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Species assembly from a regional pool into local metacommunities and how they colonize and coexist over time and space is essential to understand how communities response to their environment including abiotic and biotic factors. In highly disturbed landscapes, connectivity of isolated habitat patches is essential to maintain biodiversity and the entire ecosystem functioning. In northeast Germany, a high density of the small water bodies called kettle holes, are good systems to study metacommunities due to their condition as “aquatic islands” suitable for hygrophilous species that are surrounded by in unsuitable matrix of crop fields. The main objective of this thesis was to infer the main ecological processes shaping plant communities and their response to the environment, from biodiversity patterns and key life-history traits involved in connectivity using ecological and genetic approaches; and to provide first insights of the role of kettle holes harboring wild-bee species as important mobile linkers connecting plant communities in this insular system.
t a community level, I compared plant diversity patterns and trait composition in ephemeral vs. permanent kettle holes). My results showed that types of kettle holes act as environmental filers shaping plant diversity, community-composition and trait-distribution, suggesting species sorting and niche processes in both types of kettle holes. At a population level, I further analyzed the role of dispersal and reproductive strategies of four selected species occurring in permanent kettle holes. Using microsatellites, I found that breeding system (degree of clonality), is the main factor shaping genetic diversity and genetic divergence. Although, higher gene flow and lower genetic differentiation among populations in wind vs. insect pollinated species was also found, suggesting that dispersal mechanisms played a role related to gene flow and connectivity. For most flowering plants, pollinators play an important role connecting communities. Therefore, as a first insight of the potential mobile linkers of these plant communities, I investigated the diversity wild-bees occurring in these kettle holes. My main results showed that local habitat quality (flower resources) had a positive effect on bee diversity, while habitat heterogeneity (number of natural landscape elements surrounding kettle holes 100–300m), was negatively correlated.
This thesis covers from genetic flow at individual and population level to plant community assembly. My results showed how patterns of biodiversity, dispersal and reproduction strategies in plant population and communities can be used to infer ecological processes. In addition, I showed the importance of life-history traits and the relationship between species and their abiotic and biotic interactions. Furthermore, I included a different level of mobile linkers (pollinators) for a better understanding of another level of the system. This integration is essential to understand how communities respond to their surrounding environment and how disturbances such as agriculture, land-use and climate change might affect them. I highlight the need to integrate many scientific areas covering from genes to ecosystems at different spatiotemporal scales for a better understanding, management and conservation of our ecosystems.
A new model that links visionary leadership with team performance is
postulated. It is proposed that leader prototypicality will negatively
moderate the effect of visionary leadership on team goal monitoring and performance. This model underlines that teams will compensate for the less prototypicality of a visionary leader by engaging in more goal monitoring, which is a process that is conducive to team performance. A field study included 60 teams, 180 individuals, and 60 team leaders was conducted in Egypt. Parameters were collected on the individual level.
Aggregation measures (rwg, ICC1 & ICC2) were acceptable and the averages were calculated for each team. The proposed three-factor model exhibited a reasonable fit to the data, χ2(130) = 259.93, p-value0.01; CFI = 0.90; and RMSEA = 0.13). The hypothesized negative moderation effect of leader prototypicality on the relationship between visionary leadership and team goal monitoring was statistically significant (-0.16; s.e.= 0.06; t = -3.13; p <0.01; 95% CI: -0.31, -0.07). Results showed a significant index of moderated mediation (-0.07; s.e.= 0.05; 95% CI: -0.20, -0.01). As predicted, the indirect effect of visionary leadership on team performance mediated by team goal monitoring was more strongly positive when leader prototypicality was low (b = 0.27; s.e.= 0.16; 95% CI: 0.04, 0.68), rather than high (b = 0.13; s.e.= 0.10; 95% CI: 0.01, 0.45). A proposal for extending the dimensions of identity-based leadership is discussed. This dissertation makes four significant contributions to theory and research on leadership. First, the main contribution of this research lies in showing that visionary leadership is more strongly positively related to team performance when leader prototypicality is low, rather than high. Second, this dissertation provides a contribution toward overcoming the fragmentation in the leadership literature by desegregating the literature on visionary leadership and leader-team prototypicality. Third, team goal monitoring as a mechanism that explains the interactive effects of visionary leadership and leader prototypicality on team performance was identified. Fourth, this study tests the postulated research model in Egypt, a culture that has in the past received scant attention.
