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Invasive species play increasing roles worldwide. Invasions are considered successful when species establish and spread in their exotic range. Subsequently, dispersal is a major determinant of species’ range dynamics. Mermessus trilobatus, native to North America, has rapidly spread in Europe via aerial dispersal. Here we investigated the interplay of ecological and evolutionary processes behind its colonisation success.
First, we examined two possible ecological mechanisms. Similar to other invasive invertebrates, the colonisation success of Mermessus trilobatus might be related to human-induced habitat disturbance. Opposite to this expectation, our results showed that densities of Mermessus trilobatus decreased with soil disturbance in grasslands suggesting that its invasion success was not connected to a ruderal strategy. Further, invasive species often escape the ecological pressures from novel enemies in their exotic ranges. Unexpectedly, invasive Mermessus trilobatus was more sensitive to a native predator than native Erigone dentipalpis during our predator susceptibility trials. This indicates that the relation between the invasive spider and its native predator is dominated by prey naïveté rather than enemy release.
The remaining three chapters of the thesis investigated the dispersal behaviour of this invasive species. Hitherto, studies of passive aerial dispersal used wind as the primary dispersal-initiating factor despite a recent demonstration of the effects of the atmospheric electric fields on spiders’ pre-dispersal behaviour. During our experiments, only the wind facilitated the flight, although electric fields induced pre-dispersal behaviour in spiders. Consequently, studies around passive aerial dispersal should control electric fields but use wind as a stimulating factor.
Rapidly expanding species might be disproportionately distributed in their exotic range, with an accumulation of dispersive genotypes at the leading edge of their range. Such imbalanced spatial segregation is possible when the dispersal behaviour of expanding species is heritable. Our results showed that the dispersal traits of Mermessus trilobatus were heritable through both parents and for both sexes with recessive inheritance of high dispersal ability in this species.
Following the heritability experiments, we documented an accelerated spread of Mermessus trilobatus in Europe and tested whether dispersal, reproduction or competing ability was at the source of this pattern. Our results showed that the accumulation of more mobile but not reproductive or competitive genotypes at the expansion front of this invasive species gave rise to an accelerated range expansion by more than 1350 km in under 45 years.
Invasive Mermessus trilobatus is inferior to native sympatric species with respect to competing ability (Eichenberger et al., 2009), disturbance tolerance and predation pressure. Nevertheless, the species successfully established in its exotic range and spread by accelerating its expansion rate. Rapid reproduction that balances the high ecological pressures might be the other potential mechanism behind its colonisation success in Europe and deserves further investigation.
Soziale Netzwerke sind allgegenwärtige Strukturen, die wir jeden Tag generieren und bereichern, während wir uns über Plattformen der sozialen Medien, E-Mails und jede andere Art von Interaktion mit Menschen verbinden. Während diese Strukturen für uns nicht greifbar sind, sind sie sehr wichtige Informationsträger. Zum Beispiel kann die politische Neigung unserer Freunde ein Näherungswert sein, um unsere eigenen politischen Präferenzen zu identifizieren. Gleichermaßen
kann die Kreditwürdigkeit unserer Freunde entscheidend bei der Gewährung oder Ablehnung unserer eigenen Kredite sein. Diese Erklärungskraft wird bei der Gesetzgebung, bei Unternehmensentscheidungen und in der Forschung genutzt, da sie maschinellen Lerntechniken hilft, genaue Vorhersagen zu treffen. Diese Verallgemeinerungen kommen jedoch häufig nur der Mehrheit der Menschen zugute, welche die allgemeine Struktur des Netzwerks prägen, und benachteiligen unterrepräsentierte Gruppen, indem sie ihre Mittel und Möglichkeiten begrenzen. Daher ist es wichtig zuerst zu verstehen, wie sich soziale Netzwerke bilden, um dann zu überprüfen, inwieweit ihre Mechanismen der Kantenbildung dazu beitragen, soziale Ungleichheiten in Algorithmen des maschinellen Lernens zu verstärken.
