Heterotrophic bacteria utilize dissolved organic matter, and the carbon flow through an ecosystem depends on the fractions of the utilized carbon that is either respired or transferred to higher trophic levels. The major aim this thesis is to investigate 1) the relationship between composition and functioning in heterotrophic bacterioplankton communities and 2) the influence of environmental conditions on both parameters. I set up several batch culture experiments, where lake water filtrates containing bacteria but no grazers were inoculated into sterile freshwater medium to investigate the importance of the origin of the source community (the inoculum) versus the environmental conditions (the medium) for the composition and functional performance of bacterial communities. In some experiments the medium was manipulated to simulate changes in salinity, pH and dissolved organic matter quantity and quality. Functional parameters (biomass yield, respiration, growth efficiency and enzyme activities) and the genetic composition of the emerging bacterial communities were determined. When bacterial inocula obtained from different habitats were re-grown under identical conditions, differently composed communities emerged. This indicates that the history and distribution of taxa within the inoculum was an important regulating factor of community composition. The coupling between community composition and functioning was not very tight, and there was functional equivalency with respect to aggregated functions important at the ecosystem scale (e.g., biomass production and respiration). The functional performance of bacterial communities could to a large extent be predicted from the medium alone, except when it deviated strongly from the ambient settings. When bacterial communities were exposed to dilution, a strong change in pH or an increase in salinity, growth of structurally and functionally distinct communities occurred. I therefore suggest that it depends on the disturbance regime how bacterial community structure and function are related to each other.

The objective of this study was to characterize the wild bee fauna of a managed mixed-grass prairie in southwestern Manitoba. Weekly sampling using two methods, sweep-netting and bee bowls, was conducted over two years (2005-2006) at three sites within the Yellow Quill Mixed-grass Prairie Preserve. Spatial and seasonal patterns in diversity indices, taxonomic composition and ecological composition of the bee fauna were identified and investigated in relation to sampling method, environmental conditions, and floral resource availability. A total of 7014 individual bees representing five families and 100 species were collected. Numerically, social nesters from the genera Lasioglossum and Bombus dominated, while mining species of Andrena represented the greatest species richness. Observed spatial and seasonal patterns in the abundance, diversity and composition of the bee community were strongly modified by sampling method, resource limitation in the second year and the presence of the exotic invasive plant leafy spurge (Euphorbia esula). / October 2007

Title from first page of PDF document. Includes bibliographical references (p. 22-27).

The objective of this study was to characterize the wild bee fauna of a managed mixed-grass prairie in southwestern Manitoba. Weekly sampling using two methods, sweep-netting and bee bowls, was conducted over two years (2005-2006) at three sites within the Yellow Quill Mixed-grass Prairie Preserve. Spatial and seasonal patterns in diversity indices, taxonomic composition and ecological composition of the bee fauna were identified and investigated in relation to sampling method, environmental conditions, and floral resource availability. A total of 7014 individual bees representing five families and 100 species were collected. Numerically, social nesters from the genera Lasioglossum and Bombus dominated, while mining species of Andrena represented the greatest species richness. Observed spatial and seasonal patterns in the abundance, diversity and composition of the bee community were strongly modified by sampling method, resource limitation in the second year and the presence of the exotic invasive plant leafy spurge (Euphorbia esula).

