TY - JOUR A1 - Moustakas, Aristides A1 - Günther, Matthias A1 - Wiegand, Kerstin A1 - Müller, Karl-Heinz A1 - Ward, David A1 - Meyer, Katrin M. A1 - Jeltsch, Florian T1 - Long-term mortality patterns of the deep-rooted Acacia erioloba BT - The middle class shall die! JF - Journal of vegetation science N2 - Question: Is there a relationship between size and death in the Iona-lived, deep-rooted tree, Acacia erioloba, in a semi-arid savanna? What is the size-class distribution of A. erioloba mortality? Does the mortality distribution differ from total tree size distribution? Does A. erioloba mortality distribution match the mortality distributions recorded thus far in other environments? Location: Dronfield Ranch, near Kimberley, Kalahari, South Africa. Methods: A combination of aerial photographs and a satellite image covering 61 year was used to provide long-term spatial data on mortality. We used aerial photographs of the study area from 1940, 1964, 1984, 1993 and a satellite image from 2001 to follow three plots covering 510 ha. We were able to identify and individually follow ca. 3000 individual trees from 1940 till 2001. Results: The total number of trees increased over time. No relationship between total number of trees and mean tree size was detected. There were no trends over time in total number of deaths per plot or in size distributions of dead trees. Kolmogorov-Smirnov tests showed no differences in size class distributions for living trees through time. The size distribution of dead trees was significantly different from the size distribution of all trees present on the plots. Overall, the number of dead trees was low in small size classes, reached a peak value when canopy area was 20 - 30 m(2), and declined in lamer size-classes. Mortality as a ratio of dead vs. total trees peaked at intermediate canopy sizes too. Conclusion: A. erioloba mortality was size-dependent, peaking at intermediate sizes. The mortality distribution differs from all other tree mortality distributions recorded thus far. We suggest that a possible mechanism for this unusual mortality distribution is intraspecific competition for water in this semi-arid environment. KW - competition KW - long-term data KW - remote sensing KW - savanna KW - size dependent mortality KW - size distribution KW - tree death Y1 - 2006 U6 - https://doi.org/10.1111/j.1654-1103.2006.tb02468.x SN - 1100-9233 VL - 17 SP - 473 EP - 480 PB - Blackwell CY - Malden ER - TY - JOUR A1 - Reichard, Christoph T1 - Strengthening competitiveness of local public service providers in Germany JF - International review of administrative sciences : an international journal of comparative public administration N2 - This article discusses the challenges for providers of local public services to adapt to increasing marketization and competition in the public sector. Based on some empirical evidence from local government in Germany, the article describes different adaptive measures in the past and shows the legal restrictions to strengthening performance and particularly competitiveness. Furthermore, the article presents some findings from good practice cases of local service providers in Germany who have successfully exposed themselves to market mechanisms. Finally, the article discusses observed results of increased competitiveness in the local government sector, with special regard to quality, efficiency and public employment. The article concludes with describing necessary elements of a competitive regime for public services and with some general reflections about the role of competition in the public sector. KW - competition KW - competitiveness KW - contractor/provider split KW - ensuring state KW - marketization KW - service provider strategies Y1 - 2006 U6 - https://doi.org/10.1177/0020852306070079 SN - 0020-8523 VL - 72 IS - 4 SP - 473 EP - 492 PB - Sage CY - London ER - TY - THES A1 - Geißler, Katja T1 - Lebensstrategien seltener Stromtalpflanzen : autökologische Untersuchung von Cnidium dubium, Gratiola officinalis und Juncus atratus unter besonderer Berücksichtigung ihrer Stressresistenz T1 - Life strategies of rare river corridor plants : autecological investigation of Cnidium dubium, Gratiola officinalis and Juncus atratus with special consideration of their stress resistance N2 - Die vorliegende Dissertation behandelt die Ökologie von Cnidium dubium (Schkuhr) Thell. (Sumpf-Brenndolde), Gratiola officinalis L. (Gottes-Gnadenkraut) und Juncus atratus Krocker (Schwarze Binse), drei gefährdeten Arten, die als sogenannte Stromtalpflanzen in Mitteleuropa in ihrem Vorkommen eng an die Flussauen gebunden sind. Die Arbeit basiert auf verschiedenen Simulationsexperimenten und Feldstudien in der Unteren Havelniederung, einem „Feuchtgebiet von internationaler Bedeutung“. Sie behandelt Themenkomplexe wie das Samenbankverhalten, die Samenkeimung, die Stickstofflimitierung, die Konkurrenzkraft, das Verhalten der Pflanzen nach einer Sommertrockenheit und nach einer Winter/Frühjahrsüberflutung. Ferner widmet