@phdthesis{Bergholz2018,
  author    = {Bergholz, Kolja},
  title     = {Trait-based understanding of plant species distributions along environmental gradients},
  doi       = {10.25932/publishup-42634},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-426341},
  school      = {Universit{\"a}t Potsdam},
  pages     = {128},
  year      = {2018},
  abstract  = {For more than two centuries, plant ecologists have aimed to understand how environmental gradients and biotic interactions shape the distribution and co-occurrence of plant species. In recent years, functional trait-based approaches have been increasingly used to predict patterns of species co-occurrence and species distributions along environmental gradients (trait-environment relationships). Functional traits are measurable properties at the individual level that correlate well with important processes. Thus, they allow us to identify general patterns by synthesizing studies across specific taxonomic compositions, thereby fostering our understanding of the underlying processes of species assembly. However, the importance of specific processes have been shown to be highly dependent on the spatial scale under consideration. In particular, it remains uncertain which mechanisms drive species assembly and allow for plant species coexistence at smaller, more local spatial scales. Furthermore, there is still no consensus on how particular environmental gradients affect the trait composition of plant communities. For example, increasing drought because of climate change is predicted to be a main threat to plant diversity, although it remains unclear which traits of species respond to increasing aridity. Similarly, there is conflicting evidence of how soil fertilization affects the traits related to establishment ability (e.g., seed mass). In this cumulative dissertation, I present three empirical trait-based studies that investigate specific research questions in order to improve our understanding of species distributions along environmental gradients. In the first case study, I analyze how annual species assemble at the local scale and how environmental heterogeneity affects different facets of biodiversity—i.e. taxonomic, functional, and phylogenetic diversity—at different spatial scales. The study was conducted in a semi-arid environment at the transition zone between desert and Mediterranean ecosystems that features a sharp precipitation gradient (Israel). Different null model analyses revealed strong support for environmentally driven species assembly at the local scale, since species with similar traits tended to co-occur and shared high abundances within microsites (trait convergence). A phylogenetic approach, which assumes that closely related species are functionally more similar to each other than distantly related ones, partly supported these results. However, I observed that species abundances within microsites were, surprisingly, more evenly distributed across the phylogenetic tree than expected (phylogenetic overdispersion). Furthermore, I showed that environmental heterogeneity has a positive effect on diversity, which was higher on functional than on taxonomic diversity and increased with spatial scale. The results of this case study indicate that environmental heterogeneity may act as a stabilizing factor to maintain species diversity at local scales, since it influenced species distribution according to their traits and positively influenced diversity. All results were constant along the precipitation gradient. In the second case study (same study system as case study one), I explore the trait responses of two Mediterranean annuals (Geropogon hybridus and Crupina crupinastrum) along a precipitation gradient that is comparable to the maximum changes in precipitation predicted to occur by the end of this century (i.e., -30\%). The heterocarpic G. hybridus showed strong trends in seed traits, suggesting that dispersal ability increased with aridity. By contrast, the homocarpic C. crupinastrum showed only a decrease in plant height as aridity increased, while leaf traits of both species showed no consistent pattern along the precipitation gradient. Furthermore, variance decomposition of traits revealed that most of the trait variation observed in the study system was actually found within populations. I conclude that trait responses towards aridity are highly species-specific and that the amount of precipitation is not the most striking environmental factor at this particular scale. In the third case study, I assess how soil fertilization mediates—directly by increased nutrient addition and indirectly by increased competition—the effect of seed mass on establishment ability. For this experiment, I used 22 species differing in seed mass from dry grasslands in northeastern Germany and analyzed the interacting effects of seed mass with nutrient availability and competition on four key components of seedling establishment: seedling emergence, time of seedling emergence, seedling survival, and seedling growth. (Time