Mikrobielle Gemeinschaften werden direkt und indirekt von einem komplexen System verschiedenster Interaktionen zwischen biotischen und abiotischen Faktoren beeinflusst. So zum Beispiel von verschiedenen Pflanzenarten und ihren jeweiligen Eigenschaften, dem Nährstoffgehalt des Bodens, sowie dem pH-Wert. Im Gegenzug gestalten Mikroorganismen als wichtige Treiber der C- und N-Kreisläufe ihre Umwelt. Im Rahmen der vorliegenden Arbeit wurden mehrere Studien unter kontrollierten Feld- und Laborbedingungen, sowie unter natürlichen Bedingungen im Freiland durchgeführt, um verschiedene Einflussfaktoren zu bestimmen und den Grad ihres Einflusses zu ermitteln. Die Zusammensetzung der prokaryotischen Gemeinschaften in den verschiedenen Bodenproben wurden mit Hilfe phylogenetischer Marker, der 16S-rRNA Gene und der 16S-rRNA, analysiert. Die erhaltenen Amplikon-basierten Daten wurden dann prozessiert und die Indices für Artenvielfalt und Artenreichtum berechnet. Zusätzlich wurden Betadiversitätsanalysen durchgeführt, um Unterschiede in der Zusammensetzung der bakteriellen Gemeinschaft zwischen den verschiedenen Behandlungen sichtbar zu machen. Des Weiteren wurden die erhaltenen DGGE Profile für Clusteranalysen verwendet, um Ähnlichkeiten oder Unterschiede in der Struktur der Bakteriengemeinschaft zwischen den verschiedenen Behandlungen aufzuzeigen. Die vorliegende Arbeit gibt einen Einblick über den Einfluss der Baumarten, Baumartendiversität, des Laubes und des Probennahmezeitpunktes auf die Zusammensetzung und Diversität von Bakteriengemeinschaften in Böden. Die erhaltenen Daten zeigten, dass die Laubschicht der Haupteinflussfaktor auf die Zusammensetzung der bakteriellen Gemeinschaft in der Rhizosphäre von jungen Buchen und Eschen ist. Des Weiteren zeigte sich, das verschiedene Baumarten, deren Diversität, sowie saisonale Unterschiede nur einen geringen Einfluss auf die Struktur der bakteriellen Gemeinschaft haben. Zusätzlich konnte gezeigt werden, dass die mikrobielle Gemeinschaftsstruktur nicht signifikant von Buchen- und Eschensetzlingen beeinflusst wird, vermutlich aufgrund des frühen Entwicklungsstadiums der verwendeten Baumsetzlinge. Weiterhin konnte gezeigt werden, dass die Buchensetzlinge das Wachstum von Bakterien inhibierten, während das Pilzwachstum gefördert wurde. Dies wurde vermutlich hervorgerufen durch eine Verschiebung des pH-Wertes im Boden verursacht durch buchenspezifische Wurzelausscheidungen. Morphologisch unterschiedliche Baumarten beeinflussen die Struktur und Diversität mikrobieller Gemeinschaften auf verschiedenen Wegen. Die Analyse der Bakterien- und Pilzgemeinschaften in natürlichen Waldböden unter erwachsenen Buchen und Fichten zeigte einen signifikanten Einfluss der untersuchten Baumarten auf deren Zusammensetzung. Es konnte ein Einfluss des pH-Werts auf die Bakterien- und Pilzvielfalt unter den analysierten Fichtenbeständen gezeigt werden. Des Weiteren wurden die Auswirkungen hoher NO3- Depositionen auf die CH4 und N2O Gasflüsse und die aktiven Bakterien- und Archeengemeinschaften in gemäßigten Laubwaldböden mit Hilfe von Mesokosmen untersucht. Es konnte ein starker Effekt der NO3- Düngung auf die CH4 Aufnahmeraten und N2O Emissionen des gedüngten Laubwaldbodens gezeigt werden. Die N-Düngung hemmte die CH4 Aufnahme des Bodens, während die N2O Emission stieg. Die Bakteriengemeinschaft in den gedüngten Mikrokosmen verschob sich im Verlauf des Versuches in Richtung einer denitrifizierenden Gemeinschaft, dominiert durch die Gattung Rhodanobacter. Darüber hinaus konnte eine Reduzierung der bakteriellen Vielfalt und der CO2 Emission innerhalb der N-gedüngten Mikrokosmen gezeigt werden. Des Weiteren sanken die CO2 Emissionsraten in beiden Behandlungen im Verlauf des Experiments. Dies deutet auf eine reduzierte Aktivität der vorhandenen Bodenmikroorganismen hin, möglicherweise hervorgerufen durch eine C Limitierung des verwendeten Waldbodens. Obwohl eine Verschiebung in der relativen Häufigkeit der auftretenden nitrifizierenden Archeen der Gattung Nitrosotalea nachgewiesen wurde, konnte eine signifikante Veränderung in der Zusammensetzung der gesamten Archeengemeinschaft nicht beobachtet werden. Die Ergebnisse zeigten jedoch einen erheblichen Beitrag methylotropher, methanotropher und nitrifizierender Bakterien, welche in geringer Zahl auftraten, in Bezug auf die gemessene CH4 Aufnahme. Des Weiteren wurden die Auswirkungen der Anwesenheit von Ameisen und ihrer Aktivitäten auf die Aktivität und Vielfalt der mikrobiellen Gemeinschaften im Boden und Ameisennest untersucht. Ameisen transportierten den von Läusen gewonnenen Honigtau in den Boden und verursachten damit eine Abnahme der mikrobiellen Biomasse in der Streuschicht, während die δ15N-Signatur, die basale Atmung und die mikrobielle Biomasse im Boden erhöht wurden. Im Gegensatz dazu konnten mittels Cluster-Analyse der erstellten DGGE Profile keine deutlichen Unterschiede der mikrobiellen Gemeinschaftsstruktur in den untersuchten Mikrokosmen gezeigt werden. Im Gegensatz dazu beeinflusste die Nestbauaktivität und der Eintrag von organischen Substanzen in den Boden durch die Ameisen jedoch die Struktur der Bakteriengemeinschaften im Freiland. Die Cluster-Analyse der erhaltenen DGGE Profile zeigte Unterschiede in der Zusammensetzung der bakteriellen Gemeinschaft in Abhängigkeit vom Probenentnahmeort und der Ameisenaktivität. Außerdem konnte gezeigt werden, dass sich die Struktur der Bakteriengemeinschaft in den Ameisennestern von der im Umgebungsboden unterschied. Ein sekundäres Projekt dieser Arbeit war die Erfassung und der Vergleich der mikrobiellen Gemeinschaften in biologischen Bodenkrusten zweier unterschiedlicher Standorte in extrazonalen, trockenen Bergsteppen der nördlichen Mongolei. Die Studie zeigte deutliche Unterschiede in der mikrobiellen Gemeinschaftsstruktur der beiden Standorte, welche sich im Grad der Störung unterschieden.

