@article{SteinUnsickerKahmenetal.2010, author = {Stein, Claudia and Unsicker, Sybille B. and Kahmen, Ansgar and Wagner, Markus and Audorff, Volker and Auge, Harald and Prati, Daniel and Weisser, Wolfgang W.}, title = {Impact of invertebrate herbivory in grasslands depends on plant species diversity}, issn = {0012-9658}, doi = {10.1890/09-0600.1}, year = {2010}, abstract = {Invertebrate herbivores are ubiquitous in most terrestrial ecosystems, and theory predicts that their impact on plant community biomass should depend on diversity and productivity of the associated plant communities. To elucidate general patterns in the relationship between invertebrate herbivory, plant diversity, and productivity, we carried out a long-term herbivore exclusion experiment at multiple grassland sites in a mountainous landscape of central Germany. Over a period of five years, we used above-and belowground insecticides as well as a molluscicide to manipulate invertebrate herbivory at 14 grassland sites, covering a wide range of plant species diversity (13-38 species/m(2)) and aboveground plant productivity (272-1125 g.m(-2).yr(-1)), where plant species richness and productivity of the sites were not significantly correlated. Herbivore exclusion had significant effects on the plant communities: it decreased plant species richness and evenness, and it altered plant community composition. In particular, exclusion of belowground herbivores promoted grasses at the expense of herbs. In contrast to our expectation, herbivore effects on plant community biomass were not influenced by productivity. However, effect size of invertebrate herbivores was negatively correlated with plant diversity of the grasslands: the effect of herbivory on biomass tended to be negative at sites of high diversity and positive at sites of low diversity. In general, the effects of aboveground herbivores were relatively small as compared to belowground herbivores, which were important drivers of plant community composition. Our study is the first to show that variation in the effects of invertebrate herbivory on plant communities across a landscape is significantly influenced by plant species richness.}, language = {en} } @misc{WagnerPywellKnoppetal.2011, author = {Wagner, Markus and Pywell, Richard F. and Knopp, Tatjana and Bullock, James M. and Heard, Matthew S.}, title = {The germination niches of grassland species targeted for restoration}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe}, number = {675}, issn = {1866-8372}, doi = {10.25932/publishup-41343}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-413438}, pages = {117 -- 131}, year = {2011}, abstract = {Restoration of semi-natural grassland communities involves a combination of (1) sward disturbance to create a temporal window for establishment, and (2) target species introduction, the latter usually by seed sowing. With great regularity, particular species establish only poorly. More reliable establishment could improve outcome of restoration projects and increase cost-effectiveness. We investigated the abiotic germination niche of ten poorly establishing calcareous grassland species by simultaneously exploring the effects of moisture and light availability and temperature fluctuation on percentage germina- tion and speed of germination. We also investigated the effects of three different pre-treatments used to enhance seed germination - cold-stratification, osmo- tic priming and priming in combination with gibberellic acid (GA 3 ) - and how these affected abiotic germination niches. Species varied markedly in width of abiotic germination niche, ranging from Carex flacca with very strict abiotic requirements, to several species reliably germinating across the whole range of abiotic conditions. Our results suggest pronounced differ- ences between species in gap requirements for establishment. Germination was improved in most species by at least one pre-treatment. Evidence for positive effects of adding GA 3 to seed priming solutions was limited. In several species, pre-treated seeds germinated under a wider range of abiotic conditions than untreated seeds. Improved knowledge of species-specific germination niches and the effects of seed pre-treatments may help to improve species establishment by sowing, and to identify species for which sowing at a later stage of restoration or introduction as small plants may represent a more viable strategy.