Suchmaschinen - Eine industrieökonomische Analyse der Konzentration und ihrer Ursachen

The main topic of this doctoral thesis is to investigate the concentration in search engine markets. It is investigated, whether the structural characteristics of the market, favors a natural concentration (monopoly/oligopoly) or if an abuse of a dominant position are responsible for this. Further the (qualitative) efficiency of the providers is examined based on surveys of quality and satisfaction. In succession to the introduction, Chapter 2 depicts background information to support a better understanding of the analysis. The 3rd Chapter describes the structure and operation of a search engine. The service is split into sub-processes and particular functions are analyzed regarding their contribution to the search engine quality. The 4th chapter analyzes the demand side characteristics. The focuses are: possible switching costs, network effects, and platform properties. The hypothesis is supported by behavioral studies. The service side of a search engine is considered in the 5th chapter. Especially the cost structure to maintain a search engine service is being investigated. In chapter 6, the high concentration of the search engine market is empirically analyzed. The Chapter 7 addresses whether the concentration can be justified by the search engines quality or by the determined economic characteristics. The barriers to entry and the concentration process (winner takes it all) are distinguished. In the final analytical section, the concentration factors are analyzed in chronological sequence and the search engines are examined within the framework of the theory of contestable markets. The thesis concludes with a summary and a discussion of the regulatory proposals.Hauptinteresse der vorliegenden Arbeit besteht darin, die bestehende hohe Konzentration der Suchmaschinenmärkte zu ergründen. Vor allem wird untersucht, ob diese auf die strukturellen Eigenschaften der Märkte zurückzuführen ist und somit eine natürliche Konzentration (Monopol/Oligopol) darstellt oder ob diese auf missbräuchliche Verhaltensweisen der etablierten Suchmaschinenbetreiber zurückzuführen ist. Als weiterer Erklärungsansatz der Konzentration wird anhand der Qualitäts- und Zufriedenheitsstudien eine höhere (qualitative) Effizienz der Betreiber untersucht.Im Anschluss an eine Einleitung werden im 2. Kapitel Hintergrundinformationen für das bessere Verständnis der durchgeführten Untersuchung dargestellt. Im 3. Kapitel werden der Aufbau und die Funktionsweise einer Suchmaschine beschrieben. Die Zerlegung der Dienstleistung einer Suchmaschine in Teilprozesse (Wertschöpfungsstufen) sowie die Ermittlung der Bedeutung einzelner Funktionen für die Suchmaschinenqualität bilden die Grundlagen für die Analyse der ökonomischen Eigenschaften in den Kapiteln 4 und 5.Das 4. Kapitel befasst sich mit den nachfrageseitigen Eigenschaften. Die wichtigsten Untersuchungspunkte sind hierbei: die möglichen Wechselbarrieren der Nachfragegruppen; die zwischen den und innerhalb der Nachfragegruppen bestehenden Netzwerkeffekte sowie die auf den Netzwerkeffekten aufbauende Analyse der Plattformeigenschaften. Zur Untermauerung der argumentativen Untersuchung werden Verhaltensstudien verwendet.Im 5. Kapitel der Arbeit wird die Angebotsseite einer Suchmaschine betrachtet. Hierbei wird die Kostenstruktur zur Unterhaltung einer Suchmaschine analysiert, um unter anderem mögliche Betriebsgrößen- oder Verbundvorteile zu erfassen. Im 6. Kapitel wird die hohe Konzentration der Suchmaschinenmärkte empirisch analysiert. Daran anschließend wird im 7. Kapitel die Konzentration anhand von Studien zur Qualität von Suchmaschinen sowie anhand der ermittelten ökonomischen Eigenschaften begründet. Hierbei werden die Markteintrittsbarrieren und der Konzentrationsprozess (Winner takes all) unterschieden. Im letzten analytischen Abschnitt werden die Konzentrationsfaktoren im zeitlichen Ablauf sowie die Suchmaschinen auf bestreitbare natürliche Monopole analysiert.Die Arbeit schließt mit einer Schlussbetrachtung, in der die Erkenntnisse zusammengefasst sowie Regulierungsvorhaben diskutiert werden

Exact asymptotic analysis for metapopulation dynamics on correlated dynamic landscapes

We compute the mean patch occupancy for a stochastic, spatially explicit patch-occupancy metapopulation model on a dynamic, correlated landscape, using a mathematically exact perturbation expansion about a mean-field limit that applies when dispersal range is large. Stochasticity in the metapopulation and landscape dynamics gives negative contributions to patch occupancy, the former being more important at high occupancy and the latter at low occupancy. Positive landscape correlations always benefit the metapopulation, but are only significant when the correlation length is comparable to, or smaller than, the dispersal range. Our analytical results allow us to consider the importance of spatial kernels in all generality. We find that the shape of the landscape correlation function is typically unimportant, and that the variance is overwhelmingly the most important property of the colonisation kernel. However, short-range singularities in either the colonisation kernel or landscape correlations can give rise to qualitatively different behaviour