of) seedling emergence was not affected by seed mass. However, I observed that the positive effect of seed mass on seedling survival is lowered under conditions of high nutrient availability, whereas the positive effect of seed mass on seedling growth was only reduced by competition. Based on these findings, I developed a conceptual model of how seed mass should change along a soil fertility gradient in order to reconcile conflicting findings from the literature. In this model, seed mass shows a U-shaped pattern along the soil fertility gradient as a result of changing nutrient availability and competition. Overall, the three case studies highlight the role of environmental factors on species distribution and co-occurrence. Moreover, the findings of this thesis indicate that spatial heterogeneity at local scales may act as a stabilizing factor that allows species with different traits to coexist. In the concluding discussion, I critically debate intraspecific trait variability in plant community ecology, the use of phylogenetic relationships and easily measured key functional traits as a proxy for species' niches. Finally, I offer my outlook for the future of functional plant community research.},
  language  = {en}
}
@phdthesis{Czempas2013,
  author    = {Czempas, Alexander},
  title     = {Die B{\"u}ndelung von Payments for Environmental Services als M{\"o}glichkeit eines effizienten Schutzes von Biodiversit{\"a}t},
  publisher = {Universit{\"a}tsverlag Potsdam},
  address   = {Potsdam},
  isbn      = {978-3-86956-238-4},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-64572},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XV, 358},
  year      = {2013},
  abstract  = {In dieser Dissertation erfolgt eine Analyse des Schutzes von Biodiversit{\"a}t durch Payments for Environmental Services (PES) und, insbesondere im empirischen Teil, innerhalb des Ansatzes Reducing Emissions from Deforestation and Forest Degradation plus (REDDplus). Die Anwendung von PES-Programmen zum Schutz von Biodiversit{\"a}t gewinnt im umweltpolitischen Bereich immer mehr an Bedeutung. Gleichzeitig ist die Umsetzung solcher Schutzprogramme jedoch mit erheblichen Transaktionskosten und damit der Gefahr von Ineffizienzen verbunden. Die M{\"o}glichkeit der B{\"u}ndelung von Biodiversit{\"a}t mit einer weiteren {\"O}kosystemleistung, hier der Speicherung von Kohlenstoffdioxid, wird hinsichtlich der Wirkungen auf die Schutzniveaus beider {\"O}kosystemleistungen und der Ver{\"a}nderung der Produktionsweise des landwirtschaftlichen Sektors in einem monopsonistischen Modelansatz analysiert. Durch die formale Analyse zeigt sich, dass f{\"u}r einen effizienteren Schutz der beiden {\"O}kosystemleistungen economies of scope bei den Transaktionskosten mit der B{\"u}ndelung von PES-Programmen realisiert werden m{\"u}ssen. Ein Beispiel f{\"u}r die praktische Umsetzung von Payments for Environmental Services ist der REDDplus-Ansatz. Das Ziel ist die Reduzierung von Treibhausgasemissionen durch den Erhalt und die nachhaltige Bewirtschaftung von tropischen W{\"a}ldern, aber auch der Schutz von Biodiversit{\"a}t. Innerhalb des empirischen Teiles der Dissertation wird untersucht, inwiefern es durch die Verfolgung beider Ziele zur Realisierung von economies of scope bei den Transaktionskosten kommt. In die Analyse werden sechs L{\"a}nder (Costa-Rica, Indonesien, Mexiko, Kambodscha, Peru und Vietnam) einbezogen. Die Analyse erfolgt auf der Grundlage von Szenarien, welche mit Hilfe der Readiness Proposals der L{\"a}nder f{\"u}r den Zeitraum von 2008 bis 2030 erstellt wurden. Anhand der Ergebnisse kann gezeigt werden, dass es nicht automatisch durch die Zusammenlegung von PES-Programmen zu einer Realisierung von economies of scope kommt. Eine B{\"u}ndelung solcher Programme ist daher nicht in allen Phasen ihrer Umsetzung ratsam.},
  language  = {de}
}
@phdthesis{Guill2022,
  author    = {Guill, Christian},
  title     = {Structure, stability and functioning of food webs},
  doi       = {10.25932/publishup-56115},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-561153},
  school      = {Universit{\"a}t Potsdam},
  pages     = {250},
  year      = {2022},
  abstract  = {In this thesis, a collection of studies is presented that advance research on complex food webs in several directions. Food webs, as the networks of predator-prey interactions in ecosystems, are responsible for distributing the resources every organism needs to stay alive. They are thus central to our understanding of the mechanisms that support biodiversity, which in the face of increasing severity of anthropogenic global change and accelerated species loss is of highest importance, not least for our own well-being. The studies in the first part of the thesis are concerned with general mechanisms that determine the structure and stability of food webs. It is shown how the allometric scaling of metabolic rates with the species' body masses supports their persistence in size-structured food webs (where predators are larger than their prey), and