Zu diesem Zweck schlage ich im ersten Teil dieser Arbeit HopRank und Janus vor, zwei Methoden um die Mechanismen der Kantenbildung in realen ungerichteten sozialen Netzwerken zu charakterisieren. HopRank ist ein Modell der Daten-Hamsterei in Netzwerken. Sein Schlüsselkonzept ist ein gezinkter zufälliger Wanderer, der auf Übergangswahrscheinlichkeiten zwischen K-Hop-Nachbarschaften basiert. Janus ist ein Bayessches Rahmenwerk, mit dem wir plausible Hypothesen der Kantenbildung in Fällen identifizieren und bewerten können, in denen Knoten zusätzliche Daten enthalten. Im zweiten Teil dieser Arbeit untersuche ich die Auswirkungen dieser Mechanismen - welche die Kantenbildung in sozialen Netzwerken erklären - auf das maschinelle Lernen. Insbesondere untersuche ich den Einfluss von Homophilie, bevorzugter Bindung, Kantendichte, Anteil von Minderheiten und der Richtung von Verbindungen sowohl auf Leistung als auch auf systematische Fehler von kollektiver Klassifizierung und auf die Sichtbarkeit von Minderheiten in Top-K-Rängen. Meine Ergebnisse zeigen eine starke Korrelation zwischen der Netzwerkstruktur und den Ergebnissen des maschinellen Lernens. Dies legt nahe, dass die systematische Diskriminierung spezieller Personen: (i) durch den Netzwerktyp vorweggenommen und (ii) durch strategisches Verbinden im Netzwerk verhindert werden kann.
The ongoing loss of species is a global threat to biodiversity, affecting ecosystems worldwide. This also concerns arthropods such as insects and spiders, which are especially endangered in agricultural ecosystems. Here, one of the main causing factors is management intensification. In areas with a high proportion of traditionally managed grassland, extensive hay meadows that are cut only once per year can still hold high levels of biodiversity, but are threatened by conversion into highly productive silage grassland. The Westerwald mountain range, western Germany, is such a region. In this thesis, I compare the local diversity of bees, beetles, hoverflies, leafhoppers, and spiders of five grassland management regimes along a gradient of land-use intensity. These comprise naturally occurring grassland fallows, three types of traditionally managed hay meadows, and intensively used silage grassland. By using three different sampling methods, I recorded ground-dwelling, flower-visiting, and vegetation-dwelling species. The results show that in most cases species richness and diversity are highest on fallows, whereas variation among different managed grassland types is very low. Also, for most sampled taxa, fallows harbour the most distinct species assemblages, while that of other management regimes are largely overlapping. Management has the largest effect on species composition, whereas environmental parameters are of minor importance. Long-term grassland fallows seem to be highly valuable for arthropod conservation, even in a landscape with a low overall land-use intensity, providing structural heterogeneity. In conclusion, such fallows should be subsidized agri-environmental schemes, to preserve insect and spider diversity.