sie sich der Populationsbiologie der Arten und dem Verhalten der Pflanzen nach besonderen Störungsereignissen wie Mahd, Herbivorie und der Sommerflut 2002. Der Leser erfährt, wie die Pflanzen in verschiedenen Lebensphasen auf die auentypische Umwelt reagieren und erhält umfassende Einblicke in physiologische Mechanismen, die der Anpassung an die typischen Bedingungen einer mitteleuropäischen Flussaue dienen. Eine Interpretation der Ergebnisse zeigt auf, welche der spezifischen Eigenschaften zur Gefährdung der drei Stromtalarten beitragen. Die Arbeit ist für den Arten-, Biotop- und Landschaftsschutz interessant. Darüber hinaus bietet sie zahlreiche Anknüpfungspunkte zur ökophysiologischen Grundlagenforschung. Die verstärkte Nutzung physiologischer Methoden bei der Klärung ökologischer Fragestellungen wird angeregt. N2 - The thesis deals with the ecology of three endangered European river corridor angiosperms Cnidium dubium (Schkuhr) Thell., Gratiola officinalis L. und Juncus atratus Krocker. The study is based on different experimental approaches and field surveys in a wetland along the Lower Havel River, a designated German Ramsar-site (Wetland of International Importance). This involves the examination of aspects of seed bank dynamics, germination, nitrogen limitation, competitive ability, and the response of plants to summer drought and/or winter/spring flooding. The thesis continues with a detailed study of the population biology of the species at natural sites and the response of these plants to specific disturbances like mowing, herbivory and the severe summer flooding in 2002. The reader learns about the traits of the three plant species to tolerate the typical conditions their natural sites are exposed to in different phases of their life cycle. He gets a comprehensive look at physiological means by which plants can adapt to the prevailing conditions of European river lowlands. The interpretation of the results is used to reveal specific plant traits, which may contribute to the endangerment of the three river corridor plants. As such, this thesis is interesting for protection of species, biotopes and landscapes. Furthermore, it provides numerous close connections to fundamental research from an ecophysiological perspective. The increased use of physiological methods is recommended in order to be able to adequately resolve ecological problems. KW - untere Havelniederung KW - seltene Pflanzen KW - Stoffwechsel KW - Wachstum KW - Samen KW - Hypoxie KW - Trockenstress KW - Konkurrenz KW - Mahd KW - lower Havel river wetland KW - rare plants KW - metabolism KW - growth KW - seeds KW - hypoxia KW - drought stress KW - competition KW - mowing Y1 - 2008 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17468 ER - TY - JOUR A1 - Rocha, Marcia R. A1 - Gaedke, Ursula A1 - Vasseur, David A. T1 - Functionally similar species have similar dynamics JF - The journal of ecology N2 - 1. Improving the mechanistic basis of biodiversity-ecosystem function relationships requires a better understanding of how functional traits drive the dynamics of populations. For example, environmental disturbances or grazing may increase synchronization of functionally similar species, whereas functionally different species may show independent dynamics, because of different responses to the environment. Competition for resources, on the other hand, may yield a wide range of dynamic patterns among competitors and lead functionally similar and different species to display synchronized to compensatory dynamics. The mixed effect of these forces will influence the temporal fluctuations of populations and, thus, the variability of aggregate community properties. 2. To search for a relationship between functional and dynamics similarity, we studied the relationship between functional trait similarity and temporal dynamics similarity for 36 morphotypes of phytoplankton using long-term high-frequency measurements. 3. Our results show that functionally similar morphotypes exhibit dynamics that are more synchronized than those of functionally dissimilar ones. Functionally dissimilar morphotypes predominantly display independent temporal dynamics. This pattern is especially strong when short time-scales are considered. 4. Negative correlations are present among both functionally similar and dissimilar phytoplankton morphotypes, but are rarer and weaker than positive ones over all temporal scales. 