how this interacts with the adaptive adjustment of foraging efforts by consumer species to create stable food webs with a large number of coexisting species. The importance of the master trait body mass for structuring communities is further exemplified by demonstrating that the specific way the body masses of species engaging in empirically documented predator-prey interactions affect the predator's feeding rate dampens population oscillations, thereby helping both species to survive. In the first part of the thesis it is also shown that in order to understand certain phenomena of population dynamics, it may be necessary to not only take the interactions of a focal species with other species into account, but to also consider the internal structure of the population. This can refer for example to different abundances of age cohorts or developmental stages, or the way individuals of different age or stage interact with other species. Building on these general insights, the second part of the thesis is devoted to exploring the consequences of anthropogenic global change on the persistence of species. It is first shown that warming decreases diversity in size-structured food webs. This is due to starvation of large predators on higher trophic levels, which suffer from a mismatch between their respiration and ingestion rates when temperature increases. In host-parasitoid networks, which are not size-structured, warming does not have these negative effects, but eutrophication destabilises the systems by inducing detrimental population oscillations. In further studies, the effect of habitat change is addressed. On the level of individual patches, increasing isolation of habitat patches has a similar effect as warming, as it leads to decreasing diversity due to the extinction of predators on higher trophic levels. In this case it is caused by dispersal mortality of smaller and therefore less mobile species on lower trophic levels, meaning that an increasing fraction of their biomass production is lost to the inhospitable matrix surrounding the habitat patches as they become more isolated. It is further shown that increasing habitat isolation desynchronises population oscillations between the patches, which in itself helps species to persist by dampening fluctuations on the landscape level. However, this is counteracted by an increasing strength of local population oscillations fuelled by an indirect effect of dispersal mortality on the feeding interactions. Last, a study is presented that introduces a novel mechanism for supporting diversity in metacommunities. It builds on the self-organised formation of spatial biomass patterns in the landscape, which leads to the emergence of spatio-temporally varying selection pressures that keep local communities permanently out of equilibrium and force them to continuously adapt. Because this mechanism relies on the spatial extension of the metacommunity, it is also sensitive to habitat change. In the third part of the thesis, the consequences of biodiversity for the functioning of ecosystems are explored. The studies focus on standing stock biomass, biomass production, and trophic transfer efficiency as ecosystem functions. It is first shown that increasing the diversity of animal communities increases the total rate of intra-guild predation. However, the total biomass stock of the animal communities increases nevertheless, which also increases their exploitative pressure on the underlying plant communities. Despite this, the plant communities can maintain their standing stock biomass due to a shift of the body size spectra of both animal and plant communities towards larger species with a lower specific respiration rate. In another study it is further demonstrated that the generally positive relationship between diversity and the above mentioned ecosystem functions becomes steeper when not only the feeding interactions but also the numerous non-trophic interactions (like predator interference or competition for space) between the species of an ecosystem are taken into account. Finally, two studies are presented that demonstrate the power of functional diversity as explanatory variable. It is interpreted as the range spanned by functional traits of the species that determine their interactions. This approach allows to mechanistically understand how the ecosystem functioning of food webs with multiple trophic levels is affected by all parts of the food web and why a high functional diversity is required for efficient transportation of energy from primary producers to the top predators. The general discussion draws some synthesising conclusions, e.g. on the predictive power of ecosystem functioning to explain diversity, and provides an outlook on future research directions.},
  language  = {en}
}
@phdthesis{Kettner2018,
  author    = {Kettner, Marie Therese},
  title     = {Microbial colonization of microplastic particles in aquatic systems},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-418854},
  school      = {Universit{\"a}t Potsdam},
