On the impact of dispersal asymmetry on metapopulation persistence

Metapopulation theory for a long time has assumed dispersal to be symmetric, i.e. patches are connected through migrants dispersing bi-directionally without a preferred direction. However, for natural populations symmetry is often broken, e.g. for species in the marine environment dispersing through the transport of pelagic larvae with ocean currents. The few recent studies of asymmetric dispersal concluded, that asymmetry has a distinct negative impact on the persistence of metapopulations. Detailed analysis however revealed, that these previous studies might have been unable to properly disentangle the effect of symmetry from other potentially confounding properties of dispersal patterns. We resolve this issue by systematically investigating the symmetry of dispersal patterns and its impact on metapopulation persistence. Our main analysis based on a metapopulation model equivalent to previous studies but now applied on regular dispersal patterns aims to isolate the effect of dispersal symmetry on metapopulation persistence. Our results suggest, that asymmetry in itself does not imply negative effects on metapopulation persistence. For this reason we recommend to investigate it in connection with other properties of dispersal instead of in isolation.Comment: 19 pages, 5 figure

Estimation of drift and diffusion functions from time series data: A maximum likelihood framework

Complex systems are characterized by a huge number of degrees of freedom often interacting in a non-linear manner. In many cases macroscopic states, however, can be characterized by a small number of order parameters that obey stochastic dynamics in time. Recently techniques for the estimation of the corresponding stochastic differential equations from measured data have been introduced. This contribution develops a framework for the estimation of the functions and their respective (Bayesian posterior) confidence regions based on likelihood estimators. In succession approximations are introduced that significantly improve the efficiency of the estimation procedure. While being consistent with standard approaches to the problem this contribution solves important problems concerning the applicability and the accuracy of estimated parameters.Comment: 18 pages, 2 figure

Energy system modelling – interactions and synergies in a highly renewable Pan-European power system

It is very likely that the European power supply system will be transformed in the next decades to a low carbon system based almost entirely on Renewable Energy Sources (RES). However, due to the natural fluctuations of the most powerful RES (wind and solar energy), it is also very likely that a significant amount of balancing and controllable backup power capacities will be required to ensure a stable grid operation. This implies high additional investments and operating costs. Therefore this work provides an overview of potential options and possibly more cost-effective alternatives to the installation of costly storage capacities, namely grid expansion, demand side management, an optimised mix between different RES as well as the use of overcapacities. Furthermore, the paper provides an approximation of the maximum RES penetration of the German electricity system in the absence of significant storage capacities. Our calculations show that from a numerical perspective on average approximately half of the load can be met by RES if flexible conventional power stations would provide the remaining electricity demand. However, in a 100% RES scenario a significant amount of storage capacities as well as limited overcapacities are required to ensure a reliable electricity supply

Stochastische Modellierung komplexer Systeme:Von den theoretischen Grundlagen zur Simulation athmosphärischer Windfelder

Ein erster Schwerpunkt dieser Arbeit liegt auf Methoden zur statistischen Analyse der Dynamik komplexer Systeme. Die Grundlage bildet hierbei ein von Friedrich und Peinke entwickeltes Verfahren zum Schätzen von Drift- und Diffusionsfunktionen aus Messdaten. Im Anschluss daran werden Continuous Time Random Walks (CTRWs) betrachtet, die die Modellierung von nicht-Markov-Prozessen, die im Ensemble anomales Diffusionsverhalten zeigen, ermöglichen. Insbesondere wird ein Algorithmus zur numerischen Simulation stetiger Trajektorien solcher Prozesse eingeführt. Auf der Basis von CTRWs wird schließlich ein Modell für atmosphärische Windfelder, die für eine bessere Charakterisierung von Windkraftanlagen in der atmosphärischen Grenzschicht benötigt werden, entwickelt, das einige intermittente Eigenschaften der atmosphärischen Turbulenz reproduzieren kann. Die Arbeit schließt mit ersten Ergebnissen von Tests dieses Windfeldmodells an aktuellen Windkraftanlagen

On the proper reconstruction of complex dynamical systems spoilt by strong measurement noise

This article reports on a new approach to properly analyze time series of dynamical systems which are spoilt by the simultaneous presence of dynamical noise and measurement noise. It is shown that even strong external measurement noise as well as dynamical noise which is an intrinsic part of the dynamical process can be quantified correctly, solely on the basis of measured times series and proper data analysis. Finally real world data sets are presented pointing out the relevance of the new approach

Isolation of a potassium bis(1,2,3-triazol-5-ylidene) carbazolide: a stabilizing pincer ligand for reactive late transition metal complexes

The synthesis and X-ray crystal structure of a potassium adduct of a monoanionic CNC-pincer ligand featuring two mesoionic carbenes is reported. Owing to the peculiar electronic and steric properties of this ligand, the first neutral stable Ni(II)-hydride, and an unusual Cu(II) complex displaying a seesaw geometry, have been isolated