5. Synthesis. We demonstrate that diversity in functional traits decreases community variability and ecosystem-level properties by decoupling the dynamics of individual morphotypes. KW - compensatory dynamics KW - competition KW - environmental forcing KW - functional diversity KW - functional traits KW - grazing KW - phytoplankton KW - plant population and community dynamics KW - synchrony KW - temporal dynamics Y1 - 2011 U6 - https://doi.org/10.1111/j.1365-2745.2011.01893.x SN - 0022-0477 VL - 99 IS - 6 SP - 1453 EP - 1459 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Lin, Yue A1 - Berger, Uta A1 - Grimm, Volker A1 - Ji, Qian-Ru T1 - Differences between symmetric and asymmetric facilitation matter - exploring the interplay between modes of positive and negative plant interactions JF - The journal of ecology N2 - Facilitation (positive interaction) has received increasing attention in plant ecology over the last decade. Just as for competition, distinguishing different modes of facilitation (mutualistic, commensal or even antagonistic) may be crucial. We therefore introduce the new concept of symmetric versus asymmetric facilitation and present a generic individual-based zone-of-influence model. The model simultaneously implements different modes of both facilitation and competition among individual plants via their overlapping zone of influence. Because we consider facilitation modes as a continuum related to environmental context, we integrated this concept with the stress-gradient hypothesis (SGH) by exploring differences in spatial pattern formation in self-thinning plants along a stress gradient in our model. The interplay among modes of interaction creates distinctly varied spatial patterns along stress gradients. When competition was symmetric, symmetric facilitation (mutualism) consistently led to plant aggregation along stress gradients. However, asymmetric facilitation (commensalism) produces plant aggregation only under more benign conditions but tends to intensify local competition and spatial segregation when conditions are harsh. When competition was completely asymmetric, different modes of facilitation contributed little to spatial aggregation. Symmetric facilitation significantly increased survival at the severe end of the stress gradient, which supports the claim of the SGH that facilitation should have generally positive net effects on plants under high stress levels. Asymmetric facilitation, however, was found to increase survival only under intermediate stress conditions, which contradicts the current predictions of the SGH. Synthesis. Our modelling study demonstrates that the interplay between modes of facilitation and competition affects different aspects of plant populations and communities, implying context-dependent outcomes and consequences. The explicit consideration of the modes and mechanisms of interactions (both facilitation and competition) and the nature of stress factors will help to extend the framework of the SGH and foster research on facilitation in plant ecology. KW - asymmetry KW - competition KW - metabolic scaling theory KW - plant population and community dynamics KW - plant-plant interaction KW - self-thinning KW - spatial pattern KW - stress-gradient hypothesis KW - symmetry Y1 - 2012 U6 - https://doi.org/10.1111/j.1365-2745.2012.02019.x SN - 0022-0477 VL - 100 IS - 6 SP - 1482 EP - 1491 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Metz, Johannes A1 - von Oppen, Jonathan A1 - Tielbörger, Katja T1 - Parental environmental effects due to contrasting watering adapt competitive ability, but not drought tolerance, in offspring of a semi-arid annual Brassicaceae JF - The journal of ecology N2 - Parental effects (PE) can be adaptive and improve offspring performance when parents and offspring experience similar environmental conditions. However, it is unknown whether adaptive PE exist also in habitats where such similarity is unlikely due to strong temporal variation. In particular, we do not know whether PE can adapt offspring to fluctuating levels of neighbour competition in such habitats. Here, we tested for adaptive PE in terms of two key environmental factors in a semi-arid annual system, competition and drought. While rainfall was stochastic in the study site, the competitive environment was partly predictable: higher plant densities followed after favourable (rainy) years due to high seed production. We therefore expected PE to adapt the offspring's competitive ability to these (predictable) fluctuations in plant densities, rather than to adapt the offspring's drought tolerance to the (unpredictable) occurrence of intensified drought. Parental plants of Biscutella didyma, an annual Brassicaceae, were raised under favourable watering and under drought conditions. Offspring performance was then tested under a full-factorial combination of two neighbour regimes and six watering levels in the glasshouse. Offspring of parents grown under favourable conditions were stronger competitors. This was associated with a small shift in phenology but not with higher parental seed provisioning. Offspring from parents grown under drought showed no improved drought tolerance. Moreover, no PE were detectable when offspring were grown without neighbours. Our results suggest a novel path of adaptive PE: higher competitive ability was induced in offspring that were more likely to experience high neighbour densities. Together with the lack of adaptive PE towards drought tolerance, this emphasizes that a correlation between parental and offspring environment is crucial for adaptive