  pages     = {139},
  year      = {2018},
  abstract  = {The continuously increasing pollution of aquatic environments with microplastics (plastic particles < 5 mm) is a global problem with potential implications for organisms of all trophic levels. For microorganisms, trillions of these floating microplastics particles represent a huge surface area for colonization. Due to the very low biodegradability, microplastics remain years to centuries in the environment and can be transported over thousands of kilometers together with the attached organisms. Since also pathogenic, invasive, or otherwise harmful species could be spread this way, it is essential to study microplastics-associated communities. For this doctoral thesis, eukaryotic communities were analyzed for the first time on microplastics in brackish environments and compared to communities in the surrounding water and on the natural substrate wood. With Illumina MiSeq high-throughput sequencing, more than 500 different eukaryotic taxa were detected on the microplastics samples. Among them were various green algae, dinoflagellates, ciliates, fungi, fungal-like protists and small metazoans such as nematodes and rotifers. The most abundant organisms was a dinoflagellate of the genus Pfiesteria, which could include fish pathogenic and bloom forming toxigenic species. Network analyses revealed that there were numerous interaction possibilities among prokaryotes and eukaryotes in microplastics biofilms. Eukaryotic community compositions on microplastics differed significantly from those on wood and in water, and compositions were additionally distinct among the sampling locations. Furthermore, the biodiversity was clearly lower on microplastics in comparison to the diversity on wood or in the surrounding water. In another experiment, a situation was simulated in which treated wastewater containing microplastics was introduced into a freshwater lake. With increasing microplastics concentrations, the resulting bacterial communities became more similar to those from the treated wastewater. Moreover, the abundance of integrase I increased together with rising concentrations of microplastics. Integrase I is often used as a marker for anthropogenic environmental pollution and is further linked to genes conferring, e.g., antibiotic resistance. This dissertation gives detailed insights into the complexity of prokaryotic and eukaryotic communities on microplastics in brackish and freshwater systems. Even though microplastics provide novel microhabitats for various microbes, they might also transport toxigenic, pathogenic, antibiotic-resistant or parasitic organisms; meaning their colonization can pose potential threats to humans and the environment. Finally, this thesis explains the urgent need for more research as well as for strategies to minimize the global microplastic pollution.},
  language  = {en}
}
@phdthesis{Kolk2019,
  author    = {Kolk, Jens},
  title     = {The long-term legacy of historical land cover changes},
  doi       = {10.25932/publishup-43939},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-439398},
  school      = {Universit{\"a}t Potsdam},
  pages     = {196},
  year      = {2019},
  abstract  = {Over the last years there is an increasing awareness that historical land cover changes and associated land use legacies may be important drivers for present-day species richness and biodiversity due to time-delayed extinctions or colonizations in response to historical environmental changes. Historically altered habitat patches may therefore exhibit an extinction debt or colonization credit and can be expected to lose or gain species in the future. However, extinction debts and colonization credits are difficult to detect and their actual magnitudes or payments have rarely been quantified because species richness patterns and dynamics are also shaped by recent environmental conditions and recent environmental changes. In this thesis we aimed to determine patterns of herb-layer species richness and recent species richness dynamics of forest herb layer plants and link those patterns and dynamics to historical land cover changes and associated land use legacies. The study was conducted in the Prignitz, NE-Germany, where the forest distribution remained stable for the last ca. 100 years but where a) the deciduous forest area had declined by more than 90 per cent (leaving only remnants of "ancient forests"), b) small new forests had been established on former agricultural land ("post-agricultural forests"). Here, we analyzed the relative importance of land use history and associated historical land cover changes for herb layer species richness compared to recent environmental factors and determined magnitudes of extinction debt and colonization credit and their payment in ancient and post-agricultural forests, respectively. We showed that present-day species richness patterns were still shaped by historical land cover changes that ranged back to more than a century. Although recent environmental conditions