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  • 1
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    Beyond the Plankton Ecology Group (PEG) Model: Mechanisms Driving Plankton Succession (2012)
    Annual Reviews Inc.
    In:  Annual Review of Ecology, Evolution, and Systematics, 43 (1). pp. 429-448.
    Details
    Publication Date: 2019-01-21
    Description: 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.
    Type: Article , PeerReviewed
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  • 2
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    High predictability of spring phytoplankton biomass in mesocosms at the species, functional group and community level (2012)
    In:  [Talk] In: 2012 ASLO Aquatic Sciences Meeting, 08.-13.07.2012, Lake Biwa, Otsu, Shiga, Japan .
    Details
    Publication Date: 2012-12-18
    Description: 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 imperfect. Thus, if phytoplankton dynamics are sensitive to small variations in initial conditions, they are difficult to predict. We used time-series data from indoor mesocosm experiments with natural phyto- and zooplankton communities to quantify to which extent small initial differences in the species, functional group and community biomass in parallel treatments got amplified or buffered over time.We compared the differences in dynamics between replicates and among all mesocosms of one year. Temperature-sensitive grazing during the exponential growth phase of phytoplankton caused divergence. In contrast, negative density-dependence caused convergence. 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.
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 3
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    Diversity, Functional Similarity, and Top-Down Control Drive Synchronization and the Reliability of Ecosystem Function (2014)
    University of Chicago Press
    In:  The American Naturalist, 183 (3). pp. 394-409.
    Details
    Publication Date: 2019-01-21
    Description: The concept that diversity promotes reliability of ecosystem function depends on the pattern that community-level biomass shows lower temporal variability than species-level biomasses. However, this pattern is not universal, as it relies on compensatory or independent species dynamics. When in contrast within–trophic level synchronization occurs, variability of community biomass will approach population-level variability. Current knowledge fails to integrate how species richness, functional distance between species, and the relative importance of predation and competition combine to drive synchronization at different trophic levels. Here we clarify these mechanisms. Intense competition promotes compensatory dynamics in prey, but predators may at the same time increasingly synchronize, under increasing species richness and functional similarity. In contrast, predators and prey both show perfect synchronization under strong top-down control, which is promoted by a combination of low functional distance and high net growth potential of predators. Under such conditions, community-level biomass variability peaks, with major negative consequences for reliability of ecosystem function.
    Type: Article , PeerReviewed
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  • 4
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    Multitrophic diversity effects depend on consumer specialization and species-specific growth and grazing rates (2014)
    Wiley-Blackwell
    In:  Oikos, 123 (8). pp. 912-922.
    Details
    Publication Date: 2017-01-31
    Description: Ecosystem functioning is affected by horizontal (within trophic groups) and vertical (across trophic levels) biodiversity. Theory predicts that the effects of vertical biodiversity depend on consumer specialization. In a microcosm experiment, we investigated ciliate consumer diversity and specialization effects on algal prey biovolume, evenness and composition, and on ciliate biovolume production. The experimental data was complemented by a process-based model further analyzing the ecological mechanisms behind the observed diversity effects. Overall, increasing consumer diversity had no significant effect on prey biovolume or evenness. However, consumer specialization affected the prey community. Specialist consumers showed a stronger negative impact on prey biovolume and evenness than generalists. The model confirmed that this pattern was mainly driven by a single specialist with a high per capita grazing rate, consuming the two most productive prey species. When these were suppressed, the prey assemblage became dominated by a less productive species, consequently decreasing prey biovolume and evenness. Consumer diversity increased consumer biovolume, which was stronger for generalists than for specialists and highest in mixed combinations, indicating that consumer functional diversity, i.e. more diverse feeding strategies, increased resource use efficiency. Overall, our results indicate that consumer diversity effects on prey and consumers strongly depend on species-specific growth and grazing rates, which may be at least equally important as consumer specialization in driving consumer diversity effects across trophic levels.
    Type: Article , PeerReviewed
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  • 5
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    Diversity, functional similarity and top-down control drive synchronization and the reliability of ecosystem function (2013)
    In:  [Talk] In: Oberseminar ICBM, 06.06.2013, Oldenburg, Germany .