Soziale Medien bieten eine leistungsstarke Möglichkeit für Menschen, Meinungen und Gefühle zu einem bestimmten Thema auszutauschen, sodass andere von diesen Gedanken und Gefühlen profitieren können. Dieses Verfahren erzeugt eine riesige Menge an unstrukturierten Daten, wie Texte, Bilder und Verweise, die durch täglich anwachsende Kommentare zu verwandten Diskussionen ständig zunimmt. Die riesige Menge an unstrukturierten Daten stellt jedoch ein Risiko für den Prozess der Informationsextraktion dar, sodass die Entscheidungsfindung zu einer großen Herausforderung wird. Dies liegt daran, dass die Datenflut zu einem Verlust von nützlichen Daten aufgrund ihrer unangemessenen Darstellung und ihrer Anhäufung führen kann. Insofern leistet diese Arbeit einen Beitrag zum Gebiet der Sentimentanalyse und des Opinion Mining, das darauf abzielt, Emotionen und Meinungen aus riesigen Text- und Bilddatensätzen zu extrahieren. Das ultimative Ziel ist es, jeden Text oder jedes Bild als Ausdruck einer positiven, negativen oder neutralen Emotion zu klassifizieren, um bei der Entscheidungsfindung zu helfen. Sentiment- und Meinungsklassifikatoren wurden für Text- und Bilddatensätze aus sozialen Medien entwickelt, z. B. für Firmen- oder Produktbewertungen, Blogbeiträge und sogar Twitter-Nachrichten. In dieser Arbeit wird zunächst eine neue Methode zur Reduktion der Dimension von Textdaten auf Basis von Data-Mining-Ansätzen vorgestellt und anschließend das Sentiment auf Basis von neuronalen und Deep Neural Network-Klassifikationsalgorithmen untersucht. Anschließend untersuchen wir im Gegensatz zur Sentiment-Analyseforschung in Textdatensätzen die Sentiment Ausdrucks- und Polaritätsklassifikation innerhalb und über Bilddatensätze hinweg, indem wir tiefe neuronale Netze auf Basis des Aufmerksamkeitsmechanismus aufbauen.
This thesis was motivated by the need to advance the knowledge on the variability and dynamics of energy fluxes in lakes and reservoirs, as well as about the physical processes that regulate the fluxes at both the air and water side of the air-water interface.
In the first part, I re-examine how mechanical energy, resulting from its major source – the vertical wind energy flux - distributes into the various types of water motions, including turbulent flows and surface and internal waves. Although only a small fraction of the wind energy flux from the atmosphere is transferred to the water, it is crucial for physical, biogeochemical and ecological processes in lentic ecosystems. Based on extensive air- and water-side measurements collected at two small water bodies (< 10 km2), we estimated the energy fluxes and energy content in surface and in internal waves. Overall, the estimated energy fluxes and energy content agree well with results reported for larger water bodies, suggesting that the energetics driving the water motions in enclosed basins is similar, independently of the basin size. Our findings highlight the importance of the surface waves that receive the largest fraction of the wind energy flux, which strongly nonlinearly increases for wind speeds exceeding 3 m s-1. We found that the existing parameterization of the wave height as a function of wind speed and fetch length did not reproduce the measured wave amplitude in lakes. On average, the highest energy content was observed in basin-scale internal waves, together with high-frequency internal waves exhibiting seasonal variability and varies among the aquatic systems. During our analysis, we discovered the diurnal variability of the energy dissipation rates in the studied lake, suggesting biogenic turbulence generation, which appears to be a widespread phenomenon in lakes and reservoirs.
In the second part of the thesis, I addressed current knowledge gaps related to the bulk transfer coefficients (also known as the drag coefficient, the Stanton number and the Dalton number), which are of a particular importance for the bulk estimation of the surface turbulent fluxes of momentum, sensible and latent heat in the atmospheric boundary layer. Their inaccurate representation may lead to significant errors in flux estimates, affecting, for example, the weather and climate predictions or estimations of the near-surface current velocities in lake hydrodynamic models. Although the bulk transfer coefficients have been extensively studied over the past several decades (mainly in marine and large-lake environments), there has been no systematic analysis of measurements obtained at lakes of different size. A significant increase of the transfer coefficients at low wind speeds (< 3 m s-1) has been observed in several studies, but, to date, it has remained unexplained. We evaluated
the bulk transfer coefficients using flux measurements from 31 lakes and reservoirs. The estimates were generally within the range reported in previous studies for large lakes and oceans. All transfer coefficients increased substantially at low wind speeds, which was found to be associated with the presence of gusts and capillary waves (except the Dalton number). We found that the Stanton number is systematically higher than the Dalton number. This challenges the assumption made in the Bowen-ratio method, which is widely used for estimating evaporation rates from micrometeorological measurements. We found that the variability of the transfer coefficients among the lakes could be associated with lake surface area. In flux parameterizations at lake surfaces, it is recommended to consider variations in the drag coefficient and the Stanton number due to wind gustiness and capillary wave roughness while the Dalton number could be considered as constant at all wind speeds.