Alexander Rhode investigates performance-oriented measures of Contracting Authorities in public tenders conducted within the EU. He finds that Contracting Authorities can improve their performance and attract more suppliers by publishing (as precise as possible) starting prices in the beginning of a tender. First, he reports that compared with private-sector negotiations, starting prices do not create entry barriers in public procurement. Second, he finds that increased numerical precision of starting prices is linearly correlated with better performance and a higher number of bids. In public procurement, suppliers tend to attribute increased credibility to precise starting prices which reduces their (perceived) entry risks.
Im Netz der Zeit
(2019)
In der vorliegenden Schrift, die aus der Dissertation der Zwillinge Konstantin und Kornelius Keulen im Fach Philosophie hervorgegangen ist, werden die vielfältigen Verwebungs- und Vernetzungszusammenhänge des Internet zeit- und ereignisphilosophischer Ausdeutung weist nach Meinung der Autoren den Weg, das Konglomerat Internet als technomediales menschliches Produkt in seinen sozio-kulturellen, politisch-ökonomischen und psychosozialen Komplexitäten ausdeutbar zu machen.
Die Wissenschaftsfreiheit ist ein Grundrecht, dessen Sinn und Auslegung im Rahmen von Reformen des Hochschulsystems nicht nur der Justiz, sondern auch der Wissenschaft selbst immer wieder Anlass zur Diskussion geben, so auch im Zuge der Einführung des so genannten Qualitätsmanagements von Studium und Lehre an deutschen Hochschulen. Die vorliegende Dissertationsschrift stellt die Ergebnisse einer empirischen Studie vor, die mit einer soziologischen Betrachtung des Qualitätsmanagements unterschiedlicher Hochschulen zu dieser Diskussion beiträgt.
Auf Grundlage der Prämisse, dass Verlauf und Folgen einer organisationalen Innovation nur verstanden werden können, wenn der alltägliche Umgang der Organisationsmitglieder mit den neuen Strukturen und Prozessen in die Analyse einbezogen wird, geht die Studie von der Frage aus, wie Akteurinnen und Akteure an deutschen Hochschulen die Qualitätsmanagementsysteme ihrer Organisationen nutzen. Die qualitative inhaltsanalytische Auswertung von 26 Leitfaden-Interviews mit Prorektorinnen und -rektoren, Qualitätsmanagement-Personal und Studiendekaninnen und -dekanen an neun Hochschulen ergibt, dass die Strategien der Akteursgruppen an den Hochschulen im Zusammenspiel mit strukturellen Aspekten unterschiedliche Dynamiken entstehen lassen, mit denen Implikationen für die Lehrfreiheit verbunden sind: Während die Autonomie der Lehrenden durch das Qualitätsmanagement an einigen Hochschulen unterstützt wird, sind sowohl Autonomie als auch Verantwortung für Studium und Lehre an anderen Hochschulen Gegenstand andauernder Konflikte, die auch das Qualitätsmanagement einschließen.
The Atlantic Meridional Overturning Circulation (AMOC) is likely the most well-known system of ocean currents on Earth, redistributing heat, nutrients and carbon over a large part of the Earth’s surface and affecting global climate as a result. Due to enhanced freshwater fluxes into the subpolar North Atlantic as a response to global warming, the AMOC is expected, and may have already started, to weaken and these changes will likely have global impacts. It is therefore of considerable relevance to improve our understanding of past and future AMOC changes. My thesis tries to answer some of the open questions in this field by giving strong evidence that the AMOC has already weakened over the last century, by narrowing future projections of this slowdown and
by studying the impacts on global surface warming.
While there have been various studies trying to reconstruct the strength of the overturning circulation in the past, often based on model simulations in combination with observations (Jackson et al., 2016, Kanzow et al., 2010) or proxies (Frajka-Williams, 2015, Latif et al., 2006), the results so far, due to lack of direct measurements, have been inconclusive. In the first paper I build on previous work that links the anomalously low sea surface temperatures (SSTs) in the North Atlantic with the reduced meridional heat transport due to a weaker AMOC. Using the output of a high-resolution global climate model, I derive a characteristic spatial and seasonal SST fingerprint of an AMOC slowdown and an improved SST-based AMOC index. The same fingerprint is seen in
the observational SSTs since the late 19th Century, giving strong evidence that since then the AMOC has slowed down. In addition, the reconstruction of the historical overturning strength with the new AMOC index agrees well with and extends the results of earlier studies as well as the direct measurements from the RAPID project and shows a strong decline of the AMOC by about 15% (3±1 Sv) since the mid-20th Century (Caesar et al., 2018).
