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This thesis considers on the one hand the construction of point processes via conditional intensities, motivated by the partial Integration of the Campbell measure of a point process. Under certain assumptions on the intensity the existence of such a point process is shown. A fundamental example turns out to be the Pólya sum process, whose conditional intensity is a generalisation of the Pólya urn dynamics. A Cox process representation for that point process is shown. A further process considered is a Poisson process of Gaussian loops, which represents a noninteracting particle system derived from the discussion of indistinguishable particles. Both processes are used to define particle systems locally, for which thermodynamic limits are determined.
This study presents noble gas compositions (He, Ne, Ar, Kr, and Xe) of lavas from several Hawaiian volcanoes. Lavas from the Hawaii Scientific Drilling Project (HSDP) core, surface samples from Mauna Kea, Mauna Loa, Kilauea, Hualalai, Kohala and Haleakala as well as lavas from a deep well on the summit of Kilauea were investigated. Noble gases, especially helium, are used as tracers for mantle reservoirs, based on the assumption that high 3He/4He ratios (>8 RA) represent material from the deep and supposedly less degassed mantle, whereas lower ratios (~ 8 RA) are thought to represent the upper mantle. Shield stage Mauna Kea, Kohala and Kilauea lavas yielded MORB-like to moderately high 3He/4He ratios, while 3He/4He ratios in post-shield stage Haleakala lavas are MORB-like. Few samples show 20Ne/22Ne and 21Ne/22Ne ratios different from the atmospheric values, however, Mauna Kea and Kilauea lavas with excess in mantle Ne agree well with the Loihi-Kilauea line in a neon three-isotope plot, whereas one Kohala sample plots on the MORB correlation line. The values in the 4He/40Ar* (40Ar* denotes radiogenic Ar) versus 4He diagram imply open system fractionation of He from Ar, with a deficiency in 4He. Calculated 4He/40Ar*, 3He/22Nes (22NeS denotes solar Ne) and 4He/21Ne ratios for the sample suite are lower than the respective production and primordial ratios, supporting the observation of a fractionation of He from the heavier noble gases, with a depletion of He with respect to Ne and Ar. The depletion of He is interpreted to be partly due to solubility controlled gas loss during magma ascent. However, the preferential He loss suggests that He is more incompatible than Ne and Ar during magmatic processes. In a binary mixing model, the isotopic He and Ne pattern are best explained by a mixture of a MORB-like end-member with a plume like or primordial end-member with a fractionation in 3He/22Ne, represented by a curve parameter r of 15 (r=(³He/²²Ne)MORB/(³He/²²Ne)PLUME or PRIMORDIAL). Whether the high 3He/4He ratios in Hawaiian lavas are indicative of a primitive component within the Hawaiian plume or are rather a product of the crystal-melt- partitioning behavior during partial melting remains to be resolved.
The recent discovery of an intricate and nontrivial interaction topology among the elements of a wide range of natural systems has altered the manner we understand complexity. For example, the axonal fibres transmitting electrical information between cortical regions form a network which is neither regular nor completely random. Their structure seems to follow functional principles to balance between segregation (functional specialisation) and integration. Cortical regions are clustered into modules specialised in processing different kinds of information, e.g. visual or auditory. However, in order to generate a global perception of the real world, the brain needs to integrate the distinct types of information. Where this integration happens, nobody knows. We have performed an extensive and detailed graph theoretical analysis of the cortico-cortical organisation in the brain of cats, trying to relate the individual and collective topological properties of the cortical areas to their function. We conclude that the cortex possesses a very rich communication structure, composed of a mixture of parallel and serial processing paths capable of accommodating dynamical processes with a wide variety of time scales. The communication paths between the sensory systems are not random, but largely mediated by a small set of areas. Far from acting as mere transmitters of information, these central areas are densely connected to each other, strongly indicating their functional role as integrators of the multisensory information. In the quest of uncovering the structure-function relationship of cortical networks, the peculiarities of this network have led us to continuously reconsider the stablished graph measures. For example, a normalised formalism to identify the “functional roles” of vertices in networks with community structure is proposed. The tools developed for this purpose open the door to novel community detection techniques which may also characterise the overlap between modules. The concept of integration has been revisited and adapted to the necessities of the network under study. Additionally, analytical and numerical methods have been introduced to facilitate understanding of the complicated statistical interrelations between the distinct network measures. These methods are helpful to construct new significance tests which may help to discriminate the relevant properties of real networks from side-effects of the evolutionary-growth processes.