}, language = {en} } @article{QuinzanGoebelWagneretal.2021, author = {Quinzan, Francesco and G{\"o}bel, Andreas and Wagner, Markus and Friedrich, Tobias}, title = {Evolutionary algorithms and submodular functions}, series = {Natural computing : an innovative journal bridging biosciences and computer sciences ; an international journal}, volume = {20}, journal = {Natural computing : an innovative journal bridging biosciences and computer sciences ; an international journal}, number = {3}, publisher = {Springer Science + Business Media B.V.}, address = {Dordrecht}, issn = {1572-9796}, doi = {10.1007/s11047-021-09841-7}, pages = {561 -- 575}, year = {2021}, abstract = {A core operator of evolutionary algorithms (EAs) is the mutation. Recently, much attention has been devoted to the study of mutation operators with dynamic and non-uniform mutation rates. Following up on this area of work, we propose a new mutation operator and analyze its performance on the (1 + 1) Evolutionary Algorithm (EA). Our analyses show that this mutation operator competes with pre-existing ones, when used by the (1 + 1) EA on classes of problems for which results on the other mutation operators are available. We show that the (1 + 1) EA using our mutation operator finds a (1/3)-approximation ratio on any non-negative submodular function in polynomial time. We also consider the problem of maximizing a symmetric submodular function under a single matroid constraint and show that the (1 + 1) EA using our operator finds a (1/3)-approximation within polynomial time. This performance matches that of combinatorial local search algorithms specifically designed to solve these problems and outperforms them with constant probability. Finally, we evaluate the performance of the (1 + 1) EA using our operator experimentally by considering two applications: (a) the maximum directed cut problem on real-world graphs of different origins, with up to 6.6 million vertices and 56 million edges and (b) the symmetric mutual information problem using a four month period air pollution data set. In comparison with uniform mutation and a recently proposed dynamic scheme, our operator comes out on top on these instances.}, language = {en} } @article{SteigertKojdaIbacetaJanaetal.2022, author = {Steigert, Alexander and Kojda, Sandrino Danny and Ibaceta-Ja{\~n}a, Josefa Fernanda and Abou-Ras, Daniel and Gunder, Ren{\´e} and Alktash, Nivin and Habicht, Klaus and Wagner, Markus Raphael and Klenk, Reiner and Raoux, Simone and Szyszka, Bernd and Lauermann, Iver and Muydinov, Ruslan}, title = {Water-assisted crystallization of amorphous indium zinc oxide films}, series = {Materials today. Communications}, volume = {31}, journal = {Materials today. Communications}, publisher = {Elsevier}, address = {Amsterdam}, issn = {2352-4928}, doi = {10.1016/j.mtcomm.2022.103213}, pages = {10}, year = {2022}, abstract = {Transparent conductive materials based on indium oxide remain yet irreplaceable in various optoelectronic applications. Amorphous oxides appear especially attractive for technology as they are isotropic, demonstrate relatively high electron mobility and can be processed at low temperatures. Among them is indium zinc oxide (IZO) with a large zinc content that is crucial for keeping the amorphous state but redundant for the doping. In this work we investigated water-free and water containing IZO films obtained by radio frequency sputtering. The correlation between temperature driven changes of the chemical state, the optical and electrical properties as well as the progression of crystallization was in focus. Such characterization methods as: scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, temperature dependent Hall-effect measurements and others were applied. Temperature dependent electrical properties of amorphous IZO and IZO:H2O films were found to evolve similarly. Based on our experience in In2O3:H2O (In2O3:H or IOH) we proposed an explanation for the changes observed. Water admixture was found to decrease crystallization temperature of IZO significantly from similar to 550 degrees C to similar to 280 degrees C. Herewith, the presence and concentration of water and/or hydroxyls was found to determine Zn distribution in the film. In particular, Zn enrichment was detected at the film's surface respective to the high water and/or hydroxyl amount. Raman spectra revealed a two-dimensional crystallization of w-ZnO which precedes regardless water presence an extensive In2O3 crystallization. An abrupt loss of electron mobility as a result of crystallization was attributed to the formation of ZnO interlayer on grain boundaries.}, language = {en} }