense features needs further improvement

    Phenological dynamics of four populations of Handroanthus spongiosus in seasonally dry tropical forest in Brazil.

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    The scarcity of phenological studies based on different populations of tropical forest trees limits seed management and collection for reforestation efforts. Precipitation is the primary factor driving tropical plant phenology in seasonal environments, although other environmental variables and plant traits may be associated. We examined the seasonality, synchrony, and intensities of the vegetative and reproductive phenophases of four populations of Handroanthus spongiosus, an endangered species, under similar climate regimes in a seasonally dry tropical forest, in northeastern Brazil. We expected to observe some divergence in the phenologies of the populations related to distinct functional traits selected for by differences in rainfall and soil properties. Mature trees (n = 87) were monitored during a three-year period. Seasonality was examined using circular statistics, and the influences of environmental variables on phenophases were investigated using generalized additive models. Variations in intensities and activity indices were identified among the different populations. Vegetative phenophases were seasonal, driven by precipitation and photoperiod, with leaf longevity of up to 7 months; budding peaked in February-March, while leaf fall peaked in April and October. The reproductive phenophases were found to be seasonal, during the rainy season (November to April), influenced by temperature and photoperiod. The slight divergences noted among the phenological behaviors of the populations were related to distinct functional traits (e.g., tree height, stem diameter) selected for by differences in certain environmental variables (rainfall volumes and soil properties). Given ongoing global climate changes, increases in leaf fall and reductions of flowering intensity, as verified here, will likely be observed

    Urbanising the Security-Development Nexus: A Revisited Perspective on Segregation Governance in Miskolc, Hungary

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    The thesis develops a critique of two competing visions of urban segregation governance in Miskolc, a medium-sized post-industrial city in Northern Hungary. At one end of the spectrum lies a penal populist agenda of displacing the marginalised, and primarily the city’s Roma population, through slum clearances and policing interventions to prevent said groups from circulating back into the city. At the other end is an emancipatory and pro-welfare social policy approach that works on social divides in situated, sensitive, and sympathetic ways. The two perspectives are by no means mutually exclusive, however. Instead, they are wielded in tandem with varying intensity depending on the political stance and options of the municipal administration, and ultimately orchestrate the same hegemonic vision of keeping unwanted surplus populations at bay. The study demonstrates that the overlapping domains of penal and social policy in Miskolc are shot through with the notions of security and development in their discursive and practical mobilisations alike. To make sense of these relationships, the security-development nexus (SDN) – a concept predominantly utilised in international geopolitical and development research thus far – is adapted to the urban level. An SDN-based perspective allows us to understand the ways that social divides are governed in Miskolc through a joint operation of sovereign power and biopower. Additionally, it enables a holistic and interconnected view of segregation governance in neoliberal cities rather than being siloed to either security or development alone. The study reflects on the above outlined dynamics against the backdrop of right-wing populism, which continues to dominate mainstream Hungarian politics

    Fine-scale genetic structure of <em>Magnolia iltisiana</em> in forest regeneration sites with a history of selective logging

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    Background: Selective logging is a frequent practice in the Tropical Montane Cloud Forest which can impact forest regeneration and the genetic makeup of successive generations of trees. The spatial clustering of genetically related individuals, fine-scale genetic structure (FSGS), can develop from the reduction of gene dispersal and the decrease in the number of reproductive individuals at the local scale due to selective logging. Questions: In regeneration sites with a history of selective logging, does FSGS differ from a site without such a history? Is FSGS stronger in seedlings and saplings relative to juveniles and adults? Is genetic diversity similar among life stages and sites? Studied species: Magnolia iltisiana an endemic tree. Study site and dates: Sierra de Manantlan Biosphere Reserve, Jalisco, Mexico. 2020. Methods: We evaluated genetic diversity, genetic structure, and FSGS across four life stages (seedlings, saplings, juveniles, and adults) by genotyping 211 individuals with seven nuclear microsatellite loci in two regeneration and one conserved site. Results: We found statistically significant FSGS in the two regeneration sites only for seedlings and saplings, while no evidence of FSGS was detected in the conserved site. No differences in genetic diversity estimates and structure were found among life stages. Conclusions: Our study does not suggest an effect of selective logging on genetic diversity on the contrasted conditions and an FSGS pattern only in the earlier stages of the regeneration sites in M. iltisiana

    Unveiling the initial conditions of open star cluster formation

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    Open clusters (OCs) are infrequent survivors of embedded clusters gestated in molecular clouds. Up to now, little is known about the initial conditions for the formation of OCs. Here, we studied this issue using high-precision astrometric parameters provided by Gaia data release 3. The statistics show that the peculiar motion velocities of OCs vary little from infancy to old age, providing a remarkable opportunity to use OCs to trace their progenitors. Adopting a dynamical method, we derived the masses of the progenitor clumps where OCs were born, which have statistical characteristics comparable to previously known results for clumps observed in the Galaxy. Moreover, the masses of the progenitor clumps of OCs indicate they should be capable of gestating massive O-type stars. In fact, after inspecting the observed OCs and O-type stars, we found that there are many O-type stars in OCs. The destructive stellar feedback from O-type stars may disintegrate the vast majority of embedded clusters, and only those sufficiently dense ones can survive as OCs.Comment: 8 figures, 1 table, Accepted for publication in RA

    Prehistoric pathways to Anthropocene adaptation: Evidence from the Red River Delta, Vietnam

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    Over the past twenty years, government advisory bodies have placed increasing emphasis on the need for adaptive measures in response to the effects of human-induced climate change. Integrated Assessment Models (IAMs), which incorporate macroeconomic and climate variables, feature prominently in advisory content, though they rarely draw on data from outside strictly constrained hypothetical systems. This has led to assertions that they are not well-suited to approximate complex systemic human-environment processes. Modular, interdisciplinary approaches have offered a way to address this shortcoming; however, beyond climate records, prehistoric data continue to be under-utilised in developing such models. In this paper we highlight the contribution that archaeology and palaeoecology can make to the development of the next generation IAMs that are expected to enhance provision for more local and pro-active adaptations to future climate change. We present data from one of Southeast Asia’s most heavily developed river deltas: the Red River (Song Hong) Delta, in Vietnam and localised analysis from the Tràng An Landscape Complex World Heritage Site, on the delta’s southern margin. Comparison is made between Shared Socio-economic Pathways (SSP) 5–8.5 and SSP2–4.5 emission projection models and the Mid-Holocene inundation of the Red River Basin. We highlight the value to taking a scientific long view of coastal evolution through an illustrative set of eight research foci where palaeo-data can bring new and localised empirical data to bear on future risk management planning. We proceed to demonstrate the applicability of palaeoenvironmental, zooarchaeological and historical evidence to management and the development of sustainable conservation strategies using Tràng An as a case study. In so doing, we further highlight the importance of knowledge exchange between scientific, corporate, non-governmental, local, and state stakeholders to achieve tangible results on the ground
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