The seismicity of the Dead Sea fault zone (DSFZ) during the last two millennia is characterized by a number of damaging and partly devastating earthquakes. These events pose a considerable seismic hazard and seismic risk to Syria, Lebanon, Palestine, Jordan, and Israel. The occurrence rates for large earthquakes along the DSFZ show indications to temporal changes in the long-term view. The aim of this thesis is to find out, if the occurrence rates of large earthquakes (Mw ≥ 6) in different parts of the DSFZ are time-dependent and how. The results are applied to probabilistic seismic hazard assessments (PSHA) in the DSFZ and neighboring areas. Therefore, four time-dependent statistical models (distributions), including Weibull, Gamma, Lognormal and Brownian Passage Time (BPT), are applied beside the exponential distribution (Poisson process) as the classical time-independent model. In order to make sure, if the earthquake occurrence rate follows a unimodal or a multimodal form, a nonparametric bootstrap test of multimodality has been done. A modified method of weighted Maximum Likelihood Estimation (MLE) is applied to estimate the parameters of the models. For the multimodal cases, an Expectation Maximization (EM) method is used in addition to the MLE method. The selection of the best model is done by two methods; the Bayesian Information Criterion (BIC) as well as a modified Kolmogorov-Smirnov goodness-of-fit test. Finally, the confidence intervals of the estimated parameters corresponding to the candidate models are calculated, using the bootstrap confidence sets. In this thesis, earthquakes with Mw ≥ 6 along the DSFZ, with a width of about 20 km and inside 29.5° ≤ latitude ≤ 37° are considered as the dataset. The completeness of this dataset is calculated since 300 A.D. The DSFZ has been divided into three sub zones; the southern, the central and the northern sub zone respectively. The central and the northern sub zones have been investigated but not the southern sub zone, because of the lack of sufficient data. The results of the thesis for the central part of the DSFZ show that the earthquake occurrence rate does not significantly pursue a multimodal form. There is also no considerable difference between the time-dependent and time-independent models. Since the time-independent model is easier to interpret, the earthquake occurrence rate in this sub zone has been estimated under the exponential distribution assumption (Poisson process) and will be considered as time-independent with the amount of 9.72 * 10-3 events/year. The northern part of the DSFZ is a special case, where the last earthquake has occurred in 1872 (about 137 years ago). However, the mean recurrence time of Mw ≥ 6 events in this area is about 51 years. Moreover, about 96 percent of the observed earthquake inter-event times (the time between two successive earthquakes) in the dataset regarding to this sub zone are smaller than 137 years. Therefore, it is a zone with an overdue earthquake. The results for this sub zone verify that the earthquake occurrence rate is strongly time-dependent, especially shortly after an earthquake occurrence. A bimodal Weibull-Weibull model has been selected as the best fit for this sub zone. The earthquake occurrence rate, corresponding to the selected model, is a smooth function of time and reveals two clusters within the time after an earthquake occurrence. The first cluster begins right after an earthquake occurrence, lasts about 80 years, and is explicitly time-dependent. The occurrence rate, regarding to this cluster, is considerably lower right after an earthquake occurrence, increases strongly during the following ten years and reaches its maximum about 0.024 events/year, then decreases over the next 70 years to its minimum about 0.0145 events/year. The second cluster begins 80 years after an earthquake occurrence and lasts until the next earthquake occurs. The earthquake occurrence rate, corresponding to this cluster, increases extremely slowly, such as it can be considered as an almost constant rate about 0.015 events/year. The results are applied to calculate the time-dependent PSHA in the northern part of the DSFZ and neighbouring areas.
This thesis presents investigations on sediments from two African lakes which have been recording changes in their surrounding environmental and climate conditions since more than 200,000 years. Focus of this work is the time of the last Glacial and the Holocene (the last ~100,000 years before present [in the following 100 kyr BP]). One important precondition for this kind of research is a good understanding of the present ecosystems in and around the lakes and of the sediment formation under modern climate conditions. Both studies therefore include investigations on the modern environment (including organisms, soils, rocks, lake water and sediments). A 90 m long sediment sequence was investigated from Lake Tswaing (north-eastern South Africa) using geochemical analyses. These investigations document alternating periods of high detrital input and low (especially autochthonous) organic matter content and periods of low detrital input, carbonatic or evaporitic sedimentation and high autochthonous organic matter content. These alternations are interpreted as changes between relatively humid and arid conditions, respectively. Before c. 75 kyr BP, they seem to follow changes in local insolation whereas afterwards they appear to be acyclic and are probably caused by changes in ocean circulation and/or in the mean position of the Inter-Tropical Convergence Zone (ITCZ). Today, these factors have main influence on precipitation in this area where rainfall occurs almost exclusively during austral summer. All modern organisms were analysed for their biomarker and bulk organic and compound-specific stable carbon isotope composition. The same investigations on sediments from the modern lake floor document the mixed input of the investigated individual organisms and reveal additional influences by methanotrophic bacteria. A comparison of modern sediment characteristics with those of sediments covering the time 14 to 2 kyr BP shows changes in the productivity of the lake and the surrounding vegetation which are best explained by changes in hydrology. More humid conditions are indicated for times older than 10 kyr BP and younger than 7.5 kyr BP, whereas arid conditions prevailed in between. These observations agree with the results from sediment composition and indications from other climate archives nearby. The second lake study deals with Lake Challa, a small, deep crater lake on the foot of Mount Kilimanjaro. In this lake form mm-scale laminated sediments which were analyses with micro-XRF scanning for changes in the element composition. By comparing these results with investigations on thin sections, results from ongoing sediment trap studies, meteorological data, and investigations on the surrounding rocks and soils, I develop a model for seasonal variability in the limnology and sedimentation of Lake Challa. The lake appears to be stratified during the warm rain seasons (October – December and March – May) during which detrital material is delivered to the lake and carbonates precipitate. On the lake floor forms a dark lamina with high contents of Fe and Ti and high Ca/Al and low Mn/Fe ratios. Diatoms bloom during the cool and windy season (June – September) when mixing down to c. 60 m depth provides easily bio-available nutrients. Contemporaneously, Fe and Mn-oxides are precipitating which cause high Mn/Fe ratios in the light diatom-rich laminae of the sediments. Trends in the Mn/Fe ratio of the sediments are interpreted to reflect changes in the intensity or duration of seasonal mixing in Lake Challa. This interpretation is supported by parallel changes in the organic matter and biogenic silica content observed in the 22 m long profile recovered from Lake Challa. This covers the time of the last 25 kyr BP. It documents a transition around 16 kyr BP from relatively well-mixed conditions with high detrital input during glacial times to stronger stratified conditions which are probably related to increasing lake levels in Challa and generally more humid conditions in East Africa. Intensified mixing is recorded for the time of the Younger Dryas and the period between 11.4 and 10.7 kyr BP. For these periods, reduced intensity of the SW monsoon and intensified NE monsoon are reported from archives of the Indian-Asian Monsoon region, arguing for the latter as a probable source for wind mixing in Lake Challa. This connection is probably also responsible for contemporaneous events in the Mn/Fe ratios of the Lake Challa sediments and in other records of northern hemisphere monsoon intensity during the Holocene and underlines the close interaction of global low latitude atmospheric circulation.
