@article{KlauschiesCoutinhoGaedke2018, author = {Klauschies, Toni and Coutinho, Renato Mendes and Gaedke, Ursula}, title = {A beta distribution-based moment closure enhances the reliability of trait-based aggregate models for natural populations and communities}, series = {Ecological modelling : international journal on ecological modelling and engineering and systems ecolog}, volume = {381}, journal = {Ecological modelling : international journal on ecological modelling and engineering and systems ecolog}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0304-3800}, doi = {10.1016/j.ecolmodel.2018.02.001}, pages = {46 -- 77}, year = {2018}, abstract = {Ecological communities are complex adaptive systems that exhibit remarkable feedbacks between their biomass and trait dynamics. Trait-based aggregate models cope with this complexity by focusing on the temporal development of the community's aggregate properties such as its total biomass, mean trait and trait variance. They are based on particular assumptions about the shape of the underlying trait distribution, which is commonly assumed to be normal. However, ecologically important traits are usually restricted to a finite range, and empirical trait distributions are often skewed or multimodal. As a result, normal distribution-based aggregate models may fail to adequately represent the biomass and trait dynamics of natural communities. We resolve this mismatch by developing a new moment closure approach assuming the trait values to be beta-distributed. We show that the beta distribution captures important shape properties of both observed and simulated trait distributions, which cannot be captured by a Gaussian. We further demonstrate that a beta distribution-based moment closure can strongly enhance the reliability of trait-based aggregate models. We compare the biomass, mean trait and variance dynamics of a full trait distribution (FD) model to the ones of beta (BA) and normal (NA) distribution-based aggregate models, under different selection regimes. This way, we demonstrate under which general conditions (stabilizing, fluctuating or disruptive selection) different aggregate models are reliable tools. All three models predicted very similar biomass and trait dynamics under stabilizing selection yielding unimodal trait distributions with small standing trait variation. We also obtained an almost perfect match between the results of the FD and BA models under fluctuating selection, promoting skewed trait distributions and ongoing oscillations in the biomass and trait dynamics. In contrast, the NA model showed unrealistic trait dynamics and exhibited different alternative stable states, and thus a high sensitivity to initial conditions under fluctuating selection. Under disruptive selection, both aggregate models failed to reproduce the results of the FD model with the mean trait values remaining within their ecologically feasible ranges in the BA model but not in the NA model. Overall, a beta distribution-based moment closure strongly improved the realism of trait-based aggregate models.}, language = {en} } @article{SchmidtkeGaedkeWeithoff2010, author = {Schmidtke, Andrea and Gaedke, Ursula and Weithoff, Guntram}, title = {A mechanistic basis for underyielding in phytoplankton communities}, issn = {0012-9658}, year = {2010}, abstract = {Species richness has been shown to increase biomass production of plant communities. Such overyielding occurs when a community performs better than its component monocultures due to the complementarity or dominance effect and is mostly detected in substrate-bound plant communities (terrestrial plants or submerged macrophytes) where resource use complementarity can be enhanced due to differences in rooting architecture and depth. Here, we investigated whether these findings arc generalizeable for free-floating phytoplankton with little potential for spatial differences in resource use. We performed aquatic microcosm experiments with eight phytoplankton species belonging to four functional groups to determine the manner in which species and community biovolume varies in relation to the number of functional groups and hypothesized that an increasing number of functional groups within a community promotes overyielding. Unexpectedly, we did not detect overyielding in any algal community. Instead. total community biovolume tended to decrease with all increasing, number of functional groups. This underyielding was mainly caused by the negative dominance effect that originated from a trade-off between growth rate and filial biovolume. In monoculture, slow-groing species built up higher biovolumes that fast-growing ones, whereas in mixture a fast-growing but low-productive species monopolized most of the nutrients and prevented competing species from developing high biovolumes expected from monocultures. Our results indicated that the Magnitude of the community biovolume was largely determined by the identify of one species. Functional diversity and resource use complementarity were of minor Importance among free-floating phytoplankton, possibly reflecting the lack of spatially heterogeneous resource distribution. As a consequence, biodiversity-ecosystem functioning relationships may not be easily generalizeable from substrate-bound plant to phytoplankton communities and vice versa.