Expansion rate & dispersal pattern of the non-native Roesel’s bush-cricket in Sweden

Environmental change and anthropogenic activities influence species distributions. Species introductions have become increasingly common in an era of globalization and increased international trade and travel. The establishment of introduced species outside their native range and subsequent spread are of great conservation concern. Introduced species that become invasive, spread rapidly and reach high abundance, may cause the extinction of native species, disrupt ecosystem functioning and pose a threat to human health and the economy. It is therefore of great interest to understand the processes and mechanisms involved in species range expansion in order to develop effective management strategies. In this thesis I examine the influence of the landscape on species’ distribution and analyse patterns of range expansion of a non-native insect in south-central Sweden. Roesel’s bush-cricket (Metrioptera roeselii) was chosen as a model organism as its biology is well studied and its range expansion has been documented not only in Sweden but also in several other European countries. The aims of this thesis were (I) to identify landscape variables that predict the species distribution, (II) to estimate the rate of range expansion, (III) to identify the source of range expansion in south-central Sweden and to assess the dispersal pattern using population genetic data, and (IV) to analyse the influence of landscape composition and structure on population connectivity. I analysed species distribution, genetic and landscape data using a range of statistical modelling techniques in combination with geographic information systems (GIS). The results showed that the amounts of arable land, pasture and rural settlements as well as linear habitat elements are important predictors of the species’ distribution. During the last three decades, Metrioptera roeselii has expanded its range from the northern shores of the Lake Mälaren at an estimated rate of 0.3 - 3.16 km/year. The genetic diversity across the range was surprisingly high and degree of population differentiation was low to moderate likely due to frequent gene flow between populations in the centre of the species range and decreased gene flow towards the range margin. It appears the species establishes populations through infrequent long-distance and frequent short-distance dispersal (natural, human-mediated)

Entropic Priors

The method of Maximum (relative) Entropy (ME) is used to translate the information contained in the known form of the likelihood into a prior distribution for Bayesian inference. The argument is guided by intuition gained from the successful use of ME methods in statistical mechanics. For experiments that cannot be repeated the resulting "entropic prior" is formally identical with the Einstein fluctuation formula. For repeatable experiments, however, the expected value of the entropy of the likelihood turns out to be relevant information that must be included in the analysis. As an example the entropic prior for a Gaussian likelihood is calculated.Comment: Presented at MaxEnt'03, the 23d International Workshop on Bayesian Inference and Maximum Entropy Methods (August 3-8, 2003, Jackson Hole, WY, USA

The True Destination of EGO is Multi-local Optimization

Efficient global optimization is a popular algorithm for the optimization of expensive multimodal black-box functions. One important reason for its popularity is its theoretical foundation of global convergence. However, as the budgets in expensive optimization are very small, the asymptotic properties only play a minor role and the algorithm sometimes comes off badly in experimental comparisons. Many alternative variants have therefore been proposed over the years. In this work, we show experimentally that the algorithm instead has its strength in a setting where multiple optima are to be identified

Social Bots: Human-Like by Means of Human Control?

Social bots are currently regarded an influential but also somewhat mysterious factor in public discourse and opinion making. They are considered to be capable of massively distributing propaganda in social and online media and their application is even suspected to be partly responsible for recent election results. Astonishingly, the term `Social Bot' is not well defined and different scientific disciplines use divergent definitions. This work starts with a balanced definition attempt, before providing an overview of how social bots actually work (taking the example of Twitter) and what their current technical limitations are. Despite recent research progress in Deep Learning and Big Data, there are many activities bots cannot handle well. We then discuss how bot capabilities can be extended and controlled by integrating humans into the process and reason that this is currently the most promising way to go in order to realize effective interactions with other humans.Comment: 36 pages, 13 figure

Operator product expansion of the energy momentum tensor in 2D conformal field theories on manifolds with boundary

Starting from the well-known expression for the trace anomaly we derive the $T\cdot T$ operator product expansion of the energy-momentum tensor in 2D conformal theories defined in the upper halfplane $without$ making use of the additional condition of no energy-momentum flux across the boundary. The OPE turns out to be the same as in the absence of the boundary. For this result it is crucial that the trace anomaly is proportional to the Gau\ss-Bonnet density. Some relations to the $\sigma$ - model approach for open strings are discussed.Comment: 8 pages, Latex, HU Berlin-IEP-93/

Pseudogaps and their Interplay with Magnetic Excitations in the doped 2D Hubbard Model

On the basis of Quantum Monte Carlo simulations of the two-dimensional Hubbard model which cover the doping range from the under- to the over-doped regime, we find that the single-particle spectral weight $A (\vec k,\omega)$ qualitatively reproduces both the momentum ($d_{x^2-y^2}$--symmetry) and doping dependence of the pseudogap as found in photoemission experiments. The drastic doping dependence of the spin response $\chi_{s} (\vec q,\omega)$ which is sharp in both $\vec q (\approx(\pi,\pi))$ and $\omega$ in the under-doped regime but broad and structureless otherwise, identifies remnants of the antiferromagnetic order as the driving mechanism behind the pseudogap and its evolution with doping.Comment: 4 pages, Rev-Tex, includes 3 figure

Marginalization using the metric of the likelihood

Although the likelihood function is normalizeable with respect to the data there is no guarantee that the same holds with respect to the model parameters. This may lead to singularities in the expectation value integral of these parameters, especially if the prior information is not sufficient to take care of finite integral values. However, the problem may be solved by obeying the correct Riemannian metric imposed by the likelihood. This will be demonstrated for the example of the electron temperature evaluation in hydrogen plasmas.Comment: 8 pages, 2 figures, Presented at the MaxEnt 2000 conference in Gif-sur-Yvette/Pari