@misc{SommerAdrianDomisetal.2012, author = {Sommer, Ulrich and Adrian, Rita and Domis, Lisette Nicole de Senerpont and Elser, James J. and Gaedke, Ursula and Ibelings, Bas and Jeppesen, Erik and Lurling, Miquel and Molinero, Juan Carlos and Mooij, Wolf M. and van Donk, Ellen and Winder, Monika}, title = {Beyond the Plankton Ecology Group (PEG) Model mechanisms driving plankton succession}, series = {Annual review of ecology, evolution, and systematics}, volume = {43}, journal = {Annual review of ecology, evolution, and systematics}, number = {2-4}, editor = {Futuyma, DJ}, publisher = {Annual Reviews}, address = {Palo Alto}, isbn = {978-0-8243-1443-9}, issn = {1543-592X}, doi = {10.1146/annurev-ecolsys-110411-160251}, pages = {429 -- 448}, year = {2012}, abstract = {The seasonal succession of plankton is an annually repeated process of community assembly during which all major external factors and internal interactions shaping communities can be studied. A quarter of a century ago, the state of this understanding was described by the verbal plankton ecology group (PEG) model. It emphasized the role of physical factors, grazing and nutrient limitation for phytoplankton, and the role of food limitation and fish predation for zooplankton. Although originally targeted at lake ecosystems, it was also adopted by marine plankton ecologists. Since then, a suite of ecological interactions previously underestimated in importance have become research foci: overwintering of key organisms, the microbial food web, parasitism, and food quality as a limiting factor and an extended role of higher order predators. A review of the impact of these novel interactions on plankton seasonal succession reveals limited effects on gross seasonal biomass patterns, but strong effects on species replacements.}, language = {en} } @article{GaedkeRuhenstrothBauerWiegandetal.2010, author = {Gaedke, Ursula and Ruhenstroth-Bauer, Miriam and Wiegand, Ina and Tirok, Katrin and Aberle-Malzahn, Nicole and Breithaupt, Petra and Lengfellner, Kathrin and Wohlers, Julia and Sommer, Ulrich}, title = {Biotic interactions may overrule direct climate effects on spring phytoplankton dynamics}, issn = {1354-1013}, doi = {10.1111/j.1365-2486.2009.02009.x}, year = {2010}, abstract = {To improve our mechanistic understanding and predictive capacities with respect to climate change effects on the spring phytoplankton bloom in temperate marine systems, we used a process-driven dynamical model to disentangle the impact of potentially relevant factors which are often correlated in the field. The model was based on comprehensive indoor mesocosm experiments run at four temperature and three light regimes. It was driven by time-series of water temperature and irradiance, considered edible and less edible phytoplankton separately, and accounted for density- dependent grazing losses. It successfully reproduced the observed dynamics of well edible phytoplankton in the different temperature and light treatments. Four major factors influenced spring phytoplankton dynamics: temperature, light (cloudiness), grazing, and the success of overwintering phyto- and zooplankton providing the starting biomasses for spring growth. Our study predicts that increasing cloudiness as anticipated for warmer winters for the Baltic Sea region will retard phytoplankton net growth and reduce peak heights. Light had a strong direct effect in contrast to temperature. However, edible phytoplankton was indirectly strongly temperature-sensitive via grazing which was already important in early spring at moderately high algal biomasses and counter-intuitively provoked lower and later algal peaks at higher temperatures. Initial phyto- and zooplankton composition and biomass also had a strong effect on spring algal dynamics indicating a memory effect via the broadly under-sampled overwintering plankton community. Unexpectedly, increased initial phytoplankton biomass did not necessarily lead to earlier or higher spring blooms since the effect was counteracted by subsequently enhanced grazing. Increasing temperature will likely exhibit complex indirect effects via changes in overwintering phytoplankton and grazer biomasses and current grazing pressure. Additionally, effects on the phytoplankton composition due to the species-specific susceptibility to grazing are expected. Hence, we need to consider not only direct but also indirect effects, e.g. biotic interactions, when addressing climate change impacts.