There are many factors which make speaking and understanding a second language (L2) a highly complex challenge. Skills and competencies in in both linguistic and metalinguistic areas emerge as parts of a multi-faceted, flexible concept underlying bilingual/multilingual communication. On the linguistic level, a combination of an extended knowledge of idiomatic expressions, a broad lexical familiarity, a large vocabulary size, and the ability to deal with phonetic distinctions and fine phonetic detail has been argued necessary for effective nonnative comprehension of spoken language. The scientific interest in these factors has also led to more interest in the L2’s information structure, the way in which information is organised and packaged into informational units, both within and between clauses. On a practical level, the information structure of a language can offer the means to assign focus to a certain element considered important. Speakers can draw from a rich pool of linguistic means to express this focus, and listeners can in turn interpret these to guide them to the highlighted information which in turn facilitates comprehension, resulting in an appropriate understanding of what has been said. If a speaker doesn’t follow the principles of information structure, and the main accent in a sentence is placed on an unimportant word, then there may be inappropriate information transfer within the discourse, and misunderstandings. The concept of focus as part of the information structure of a language, the linguistic means used to express it, and the differential use of focus in native and nonnative language processing are central to this dissertation. Languages exhibit a wide range of ways of directing focus, including by prosodic means, by syntactic constructions, and by lexical means. The general principles underlying information structure seem to contrast structurally across different languages, and they can also differ in the way they express focus. In the context of L2 acquisition, characteristics of the L1 linguistic system are argued to influence the acquisition of the L2. Similarly, the conceptual patterns of information structure of the L1 may influence the organization of information in the L2. However, strategies and patterns used to exploit information structure for succesful language comprehension in the native L1, may not apply at all, or work in different ways or todifferent degrees in the L2. This means that L2 learners ideally have to understand the way that information structure is expressed in the L2 to fully use the information structural benefit in the L2. The knowledge of information structural requirements in the L2 could also imply that the learner would have to make adjustments regarding the use of information structural devices in the L2. The general question is whether the various means to mark focus in the learners’ native language are also accessible in the nonnative language, and whether a L1-L2 transfer of their usage should be considered desirable. The current work explores how information structure helps the listener to discover and structure the forms and meanings of the L2. The central hypothesis is that the ability to access information structure has an impact on the level of the learners’ appropriateness and linguistic competence in the L2. Ultimately, the ability to make use of information structure in the L2 is believed to underpin the L2 learners’ ability to effectively communicate in the L2. The present study investigated how use of focus markers affects processing speed and word recall recall in a native-nonnative language comparison. The predominant research question was whether the type of focus marking leads to more efficient and accurate word processing in marked structures than in unmarked structures, and whether differences in processing patterns can be observed between the two language conditions. Three perception studies were conducted, each concentrating on one of the following linguistic parameters: 1. Prosodic prominence: Does prosodic focus conveyed by sentence accent and by word position facilitate word recognition? 2. Syntactical means: Do cleft constructions result in faster and more accurate word processing? 3. Lexical means: Does focus conveyed by the particles even/only (German: sogar/nur) facilitate word processing and word recall? Experiments 2 and 3 additionally investigated the contribution of context in the form of preceding questions. Furthermore, they considered accent and its facilitative effect on the processing of words which are in the scope of syntactic or lexical focus marking. All three experiments tested German learners of English in a native German language condition and in English as their L2. Native English speakers were included as a control for the English language condition. Test materials consisted of single sentences, all dealing with bird life. Experiment 1 tested word recognition in three focus conditions (broad focus, narrow focus on the target, and narrow focus on a constituent than the target) in one condition using natural unmanipulated sentences, and in the other two conditions using spliced sentences. Experiment 2 (effect of syntactic focus marking) and Experiment 3 (effect of lexical focus marking) used phoneme monitoring as a measure for the speed of word processing. Additionally, a word recall test (4AFC) was conducted to assess the effective entry of target-bearing words in the listeners’ memory. Experiment 1: Focus marking by prosodic means Prosodic focus marking by pitch accent was found to highlight important information (Bolinger, 1972), making the accented word perceptually more prominent (Klatt, 1976; van Santen & Olive, 1990; Eefting, 1991; Koopmans-van Beinum & van Bergem, 1989). However, accent structure seems to be processed faster in native than in nonnative listening (Akker& Cutler, 2003, Expt. 3). Therefore, it is expected that prosodically marked words are better recognised than unmarked words, and that listeners can exploit accent structure better for accurate word recognition in their L1 than they do in the L2 (L1 > L2). Altogether, a difference in word recognition performance in L1 listening is expected between different focus conditions (narrow focus > broad focus). Results of Experiments 1 show that words were better recognized in native listening than in nonnative listening. Focal accent, however, doesn’t seem to help the German subjects recognize accented words more accurately, in both the L1 and the L2. This could be due to the focus conditions not being acoustically distinctive enough. Results of experiments with spliced materials suggest that the surrounding prosodic sentence contour made listeners remember a target word and not the local, prosodic realization of the word. Prosody seems to indeed direct