@article{CeulemansGuillGaedke2021,
  author    = {Ceulemans, Ruben and Guill, Christian and Gaedke, Ursula},
  title     = {Top predators govern multitrophic diversity effects in tritrophic food webs},
  series = {Ecology : a publication of the Ecological Society of America},
  volume    = {102},
  journal   = {Ecology : a publication of the Ecological Society of America},
  number    = {7},
  publisher = {Wiley},
  address   = {Hoboken},
  issn      = {0012-9658},
  doi       = {10.1002/ecy.3379},
  pages     = {16},
  year      = {2021},
  abstract  = {It is well known that functional diversity strongly affects ecosystem functioning. However, even in rather simple model communities consisting of only two or, at best, three trophic levels, the relationship between multitrophic functional diversity and ecosystem functioning appears difficult to generalize, because of its high contextuality. In this study, we considered several differently structured tritrophic food webs, in which the amount of functional diversity was varied independently on each trophic level. To achieve generalizable results, largely independent of parametrization, we examined the outcomes of 128,000 parameter combinations sampled from ecologically plausible intervals, with each tested for 200 randomly sampled initial conditions. Analysis of our data was done by training a random forest model. This method enables the identification of complex patterns in the data through partial dependence graphs, and the comparison of the relative influence of model parameters, including the degree of diversity, on food-web properties. We found that bottom-up and top-down effects cascade simultaneously throughout the food web, intimately linking the effects of functional diversity of any trophic level to the amount of diversity of other trophic levels, which may explain the difficulty in unifying results from previous studies. Strikingly, only with high diversity throughout the whole food web, different interactions synergize to ensure efficient exploitation of the available nutrients and efficient biomass transfer to higher trophic levels, ultimately leading to a high biomass and production on the top level. The temporal variation of biomass showed a more complex pattern with increasing multitrophic diversity: while the system initially became less variable, eventually the temporal variation rose again because of the increasingly complex dynamical patterns. Importantly, top predator diversity and food-web parameters affecting the top trophic level were of highest importance to determine the biomass and temporal variability of any trophic level. Overall, our study reveals that the mechanisms by which diversity influences ecosystem functioning are affected by every part of the food web, hampering the extrapolation of insights from simple monotrophic or bitrophic systems to complex natural food webs.},
  language  = {en}
}
@article{MarzetzWacker2021,
  author    = {Marzetz, Vanessa and Wacker, Alexander},
  title     = {Evaluating the relevance of species sorting and physiological plasticity of phytoplankton communities grown in a multifactor environment},
  series = {Freshwater biology / Freshwater Biological Association},
  volume    = {66},
  journal   = {Freshwater biology / Freshwater Biological Association},
  number    = {10},
  publisher = {Wiley-Blackwell},
  address   = {Oxford},
  issn      = {0046-5070},
  doi       = {10.1111/fwb.13810},
  pages     = {1992 -- 2003},
  year      = {2021},
  abstract  = {The two important mechanisms influencing the response of phytoplankton communities to alterations of abiotic factors in their environment are difficult to distinguish: species sorting resulting from a change in interspecific competitive pressure, and phenotypic plasticity (here explicitly physiological plasticity i.e. species-specific physiological adjustment). A shift in species composition as well as physiological adjustments in species can lead to changes in fatty acid composition that determine the food quality for zooplankton consumers. We used phytoplankton communities consisting of five species and exposed them to two different light intensities, two light conditions (constant and variable), and two levels of phosphorus supply. Changes in fatty acid and species composition were analyzed. We compared community pairs differing in one factor by calculating the Bray-Curtis similarity index for the composition of both variables. Comparing the Bray-Curtis similarity index of the species composition with the index of the fatty acid composition was used to estimate the effects of species sorting and physiological plasticity. Changes in nutrient supply influenced fatty acid responses based on species sorting and physiological plasticity the most. On one hand, the relevance of physiological plasticity was highest at cultivation in different nutrient supplies but the same light environment. Conversely with low nutrients species sorting appeared to dominate the response to changes in light, while at high nutrients physiological plasticity appeared to influence the response. Overall, under low phosphorus supply the communities showed a lower total fatty acid content per carbon and had increased proportions of saturated and monounsaturated fatty acids. Instead, communities in low light produced more of eicosapentaenoic acid. Our results suggest that the relevance of species sorting and physiological plasticity in shaping the community response highly depends on the environmental factors that influence the system. Nutrient supply had the largest effect, while light had more limited conditional effects. However, all of these factors are important in shaping the food quality of the phytoplankton community for higher trophic levels.},
  language  = {en}
}