}, language = {en} } @article{KlauschiesBauerAberleMalzahnetal.2012, author = {Klauschies, Toni and Bauer, Barbara and Aberle-Malzahn, Nicole and Sommer, Ulrich and Gaedke, Ursula}, title = {Climate change effects on phytoplankton depend on cell size and food web structure}, series = {Marine biology : international journal on life in oceans and coastal waters}, volume = {159}, journal = {Marine biology : international journal on life in oceans and coastal waters}, number = {11}, publisher = {Springer}, address = {New York}, issn = {0025-3162}, doi = {10.1007/s00227-012-1904-y}, pages = {2455 -- 2478}, year = {2012}, abstract = {We investigated the effects of warming on a natural phytoplankton community from the Baltic Sea, based on six mesocosm experiments conducted 2005-2009. We focused on differences in the dynamics of three phytoplankton size groups which are grazed to a variable extent by different zooplankton groups. While small-sized algae were mostly grazer-controlled, light and nutrient availability largely determined the growth of medium- and large-sized algae. Thus, the latter groups dominated at increased light levels. Warming increased mesozooplankton grazing on medium-sized algae, reducing their biomass. The biomass of small-sized algae was not affected by temperature, probably due to an interplay between indirect effects spreading through the food web. Thus, under the higher temperature and lower light levels anticipated for the next decades in the southern Baltic Sea, a higher share of smaller phytoplankton is expected. We conclude that considering the size structure of the phytoplankton community strongly improves the reliability of projections of climate change effects.}, language = {en} } @article{BauerSommerGaedke2013, author = {Bauer, Barbara and Sommer, Ulrich and Gaedke, Ursula}, title = {High predictability of spring phytoplankton biomass in mesocosms at the species, functional group and community level}, series = {Freshwater biology}, volume = {58}, journal = {Freshwater biology}, number = {3}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0046-5070}, doi = {10.1111/j.1365-2427.2012.02780.x}, pages = {588 -- 596}, year = {2013}, abstract = {1. Models aim to predict phytoplankton dynamics based on observed initial conditions and a set of equations and parameters. However, our knowledge about initial conditions in nature is never perfect. Thus, if phytoplankton dynamics are sensitive to small variations in initial conditions, they are difficult to predict. 2. We used time-series data from indoor mesocosm experiments with natural phyto- and zooplankton communities to quantify the extent to which small initial differences in the species, functional group and community biomass in parallel treatments were amplified or buffered over time. We compared the differences in dynamics between replicates and among all mesocosms of 1year. 3. Temperature-sensitive grazing during the exponential growth phase of phytoplankton caused divergence. In contrast, negative density dependence caused convergence. 4. Mean differences in biomass between replicates were similar for all hierarchical levels. This indicates that differences in their initial conditions were amplified to the same extent. Even though large differences in biomass occasionally occurred between replicates for a short time, dynamics returned to the same path at all hierarchical levels. This suggests that internal feedback mechanisms make the spring development of phytoplankton highly predictable.}, language = {en} } @article{MuhlRoelkeZoharyetal.2018, author = {Muhl, Rika M. W. and Roelke, Daniel L. and Zohary, Tamar and Moustaka-Gouni, Maria and Sommer, Ulrich and Borics, Gabor and Gaedke, Ursula and Withrow, Frances G. and Bhattacharyya, Joydeb}, title = {Resisting annihilation}, series = {Ecology letters}, volume = {21}, journal = {Ecology letters}, number = {9}, publisher = {Wiley}, address = {Hoboken}, issn = {1461-023X}, doi = {10.1111/ele.13109}, pages = {1390 -- 1400}, year = {2018}, abstract = {Allelopathic species can alter biodiversity. Using simulated assemblages that are characterised by neutrality, lumpy coexistence and intransitivity, we explore relationships between within-assemblage competitive dissimilarities and resistance to allelopathic species. An emergent behaviour from our models is that assemblages are more resistant to allelopathy when members strongly compete exploitatively (high competitive power). We found that neutral assemblages were the most vulnerable to allelopathic species, followed by lumpy and then by intransitive assemblages. We find support for our modeling in real-world time-series data from eight lakes of varied morphometry and trophic state. Our analysis of this data shows that a lake's history of allelopathic phytoplankton species biovolume density and dominance is related to the number of species clusters occurring in the plankton assemblages of those lakes, an emergent trend similar to that of our modeling. We suggest that an assemblage's competitive power determines its allelopathy resistance.}, language = {en} }