listeners’ attention to the focus of the sentence (see Cutler, 1976). Regarding the salience of word position, VanPatten (2002; 2004) postulated a sentence location principle for L2 processing, stating a ranking of initial > final > medial word position. Other evidence mentions a processing adantage of items occurring late in the sentence (Akker & Cutler, 2003), and Rast (2003) observed in an English L2 production study a trend of an advantage of items occurring at the outer ends of the sentence. The current Experiment 1 aimed to keep the length of the sentences to an acceptable length, mainly to keep the task in the nonnative lnaguage condition feasable. Word length showed an effect only in combination with word position (Rast, 2003; Rast & Dommergues, 2003). Therefore, word length was included in the current experiment as a secondary factor and without hypotheses. Results of Experiment 1 revealed that the length of a word doesn’t seem to be important for its accurate recognition. Word position, specifically the final position, clearly seems to facilitate accurate word recognition in German. A similar trend emerges in condition English L2, confirming Klein (1984) and Slobin (1985). Results don’t support the sentence location principle of VanPatten (2002; 2004). The salience of the final position is interpreted as recency effect (Murdock, 1962). In addition, the advantage of the final position may benefit from the discourse convention that relevant background information is referred to first, and then what is novel later (Haviland & Clark, 1974). This structure is assumed to cue the listener as to what the speaker considers to be important information, and listeners might have reacted according to this convention. Experiment 2: Focus marking by syntactic means Atypical syntactic structures often draw listeners’ attention to certain information in an utterance, and the cleft structure as a focus marking device appears to be a common surface feature in many languages (Lambrecht, 2001). Surface structure influences sentence processing (Foss & Lynch, 1969; Langford & Holmes, 1979), which leads to competing hypotheses in Experiment 2: on the one hand, the focusing effect of the cleft construction might reduce processing times. On the other, cleft constructions in German were found to be used less to mark fo than in English (Ahlemeyer & Kohlhof, 1999; Doherty, 1999; E. Klein, 1988). The complexity of the constructions, and the experience from the native language might work against an advantage of the focus effect in the L2. Results of Experiment 2 show that the cleft structure is an effective device to mark focus in German L1. The processing advantage is explained by the low degree of structural markedness of cleft structures: listeners use the focus function of sentence types headed by the dummy subject es (English: it) due to reliance on 'safe' subject-prominent SVO-structures. The benefit of cleft is enhanced when the sentences are presented with context, suggesting a substantial benefit when focus effects of syntactic surface structure and coherence relation between sentences are integrated. Clefts facilitate word processing for English native speakers. Contrary to German L1, the marked cleft construction doesn’t reduce processing times in English L2. The L1-L2 difference was interpreted as a learner problem of applying specific linguistic structures according to the principles of information structure in the target language. Focus marking by cleft did not help German learners in native or in nonnative word recall. This could be attributed to the phonological similarity of the multiple choice options (Conrad & Hull, 1964), and to a long time span between listening and recall (Birch & Garnsey, 1995; McKoon et al., 1993). Experiment 3: Focus marking by lexical means Focus particles are elements of structure that can indicate focus (König, 1991), and their function is to emphasize a certain part of the sentence (Paterson et al., 1999). I argue that the focus particles even/only (German: sogar/nur) evoke contrast sets of alternatives resp. complements to the element in focus (Ni et al., 1996), which causes interpretations of context. Therefore, lexical focus marking isn’t expected to lead to faster word processing. However, since different mechanisms of encoding seem to underlie word memory, a benefit of the focusing function of particles is expected to show in the recall task: due to focus particles being a preferred and well-used feature for native speakers of German, a transfer of this habitualness is expected, resulting in a better recall of focused words. Results indicated that focus particles seem to be the weakest option to mark focus: Focus marking by lexical particle don’t seem to reduce word processing times in either German L1, English L2, or in English L1. The presence of focus particles is likely to instantiate a complex discourse model which lets the listener await further modifying information (Liversedge et al., 2002). This semantic complexity might slow down processing. There are no indications that focus particles facilitate native language word recall in German L1 and English L1. This could be because focus particles open sets of conditions and contexts that enlarge the set of representations in listeners rather than narrowing it down to the element in the scope of the focus particle. In word recall, the facilitative effect of focus particles emerges only in the nonnative language condition. It is suggested that L2 learners, when faced with more demanding tasks in an L2, use a broad variety of means that identify focus for a better representation of novel words in the memory. In Experiments 2 and 3, evidence suggests that accent is an important factor for efficient word processing and accurate recall in German L1 and English L1, but less so in English L2. This underlines the function of accent as core speech parameter and consistent cue to the perception of prominence native language use (see Cutler & Fodor, 1979; Pitt & Samuel, 1990a; Eriksson et al., 2002; Akker & Cutler, 2003); the L1-L2 difference is attributed to patterns of expectation that are employed in the L1 but not (yet?) in the L2. There seems to exist a fine-tuned sensitivity to how accents are distributed in the native language, listeners expect an appropriate distribution and interpret it accordingly (Eefting, 1991). This pleads for accent placement as extremely important to L2 proficiency; the current results also suggest that accent and its relationship with other speech parameters has to be newly established in the L2 to fully reveal its benefits for efficient processing of speech. There is evidence that additional context facilitates processing of complex syntactic structures but that a surplus of information has no effect if the sentence