were largely comparable we found significantly more forest specialists, species with short-distance dispersal capabilities and clonals in ancient forests than in post-agricultural forests. Those species richness differences were largely contingent to a colonization credit in post-agricultural forests that ranged up to 9 species (average 4.7), while the extinction debt in ancient forests had almost completely been paid. Environmental legacies from historical agricultural land use played a minor role for species richness differences. Instead, patch connectivity was most important. Species richness in ancient forests was still dependent on historical connectivity, indicating a last glimpse of an extinction debt, and the colonization credit was highest in isolated post-agricultural forests. In post-agricultural forests that were better connected or directly adjacent to ancient forest patches the colonization credit was way smaller and we were able to verify a gradual payment of the colonization credit from 2.7 species to 1.5 species over the last six decades.},
  language  = {en}
}
@article{KusberJahn2021,
  author    = {Kusber, Wolf-Henning and Jahn, Regine},
  title     = {Christian Gottfried Ehrenbergs Zeichnungen: Eine fr{\"u}he wissenschaftliche Dokumentation mikroskopischer Organismen},
  series = {HiN : Alexander von Humboldt im Netz = Christian Gottfried Ehrenberg},
  volume    = {XXII},
  journal   = {HiN : Alexander von Humboldt im Netz = Christian Gottfried Ehrenberg},
  number    = {42},
  publisher = {Universit{\"a}tsverlag Potsdam},
  address   = {Potsdam},
  issn      = {1617-5239},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-515040},
  pages     = {105 -- 117},
  year      = {2021},
  abstract  = {Die Erforschung und Beschreibung mikroskopischer Organismen durch Christian Gottfried Ehrenberg ist durch seine publizierten Texte und Kupfertafeln in den „Infusionsthierchen", der „Mikrogeologie" sowie aus Abhandlungen der Akademie der Wissenschaften {\"u}berliefert. Zentrale Bedeutung haben seine Zeichenbl{\"a}tter, anfangs alleinige Dokumentation, sp{\"a}ter komplementiert durch tausende mikroskopischer Dauerpr{\"a}parate rezenter und fossiler Kieselschalen sowie getrockneter Einzeller. Alle Originalmaterialien Ehrenbergs stehen f{\"u}r die aktuelle Forschung in der Ehrenbergsammlung zur Verf{\"u}gung. Seine detailgenauen Zeichnungen dienten der Erstbeschreibung einer Vielzahl neuer Arten aus allen Weltteilen. Biogeografische und {\"o}kologische Fragestellungen, Beschreibungen von Lebenszyklen sowie außerordentliche Ph{\"a}nomene wie die F{\"a}rbung von Gew{\"a}ssern und Erden wurden mithilfe zeichnerischer Analysen bearbeitet.},
  language  = {de}
}
@misc{MarkschiesPaesslerGroteetal.2021,
  author    = {Markschies, Christoph and P{\"a}ßler, Ulrich and Grote, Mathias and Greenwood MacKinney, Anne and Kusber, Wolf-Henning and Jahn, Regine and Damaschun, Ferdinand and B{\"o}hme, Katrin},
  title     = {HiN : Alexander von Humboldt im Netz = Christian Gottfried Ehrenberg},
  volume    = {XXII},
  number    = {42},
  editor    = {Ette, Ottmar and Knobloch, Eberhard and P{\"a}ßler, Ulrich},
  publisher = {Universit{\"a}tsverlag Potsdam},
  address   = {Potsdam},
  issn      = {2568-3543},
  doi       = {10.25932/publishup-50141},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-501413},
  pages     = {169},
  year      = {2021},
  abstract  = {-Christoph Markschies: Geleitwort -Ulrich P{\"a}ßler: Christian Gottfried Ehrenberg: Lebensbilder eines Naturforschers -Mathias Grote: „Aus dem Kleinen bauen sich die Welten" - Christian Gottfried Ehrenbergs {\"o}kologische Mikrobiologie avant la lettre -Anne Greenwood MacKinney: Die Inszenierung naturforschender Gelehrsamkeit beim Sammeln: Christian Gottfried Ehrenbergs und Wilhelm Hemprichs nordafrikanische Forschungsreise (1820 - 1825) -Ulrich P{\"a}ßler: Reisen im Nahen Osten. Zeichnungen -Ulrich P{\"a}ßler: Christian Gottfried Ehrenberg und die Biogeographie: Die russisch-sibirische Reise mit Alexander von Humboldt (1829) -Ulrich P{\"a}ßler: Russisch-Sibirische Reise. Zeichnungen -Wolf-Henning Kusber, Regine Jahn: Christian Gottfried Ehrenbergs Zeichnungen: Eine fr{\"u}he wissenschaftliche Dokumentation mikroskopischer Organismen -Ferdinand Damaschun: Christian Gottfried Ehrenberg und die Entwicklung der Mikroskop-Technik im 19. Jahrhundert -Ulrich P{\"a}ßler: Die Reise ins Kleinste der Natur. Zeichnungen -Katrin B{\"o}hme: Das große Ganze: Christian Gottfried Ehrenberg und die Gesellschaft Naturforschender Freunde zu Berlin},
  language  = {de}
}
@phdthesis{MendesFerreira2023,
  author    = {Mendes Ferreira, Clara},
  title     = {Indirect, tri-trophic effects of fear on biodiversity},
  doi       = {10.25932/publishup-61102},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-611020},
  school      = {Universit{\"a}t Potsdam},
  pages     = {119},
  year      = {2023},