}, language = {en} } @article{VasseurGaedkeMcCann2005, author = {Vasseur, David and Gaedke, Ursula and McCann, Kevin S.}, title = {A seasonal alternation of coherent and compensatory dynamics occurs in phytoplankton}, year = {2005}, abstract = {Functional groups with diverse responses to environmental factors sum to produce communities with less temporal variability in their biomass than those lacking this diversity. The detection of these compensatory dynamics can be complicated by a spatio-temporal alternation in the environmental factors limiting growth (both abiotic and biotic), which restricts the occurrence of compensatory dynamics to certain periods or locations. Hence, resolving the spatio- temporal scale may uncover important spatial and/or temporal components in community variability. Using long-term data from Lake Constance (Bodensee), we find that a reduction in grazing pressure and relaxed competition for nutrients during winter and spring generates coherent dynamics among edible and less edible phytoplankton. During summer and fall, when both grazing pressure and nutrient limitation are present, edible and less edible phytoplankton exhibit compensatory dynamics. This study supports recent work suggesting that both abiotic and biotic interactions promote compensatory dynamics and to our knowledge, this is the first example of a system where compensatory and coherent dynamics seasonally alternate.}, language = {en} } @article{KathBoitGuilletal.2018, author = {Kath, Nadja J. and Boit, Alice and Guill, Christian and Gaedke, Ursula}, title = {Accounting for activity respiration results in realistic trophic transfer efficiencies in allometric trophic network (ATN) models}, series = {Theoretical ecology}, volume = {11}, journal = {Theoretical ecology}, number = {4}, publisher = {Springer}, address = {Heidelberg}, issn = {1874-1738}, doi = {10.1007/s12080-018-0378-z}, pages = {453 -- 463}, year = {2018}, abstract = {Allometric trophic network (ATN) models offer high flexibility and scalability while minimizing the number of parameters and have been successfully applied to investigate complex food web dynamics and their influence on food web diversity and stability. However, the realism of ATN model energetics has never been assessed in detail, despite their critical influence on dynamic biomass and production patterns. Here, we compare the energetics of the currently established original ATN model, considering only biomass-dependent basal respiration, to an extended ATN model version, considering both basal and assimilation-dependent activity respiration. The latter is crucial in particular for unicellular and invertebrate organisms which dominate the metabolism of pelagic and soil food webs. Based on metabolic scaling laws, we show that the extended ATN version reflects the energy transfer through a chain of four trophic levels of unicellular and invertebrate organisms more realistically than the original ATN version. Depending on the strength of top-down control, the original ATN model yields trophic transfer efficiencies up to 71\% at either the third or the fourth trophic level, which considerably exceeds any realistic values. In contrast, the extended ATN version yields realistic trophic transfer efficiencies 30\% at all trophic levels, in accordance with both physiological considerations and empirical evidence from pelagic systems. Our results imply that accounting for activity respiration is essential for consistently implementing the metabolic theory of ecology in ATN models and for improving their quantitative predictions, which makes them more powerful tools for investigating the dynamics of complex natural communities.