construction is less challenging for the listener. The increased amount of information to be processed seems to impede better word recall, particularly in the L2. Altogether, it seems that focus marking devices and context can combine to form an advantageous alliance: a substantial benefit in processing efficiency is found when parameters of focus marking and sentence coherence are integrated. L2 research advocates the beneficial aspects of providing context for efficient L2 word learning (Lawson & Hogben, 1996). The current thesis promotes the view that a context which offers more semantic, prosodic, or lexical connections might compensate for the additional processing load that context constitutes for the listeners. A methodological consideration concerns the order in which language conditions are presented to listeners, i.e., L1-L2 or L2-L1. Findings suggest that presentation order could enforce a learning bias, with the performance in the second experiment being influenced by knowledge acquired in the first (see Akker & Cutler, 2003). To conclude this work: The results of the present study suggest that information structure is more accessible in the native language than it is in the nonnative language. There is, however, some evidence that L2 learners have an understanding of the significance of some information-structural parameters of focus marking. This has a beneficial effect on processing efficiency and recall accuracy; on the cognitive side it illustrates the benefits and also the need of a dynamic exchange of information-structural organization between L1 and L2. The findings of the current thesis encourage the view that an understanding of information structure can help the learner to discover and categorise forms and meanings of the L2. Information structure thus emerges as a valuable resource to advance proficiency in a second language.
The present thesis aims to introduce process-based model for species range dynamics that can be fitted to abundance data. For this purpose, the well-studied Proteaceae species of the South African Cape Floristic Region (CFR) offer a great data set to fit process-based models. These species are subject to wildflower harvesting and environmental threats like habitat loss and climate change. The general introduction of this thesis presents shortly the available models for species distribution modelling. Subsequently, it presents the feasibility of process-based modelling. Finally, it introduces the study system as well as the objectives and layout. In Chapter 1, I present the process-based model for range dynamics and a statistical framework to fit it to abundance distribution data. The model has a spatially-explicit demographic submodel (describing dispersal, reproduction, mortality and local extinction) and an observation submodel (describing imperfect detection of individuals). The demographic submodel links species-specific habitat models describing the suitable habitat and process-based demographic models that consider local dynamics and anemochoric seed dispersal between populations. After testing the fitting framework with simulated data, I applied it to eight Proteaceae species with different demographic properties. Moreover, I assess the role of two other demographic mechanisms: positive (Allee effects) and negative density-dependence. Results indicate that Allee effects and overcompensatory local dynamics (including chaotic behaviour) seem to be important for several species. Most parameter estimates quantitatively agreed with independent data. Hence, the presented approach seemed to suit the demand of investigating non-equilibrium scenarios involving wildflower harvesting (Chapter 2) and environmental change (Chapter 3). The Chapter 2 addresses the impacts of wildflower harvesting. The chapter includes a sensitivity analysis over multiple spatial scales and demographic properties (dispersal ability, strength of Allee effects, maximum reproductive rate, adult mortality, local extinction probability and carrying capacity). Subsequently, harvesting effects are investigated on real case study species. Plant response to harvesting showed abrupt threshold behavior. Species with short-distance seed dispersal, strong Allee effects, low maximum reproductive rate, high mortality and high local extinction are most affected by harvesting. Larger spatial scales benefit species response, but the thresholds become sharper. The three case study species supported very low to moderate harvesting rates. Summarizing, demographic knowledge about the study system and careful identification of the spatial scale of interest should guide harvesting assessments and conservation of exploited species. The sensitivity analysis’ results can be used to qualitatively assess harvesting impacts for poorly studied species. I investigated in Chapter 3 the consequences of past habitat loss, future climate change and their interaction on plant response. I use the species-specific estimates of the best model describing local dynamics obtained in Chapter 1. Both habitat loss and climate change had strong negative impacts on species dynamics. Climate change affected mainly range size and range filling due to habitat reductions and shifts combined with low colonization. Habitat loss affected mostly local abundances. The scenario with both habitat loss and climate change was the worst for most species. However, this impact was better than expected by simple summing of separate effects of habitat loss and climate change. This is explained by shifting ranges to areas less affected by humans. Range size response was well predicted by the strength of environmental change, whereas range filling and local abundance responses were better explained by demographic properties. Hence, risk assessments under global change should consider demographic properties. Most surviving populations were restricted to refugia, serving as key conservation focus.The findings obtained for the study system as well as the advantages, limitations and potentials of the model presented here are further discussed in the General Discussion. In summary, the results indicate that 1) process-based demographic models for range dynamics can be fitted to data; 2) demographic processes improve species distribution models; 3) different species are subject to different processes and respond differently to environmental change and exploitation; 4) density regulation type and Allee effects should be considered when investigating range dynamics of species; 5) the consequences of wildflower harvesting, habitat loss and climate change could be disastrous for some species, but impacts vary depending on demographic properties; 6) wildflower harvesting impacts varies over spatial scale; 7) The effects of habitat loss and climate change are not always additive.