In the third part of the thesis, I address the key drivers of the near-surface turbulence that control the gas exchange in a large regulated river. As all inland waters, rivers are an important natural source of greenhouse gases. The effects of the widespread alteration and regulation of river flow for human demands on gas exchange is largely unknown. In particular, the near-surface turbulence in regulated rivers has been rarely measured and its drivers have not been identified. While in lakes and reservoirs, near-surface turbulence is mainly related to atmospheric forcing, in shallow rivers and streams it is generated by bottom friction of the gravity-forced flow. The studied large regulated river represents a transition between these two cases. Atmospheric forcing and gravity were the dominant drivers of the near-surface turbulence for a similar fraction of the measurement period. Based on validated scalings, we derived a simple model for estimating the relative contributions of wind and bottom friction to near-surface turbulence in lotic ecosystems with different flow depths. Large diel variability in the near-surface energy dissipation rates due to flow regulation leads to the same variability in gas exchange. This suggests that estimates of gas fluxes from rivers are biased by measurements performed predominantly during daytime.
In addition, the novelty in all the analyses described above is the use of the turbulent surface fluxes measured directly by the eddy-covariance technique – at the moment of writing, the most advanced method. Overall, this thesis is of a potential interest for a broad range of scientific disciplines, including limnology, micrometeorology and open channel hydraulics.
Manmade dams have been constructed from centuries for multiple purposes, and in the past decades they have been constructed in a fast pace, with the hotspot in tropical and subtropical regions. However, studies that explore hydrodynamics in these areas are scarce and biased to the rich literature available for temperate regions. Lakes and reservoirs have the same controlling mechanisms for physical processes and primary production, hence, analyses that were initially conceptualized for lakes are frequently applied for reservoirs. Nevertheless, longitudinal gradients in reservoirs challenges the application of these approaches.
Degradation of water quality in reservoirs is a major concern, and it is expected to be aggravated with climate change. Therefore, studies that explore mechanisms controlling water quality are essential for the maintenance of these systems, especially in tropical and subtropical regions. The aim of this thesis is to comprehend the role of hydrodynamic processes in the fate of nutrients in reservoirs and its implications on water quality, in a subtropical region. With focus on the relevance of different density current patterns. For that, analyses combining field measurements and numerical simulations were performed in a medium to small size subtropical drinking water reservoir for a complete seasonal cycle. Measurements were conducted combining several approaches: traditional sampling, sensors in high temporal and spatial resolution, and remote sensing. Besides, hydrodynamic models were set up and calibrated to reproduce observations, and to simulate scenarios that assisted on the analysis.
Results showed that different flow paths of density currents did not influence on phytoplankton dynamics. At the regions where the main nutrient supply was the river inflow (upstream), the density currents did not vary, the euphotic zone usually covered the entire depth, and vertical mixing was observed on a daily basis, turning the flow path of the density currents irrelevant. At downstream regions, the remobilization of nutrients in the sediment was the main source for primary production. Even though density currents had a seasonal pattern in the downstream region, thermal stratification conditions were the driver for variations in chlorophyll-a concentrations, with peaks after vertical mixing. This mechanism had in its favor the frequent anoxic conditions in the hypolimnion that enhanced the dissolution of reactive phosphorus from the sediment. Anoxic conditions were easily reached because the sediment in the downstream area was rich in organic matter. Phytoplankton produced in the upstream area was transported by the density currents, and for this reason, large concentrations of chl-a was observed below the euphotic zone. Further, the extensive measurements of temperature, and flow velocities, together with the hydrodynamic models, provided insights about the hydrodynamics of reservoirs. For instance, that the relevant processes occurred along the longitudinal, and mixing conditions varied along it. The relevance of inflow conditions regarding the presence of structures such as forebays and pre-dams, and the degree of stream shading in the catchment was assessed. And turbulence and internal waves had different features than the documented for high latitudes. Those findings can assist on the management of reservoirs, based on the comprehension of the physical processes.