}, language = {en} } @article{GaedkeKlauschies2017, author = {Gaedke, Ursula and Klauschies, Toni}, title = {Analyzing the shape of observed trait distributions enables a data-based moment closure of aggregate models}, series = {Limnology and Oceanography: Methods}, volume = {15}, journal = {Limnology and Oceanography: Methods}, publisher = {Wiley}, address = {Hoboken}, issn = {1541-5856}, doi = {10.1002/lom3.10218}, pages = {979 -- 994}, year = {2017}, abstract = {The shape of trait distributions may inform about the selective forces that structure ecological communities. Here, we present a new moment-based approach to classify the shape of observed biomass-weighted trait distributions into normal, peaked, skewed, or bimodal that facilitates spatio-temporal and cross-system comparisons. Our observed phytoplankton trait distributions exhibited substantial variance and were mostly skewed or bimodal rather than normal. Additionally, mean, variance, skewness und kurtosis were strongly correlated. This is in conflict with trait-based aggregate models that often assume normally distributed trait values and small variances. Given these discrepancies between our data and general model assumptions we used the observed trait distributions to test how well different aggregate models with first- or second-order approximations and different types of moment closure predict the biomass, mean trait, and trait variance dynamics using weakly or moderately nonlinear fitness functions. For weakly non-linear fitness functions aggregate models with a second-order approximation and a data-based moment closure that relied on the observed correlations between skewness and mean, and kurtosis and variance predicted biomass and often also mean trait changes fairly well and better than models with first-order approximations or a normal-based moment closure. In contrast, none of the models reflected the changes of the trait variances reliably. Aggregate model performance was often also poor for moderately nonlinear fitness functions. This questions a general applicability of the normal-based approach, in particular for predicting variance dynamics determining the speed of trait changes and maintenance of biodiversity. We evaluate in detail how and why better approximations can be obtained.}, language = {en} } @article{BoitGaedke2014, author = {Boit, Alice and Gaedke, Ursula}, title = {Benchmarking successional progress in a quantitative food web}, series = {PLoS one}, volume = {9}, journal = {PLoS one}, number = {2}, publisher = {PLoS}, address = {San Fransisco}, issn = {1932-6203}, doi = {10.1371/journal.pone.0090404}, pages = {25}, year = {2014}, abstract = {Central to ecology and ecosystem management, succession theory aims to mechanistically explain and predict the assembly and development of ecological communities. Yet processes at lower hierarchical levels, e. g. at the species and functional group level, are rarely mechanistically linked to the under-investigated system-level processes which drive changes in ecosystem properties and functioning and are comparable across ecosystems. As a model system for secondary succession, seasonal plankton succession during the growing season is readily observable and largely driven autogenically. We used a long-term dataset from large, deep Lake Constance comprising biomasses, auto-and heterotrophic production, food quality, functional diversity, and mass-balanced food webs of the energy and nutrient flows between functional guilds of plankton and partly fish. Extracting population-and system-level indices from this dataset, we tested current hypotheses about the directionality of successional progress which are rooted in ecosystem theory, the metabolic theory of ecology, quantitative food web theory, thermodynamics, and information theory. Our results indicate that successional progress in Lake Constance is quantifiable, passing through predictable stages. Mean body mass, functional diversity, predator-prey weight ratios, trophic positions, system residence times of carbon and nutrients, and the complexity of the energy flow patterns increased during succession. In contrast, both the mass-specific metabolic activity and the system export decreased, while the succession rate exhibited a bimodal pattern. The weighted connectance introduced here represents a suitable index for assessing the evenness and interconnectedness of energy flows during succession. Diverging from earlier predictions, ascendency and eco-exergy did not increase during succession. Linking aspects of functional diversity to metabolic theory and food web complexity, we reconcile previously disjoint bodies of ecological theory to form a complete picture of successional progress within a pelagic food web. This comprehensive synthesis may be used as a benchmark for quantifying successional progress in other ecosystems.