5. Microbially dominated ecosystems 5.1 Defining microbial ecosystems Ecosystems consist of habitats, conditions and organisms. Habitats separated by physically defined boundaries. Conditions are defined by chemical and physical determinants changing in time and space. Organisms, present as communities (= multitude of populations) can change conditions and migrate across boundaries. Cross-boundary transmitting agents: Arthropods, Chordates, Annelids, Protozoa; transport vehicles: water, aerosols, food; transport mechanisms: ingestion, inhalation, surface contact. Niches: physiologically defined ecosystem functions changing through the presence and the evolution of organims. Barriers are limitations for microbial migration and functioning. Physical barriers: temperature, radiation, pressure, pore size, adhesion attraction; chemical barriers: pH, salinity, oxidant, denaturant, surfactant, toxicity; biological barriers: immune response, trophic competition, predator-prey, viral attack, resistance, surface protection. The role of microbes in ecosystem functioning. Linking structures with functions in microbial ecosystems. 5.2 Biodiversity in functionally stabilized ecosystems (an overview). Diversity of aquatic ecosystems in altitudinal gradients and transients: nival zone, alpine, subalpine, highland, lowland, riverine, estuarine, littoral, shelf, continental slope, abyssal. Freshwater vs. marine habitats. Lakes and reservoirs in temperate and tropic climatic zones. Oxic and anoxic sediments of lakes and oceans. Subsurface aquifers: oligotrophy and bioremediation. Microbial mats and biofilms. Hot spring cyanobacterial mats. Hydrothermal vent environments. Cryoenvironments in snow and ice. Endolithic and rock surface environments (e.g. lichens). Syntrophy in animal digestive systems: gastro-intestinal tracts, microniches in gut habitats. Host-microbe interactions: plant, animal and human hosts for pathogens. Skin &endash; a dry hostile environment.
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