TY - THES A1 - Tirok, Katrin T1 - Predator-prey dynamics under the influence of exogenous and endogenous regulation : a data-based modeling study on spring plankton with respect to climate change T1 - Räuber-Beute Beziehungen unter dem Einfluss exogener und endogener Regulation : eine datenbasierte Modellstudie zur Planktonentwicklung im Frühjahr mit Bezug auf den Klimawandel N2 - Understanding the interactions of predators and their prey and their responses to environmental changes is one of the striking features of ecological research. In this thesis, spring dynamics of phytoplankton and its consumers, zooplankton, were considered in dependence on the environmental conditions in a deep lake (Lake Constance) and a shallow marine water (mesocosms from Kiel Bight), using descriptive statistics, multiple regression models, and process-oriented dynamic simulation models. The development of the spring phytoplankton bloom, representing a dominant feature in the plankton dynamics in temperate and cold oceans and lakes, may depend on temperature, light, and mixing intensity, and the success of over-wintering phyto- and zooplankton. These factors are often correlated in the field. Unexpectedly, irradiance often dominated algal net growth rather than vertical mixing even in deep Lake Constance. Algal net losses from the euphotic layer to larger depth were induced by vertical mixing, but were compensated by the input from larger depth when algae were uniformly distributed over the water column. Dynamics of small, fast-growing algae were well predicted by abiotic variables, such as surface irradiance, vertical mixing intensity, and temperature. A simulation model additionally revealed that even in late winter, grazing may represent an important loss factor of phytoplankton during calm periods when losses due to mixing are small. The importance of losses by mixing and grazing changed rapidly as it depended on the variable mixing intensity. Higher temperature, lower global irradiance and enhanced mixing generated lower algal biomass and primary production in the dynamic simulation model. This suggests that potential consequences of climate change may partly counteract each other. The negative effect of higher temperatures on phytoplankton biomass was due to enhanced temperature-sensitive grazing losses. Comparing the results from deep Lake Constance to those of the shallow mesocosm experiments and simulations, confirmed the strong direct effect of light in contrast to temperature, and the importance of grazing already in early spring as soon as moderate algal biomasses developed. In Lake Constance, ciliates dominated the herbivorous zooplankton in spring. The start of ciliate net growth in spring was closely linked to that of edible algae, chlorophyll a and the vertical mixing intensity but independent of water temperature. The duration of ciliate dominance in spring was largely controlled by the highly variable onset of the phytoplankton bloom, and little by the less variable termination of the ciliate bloom by grazing of meta-zooplankton. During years with an extended spring bloom of algae and ciliates, they coexisted at relatively high biomasses over 15-30 generations, and internally forced species shifts were observed in both communities. Interception feeders alternated with filter feeders, and cryptomonads with non-cryptomonads in their relative importance. These dynamics were not captured by classical 1-predator-1-prey models which consistently predict pronounced predator-prey cycles or equilibria with either the predator or the prey dominating or suppressed. A multi-species predator-prey model with predator species differing in their food selectivity, and prey species in their edibility reproduced the observed patterns. Food-selectivity and edibility were related to the feeding and growth characteristics of the species, which represented ecological trade-offs. For example, the prey species with the highest edibility also had the highest maximum growth rate. Data and model revealed endogenous driven ongoing species alternations, which yielded a higher variability in species-specific biomasses than in total predator and prey biomass. This holds for a broad parameter space as long as the species differ functionally. A more sophisticated model approach enabled the simulation of a continuum of different functional types and adaptability of predator and prey communities to altered environmental conditions, and the maintenance of a rather low model complexity, i.e., low number of equations and free parameters. The