}, language = {en} } @article{LischkeMehnerHiltetal.2017, author = {Lischke, Betty and Mehner, Thomas and Hilt, Sabine and Attermeyer, Katrin and Brauns, Mario and Brothers, Soren M. and Grossart, Hans-Peter and Koehler, Jan and Scharnweber, Inga Kristin and Gaedke, Ursula}, title = {Benthic carbon is inefficiently transferred in the food webs of two eutrophic shallow lakes}, series = {Freshwater biology}, volume = {62}, journal = {Freshwater biology}, publisher = {Wiley}, address = {Hoboken}, issn = {0046-5070}, doi = {10.1111/fwb.12979}, pages = {1693 -- 1706}, year = {2017}, abstract = {The sum of benthic autotrophic and bacterial production often exceeds the sum of pelagic autotrophic and bacterial production, and hence may contribute substantially to whole-lake carbon fluxes, especially in shallow lakes. Furthermore, both benthic and pelagic autotrophic and bacterial production are highly edible and of sufficient nutritional quality for animal consumers. We thus hypothesised that pelagic and benthic transfer efficiencies (ratios of production at adjacent trophic levels) in shallow lakes should be similar. We performed whole ecosystem studies in two shallow lakes (3.5ha, mean depth 2m), one with and one without submerged macrophytes, and quantified pelagic and benthic biomass, production and transfer efficiencies for bacteria, phytoplankton, epipelon, epiphyton, macrophytes, zooplankton, macrozoobenthos and fish. We expected higher transfer efficiencies in the lake with macrophytes, because these provide shelter and food for macrozoobenthos and may thus enable a more efficient conversion of basal production to consumer production. In both lakes, the majority of the whole-lake autotrophic and bacterial production was provided by benthic organisms, but whole-lake primary consumer production mostly relied on pelagic autotrophic and bacterial production. Consequently, transfer efficiency of benthic autotrophic and bacterial production to macrozoobenthos production was an order of magnitude lower than the transfer efficiency of pelagic autotrophic and bacterial production to rotifer and crustacean production. Between-lake differences in transfer efficiencies were minor. We discuss several aspects potentially causing the unexpectedly low benthic transfer efficiencies, such as the food quality of producers, pelagic-benthic links, oxygen concentrations in the deeper lake areas and additional unaccounted consumer production by pelagic and benthic protozoa and meiobenthos at intermediate or top trophic levels. None of these processes convincingly explain the large differences between benthic and pelagic transfer efficiencies. Our data indicate that shallow eutrophic lakes, even with a major share of autotrophic and bacterial production in the benthic zone, can function as pelagic systems with respect to primary consumer production. We suggest that the benthic autotrophic production was mostly transferred to benthic bacterial production, which remained in the sediments, potentially cycling internally in a similar way to what has previously been described for the microbial loop in pelagic habitats. Understanding the energetics of whole-lake food webs, including the fate of the substantial benthic bacterial production, which is either mineralised at the sediment surface or permanently buried, has important implications for regional and global carbon cycling.}, language = {en} } @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{CoutinhoKlauschiesGaedke2016, author = {Coutinho, Renato Mendes and Klauschies, Toni and Gaedke, Ursula}, title = {Bimodal trait distributions with large variances question the reliability of trait-based aggregate models}, series = {Theoretical ecology}, volume = {9}, journal = {Theoretical ecology}, publisher = {Springer}, address = {Heidelberg}, issn = {1874-1738}, doi = {10.1007/s12080-016-0297-9}, pages = {389 -- 408}, year = {2016}, abstract = {Functionally diverse communities can adjust their species composition to altered environmental conditions, which may influence food web dynamics. Trait-based aggregate models cope with this complexity by ignoring details about species identities and focusing on their functional characteristics (traits). They describe the temporal changes of the aggregate properties of entire communities, including their total biomasses, mean trait values, and trait variances. The applicability of aggregate models depends on the validity of their underlying assumptions that trait distributions are normal and exhibit small variances. We investigated to what extent this can be expected to work by comparing an innovative model that accounts for the full trait distributions of predator and prey communities to a corresponding aggregate model. We used a food web structure with well-established trade-offs among traits promoting mutual adjustments between prey edibility and predator selectivity in response to selection. We altered the shape of the trade-offs to compare the outcome of the two models under different selection regimes, leading to trait distributions increasingly deviating from normality. Their biomass and trait dynamics agreed very well for stabilizing selection and reasonably well for directional selection, under which different trait values are favored at different times. However, for disruptive selection, the results of the aggregate model strongly deviated from the full trait distribution model that showed bimodal trait distributions with large variances. Hence, the outcome of aggregate models is reliable under ideal conditions but has to be questioned when confronted with more complex selection regimes and trait distributions, which are commonly observed in nature.