PE to evolve. Our results also call for the inclusion of competitive effects in future PE studies.Synthesis. This study demonstrates the important role of adaptive PE for plant fitness (regarding competition) but also their limits (regarding drought) in temporally variable environments, based on the predictability of the respective environmental factor. KW - annual plants KW - Biscutella didyma KW - competition KW - dryland ecosystems KW - maternal environmental effects KW - phenology KW - plant population and community dynamics KW - plant-plant interactions KW - transgenerational plasticity KW - water stress Y1 - 2015 U6 - https://doi.org/10.1111/1365-2745.12411 SN - 0022-0477 SN - 1365-2745 VL - 103 IS - 4 SP - 990 EP - 997 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Wacker, Alexander A1 - Marzetz, Vanessa A1 - Spijkerman, Elly T1 - Interspecific competition in phytoplankton drives the availability of essential mineral and biochemical nutrients JF - Ecology : a publication of the Ecological Society of America N2 - The underlying mechanisms and consequences of competition and diversity are central themes in ecology. A higher diversity of primary producers often results in higher resource use efficiency in aquatic and terrestrial ecosystems. This may result in more food for consumers on one hand, while, on the other hand, it can also result in a decreased food quality for consumers; higher biomass combined with the same availability of the limiting compound directly reduces the dietary proportion of the limiting compound. Here we tested whether and how interspecific competition in phytoplankton communities leads to changes in resource use efficiency and cellular concentrations of nutrients and fatty acids. The measured particulate carbon : phosphorus ratios (C:P) and fatty acid concentrations in the communities were compared to the theoretically expected ratios and concentrations of measurements on simultaneously running monocultures. With interspecific competition, phytoplankton communities had higher concentrations of the monounsaturated fatty acid oleic acid and also much higher concentrations of the ecologically and physiologically relevant long-chain polyunsaturated fatty acid eicosapentaenoic acid than expected concentrations based on monocultures. Such higher availability of essential fatty acids may contribute to the positive relationship between phytoplankton diversity and zooplankton growth, and may compensate limitations by mineral nutrients in higher trophic levels. KW - biodiversity KW - C:P ratio KW - competition KW - eicosapentaenoic acid KW - elemental composition KW - EPA KW - food quality KW - minerals KW - phosphorus KW - polyunsaturated fatty acids KW - PUFA KW - resource use efficiency Y1 - 2015 U6 - https://doi.org/10.1890/14-1915.1 SN - 0012-9658 SN - 1939-9170 VL - 96 IS - 9 SP - 2467 EP - 2477 PB - Wiley CY - Washington ER - TY - THES A1 - Ansel, Simon T1 - Die Diffusion von Innovationen in deutschen Kommunen T1 - Diffusion of e-government at the local level BT - eine Untersuchung zu Komponenten des E-Governement BT - empirical evidence from German municipalities N2 - Die fortschreitende Diffusion von E-Government ist ein Phänomen, dem in der internationa-len Forschungsliteratur bereits viel Aufmerksamkeit zu Teil wurde. Erstaunlich wenige Studien widmen sich bislang jedoch dezidiert dem Faktor Interdependenz, der eigentlichen Ursache von Diffusionsprozessen. In dieser Arbeit werden Interdependenzbeziehungen anhand dreier spezifischer Mechanismen der Diffusion, namentlich „Nachahmung“, „Wettbewerb“ und „Lernen“, untersucht. Auf Basis einer empirischen Analyse mit Daten zur Einführung von E-Government-Komponenten in 183 deutschen Städten über den Zeitraum von 1995 bis 2014 konnte ein Einfluss der Mechanismen „Nachahmung“ und „Lernen“ auf das Innovationsverhalten von Kommunen festgestellt werden. Für das Vorliegen von Wettbe-werbsdynamiken ließen sich demgegenüber keine Anhaltspunkte finden. Für zukünftige Forschungen zur Diffusion von Innovationen wird angeregt, verstärkt an die mechanismen- und prozessbasierte Perspektive von Diffusion als theoretischem Rahmenkonzept anzuknüpfen. N2 - The ongoing diffusion of e-government is a phenomenon that has already attracted consid-erable attention in the international research literature. However, few studies have so far focused on the factor of interdependence, the root cause of diffusion processes. This paper deals with interdependence by specifying three causal mechanisms of diffusion, namely "imitation", "competition" and "learning". Drawing upon data collected on the introduction of e-government in 183 German cities over the period from 1995-2014, the empirical analysis identified "imitation" and "learning" as predictors of municipal innovative behavior. Furthermore, no evidence was found supporting the role of “competition”. With regard to future research on innovation diffusion, it is suggested to incorporate the mechanism- and process-based perspective of diffusion