Characterization of the first potent and selective PDE9 inhibitor using a cGMP reporter cell

ABSTRACT We report here the in vitro characterization of 1-(2-chlorophenyl)-6-[(2R)-3,3,3-trifluoro-2-methylpropyl]-1,5-dihydro-4H-pyrazolo [3,4-d]pyrimidine-4-one , the first potent and selective inhibitor of phosphodiesterase 9 (PDE9), which is currently under preclinical development for the treatment of Alzheimer's disease. This compound selectively inhibits human (IC 50 ϭ 55 nM) and murine (IC 50 ϭ 100 nM) PDE9 activity in vitro and shows only moderate activity against other cyclic nucleotide-specific phosphodiesterases. We also report the generation and characterization of a stably transfected PDE9 Chinese hamster ovary cell line, additionally expressing soluble guanylate cyclase (sGC), the olfactory cyclic nucleotide-gated cation channel CNGA2 and the photoprotein aequorin. In this cell line, intracellular cGMP levels can be monitored in real-time via aequorin luminescence induced by Ca 2ϩ influx through CNGA2, acting as the intracellular cGMP sensor. This simple and sensitive assay system was used for the characterization of the cellular activity of the new PDE9 inhibitor. BAY 73-6691 alone did not significantly increase basal cGMP levels in this experimental setting. However, in combination with submaximal stimulating concentrations of the sGC activator 4-[((4-carboxybutyl){2-[(4-phenethylbenzyl)oxy]phenethyl}amino)methyl] benzoic acid (BAY 58-2667), the compound induced concentration-dependent luminescence signals and intracellular cGMP accumulation. The PDE9 inhibitor significantly potentiated the cGMP signals generated by sGC activating compounds such as BAY 58-2667 or 5-cyclopropyl-2-[1-(2-fluorobenzyl)-1H-pyrazolo [3,4-b]pyridin-3-yl]pyrimidin-4-ylamine (BAY 41-2272) and induced leftward shifts of the corresponding concentration-response curves. Using our newly generated PDE9 reporter cell line, we could show that BAY 73-6691 is able to efficiently penetrate cells and to inhibit intracellular PDE9 activity

Immigration Rates in Fragmented Landscapes – Empirical Evidence for the Importance of Habitat Amount for Species Persistence

BACKGROUND: The total amount of native vegetation is an important property of fragmented landscapes and is known to exert a strong influence on population and metapopulation dynamics. As the relationship between habitat loss and local patch and gap characteristics is strongly non-linear, theoretical models predict that immigration rates should decrease dramatically at low levels of remaining native vegetation cover, leading to patch-area effects and the existence of species extinction thresholds across fragmented landscapes with different proportions of remaining native vegetation. Although empirical patterns of species distribution and richness give support to these models, direct measurements of immigration rates across fragmented landscapes are still lacking. METHODOLOGY/PRINCIPAL FINDINGS: Using the Brazilian Atlantic forest marsupial Gray Slender Mouse Opossum (Marmosops incanus) as a model species and estimating demographic parameters of populations in patches situated in three landscapes differing in the total amount of remaining forest, we tested the hypotheses that patch-area effects on population density are apparent only at intermediate levels of forest cover, and that immigration rates into forest patches are defined primarily by landscape context surrounding patches. As expected, we observed a positive patch-area effect on M. incanus density only within the landscape with intermediate forest cover. Density was independent of patch size in the most forested landscape and the species was absent from the most deforested landscape. Specifically, the mean estimated numbers of immigrants into small patches were lower in the landscape with intermediate forest cover compared to the most forested landscape. CONCLUSIONS/SIGNIFICANCE: Our results reveal the crucial importance of the total amount of remaining native vegetation for species persistence in fragmented landscapes, and specifically as to the role of variable immigration rates in providing the underlying mechanism that drives both patch-area effects and species extinction thresholds

Changing organisms in rapidly changing anthropogenic landscapes: the significance of the ‘Umwelt’-concept and functional habitat for animal conservation

There is a growing recognition for the significance of evolutionary thinking in ecology and conservation biology. However, ecology and conservation studies often work with species-specific, fixed traits that ignore intraspecific variation. The way the habitat of a species is considered is an example of typological thinking biased by human perception. Structural habitat units (e.g., land cover types) as perceived by humans may not represent functional habitat units for other organisms. Human activity may also interfere with the environmental information used by organisms. Therefore, the Umwelt-concept from ethology needs to be integrated in the way we think about habitat and habitat selection. It states that different organisms live in different perceptual worlds dealing with specific subsamples of the environment as a result of their evolutionary and developmental history. The resource-based habitat concept is a functional habitat model based on resource distributions (consumables and conditions) and individual movements. This behavioural approach takes into account aspects that relate to the perceptual world of organisms. This approach may offer new opportunities for conservation and may help avoid failures with habitat restoration. Perceptual ability may be subject to adaptive change, but it may also constrain organisms from showing adaptive behaviours in rapidly changing environments