community compositions were described by mean functional traits --- prey edibility and predator food-selectivity --- and their variances. The latter represent the functional diversity of the communities and thus, the potential for adaptation. Oscillations in the mean community trait values indicated species shifts. The community traits were related to growth and grazing characteristics representing similar trade-offs as in the multi-species model. The model reproduced the observed patterns, when nonlinear relationships between edibility and capacity, and edibility and food availability for the predator were chosen. A constant minimum amount of variance represented ongoing species invasions and thus, preserved a diversity which allows adaptation on a realistic time-span. N2 - Eine der großen Herausforderungen der heutigen ökologischen Forschung ist es, Veränderungen von Ökosys­temen vorher­zusagen, die mit dem Klimawandel einhergehen. Dafür sind ein umfassendes Verständnis der ver­schiedenen Steuerungsfaktoren des entsprechenden Systems und Kenntnisse zur Anpassungs­fähigkeit des Systems nötig. Auf der Grundlage dieses Wissens, können mit mathemati­schen Modellen Klima­szenarien gerechnet und Vorhersagen erstellt werden. Die vorliegende Arbeit untersuchte die Regulation des Phytoplanktons (kleine freischwebende einzellige Algen) und seiner Konsumenten (Zooplankton, tierische Kleinstlebewesen) sowie deren Wechselspiel während des Frühjahrs mit Bezug auf den Klimawandel. Als Basis dienten langjährige Daten von einem großen tiefen See (Bodensee) sowie Daten von Versuchen mit Organis­men aus einem flachen marinen Ge­wässer (Kieler Förde, Ostsee). Diese Daten wurden mit statistischen Verfahren und mathematischen Modellen ausge­wertet. In Gewässern sind Algen als Primärproduzenten die Nahrungsgrundlage für tieri­sche Organismen bis hin zu Fischen und Meeresfrüchten, und bestimmen die Wasserqualität der Ge­wässer. Daher ist es wichtig zu verstehen, welche Mechanismen die Dynamik der Algen steuern. Der Grundstein für die saisonale Entwicklung von Phyto- und Zooplankton in Gewässern un­serer Breiten wird mit dem Be­ginn des Wachstums im Frühjahr gelegt. Diese Arbeit zeigt, dass es bereits im zeitigen, noch kalten Frühjahr ein Wechselspiel physikalischer und biologischer Steuerungsmechanismen für die Algenent­wicklung gibt. Physikalische Faktoren sind die Wassertemperatur, die Globalstrahlung und die Durchmischung des Gewässers, die durch die Stärke des Windes beeinflusst wird. All diese Steue­rungsmechanismen sind eng miteinander verwoben und werden unterschiedlich stark vom Klimawan­del beeinflusst. Mit mathematischen Modellen gelang es den Einfluss einzelner Faktoren voneinander zu trennen und zu zeigen, dass Effekte durch den Klimawandel sich gegenseitig aufheben oder aber auch verstärken können. Schon geringe Änderungen an der Basis der Nahrungsnetze können weitrei­chende Auswirkungen auf höhere Ebenen habe. Wie stark diese Auswirkungen im Einzelnen sind, hängt entscheidend von der Anpassungsfähigkeit gesamter Ökosysteme und ihrer Artengemeinschaf­ten sowie einzelner Individuen ab. Beispielsweise reagiert die Algengemeinschaft auf einen starken Fraßdruck ihrer Räuber mit einer Verschiebung zu weniger gut fressbaren Algenarten. Diese weniger gut fressbaren Arten unterscheiden sich jedoch auch in anderen Eigenschaften, wie zum Beispiel der Ressourcenausnutzung, von besser fressbaren Algen. In dieser Arbeit wurden Modellansätze entwi­ckelt, die diese Fähigkeit zur Anpassung berücksichtigen. Auf dieser Grundlage und mit Einbeziehung der physikalischen Steuerungsfaktoren können Klimaszenarien gerechnet werden und Vorhersagen für den Einfluss des Klimawandels auf unsere Gewässer gemacht werden, die letztlich auch Perspektiven für Handlungsmöglichkeiten aufzeigen. KW - Ökologie KW - mathematische Simulationsmodelle KW - Plankton KW - Tiefer See KW - Räuber-Beute Beziehungen KW - ecology KW - mathematical simulation models KW - plankton KW - deep lake KW - predator-prey relationships Y1 - 2008 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-24528 ER - TY - GEN A1 - de Castro, Francisco A1 - Gaedke, Ursula A1 - Boenigk, Jens T1 - Reverse evolution : driving forces behind the loss of acquired photosynthetic traits N2 - Background: The loss of photosynthesis has occurred often in eukaryotic evolution, even more than its acquisition, which occurred at least nine times independently and which generated the evolution of the supergroups Archaeplastida, Rhizaria, Chromalveolata and Excavata. This secondary loss