as a theoretical framework. T3 - Schriftenreihe für Public und Nonprofit Management - 20 KW - Diffusion KW - E-Government KW - eGovernment KW - öffentlicher Sektor KW - Kommune KW - kommunal KW - diffusion KW - e-government KW - electronic government KW - public sector KW - local KW - municipal KW - Nachahmung KW - Wettbewerb KW - Lernen KW - imitation KW - competition KW - learning Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-80370 SN - 2190-4561 ER - TY - JOUR A1 - Metz, Johannes A1 - Tielboerger, Katja T1 - Spatial and temporal aridity gradients provide poor proxies for plant-plant interactions under climate change: a large-scale experiment JF - Functional ecology : an official journal of the British Ecological Society N2 - 1. Plant-plant interactions may critically modify the impact of climate change on plant communities. However, the magnitude and even direction of potential future interactions remains highly debated, especially for water-limited ecosystems. Predictions range from increasing facilitation to increasing competition with future aridification. 2. The different methodologies used for assessing plant-plant interactions under changing environmental conditions may affect the outcome but they are not equally represented in the literature. Mechanistic experimental manipulations are rare compared with correlative approaches that infer future patterns from current observations along spatial climatic gradients. 3. Here, we utilize a unique climatic gradient in combination with a large-scale, long-term experiment to test whether predictions about plant-plant interactions yield similar results when using experimental manipulations, spatial gradients or temporal variation. We assessed shrub-annual interactions in three different sites along a natural rainfall gradient (spatial) during 9 years of varying rainfall (temporal) and 8 years of dry and wet manipulations of ambient rainfall (experimental) that closely mimicked regional climate scenarios. 4. The results were fundamentally different among all three approaches. Experimental water manipulations hardly altered shrub effects on annual plant communities for the assessed fitness parameters biomass and survival. Along the spatial gradient, shrub effects shifted from clearly negative to mildly facilitative towards drier sites, whereas temporal variation showed the opposite trend: more negative shrub effects in drier years. 5. Based on our experimental approach, we conclude that shrub-annual interaction will remain similar under climate change. In contrast, the commonly applied space-for-time approach based on spatial gradients would have suggested increasing facilitative effects with climate change. We discuss potential mechanisms governing the differences among the three approaches. 6. Our study highlights the critical importance of long-term experimental manipulations for evaluating climate change impacts. Correlative approaches, for example along spatial or temporal gradients, may be misleading and overestimate the response of plant-plant interactions to climate change. KW - annual plant communities KW - climate manipulation KW - competition KW - facilitation KW - Mediterranean shrubland KW - nurse plant KW - rainfall gradient KW - Sarcopoterium spinosum KW - semi-arid KW - stress-gradient hypothesis Y1 - 2016 U6 - https://doi.org/10.1111/1365-2435.12599 SN - 0269-8463 SN - 1365-2435 VL - 30 SP - 20 EP - 29 PB - Wiley-Blackwell CY - Hoboken ER - TY - GEN A1 - Makowicz, Amber M. A1 - Tiedemann, Ralph A1 - Steele, Rachel N. A1 - Schlupp, Ingo T1 - Kin recognition in a clonal fish, Poecilia formosa T2 - PLoS ONE N2 - Relatedness strongly influences social behaviors in a wide variety of species. For most species, the highest typical degree of relatedness is between full siblings with 50% shared genes. However, this is poorly understood in species with unusually high relatedness between individuals: clonal organisms. Although there has been some investigation into clonal invertebrates and yeast, nothing is known about kin selection in clonal vertebrates. We show that a clonal fish, the Amazon molly (Poecilia formosa), can distinguish between different clonal lineages, associating with genetically identical, sister clones, and use multiple sensory modalities. Also, they scale their aggressive behaviors according to the relatedness to other females: they are more aggressive to non-related clones. Our results demonstrate that even in species with very small genetic differences between individuals, kin recognition can be adaptive. Their discriminatory abilities and regulation of costly behaviors provides a powerful example of natural selection in species with limited genetic diversity. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 431 KW - toxic hydrogen-sulfide KW - sexual selection KW - hybrid origin KW - discrimination KW - behavior KW - competition KW - aggression KW - cues KW - consequences KW - avoidance Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-411329 ER -