New density estimates of a threatened sifaka species (Propithecus coquereli) in Ankarafantsika National Park

Propithecus coquereli is one of the last sifaka species for which no reliable and extensive density estimates are yet available. Despite its endangered conservation status [IUCN, 2012] and recognition as a flagship species of the northwestern dry forests of Madagascar, its population in its last main refugium, the Ankarafantsika National Park (ANP), is still poorly known. Using line transect distance sampling surveys we estimated population density and abundance in the ANP. Furthermore, we investigated the effects of road, forest edge, river proximity and group size on sighting frequencies, and density estimates. We provide here the first population density estimates throughout the ANP. We found that density varied greatly among surveyed sites (from 5 to ∼100 ind/km2) which could result from significant (negative) effects of road, and forest edge, and/or a (positive) effect of river proximity. Our results also suggest that the population size may be ∼47,000 individuals in the ANP, hinting that the population likely underwent a strong decline in some parts of the Park in recent decades, possibly caused by habitat loss from fires and charcoal production and by poaching. We suggest community-based conservation actions for the largest remaining population of Coquerel's sifaka which will (i) maintain forest connectivity; (ii) implement alternatives to deforestation through charcoal production, logging, and grass fires; (iii) reduce poaching; and (iv) enable long-term monitoring of the population in collaboration with local authorities and researchers.Optimus!Alive- IGC fellowship, FCT fellowship: (SFRH/BD/64875/2009), University of Mahajanga, Groupement de Recherche International (GDRI), "Laboratoire d'Excellence" (LABEX) entitled TULIP (ANR-10-LABX-41), the Rufford Small Grant Foundation grant: (10941-1)

Red noise increases extinction risk during rapid climate change

Aim: As the global climate is changing rapidly, there is a need to make conservation decisions to facilitate species' persistence under climate change. Models employed to make predictions regarding the impacts of climate change on species' distributions, and ultimately persistence, typically assume that interannual variability in environmental conditions is independent between years. However, the colour of environmental noise has been shown to affect extinction risk in populations occupying spatially static environments, and should therefore affect persistence during climate change. This study aims to investigate the importance of noise colour for extinction risk during climate-induced range shifts. Methods: We use a spatially explicit coupled map lattice with a latitudinal gradient in climatic suitability, together with time series of environmental noise, to simulate periods of directional climate change and investigate the effects of noise colour on extinction risk and range size. Results: Extinction risk increases with reddening of the environmental noise, and this effect is particularly pronounced over short time frames when climate change is rapid. Main conclusions: Given that management decisions are typically made over such short time frames, and the rapid rates of climate change currently being experienced, we highlight the importance of incorporating realistic time series of environmental noise into models used for conservation planning under climate change

An Updated Algorithm for the Generation of Neutral Landscapes by Spectral Synthesis

Background: Patterns that arise from an ecological process can be driven as much from the landscape over which the process is run as it is by some intrinsic properties of the process itself. The disentanglement of these effects is aided if it possible to run models of the process over artificial landscapes with controllable spatial properties. A number of different methods for the generation of so-called ‘neutral landscapes’ have been developed to provide just such a tool. Of these methods, a particular class that simulate fractional Brownian motion have shown particular promise. The existing methods of simulating fractional Brownian motion suffer from a number of problems however: they are often not easily generalisable to an arbitrary number of dimensions and produce outputs that can exhibit some undesirable artefacts. Methodology: We describe here an updated algorithm for the generation of neutral landscapes by fractional Brownian motion that do not display such undesirable properties. Using Monte Carlo simulation we assess the anisotropic properties of landscapes generated using the new algorithm described in this paper and compare it against a popular benchmark algorithm. Conclusion/Significance: The results show that the existing algorithm creates landscapes with values strongly correlated in the diagonal direction and that the new algorithm presented here corrects this artefact. A number of extensions of the algorithm described here are also highlighted: we describe how the algorithm can be employed to generate landscapes that display different properties in different dimensions and how they can be combined with an environmental gradient to produce landscapes that combine environmental variation at the local and macro scales

Robustness of metacommunities with omnivory to habitat destruction: disentangling patch fragmentation from patch loss

Habitat destruction, characterized by patch loss and fragmentation, is a major driving force of species extinction, and understanding its mechanisms has become a central issue in biodiversity conservation. Numerous studies have explored the effect of patch loss on food web dynamics, but ignored the critical role of patch fragmentation. Here we develop an extended patch-dynamic model for a tri-trophic omnivory system with trophic-dependent dispersal in fragmented landscapes. We found that species display different vulnerabilities to both patch loss and fragmentation, depending on their dispersal range and trophic position. The resulting trophic structure varies depending on the degree of habitat loss and fragmentation, due to a tradeoff between bottom-up control on omnivores (dominated by patch loss) and dispersal limitation on intermediate consumers (dominated by patch fragmentation). Overall, we find that omnivory increases system robustness to habitat destruction relative to a simple food chain