of autotrophic capability is essential to explain the evolution of eukaryotes and the high diversity of protists, which has been severely underestimated until recently. However, the ecological and evolutionary scenarios behind this evolutionary ‘‘step back’’ are still largely unknown. Methodology/Principal Findings: Using a dynamic model of heterotrophic and mixotrophic flagellates and two types of prey, large bacteria and ultramicrobacteria, we examine the influence of DOC concentration, mixotroph’s photosynthetic growth rate, and external limitations of photosynthesis on the coexistence of both types of flagellates. Our key premises are: large bacteria grow faster than small ones at high DOC concentrations, and vice versa; and heterotrophic flagellates are more efficient than the mixotrophs grazing small bacteria (both empirically supported). We show that differential efficiency in bacteria grazing, which strongly depends on cell size, is a key factor to explain the loss of photosynthesis in mixotrophs (which combine photosynthesis and bacterivory) leading to purely heterotrophic lineages. Further, we show in what conditions an heterotroph mutant can coexist, or even out-compete, its mixotrophic ancestor, suggesting that bacterivory and cell size reduction may have been major triggers for the diversification of eukaryotes. Conclusions/Significance: Our results suggest that, provided the mixotroph’s photosynthetic advantage is not too large, the (small) heterotroph will also dominate in nutrient-poor environments and will readily invade a community of mixotrophs and bacteria, due to its higher efficiency exploiting the ultramicrobacteria. As carbon-limited conditions were presumably widespread throughout Earth history, such a scenario may explain the numerous transitions from phototrophy to mixotrophy and further to heterotrophy within virtually all major algal lineages. We challenge prevailing concepts that affiliated the evolution of phagotrophy with eutrophic or strongly light-limited environments only. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 128 KW - Fresh-water habitats KW - Operon copy number KW - Growth-rate KW - Bacteria KW - Plankton Y1 - 2009 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-44968 ER - TY - JOUR A1 - Santana, Lucineide Maria A1 - Weithoff, Guntram A1 - Ferragut, Carla T1 - Seasonal and spatial functional shifts in phytoplankton communities of five tropical reservoirs JF - Aquatic ecology : the international forum covering research in freshwater and marine environments N2 - Trait-based approaches have become increasingly important and valuable in understanding phytoplankton community assembly and composition. These approaches allow for comparisons between water bodies with different species composition. We hypothesize that similar changes in environmental conditions lead to similar responses with regard to functional traits of phytoplankton communities, regardless of trophic state or species composition. We studied the phytoplankton (species composition, community trait mean and diversity) of five reservoirs in Brazil along a trophic gradient from ultra-oligotrophic to meso-eutrophic. Samples at two seasons (summer/rainy and winter/dry) with a horizontal and vertical resolution were taken. Using multivariate analysis, the five reservoirs separated, despite some overlap, according to their environmental variables (mainly total phosphorus, conductivity, pH, chlorophyll a). However, between the seasonal periods, the reservoirs shifted in a similar direction in the multi-dimensional space. The seasonal response of the overall phytoplankton community trait mean differed between the ultra-oligotrophic and the other reservoirs, with three reservoirs exhibiting a very similar community trait mean despite considerable differences in species composition. Within-season differences between different water layers were low. The functional diversity was also unrelated to the trophic state of the reservoirs. Thus, seasonal environmental changes had strong influence on the functional characteristics of the phytoplankton community in reservoirs with distinct trophic condition and species composition. These results demonstrate that an ataxonomic trait-based approach is a relevant tool for comparative studies in phytoplankton ecology. KW - Functional traits KW - Plankton KW - Seasonality KW - Tropical system KW - Diversity indices Y1 - 2017 U6 - https://doi.org/10.1007/s10452-017-9634-3 SN - 1386-2588 SN - 1573-5125 VL - 51 SP - 531 EP - 543 PB - Springer CY - Dordrecht ER -