Warming does not always benefit the small – Results from a plankton experiment
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Ruger T, Sommer U
phytoplankton, cell size, temperature, mesocosm, Kiel indoor, 1.4 m3, Kiel, Germany
The concern about climate change has re-vitalised the interest in the relationships between body-size oforganisms and temperature both at the intraspecific level (James’ rule, Temperature-Size-Rule) and at theinterspecific level (Bergmann’s rule). In order to test the expected shifts towards smaller body size underwarming conditions, a mesocosm experiment using plankton from the Baltic Sea at three temperaturelevels was performed in April 2010. The hypothesis was tested, that a tendency well established undermonoculture conditions, would also be found in phytoplankton embedded in a semi-natural food-web.Six out of seven phytoplankton species abundant enough for analysis did not show the expected shrinkageof cell volume with increasing temperature, while volume shrinkage of the 7th species (Eutreptiella sp.)could be attributed exclusively to the axis which is affected by cell division. Thus it could not be ruledout, that the populations grown at different temperature levels were just at a different stage of the cellcycle. Similarly, we could not find an indication for a replacement of larger species by smaller ones underhigher temperature. As a consequence, mean cell size did not respond to temperature. Therefore, wecould not support the hypothesis, that warming should benefit the small.
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