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Die Arbeit ist eine Zusammenfassung von Untersuchungen über die Ökologie der Wasservegetation in naturnahen Stillgewässern in Polen, die am Lehrstuhl für Phytogeographie der Warschauer Universität durchgeführt wurde. Insgesamt wurden 532 Bestände von 18 Assoziationen aus den Klassen Lemnetea minoris Koch et Tx. 1954, Charetea fragilis (Fukarek 1961) Krausch 1964, Potamogetonetea Tx. et Prsg. 1942, Littorelletea uniflorae Br.-Bl. et Tx. 1943 untersucht. Es wird nachgewiesen, daß über das Vorkommen und die Entwicklung der Wasserpflanzengesellschaften im großen Maße die Wassereigenschaften entscheiden, die einmal mit dem Karbonatsystem zusammenhängen (Gesamt- und Karbonathärte, Gehalt an Ca, Mg), und außerdem mit denjenigen, die für Sauberkeit und Trophie des Wassers ausschlaggebend sind (Sauerstoffsättigung, Wasserfarbe, Gehalt an PO4-P, NH4-N, ges. Fe und gel. Si02). Unter den Bodeneigenschaften haben die größte Bedeutung: Wassergehalt, Oxydierbarkeit, Gehalt an organischer Substanz, Gesamtstickstoff, gel. Si02, SO4, pH-Wert, außerdem die Hauptbestandteile der Kalkgyttja (Ca, Mg, Na). Die pflanzensoziologische Einteilung der Wasserpflanzengesellschaften in selbständige Syntaxa nach dem Prinzip der floristischen Dominanz findet ihre Bestätigung in den Standortsbedingungen. Die einzelnen Gesellschaften oder Gruppen von Gesellschaften unterscheiden sich voneinander durch die Amplituden und Optima der Standortbedingungen; sie können daher einen Bioindikationswert haben.
Es wird die Vegetationsentwicklung in einigen stehenden Gewässern in Hamburg nach der Ansiedlung von Elodea nuttallii beschrieben. Wasserpflanzen dieser in Ausdehnung, Tiefe und Arteninventar unterschiedlichen Seen anthropogener Entstehung reagieren verschiedenartig auf das Eindringen der Wasserpest. Es scheint, daß sich die Art besonders leicht in kleinen, flachen und artenarmen Seen ansiedelt; danach kann sich die Vegetation von Jahr zu Jahr erheblich verändern. In größeren und tieferen Seen mit verschiedenen Pflanzengesellschaften erscheint das Eindringen von Elodea erschwert; Veränderungen an der Vegetation sind weniger dramatisch.
Here I analyse 23 populations of D. galeata, a large-lake cladoceran, distributed mainly across the Palaearctic. I detected high levels of clonal diversity and population differentiation using variation at six microsatellite loci across Europe. Most populations were characterised by deviations from H-W equilibrium and significant heterozygote deficiencies. Observed heterozygote deficiencies might be a consequence of simultaneous hatching of individuals produced during different times of the year or of the coexistence of ecologically and genetically differentiated subpopulations. A significant isolation by distance was only found over large geographic distances (> 700 km). This pattern is mainly due to the high genetic differentiation among neighbouring populations. My results suggest that historic populations of Daphnia were once interconnected by gene flow but current populations are now largely isolated. Thus local ecological conditions which determine the level of biparental sexual reproduction and local adaptation are the main factors mediating population structure of D. galeata. The population genetic structure and diversity in D. galeata was investigated at a European scale using six microsatellite loci and 12S rDNA sequence data to infer and compare historical and contemporary patterns of gene flow. D. galeata has the potential for long-distance dispersal via ephippial resting eggs by wind and other dispersing vectors (waterfowl), but shows in general strong population differentiation even among neighbouring populations. A total of 427 individuals were analysed for microsatellite and 85 individuals for mitochondrial (mtDNA) sequence data from 12 populations across Europe. I detected genetic differentiation among populations across Europe and locations within sampling regions for both genetic marker systems (average values: mtDNA FST = 0.574; microsatellite FST = 0.389), resulting in a lack of isolation by distance. Furthermore, several microsatellite alleles and one haplotype were shared across populations. Partitioning of molecular variance was inconsistant for both marker systems. Microsatellite variation was higher within than among populations, whereas mtDNA data yielded an inverse pattern. Relative high levels of nuclear DNA diversity were found across Europe. The amount of mitochondrial diversity was low in Spain, Hungary and Denmark. Gene flow analysis at a European scale did not reveal typical pattern of population recolonization in the light of postglacial colonization hypotheses. Populations, which recently experienced an expansion or population-bottleneck were observed both in middle and northern Europe. Since these populations revealed high genetic diversity in both marker systems, I suggest these areas to represent postglacial zones of secondary contact among divergent lineages of D. galeata. In order to reveal the relationship between population genetic structure of D. galeata and the relative contribution of environmental factors, I used a statistical framework based on canonical correspondence analysis. Although I detected no single ecological gradient mediating the genetic differentiation in either lake regions, it is noteworthy that the same ecological factors were significantly correlated with intra- and interspecific genetic variation of D. galeata. For example, I found a relationship between genetic variation of D. galeata and differentiation with higher and lower trophic levels (phytoplankton, submerged macrophytes and fish) and a relationship between clonal variation and species diversity within Cladocera. Variance partitioning had only a minor contribution of each environmental category (abiotic, biomass/density and diversity) to genetic diversity of D. galeata, while the largest proportion of variation was explained by shared components. My work illustrates the important role of ecological differentiation and adaptation in structuring genetic variation, and it highlights the need for approaches incorporating a landscape context for population divergence.