  abstract  = {Predator-forager interactions are a major factor in evolutionary adaptation of many species, as predators need to gain energy by consuming prey species, and foragers needs to avoid the worst fate of mortality while still consuming resources for energetic gains. In this evolutionary arms race, the foragers have constantly evolved anti-predator behaviours (e.g. foraging activity changes). To describe all these complex changes, researchers developed the framework of the landscape of fear, that is, the spatio-temporal variation of perceived predation risk. This concept simplifies all the involved ecological processes into one framework, by integrating animal biology and distribution with habitat characteristics. Researchers can then evaluate the perception of predation risk in prey species, what are the behavioural responses of the prey and, therefore, understand the cascading effects of landscapes of fear at the resource levels (tri-trophic effects). Although tri-trophic effects are well studied at the predator-prey interaction level, little is known on how the forager-resource interactions are part of the overall cascading effects of landscapes of fear, despite the changes of forager feeding behaviour - that occur with perceived predation risk - affecting directly the level of the resources. This thesis aimed to evaluate the cascading effects of the landscape of fear on biodiversity of resources, and how the feeding behaviour and movement of foragers shaped the final resource species composition (potential coexistence mechanisms). We studied the changes caused by landscapes of fear on wild and captive rodent communities and evaluated: the cascading effects of different landscapes of fear on a tri-trophic system (I), the effects of fear on a forager's movement patterns and dietary preferences (II) and cascading effects of different types of predation risk (terrestrial versus avian, III). In Chapter I, we applied a novel measure to evaluate the cascading effects of fear at the level of resources, by quantifying the diversity of resources left after the foragers gave-up on foraging (diversity at the giving-up density). We tested the measure at different spatial levels (local and regional) and observed that with decreased perceived predation risk, the density and biodiversity of resources also decreased. Foragers left a very dissimilar community of resources based on perceived risk and resources functional traits, and therefore acted as an equalising mechanism. In Chapter II, we wanted to understand further the decision-making processes of rodents in different landscapes of fear, namely, in which resource species rodents decided to forage on (based on three functional traits: size, nutrients and shape) and how they moved depending on perceived predation risk. In safe landscapes, individuals increased their feeding activity and movements and despite the increased costs, they visited more often patches that were further away from their central-place. Despite a preference for the bigger resources regardless of risk, when perceived predation risk was low, individuals changed their preference to fat-rich resources. In Chapter III, we evaluated the cascading effects of two different types of predation risk in rodents: terrestrial (raccoon) versus avian predation risk. Raccoon presence or absence did not alter the rodents feeding behaviour in different landscapes of fear. Rodent's showed risk avoidance behaviours towards avian predators (spatial risk avoidance), but not towards raccoons (lack of temporal risk avoidance). By analysing the effects of fear in tri-trophic systems, we were able to deepen the knowledge of how non-consumptive effects of predators affect the behaviour of foragers, and quantitatively measure the cascading effects at the level of resources with a novel measure. Foragers are at the core of the ecological processes and responses to the landscape of fear, acting as variable coexistence agents for resource species depending on perceived predation risk. This newly found measures and knowledge can be applied to more trophic chains, and inform researchers on biodiversity patterns originating from landscapes of fear.},
  language  = {en}
}
@phdthesis{Raatz2019,
  author    = {Raatz, Michael},
  title     = {Strategies within predator-prey interactions - from individuals to ecosystems},
  doi       = {10.25932/publishup-42658},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-426587},
  school      = {Universit{\"a}t Potsdam},
  pages     = {175},
  year      = {2019},