The objective of this study was to characterize the wild bee fauna of a managed mixed-grass prairie in southwestern Manitoba. Weekly sampling using two methods, sweep-netting and bee bowls, was conducted over two years (2005-2006) at three sites within the Yellow Quill Mixed-grass Prairie Preserve. Spatial and seasonal patterns in diversity indices, taxonomic composition and ecological composition of the bee fauna were identified and investigated in relation to sampling method, environmental conditions, and floral resource availability. A total of 7014 individual bees representing five families and 100 species were collected. Numerically, social nesters from the genera Lasioglossum and Bombus dominated, while mining species of Andrena represented the greatest species richness. Observed spatial and seasonal patterns in the abundance, diversity and composition of the bee community were strongly modified by sampling method, resource limitation in the second year and the presence of the exotic invasive plant leafy spurge (Euphorbia esula).

Species diversity may simultaneously be a cause and a consequence of variability in population, community and ecosystem properties. Ecology has traditionally focused on elucidating the causes of biodiversity. However, in the last decade and a half ecologists have asked the opposite question: What are the consequences of species diversity? The majority of these studies elucidated the effects of species diversity within single trophic levels. Incorporating trophic complexity is the next step in this research program. In this dissertation I investigated the causes of resource species diversity, as well as the impacts that resource diversity has on rates of consumption and the stability of population, community and ecosystem properties over time in planktonic food webs. The high diversity of phytoplankton found in nature appears to defy the competitive exclusion principle, and elucidating the mechanisms which maintain this diversity continues to be a challenge. In general, variability in limiting factors is required to maintain non-neutral species diversity, but this variability can be generated by forces outside of the competitive community (i.e. exogenous), or may be the outcome of competitive interactions themselves (i.e. endogenous). Using microcosm experiments, I showed that endogenously generated variability in limiting factors was more effective at maintaining phytoplankton species diversity over the long-term, although the strength of this effect depended on the composition of the phytoplankton community. Existing resource diversity has been proposed to generally weaken consumer-resource interaction strengths and limit consumer control of resource biomass. This is because more diverse resource communities are more likely to contain inedible, unpalatable, toxic or non-nutritious species. However, when resource communities contain multiple palatable species, diversity may also accelerate consumption. Using grazing experiments with multiple zooplankton consumer species, I found that the mechanism, direction and magnitude of modulation of consumption depended on the feeding selectivity of the consumer and the composition of the resource community. By altering consumer-resource interaction strengths in the short-term, resource species diversity may impact the stability of consumer-resource dynamics in the long-term. In separate microcosm experiments, I investigated the influence of resource species diversity, community composition and consumer feeding selectivity on population, community, and ecosystem properties over time. Diversity had positive effects on phytoplankton population biomass, resource community biomass, the rate of photosynthesis, the standing stock of particulate nutrients, and the generalist consumer’s population density. It also stabilized resource community biomass and the stocks of particulate nutrients over time. Unexpectedly, diversity did not stabilize either of the consumer populations, regardless of feeding selectivity. This suggests that effects of diversity on resource community properties do not impact consumer dynamics linearly. Resource community composition was generally more important than resource species diversity in determining food web properties. The importance of community composition in determining both the causes and consequences of resource diversity in these experiments points to the importance of species’ traits and the outcomes of their interactions. I suggest that the use of complex adaptive systems theory and trait-based approaches in the future will allow a consideration of the feedbacks between the causes and consequences of species diversity in food webs. / Graduate