The reconstruction of the historical overturning strength with the AMOC index enables us to weight future AMOC projections based on their skill in modeling the historical AMOC as described in the second paper of this thesis (Olson et al., 2018). Using Bayesian model averaging we considerably narrow the projections of the CMIP5 ensemble to a decrease of -4.0 Sv and -6.8 Sv between the years 1960-1999 and 2060-2099 for the RCP4.5 and RCP8.5 emission scenarios, respectively. These values fit to, yet are at the lower end of, previously published estimates.
In the third paper I examine how the AMOC slowdown affects the global mean surface temperature (GMST) with a focus on how it will change the ocean heat uptake (OHC). Accounting for the effect of changes in the radiative forcing on the GMST, I test how AMOC variations correlate with the residual part of surface temperature changes in the past. I find that the correlation is positive which fits the understanding that the deep-water formation that is important in driving the AMOC cools the deep ocean and therefore warms the surface (Caesar et al., 2019). The future weakening of the overturning circulation could therefore delay global surface warming.
Due to nonlinear behavior and scale specific changes it can be difficult to study the dominant processes and modes that drive climate variability. In the fourth paper we develop and test a new technique based on the wavelet multiscale correlation (WMC) similarity measure to study climate variability on different temporal and spatial scales (Agarwal et al., 2018). In a fifth contribution to my thesis this method is applied to the observed sea surface temperatures. The results reconfirm well-known relations between SST anomalies such as the El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) on inter-annual and decadal timescales, respectively. They
furthermore give new insights into the characteristics and origins of long-range teleconnections, for example, that the teleconnection between ENSO and Indian Ocean dipole exist mainly between the northern part of the ENSO tongue and the equatorial Indian Ocean, and provides therefore valuable knowledge about the regions that are necessary to include when modeling regional climate variability at a certain scale (Agarwal et al., 2019).
In summary, my PhD thesis investigates past and future AMOC variability and its effects on global mean surface temperature by utilizing a combination of observational sea surface data and the output of historical and future climate model simulations from both the high-resolution CM2.6 model as well as the CMIP5 ensemble. It further includes the development and validation of a new method to study climate variability, that, applied to the observed sea surface temperatures, gives new insight about teleconnections in the Earth System. My findings provide evidence that the AMOC has already slowed down, will continue to do so in the future, and will impact the global mean temperature. Further impacts of an AMOC slowdown may include increased sea-level rise at the U.S. east coast (Ezer, 2015), heat extremes in Europe (Duchez et al., 2016) and increased storm activity in the North Atlantic region (Jackson et al., 2015), all of which have significant socio-economic implications.
Water is essential to life and thus, an essential resource. However, freshwater resources are limited and their maintenance is crucial. Pollution with chemicals and pathogens through urbanization and a growing population impair the quality of freshwater. Furthermore, water can serve as vector for the transmission of pathogens resulting in water-borne illness.
The Interdisciplinary Research Group III – "Water" of the Leibniz alliance project INFECTIONS‘21 investigated water as a hub for pathogens focusing on Clostridioides difficile and avian influenza A viruses that may be shed into the water. Another aim of this study was to characterize the bacterial communities in a wastewater treatment plant (WWTP) of the capital Berlin, Germany to further assess potential health risks associated with wastewater management practices.
Bacterial communities of WWTP inflow and effluent differed significantly. The proportion of fecal/enteric bacteria was relatively low and OTUs related to potential enteric pathogens were largely removed from inflow to effluent. However, a health risk might exist as an increased relative abundance of potential pathogenic Legionella spp. such as L. lytica was observed. Three Clostridioides difficile isolates from wastewater inflow and an urban bathing lake in Berlin (‗Weisser See‘) were obtained and sequenced. The two isolates from the wastewater did not carry toxin genes, whereas the isolate from the lake was positive for the toxin genes. All three isolates were closely related to human strains. This indicates a potential, but rather sporadic health risk. Avian influenza A viruses were detected in 38.8% of sediment samples by PCR, but virus isolation failed. An experiment with inoculated freshwater and sediment samples showed that virus isolation from sediment requires relatively high virus concentrations and worked much better in Madin-Darby Canine Kidney (MDCK) cell cultures than in embryonated chicken eggs, but low titre of influenza contamination in freshwater samples was sufficient to recover virus.