Harvesting Season?
(2022)
Seit etwa zwanzig Jahren existieren Bemühungen Kunden zum Kauf von Lebensmitteln im Internet zu bewegen. Dabei waren die Marktstrukturen des digitalen Lebensmittelhandels zu Beginn noch stark fragementiert und schlecht abgestimmt. Durch die technologische Weiterentwicklung in den vergangenen Dekade hat der digitale Lebensmittelkauf an Attraktivität gewonnen. Die Nutzungsadaption dieser Diensteleistungen variiert dabei jedoch sehr stark zwischen unterschiedlichen Regionen. Besonders in Deutschland stagniert der digitalen Lebensmittelhandel auf einem vergleichweise niedrigen Niveau. Diesbezüglich analysiert diese Dissertation sowohl die händlerseitigen Marktstrukturen, als auch die Erwartungen und Hindernisse deutscher Konsumenten gegenüber der Serviceleistung.
Das Jahr 2020 konnotiert einen Wendepunkt für den Online Lebensmittelhandel, als, im Zuge politischer Maßnahmen zur Reduzierung der COVID-19 Infektionen, tägliche Routinen wie der Lebensmitteleinkauf starken Regulierungen unterlagen. Gleichzeitig hat es der digitale Lebensmittelhandel trotz dieser Gelegenheit noch nicht geschafft sich flächendeckend in Deutschland zu etablieren. Dies kann auf fehlende Investments, aber auch unzulängliche Digitalisierungsmaßnahmen zurückgeführt werden. Eine stärkere Synchronisierung zwischen digitalem und stationärem Angebot, bessere Integration digitaler Lebensmitteldienste auf regionaler Ebene sowie angepasste, zielgruppenadäquate digitale Lösungen zum effizienten Abbau von Nutzungsbarrieren. Die Wichtigkeit stabiler Lebensmittelketten und –verteilung konnte durch die COVID-19 Pandemie illustriert werden. Weitere Forschung sollte helfen den digitalen Lebensmittelhandel zu einer nachhaltigen und stabilen Supplementierung des stationären Angebots zu entwickeln.
Background: For over a century, scientists have studied host-pathogen interactions between the crayfish plague disease agent Aphanomyces astaci and freshwater crayfish. It has been hypothesised that North American crayfish hosts are disease-resistant due to the long-lasting coevolution with the pathogen. Similarly, the increasing number of latent infections reported in the historically sensitive European crayfish hosts seems to indicate that similar coevolutionary processes are occurring between European crayfish and A. astaci. Our current understanding of these host-pathogen interactions is largely focused on the innate immunity processes in the crayfish haemolymph and cuticle, but the molecular basis of the observed disease-resistance and susceptibility remain unclear. To understand how coevolution is shaping the host’s molecular response to the pathogen, susceptible native European noble crayfish and invasive disease-resistant marbled crayfish were challenged with two A. astaci strains of different origin: a haplogroup A strain (introduced to Europe at least 50 years ago, low virulence) and a haplogroup B strain (signal crayfish in lake Tahoe, USA, high virulence). Here, we compare the gene expression profiles of the hepatopancreas, an integrated organ of crayfish immunity and metabolism.
Results: We characterised several novel innate immune-related gene groups in both crayfish spe cies. Across allchallenge groups, we detected 412 differentially expressed genes (DEGs) in the noble crayfish, and 257 DEGs in the marbled crayfish. In the noble crayfish, a clear immune response was detected to the haplogroup B strain, but not to the haplogroup A strain. In contrast, in the marbled crayfish we detected an immune response to the haplogroup A strain, but not to the haplogroup B strain. Conclusions: We highlight the hepatopancreas as an important hub for the synthesis of immune molecules in the response to A. astaci. A clear distinction between the innate immune response in the marbled crayfish and the noble crayfish is the capability of the marbled crayfish to mobilise a higher variety of innate immune response effectors.