  abstract  = {Predator-prey interactions provide central links in food webs. These interaction are directly or indirectly impacted by a number of factors. These factors range from physiological characteristics of individual organisms, over specifics of their interaction to impacts of the environment. They may generate the potential for the application of different strategies by predators and prey. Within this thesis, I modelled predator-prey interactions and investigated a broad range of different factors driving the application of certain strategies, that affect the individuals or their populations. In doing so, I focused on phytoplankton-zooplankton systems as established model systems of predator-prey interactions. At the level of predator physiology I proposed, and partly confirmed, adaptations to fluctuating availability of co-limiting nutrients as beneficial strategies. These may allow to store ingested nutrients or to regulate the effort put into nutrient assimilation. We found that these two strategies are beneficial at different fluctuation frequencies of the nutrients, but may positively interact at intermediate frequencies. The corresponding experiments supported our model results. We found that the temporal structure of nutrient fluctuations indeed has strong effects on the juvenile somatic growth rate of {\itshape Daphnia}. Predator colimitation by energy and essential biochemical nutrients gave rise to another physiological strategy. High-quality prey species may render themselves indispensable in a scenario of predator-mediated coexistence by being the only source of essential biochemical nutrients, such as cholesterol. Thereby, the high-quality prey may even compensate for a lacking defense and ensure its persistence in competition with other more defended prey species. We found a similar effect in a model where algae and bacteria compete for nutrients. Now, being the only source of a compound that is required by the competitor (bacteria) prevented the competitive exclusion of the algae. In this case, the essential compounds were the organic carbon provided by the algae. Here again, being indispensable served as a prey strategy that ensured its coexistence. The latter scenario also gave rise to the application of the two metabolic strategies of autotrophy and heterotrophy by algae and bacteria, respectively. We found that their coexistence allowed the recycling of resources in a microbial loop that would otherwise be lost. Instead, these resources were made available to higher trophic levels, increasing the trophic transfer efficiency in food webs. The predation process comprises the next higher level of factors shaping the predator-prey interaction, besides these factors that originated from the functioning or composition of individuals. Here, I focused on defensive mechanisms and investigated multiple scenarios of static or adaptive combinations of prey defense and predator offense. I confirmed and extended earlier reports on the coexistence-promoting effects of partially lower palatability of the prey community. When bacteria and algae are coexisting, a higher palatability of bacteria may increase the average predator biomass, with the side effect of making the population dynamics more regular. This may facilitate experimental investigations and interpretations. If defense and offense are adaptive, this allows organisms to maximize their growth rate. Besides this fitness-enhancing effect, I found that co-adaptation may provide the predator-prey system with the flexibility to buffer external perturbations. On top of these rather internal factors, environmental drivers also affect predator-prey interactions. I showed that environmental nutrient fluctuations may create a spatio-temporal resource heterogeneity that selects for different predator strategies. I hypothesized that this might favour either storage or acclimation specialists, depending on the frequency of the environmental fluctuations. We found that many of these factors promote the coexistence of different strategies and may therefore support and sustain biodiversity. Thus, they might be relevant for the maintenance of crucial ecosystem functions that also affect us humans. Besides this, the richness of factors that impact predator-prey interactions might explain why so many species, especially in the planktonic regime, are able to coexist.},
  language  = {en}
}
@phdthesis{Riedl2021,
  author    = {Riedl, Simon},
  title     = {Active tectonics in the Kenya Rift},
  doi       = {10.25932/publishup-53855},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-538552},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xi, 207},
  year      = {2021},
  abstract  = {Magmatische und tektonisch aktive Grabenzonen (Rifts) stellen die Vorstufen entstehender Plattengrenzen dar. Diese sich spreizenden tektonischen Provinzen zeichnen sich durch allgegenw{\"a}rtige Abschiebungen aus, und die r{\"a}umliche Verteilung, die Geometrie, und das Alter dieser Abschiebungen l{\"a}sst R{\"u}ckschl{\"u}sse auf die r{\"a}umlichen und zeitlichen Zusammenh{\"a}nge zwischen tektonischer Deformation, Magmatismus und langwelliger Krustendeformation in Rifts zu. Diese Arbeit konzentriert sich auf die St{\"o}rungsaktivit{\"a}t im Kenia-Rift des k{\"a}nozoischen Ostafrikanischen Grabensystems im Zeitraum zwischen dem mittleren Pleistoz{\"a}n und dem Holoz{\"a}n. Um die fr{\"u}hen Stadien der Entstehung kontinentaler Plattengrenzen zu untersuchen, wird in dieser Arbeit eine zeitlich gemittelte minimale Extensionsrate f{\"u}r den inneren Graben des N{\"o}rdlichen Kenia-Rifts (NKR) f{\"u}r die letzten 0,5 Mio Jahre abgeleitet. Die Analyse beruht