Abstract Plant community composition and diversity are determined by the balance between rates of immigration and extinction. Processes of immigration to a local community, i.e. propagule availability and dispersal of propagules between and within habitats, set the upper limit for the pool of species potentially capable of coexisting in a community, while local biotic interactions, i.e., competition, facilitation, herbivory and interactions with below-ground ecosystem components, and environmental factors control colonisation and establishment, and determine the persistence and dynamics of already existing species. In this thesis, I studied (1) the interactions between propagule availability, biotic and environmental constraints on colonisation, and (2) the interdependence between biotic and environmental factors regulating community processes in already established resident vegetation. First, I found that both propagule availability and competition with adult plants limited the rates of colonisation and total community diversity in a relatively low-productive tundra ecosystem. Long-term exclusion of mammalian herbivores and alleviation of nutrient limitation by fertilization increased the intensity of competition with established vegetation, and diminished immigration rates. In addition, I also found that community openness to colonization depended on the initial community properties, i.e., the functional composition and the traits of dominant plants in resident vegetation, which mediate the effects of nutrient addition and biomass removal on immigration rates. Second, adult plants in the resident vegetation experienced an increased extent of neighbourhood competition and herbivory in nutrient enriched conditions and in naturally more fertile habitats. However, the effects were also species-specific. On a community level, release from heavy grazing favoured lichens over graminoids and increased species richness. Furthermore, I also showed that plant community composition was strongly linked with soil organic matter quality and microbial community composition, and that these vegetation-soil-microbe interactions varied along a gradient of soil pH. Overall, my results emphasise that propagule availability, biotic and environmental control over community processes are strongly interconnected in tundra ecosystems. Especially, my findings highlight the role of plant competition and herbivory and their dependence on soil nutrient availability in governing colonisation and resident community dynamics. My results also indicate that plant functional composition and traits of dominant plants are of great importance in channelling community responses to external alterations and dictating plant-soil interactions.

As drivers of biogeochemical cycles and nutrient recycling, such as carbon turnover, the microbial community is essential in sustaining functioning ecosystems. Together with the metazoan community, the microbial community constitute the majority of all life in the benthos. Environmental change in biotic and abiotic factors may influence the dynamics of these communities, for example through a sorting or driving effect on the community structure through assembly processes. Environmental change, e.g. change in dissolved oxygen concentration, salinity and temperature, can directly or indirectly affect community composition. How, in what way, and to what extent, benthic bacterial and meiofaunal community composition in the eutrophied, brackish benthic environments, in the Baltic Sea sub-basin the Baltic Proper, respond to environmental change is understudied, both at local and seascape scale. This thesis aimed to study and understand the effects of environmental variation on the diversity and biogeographic patterns of Baltic Sea sediment bacterial and meiofaunal communities. A further aim was to understand the links between the different community levels by studying the interaction between meiofaunal- and macrofaunal communities in relation to environmental variation. Community diversity was analysed along a latitudinal transect of national environmental monitoring stations in the Baltic Proper using a framework of metapopulation and metacommunity theory. The analyses were based on environmental genomics, with high-throughput sequencing, bioinformatics and statistics. The total community genome was analysed using phylogenetic marker gene fragments as a proxy for taxonomic diversity, to investigate diversity, community structure and dynamics. Salinity and oxygen were found to be the main abiotic environmental drivers of benthic community composition and alpha- and beta-diversity patterns. Furthermore, macrofauna-meiofauna interactions were significantly more complex in higher salinity environments. Results also showed that both enhanced environmental gradients and dispersal following a major inflow of saline and oxygenated water from the Atlantic Ocean, influenced the composition of sediment bacterial communities at the seascape scale of the Baltic Sea, as shown by a reduced beta-diversity and increased alpha-diversity, and the development of a significant distance-decay of community similarity. This study also identified strong metapopulation dynamics of the benthic sediment bacterial communities with many satellite and a few core taxa. The outcomes from this study contribute to the understanding of how environmental variation and environmental change relate to changes in Baltic Sea benthic community diversity and composition, and important factors and processes governing community dynamics.

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