Mikrophytobenthos in sublitoralen Kaltwasserregionen : ihre ökologische Rolle und Reaktion auf sich verändernde Umweltbedingungen

In my thesis, the main aim was to study and compare subtidal microphytobenthos communities and their activity from sandy sediments of an Arctic (Spitsbergen, Svalbard) and a temperate (Helgoland, North Sea) study site. Helgoland was chosen as a comparative site because of the tight link between the North Sea and the western coast of Spitsbergen due to ocean currents. The research objective was realized in three consecutive studies. The specific questions in this study were: (i) How do MPB net photosynthesis and respiration (in terms of oxygen production and consumption) compare in Helgoland and Svalbard? Who are the main players of the MPB community, and what is the daily net oxygen budget under natural (in situ) conditions? Will the communities and their photosynthetic performances (light adaptation, maximum photosynthesis) be site‐specific, or will they be similar? (ii) Will the photosynthesis and respiration response of the temperate and sub-Arctic MPB community to short-term temperature increases be different? Will the sub-Arctic site be more adapted as it experiences higher temperature fluctuations in situ on a short term scale (daily/ hourly) than the temperate site? Will the MPB communities develop towards a net-heterotrophy as previously shown for benthic communities? (iii) Will an upward shift of the temperature baseline and increase of nutrients have consequences for the growth of MPB communities from Helgoland and Svalbard? Will the MPB community grow best under lowest, intermediate or highest temperatures from within the in situ temperature range? Will their growth be dependent on the addition of nutrients? Will they grow with the same speed and reach similar biomasses, or will there be differences because of differences in their natural light and temperature regimes

Experimental evidence that evolution by niche construction affects dissipative ecosystem dynamics

Evolution by niche construction occurs when organism-mediated modification of the environment causes an evolutionary response. Physicists have postulated that evolution in general, and evolution mediated via feedbacks between organisms and their environment in particular (i.e. evolution by niche construction), could increase the capacity of biological systems to dissipate free energy in an open thermodynamic system, and help them maintain a state far from thermodynamic equilibrium. Here, we propose using the bacterium Pseudomonas fluorescens (strain SBW25) as a model system to experimentally test theories in both evolutionary biology (e.g. niche construction) and physics (e.g. dissipative systems theory). P. fluorescens rapidly and predictably evolves multiple strategies for exploiting oxygen in unmixed culture flasks. This evolutionary dynamic is mediated by feedbacks between the modification of the oxygen gradient by P. fluorescens and the ecological and evolutionary responses of Pseudomonas to modified environmental conditions. To confirm this, we experimentally manipulated two aspects of the system that influence the strength of the feedback between P. fluorescens and oxygen gradients in the system. First, we inhibited the metabolism of the strain used to inoculate the cultures, and, second, we disturbed the formation of mats at the air–liquid interface. Overall, we found convincing experimental evidence of evolution by niche construction, and conclude that this study system is amenable to experimental investigations of both niche construction and dissipative systems theory