auf Messungen mit Hilfe des digitalen TanDEM-X-H{\"o}henmodells, um die Abschiebungen entlang der vulkanisch-tektonischen Achse des inneren Grabens des NKR zu kartieren und deren Versatzbetr{\"a}ge zu bestimmen. Mithilfe von vorhandenen Geochronologiedaten der deformierten vulkanischen Einheiten sowie in dieser Arbeit erstellten ⁴⁰Ar/³⁹Ar-Datierungen werden zeitlich gemittelte Extensionsraten berechnet. Die Auswertungen zeigen, dass im inneren Graben des NKR die langfristige Extensionsrate f{\"u}r mittelpleistoz{\"a}ne bis rezente St{\"o}rungen Mindestwerte von 1,0 bis 1,6 mm yr⁻¹ aufweist und lokal allerdings auch Werte bis zu 2,0 mm yr⁻¹ existieren. In Anbetracht der nahezu inaktiven Randst{\"o}rungen des NKR zeigt sich somit, dass sich die Extension auf die Region der aktiven vulkanisch-tektonischen Achse im inneren Graben konzentriert und somit ein fortgeschrittenes Stadium kontinentaler Extensionsprozesse im NKR vorliegt. In dieser Arbeit wird diese r{\"a}umlich fokussierte Extension zudem im Rahmen einer St{\"o}rungsanalyse der j{\"u}ngsten vulkanischen Erscheinungen des Kenia-Rifts betrachtet. Die Arbeit analysiert mithilfe von Gel{\"a}ndekartierungen und eines auf Luftbildern basierenden Gel{\"a}ndemodells die St{\"o}rungscharakteristika der etwa 36 tausend Jahre alten Menengai-Kaldera und der umliegenden Gebiete im zentralen Kenia-Rift. Im Allgemeinen sind die holoz{\"a}nen St{\"o}rungen innerhalb des Rifts reine, NNO-streichende Abschiebungen, die somit das gegenw{\"a}rtige tektonische Spannungsfeld wiederspiegeln; innerhalb der Menengai-Kaldera sind die jungen Strukturen jedoch von andauernder magmatischer Aktivit{\"a}t und von Aufdomung {\"u}berpr{\"a}gt. Die Kaldera befindet sich im Zentrum eines sich aktiv dehnenden Riftsegments und zusammen mit den anderen quart{\"a}ren Vulkanen des Kenia-Rifts lassen sich diese Bereiche als Kernpunkte der extensionalen St{\"o}rungsaktivit{\"a}t verstehen, die letztlich zu einer weiter entwickelten Phase magmengest{\"u}tzter Kontinentalseparation f{\"u}hren werden. Die bereits seit dem Terti{\"a}r andauernde St{\"o}rungsaktivit{\"a}t im Kenia-Rift f{\"u}hrt zur Zergliederung der gr{\"o}ßeren Rift-Senken in kleinere Segmente und beeinflusst die Sedimentologie und die Hydrologie dieser Riftbecken. Gegenw{\"a}rtig sind die meisten, durch St{\"o}rungen begrenzten Becken des Kenia-Rifts hydrologisch isoliert, sie waren aber w{\"a}hrend feuchter Klimaphasen hydrologisch miteinander verbunden; in dieser Arbeit untersuche ich deshalb auch diese hydrologische Verbindung der Rift-Becken f{\"u}r die Zeit der Afrikanischen Feuchteperiode des fr{\"u}hen Holoz{\"a}ns. Mithilfe der Analyse von digitalen Gel{\"a}ndemodellen, unter Ber{\"u}cksichtigung von geomorphologischen Anzeigern f{\"u}r Seespiegelhochst{\"a}nde, Radiokarbondatierungen und einer {\"U}bersicht {\"u}ber Fossiliendaten konnten zwei kaskadierende Flusssysteme aus diesen Daten abgeleitet werden: eine Flusskaskade in Richtung S{\"u}den und eine in Richtung Norden. Beide Kaskaden haben die derzeit isolierten Becken w{\"a}hrend des fr{\"u}hen Holoz{\"a}ns durch {\"u}berlaufende Seen und eingeschnittene Schluchten miteinander verbunden. Diese hydrologische Verbindung f{\"u}hrte zu der Ausbreitung aquatischer Fauna entlang des Rifts, und gleichzeitig stellte die Wasserscheide zwischen den beiden Flusssystemen den einzigen terrestrischen Ausbreitungskorridor dar, der eine {\"U}berquerung des Kenia-Rifts erm{\"o}glichte. Diese tektonisch-geomorphologische Rekonstruktion erkl{\"a}rt die heute isolierten Vorkommen nilotischer Fischarten in den Riftseen Kenias sowie die isolierten Vorkommen Guineo-Congolischer S{\"a}ugetiere in W{\"a}ldern {\"o}stlich des Kenia-Rifts, die sich {\"u}ber die Wasserscheide im Kenia-Rift ausbreiten konnten. Auf l{\"a}ngeren Zeitskalen sind solche Phasen hydrologischer Verbindung und Phasen der Isolation wiederholt aufgetreten und zeigen sich in wechselnden pal{\"a}o{\"o}kologischen Indikatoren in Sedimentbohrkernen. Hier stelle ich einen Sedimentbohrkern aus dem Koora-Becken des S{\"u}dlichen Kenia-Rifts vor, der einen Datensatz der Pal{\"a}o-Umweltbedingungen der letzten 1 Million Jahre beinhaltet. Dieser Datensatz zeigt, dass etwa vor 400 tausend Jahren die zuvor relativ stabilen Umweltbedingungen zum Erliegen kamen und tektonische, hydrologische und {\"o}kologische Ver{\"a}nderungen dazu f{\"u}hrten, dass die Wasserverf{\"u}gbarkeit, die Grasland-Vergesellschaftungen und die Bedeckung durch Baumvegetation zunehmend st{\"a}rkeren und h{\"a}ufigeren Schwankungen unterlagen. Diese großen Ver{\"a}nderungen fallen zeitlich mit Phasen zusammen, in denen das s{\"u}dliche Becken des Kenia-Rifts von vulkanischer und tektonischer Aktivit{\"a}t besonders betroffen war. Die vorliegende Arbeit zeigt deshalb deutlich, inwiefern die tektonischen und geomorphologischen Gegebenheiten im Zuge einer zeitlich langanhaltenden Extension die Hydrologie, die Pal{\"a}o-Umweltbedingungen sowie die Biodiversit{\"a}t einer Riftzone beeinflussen k{\"o}nnen.},
  language  = {en}
}