Due to the unique environmental conditions and different feedback mechanisms, the Arctic region is especially sensitive to climate changes. The influence of clouds on the radiation budget is substantial, but difficult to quantify and parameterize in models. In the framework of the PhD, elastic backscatter and depolarization lidar observations of Arctic clouds were performed during the international Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR) from Svalbard in March and April 2007. Clouds were probed above the inaccessible Arctic Ocean with a combination of airborne instruments: The Airborne Mobile Aerosol Lidar (AMALi) of the Alfred Wegener Institute for Polar and Marine Research provided information on the vertical and horizontal extent of clouds along the flight track, optical properties (backscatter coefficient), and cloud thermodynamic phase. From the data obtained by the spectral albedometer (University of Mainz), the cloud phase and cloud optical thickness was deduced. Furthermore, in situ observations with the Polar Nephelometer, Cloud Particle Imager and Forward Scattering Spectrometer Probe (Laboratoire de Météorologie Physique, France) provided information on the microphysical properties, cloud particle size and shape, concentration, extinction, liquid and ice water content. In the thesis, a data set of four flights is analyzed and interpreted. The lidar observations served to detect atmospheric structures of interest, which were then probed by in situ technique. With this method, an optically subvisible ice cloud was characterized by the ensemble of instruments (10 April 2007). Radiative transfer simulations based on the lidar, radiation and in situ measurements allowed the calculation of the cloud forcing, amounting to -0.4 W m-2. This slight surface cooling is negligible on a local scale. However, thin Arctic clouds have been reported more frequently in winter time, when the clouds' effect on longwave radiation (a surface warming of 2.8 W m-2) is not balanced by the reduced shortwave radiation (surface cooling). Boundary layer mixed-phase clouds were analyzed for two days (8 and 9 April 2007). The typical structure consisting of a predominantly liquid water layer on cloud top and ice crystals below were confirmed by all instruments. The lidar observations were compared to European Centre for Medium-Range Weather Forecasts (ECMWF) meteorological analyses. A change of air masses along the flight track was evidenced in the airborne data by a small completely glaciated cloud part within the mixed-phase cloud system. This indicates that the updraft necessary for the formation of new cloud droplets at cloud top is disturbed by the mixing processes. The measurements served to quantify the shortcomings of the ECMWF model to describe mixed-phase clouds. As the partitioning of cloud condensate into liquid and ice water is done by a diagnostic equation based on temperature, the cloud structures consisting of a liquid cloud top layer and ice below could not be reproduced correctly. A small amount of liquid water was calculated for the lowest (and warmest) part of the cloud only. Further, the liquid water content was underestimated by an order of magnitude compared to in situ observations. The airborne lidar observations of 9 April 2007 were compared to space borne lidar data on board of the satellite Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). The systems agreed about the increase of cloud top height along the same flight track. However, during the time delay of 1 h between the lidar measurements, advection and cloud processing took place, and a detailed comparison of small-scale cloud structures was not possible. A double layer cloud at an altitude of 4 km was observed with lidar at the West coast in the direct vicinity of Svalbard (14 April 2007). The cloud system consisted of two geometrically thin liquid cloud layers (each 150 m thick) with ice below each layer. While the upper one was possibly formed by orographic lifting under the influence of westerly winds, or by the vertical wind shear shown by ECMWF analyses, the lower one might be the result of evaporating precipitation out of the upper layer. The existence of ice precipitation between the two layers supports the hypothesis that humidity released from evaporating precipitation was cooled and consequently condensed as it experienced the radiative cooling from the upper layer. In summary, a unique data set characterizing tropospheric Arctic clouds was collected with lidar, in situ and radiation instruments. The joint evaluation with meteorological analyses allowed a detailed insight in cloud properties, cloud evolution processes and radiative effects.