Ponds in agricultural landscapes are often used by amphibians as breeding habitat. However, the characteristics of agricultural ponds and especially the surrounding area are usually said to be suboptimal for many amphibian species. Using suboptimal habitats might allow a species’ survival and reproduction, but can have negative consequences at the individual and population level. In the present study, we investigated Palmate Newt (Lissotriton helveticus) populations from an intensive wine-growing region in southern Germany and compared them with populations located in a nearby forested area in terms of biometric traits, age and genetic structure. By analyzing over 900 adult newts from 11 ponds, we could show that newts reproducing in forest ponds were larger than newts reproducing in agricultural ponds. We did not find differences in the newt age and growth rate between habitat types. Therefore, differences in the body size of newts might already existed in larvae and/or juveniles, what might be related to a lower habitat quality for larvae and/or juveniles in the agricultural landscape. Body mass, body condition and sexual dimorphic traits (length of the caudal filament and max. height of the tail) correlated with body size, but no additional effect of the habitat type was found. The analysis of microsatellites revealed a higher genetic diversity in forest ponds. However, no clear sign of inbreeding was observed in any agricultural population, suggesting some degree of gene flow between them. We conclude, that agricultural ponds can be suitable habitats for the Palmate Newt and that conservation effort should aim to preserve them. The observed effects on body size indicate the need to increase the quality of the aquatic and terrestrial habitat for early life stages of this newt species in agricultural landscapes.
Softwaresprachen und Technologien zu verstehen, die bei der Entwicklung einer Software verwendet werden, ist eine alltägliche Herausforderung für Software Engineers. Textbasierte Dokumentationen und Codebeispiele sind typische Hilfsmittel, die zu einem besseren Verständnis führen sollen. In dieser Dissertation werden verschiedene Forschungsansätze beschrieben, wie existierende Textpassagen und Codebeispiele identifiziert und miteinander verbunden werden können. Die Entdeckung solcher bereits existierender Ressourcen soll dabei helfen Softwaresprachen und Technologien auf einem konzeptionellen Level zu verstehen und zu vergleichen. Die Forschungsbeiträge fokussieren sich auf die folgenden Fragen, die später präzisiert werden. Welche existierenden Ressourcen lassen sich systematisch identifizieren, um strukturiertes Wissen zu extrahieren? Wie lassen sich die Ressourcen extrahieren? Welches Vokabular wird bereits in der Literatur verwendet, um konzeptionelles Wissen zur Struktur und Verwendung einer Software auszudrücken? Wie lassen sich Beiträge auf Wikipedia wiederverwenden? Wie können Codebeispiele zur Verwendung von ausgewählten Technologien auf GitHub gefunden werden? Wie kann ein Modell, welches Technologieverwendung repräsentiert, reproduzierbar konstruiert werden? Zur Beantwortung der Forschungsfragen werden qualitative Forschungsmethoden verwendet, wie zum Beispiel Literaturstudien. Des Weiteren werden Methoden entwickelt und
evaluiert, um relevante Artikel auf Wikipedia, relevante Textpassagen in der Literatur und Codebeispiele auf GitHub zu verlinken. Die theoretischen Beiträge werden in Fallstudien evaluiert. Die folgenden wissenschaftlichen Beiträge werden dabei erzielt: i.) Eine Referenzsemantik zur Formalisierung von Typen und Relationen in einer sprachfokussierten Beschreibung von Software; ii.) Ein Korpus bestehend aus Wikipedia Artikeln zu einzelnen Softwaresprachen; iii) Ein Katalog mit textuell beschriebenen Verwendungsmustern einer Technologie zusammen mit Messergebnissen zu deren Frequenz auf GitHub; iv.) Technologiemodelle, welche sowohl mit verschiedenen existierenden Codebeispielen als auch mit Textpassagen verknüpft sind.