    Details
    Publication Date: 2013-06-25
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 6
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    Resisting annihilation: relationships between functional trait dissimilarity, assemblage competitive power and allelopathy (2018)
    Wiley
    In:  Ecology Letters, 21 (9). pp. 1390-1400.
    Details
    Publication Date: 2021-02-08
    Description: 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.
    Type: Article , PeerReviewed
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  • 7
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    Climate change effects on phytoplankton depend on cell size and food web structure (2012)
    Springer
    In:  Marine Biology, 159 . pp. 2455-2478.
    Details
    Publication Date: 2019-07-09
    Description: 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.
    Type: Article , PeerReviewed
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  • 8
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    High predictability of spring phytoplankton biomass in mesocosms at the species, functional group and community level (2013)
    Wiley
    In:  Freshwater Biology, 58 (3). pp. 588-596.
    Details
    Publication Date: 2019-09-23
    Description: 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 1 year. 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.
    Type: Article , PeerReviewed
    Format: text
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  • 9
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    The first decade of oligotrophication of Lake Constance (1993)
    Springer
    In:  Oecologia, 93 (2). pp. 276-284.
    Details
    Publication Date: 2017-10-09
    Description: In Lake Constance, after several decades of cutrophication, a decrease in phosphorus loading over the last decade has lead to a partial recovery from eutrophication. Here we analyse the shift in the taxonomic composition of phytoplankton during the first decade of oligotrophication in Lake Constance. During the 1980s, spring total P concentrations decreased from ca. 130 to less than 50 mgr·l–1. This decrease was reflected by an approximately proportional decrease in summer phytoplankton biomass while spring phytoplankton biomass seemed unresponsive. Major taxonomic changes occured during both growth seasons. In spring, the proportion of diatoms, green algae and Chrysophyta increased while the proportion of Cryptophyta decreased. The summer trend was very different: the relative importance of diatoms decreased and Cryptophyta and Chrysophyta increased, while Chlorophyta reached their peak around 1985. These trends are also analysed at the genus level. Comparison with taxonomic trends during the eutrophication period shows the expected reversals in most cases. Comparison with other lakes shows general similarities, with the notable exception that Planktothrix rubescens has never been important in Lake Constance. The increase of diatoms during spring is attributed to their improved competitive performance with increasing Si:P ratios. Their decrease during summer is explained by the increasing silicate removal from the epilimnion by increasing spring populations.
    Type: Article , PeerReviewed
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  • 10
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    Coupled changes in traits and biomasses cascading through a tritrophic plankton food web (2021)
    Details
    Publication Date: 2021-12-06
    Description: Trait-based approaches have broadened our understanding of how the composition of ecological communities responds to environmental drivers. This research has mainly focussed on abiotic factors and competition determining the community trait distribution, while effects of trophic interactions on trait dynamics, if considered at all, have been studied for two trophic levels at maximum. However, natural food webs are typically at least tritrophic. This enables indirect interactions of traits and biomasses among multiple trophic levels leading to underexplored effects on food web dynamics. Here, we demonstrate the occurrence of mutual trait adjustment among three trophic levels in a natural plankton food web (Lake Constance) and in a corresponding mathematical model. We found highly recurrent seasonal biomass and trait dynamics, where herbivorous zooplankton increased its size, and thus its ability to counter phytoplankton defense, before phytoplankton defense actually increased. This is contrary to predictions from bitrophic systems where counter-defense of the consumer is a reaction to prey defense. In contrast, counter-defense of carnivores by size adjustment followed the defense of herbivores as expected. By combining observations and model simulations, we show how the reversed trait dynamics at the two lower trophic levels result from a “trophic biomass–trait cascade” driven by the carnivores. Trait adjustment between two trophic levels can therefore be altered by biomass or trait changes of adjacent trophic levels. Hence, analyses of only pairwise trait adjustment can be misleading in natural food webs, while multitrophic trait-based approaches capture indirect biomass–trait interactions among multiple trophic levels.
    Keywords: 577.2 ; Lake Constance ; food web dynamics
    Language: English
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