Submarine landslides can generate local tsunamis posing a hazard to human lives and coastal facilities. Two major related problems are: (i) quantitative estimation of tsunami hazard and (ii) early detection of the most dangerous landslides. This thesis focuses on both those issues by providing numerical modeling of landslide-induced tsunamis and by suggesting and justifying a new method for fast detection of tsunamigenic landslides by means of tiltmeters. Due to the proximity to the Sunda subduction zone, Indonesian coasts are prone to earthquake, but also landslide tsunamis. The aim of the GITEWS-project (German-Indonesian Tsunami Early Warning System) is to provide fast and reliable tsunami warnings, but also to deepen the knowledge about tsunami hazards. New bathymetric data at the Sunda Arc provide the opportunity to evaluate the hazard potential of landslide tsunamis for the adjacent Indonesian islands. I present nine large mass movements in proximity to Sumatra, Java, Sumbawa and Sumba, whereof the largest event displaced 20 km³ of sediments. Using numerical modeling, I compute the generated tsunami of each event, its propagation and runup at the coast. Moreover, I investigate the age of the largest slope failures by relating them to the Great 1977 Sumba earthquake. Continental slopes off northwest Europe are well known for their history of huge underwater landslides. The current geological situation west of Spitsbergen is comparable to the continental margin off Norway after the last glaciation, when the large tsunamigenic Storegga slide took place. The influence of Arctic warming on the stability of the Svalbard glacial margin is discussed. Based on new geophysical data, I present four possible landslide scenarios and compute the generated tsunamis. Waves of 6 m height would be capable of reaching northwest Europe threatening coastal areas. I present a novel technique to detect large submarine landslides using an array of tiltmeters, as a possible tool in future tsunami early warning systems. The dislocation of a large amount of sediment during a landslide produces a permanent elastic response of the earth. I analyze this response with a mathematical model and calculate the theoretical tilt signal. Applications to the hypothetical Spitsbergen event and the historical Storegga slide show tilt signals exceeding 1000 nrad. The amplitude of landslide tsunamis is controlled by the product of slide volume and maximal velocity (slide tsunamigenic potential). I introduce an inversion routine that provides slide location and tsunamigenic potential, based on tiltmeter measurements. The accuracy of the inversion and of the estimated tsunami height near the coast depends on the noise level of tiltmeter measurements, the distance of tiltmeters from the slide, and the slide tsunamigenic potential. Finally, I estimate the applicability scope of this method by employing it to known landslide events worldwide.
The Tibetan Plateau is the largest elevated landmass in the world and profoundly influences atmospheric circulation patterns such as the Asian monsoon system. Therefore this area has been increasingly in focus of palaeoenvironmental studies. This thesis evaluates the applicability of organic biomarkers for palaeolimnological purposes on the Tibetan Plateau with a focus on aquatic macrophyte-derived biomarkers. Submerged aquatic macrophytes have to be considered to significantly influence the sediment organic matter due to their high abundance in many Tibetan lakes. They can show highly 13C-enriched biomass because of their carbon metabolism and it is therefore crucial for the interpretation of δ13C values in sediment cores to understand to which extent aquatic macrophytes contribute to the isotopic signal of the sediments in Tibetan lakes and in which way variations can be explained in a palaeolimnological context. Additionally, the high abundance of macrophytes makes them interesting as potential recorders of lake water δD. Hydrogen isotope analysis of biomarkers is a rapidly evolving field to reconstruct past hydrological conditions and therefore of special relevance on the Tibetan Plateau due to the direct linkage between variations of monsoon intensity and changes in regional precipitation / evaporation balances. A set of surface sediment and aquatic macrophyte samples from the central and eastern Tibetan Plateau was analysed for composition as well as carbon and hydrogen isotopes of n-alkanes. It was shown how variable δ13C values of bulk organic matter and leaf lipids can be in submerged macrophytes even of a single species and how strongly these parameters are affected by them in corresponding sediments. The estimated contribution of the macrophytes by means of a binary isotopic model was calculated to be up to 60% (mean: 40%) to total organic carbon and up to 100% (mean: 66%) to mid-chain n-alkanes. Hydrogen isotopes of n-alkanes turned out to record δD of meteoric water of the summer precipitation. The apparent enrichment factor between water and n-alkanes was in range of previously reported ones (≈-130‰) at the most humid sites, but smaller (average: -86‰) at sites with a negative moisture budget. This indicates an influence of evaporation and evapotranspiration on δD of source water for aquatic and terrestrial plants. The offset between δD of mid- and long-chain n-alkanes was close to zero in most of the samples, suggesting that lake water as well as soil and leaf water are affected to a similar extent by those effects. To apply biomarkers in a palaeolimnological context, the aliphatic biomarker fraction of a sediment core from Lake Koucha (34.0° N; 97.2° E; eastern Tibetan Plateau) was analysed for concentrations, δ13C and δD values of compounds. Before ca. 8 cal ka BP, the lake was dominated by aquatic macrophyte-derived mid-chain n-alkanes, while after 6 cal ka BP high concentrations of a C20 highly branched isoprenoid compound indicate a predominance of phytoplankton. Those two principally different states of the lake were linked by a transition period with high abundances of microbial biomarkers. δ13C values were relatively constant for long-chain n-alkanes, while mid-chain n-alkanes showed variations between -23.5 to -12.6‰. Highest values were observed for the assumed period of maximum macrophyte growth during the late glacial and for the phytoplankton maximum during the middle and late Holocene. Therefore, the enriched values were interpreted to be caused by carbon limitation which in turn was induced by high macrophyte and primary productivity, respectively. Hydrogen isotope signatures of mid-chain n-alkanes have been shown to be able to track a previously deduced episode of reduced moisture availability between ca. 10 and 7 cal ka BP, indicated by a 20‰ shift towards higher δD values. Indications for cooler episodes at 6.0, 3.1 and 1.8 cal ka BP were gained from drops of biomarker concentrations, especially microbial-derived hopanoids, and from coincidental shifts towards lower δ13C values. Those episodes correspond well with cool events reported from other locations on the Tibetan Plateau as well as in the Northern Hemisphere. To conclude, the study of recent sediments and plants improved the understanding of factors affecting the composition and isotopic signatures of aliphatic biomarkers in sediments. Concentrations and isotopic signatures of the biomarkers in Lake Koucha could be interpreted in a palaeolimnological context and contribute to the knowledge about the history of the lake. Aquatic macrophyte-derived mid-chain n-alkanes were especially useful, due to their high abundance in many Tibetan Lakes and their ability to record major changes of lake productivity and palaeo-hydrological conditions. Therefore, they have the potential to contribute to a fuller understanding of past climate variability in this key region for atmospheric circulation systems.