In conclusion, this work revealed potential health risks coming from bacterial groups with pathogenic potential such as Legionella spp. whose relative abundance is higher in the released effluent than in the inflow of the investigated WWTP. It further indicates that water bodies such as wastewater and lake sediments can serve as reservoir and vector, even for non-typical water-borne or water-transmitted pathogens such as C. difficile.
Supermassive black holes reside in the hearts of almost all massive galaxies. Their evolutionary path seems to be strongly linked to the evolution of their host galaxies, as implied by several empirical relations between the black hole mass (M BH ) and different host galaxy properties. The physical driver of this co-evolution is, however, still not understood. More mass measurements over homogeneous samples and a detailed understanding of systematic uncertainties are required to fathom the origin of the scaling relations.
In this thesis, I present the mass estimations of supermassive black holes in the nuclei of one late-type and thirteen early-type galaxies. Our SMASHING sample extends from the intermediate to the massive galaxy mass regime and was selected to fill in gaps in number of galaxies along the scaling relations. All galaxies were observed at high spatial resolution, making use of the adaptive-optics mode of integral field unit (IFU) instruments on state-of-the-art telescopes (SINFONI, NIFS, MUSE). I extracted the stellar kinematics from these observations and constructed dynamical Jeans and Schwarzschild models to estimate the mass of the central black holes robustly. My new mass estimates increase the number of early-type galaxies with measured black hole masses by 15%. The seven measured galaxies with nuclear light deficits (’cores’) augment the sample of cored galaxies with measured black holes by 40%. Next to determining massive black hole masses, evaluating the accuracy of black hole masses is crucial for understanding the intrinsic scatter of the black hole- host galaxy scaling relations. I tested various sources of systematic uncertainty on my derived mass estimates.
The M BH estimate of the single late-type galaxy of the sample yielded an upper limit, which I could constrain very robustly. I tested the effects of dust, mass-to-light ratio (M/L) variation, and dark matter on my measured M BH . Based on these tests, the typically assumed constant M/L ratio can be an adequate assumption to account for the small amounts of dark matter in the center of that galaxy. I also tested the effect of a variable M/L variation on the M BH measurement on a second galaxy. By considering stellar M/L variations in the dynamical modeling, the measured M BH decreased by 30%. In the future, this test should be performed on additional galaxies to learn how an as constant assumed M/L flaws the estimated black hole masses.
Based on our upper limit mass measurement, I confirm previous suggestions that resolving the predicted BH sphere-of-influence is not a strict condition to measure black hole masses. Instead, it is only a rough guide for the detection of the black hole if high-quality, and high signal-to-noise IFU data are used for the measurement. About half of our sample consists of massive early-type galaxies which show nuclear surface brightness cores and signs of triaxiality. While these types of galaxies are typically modeled with axisymmetric modeling methods, the effects on M BH are not well studied yet. The massive galaxies of our presented galaxy sample are well suited to test the effect of different stellar dynamical models on the measured black hole mass in evidently triaxial galaxies. I have compared spherical Jeans and axisymmetric Schwarzschild models and will add triaxial Schwarzschild models to this comparison in the future. The constructed Jeans and Schwarzschild models mostly disagree with each other and cannot reproduce many of the triaxial features of the galaxies (e.g., nuclear sub-components, prolate rotation). The consequence of the axisymmetric-triaxial assumption on the accuracy of M BH and its impact on the black hole - host galaxy relation needs to be carefully examined in the future.
In the sample of galaxies with published M BH , we find measurements based on different dynamical tracers, requiring different observations, assumptions, and methods. Crucially, different tracers do not always give consistent results. I have used two independent tracers (cold molecular gas and stars) to estimate M BH in a regular galaxy of our sample. While the two estimates are consistent within their errors, the stellar-based measurement is twice as high as the gas-based. Similar trends have also been found in the literature. Therefore, a rigorous test of the systematics associated with the different modeling methods is required in the future. I caution to take the effects of different tracers (and methods) into account when discussing the scaling relations.
I conclude this thesis by comparing my galaxy sample with the compilation of galaxies with measured black holes from the literature, also adding six SMASHING galaxies, which were published outside of this thesis. None of the SMASHING galaxies deviates significantly from the literature measurements. Their inclusion to the published early-type galaxies causes a change towards a shallower slope for the M BH - effective velocity dispersion relation, which is mainly driven by the massive galaxies of our sample. More unbiased and homogenous measurements are needed in the future to determine the shape of the relation and understand its physical origin.