The classical theorem sees heterotrophic bacterivores as the major grazers of bacteria in microbial food webs. However, recent field studies reveal that mixotrophic flagellates - protists which combine phototrophy and phagotrophy in one organism - account for a large fraction of bacterivory in the surface layers of lakes and oceans. In spite of their obvious importance as bacterivores in such systems, our conceptual understanding of the mechanisms constraining their ecological role remains rather elusive. We studied the competitive success of mixotrophs (MF) over heterotrophs (HF) in artificial food webs, under either N- or P-limitation, applying gradients of light and loss rate. Mixotrophs need to maintain cellular structures for photosynthesis and phagocytosis and in the light they exhibit a lower R* for prey, at the expense of reduced maximum growth rates, compared to heterotrophs. Based on the fundamental trade-offs between mixotrophs and their specialized heterotrophic competitors the outcome in the competition between MF and HF should be linked to light, loss rate and the identity of the limiting nutrient. The results of our experiments are largely in agreement with expectations.


Fischer, R., Carl von Ossietzky University of Oldenburg, Germany, robert.fischer@uni-oldenburg.de

Hillebrand, H., Carl von Ossietzky University of Oldenburg, Germany, helmut.hillebrand@uni-oldenburg.de

Giebel, H., Carl von Ossietzky University of Oldenburg, Germany, helge.ansgar.giebel@uni-oldenburg.de

Ptacnik, R., WasserCluster Lunz—Biologische Station GmbH, Austria, robert.ptacnik@wcl.ac.at


Oral presentation

Session #:058
Date: 2/26/2015
Time: 16:15
Location: Room B (Floor -3)

Presentation is given by student: Yes