Pectic polysaccharides, a class of plant cell wall polymers, form one of the most complex networks known in nature. Despite their complex structure and their importance in plant biology, little is known about the molecular mechanism of their biosynthesis, modification, and turnover, particularly their structure-function relationship. One way to gain insight into pectin metabolism is the identification of mutants with an altered pectin structure. Those were obtained by a recently developed pectinase-based genetic screen. Arabidopsis thaliana seedlings grown in liquid medium containing pectinase solutions exhibited particular phenotypes: they were dwarfed and slightly chlorotic. However, when genetically different A. thaliana seed populations (random T-DNA insertional populations as well as EMS-mutagenized populations and natural variations) were subjected to this treatment, individuals were identified that exhibit a different visible phenotype compared to wild type or other ecotypes and may thus contain a different pectin structure (pec-mutants). After confirming that the altered phenotype occurs only when the pectinase is present, the EMS mutants were subjected to a detailed cell wall analysis with particular emphasis on pectins. This suite of mutants identified in this study is a valuable resource for further analysis on how the pectin network is regulated, synthesized and modified. Flanking sequences of some of the T-DNA lines have pointed toward several interesting genes, one of which is PEC100. This gene encodes a putative sugar transporter gene, which, based on our data, is implicated in rhamnogalacturonan-I synthesis. The subcellular localization of PEC100 was studied by GFP fusion and this protein was found to be localized to the Golgi apparatus, the organelle where pectin biosynthesis occurs. Arabidopsis ecotype C24 was identified as a susceptible one when grown with pectinases in liquid culture and had a different oligogalacturonide mass profile when compared to ecotype Col-0. Pectic oligosaccharides have been postulated to be signal molecules involved in plant pathogen defense mechanisms. Indeed, C24 showed elevated accumulation of reactive oxygen species upon pectinase elicitation and had altered response to the pathogen Alternaria brassicicola in comparison to Col-0. Using a recombinant inbred line population three major QTLs were identified to be responsible for the susceptibility of C24 to pectinases. In a reverse genetic approach members of the qua2 (putative pectin methyltransferase) family were tested for potential target genes that affect pectin methyl-esterification. The list of these genes was determined by in silico study of the pattern of expression and co-expression of all 34 members of this family resulting in 6 candidate genes. For only for one of the 6 analyzed genes a difference in the oligogalacturonide mass profile was observed in the corresponding knock-out lines, confirming the hypothesis that the methyl-esterification pattern of pectin is fine tuned by members of this gene family. This study of pectic polysaccharides through forward and reverse genetic screens gave new insight into how pectin structure is regulated and modified, and how these modifications could influence pectin mediated signalling and pathogenicity.
Trying to do two things at once decreases performance of one or both tasks in many cases compared to the situation when one performs each task by itself. The present thesis deals with the question why and in which cases these dual-task costs emerge and moreover, whether there are cases in which people are able to process two cognitive tasks at the same time without costs. In four experiments the influence of stimulus-response (S-R) compatibility, S-R modality pairings, interindividual differences, and practice on parallel processing ability of two tasks are examined. Results show that parallel processing is possible. Nevertheless, dual-task costs emerge when: the personal processing strategy is serial, the two tasks have not been practiced together, S-R compatibility of both tasks is low (e.g. when a left target has to be responded with a right key press and in the other task an auditorily presented “A” has to be responded by saying “B”), and modality pairings of both tasks are Non Standard (i.e., visual-spatial stimuli are responded vocally whereas auditory-verbal stimuli are responded manually). Results are explained with respect to executive-based (S-R compatibility) and content-based crosstalk (S-R modality pairings) between tasks. Finally, an alternative information processing account with respect to the central stage of response selection (i.e., the translation of the stimulus to the response) is presented.