}, language = {en} } @book{GaedkeSeifriedAdrian2004, author = {Gaedke, Ursula and Seifried, Angelika and Adrian, Rita}, title = {Biomass size spectra and plankton diversity in a shallow eutrophic lake}, issn = {1434-2944}, year = {2004}, abstract = {Biomass size spectra collate structural and functional attributes of plankton communities enabling standardised temporal and cross-system comparisons and may be rapidly obtained by automated particle counters. To examine how differences in plankton communities from highly eutrophic and more oligotrophic lakes are reflected in size spectra, a three-year time series of biomass size spectra was established for polymictic, eutrophic Lake M{\"u}ggelsee, based on approximately weekly sampling and microscopic enumeration. The continuous but often bumpy size spectra reflected appropriately the seasonal and trophy-related variations in the plankton composition and growth conditions and the potential impact of daphnids on smaller plankton. We tested the hypothesis that more diverse plankton communities have smoother size spectra than impoverished ones. The spectra of L. M{\"u}ggelsee and other more less eutrophic lakes covaried roughly with the functional diversity in total plankton composition but were unrelated to taxonomical diversity within the phyto- or mesozooplankton. The slopes of the normalised size spectra of Lake M{\"u}ggelsee were generally more negative than -1, exhibited a recurrent seasonal pattern, and were strongly correlated with crustacean biomass. In contrast to less eutrophic systems, slopes could not be used to quantify energy fluxes within the foodweb due to highly variable algal P/B ratios and frequently bumpy size distributions. The latter indicated stronger deviations from the ideal concept of a steady energy flow along the size gradient than found in e. g. large, mesotrophic Lake Constance.}, 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} } @misc{MooijTrolleJeppesenetal.2010, author = {Mooij, Wolf M. and Trolle, Dennis and Jeppesen, Erik and Arhonditsis, George B. and Belolipetsky, Pavel V. and Chitamwebwa, Deonatus B. R. and Degermendzhy, Andrey G. and DeAngelis, Donald L. and Domis, Lisette Nicole de Senerpont and Downing, Andrea S. and Elliott, J. Alex and Fragoso Jr., Carlos Ruberto and Gaedke, Ursula and Genova, Svetlana N. and Gulati, Ramesh D. and H{\aa}kanson, Lars and Hamilton, David P. and Hipsey, Matthew R. and 't Hoen, Jochem and H{\"u}lsmann, Stephan and Los, F. Hans and Makler-Pick, Vardit and Petzoldt, Thomas and Prokopkin, Igor G. and Rinke, Karsten and Schep, Sebastiaan A. and Tominaga, Koji and Van Dam, Anne A. and Van Nes, Egbert H. and Wells, Scott A. and Janse, Jan H.}, title = {Challenges and opportunities for integrating lake ecosystem modelling approaches}, series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1326}, issn = {1866-8372}, doi = {10.25932/publishup-42983}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-429839}, pages = {35}, year = {2010}, abstract = {A large number and wide variety of lake ecosystem models have been developed and published during the past four decades. We identify two challenges for making further progress in this field. One such challenge is to avoid developing more models largely following the concept of others ('reinventing the wheel'). The other challenge is to avoid focusing on only one type of model, while ignoring new and diverse approaches that have become available ('having tunnel vision'). In this paper, we aim at improving the awareness of existing models and knowledge of concurrent approaches in lake ecosystem modelling, without covering all possible model tools and avenues. First, we present a broad variety of modelling approaches. To illustrate these approaches, we give brief descriptions of rather arbitrarily selected sets of specific models. We deal with static models (steady state and regression models), complex dynamic models (CAEDYM, CE-QUAL-W2, Delft 3D-ECO, LakeMab, LakeWeb, MyLake, PCLake, PROTECH, SALMO), structurally dynamic models and minimal dynamic models. We also discuss a group of approaches that could all be classified as individual based: super-individual models (Piscator, Charisma), physiologically structured models, stage-structured models and traitbased models. We briefly mention genetic algorithms, neural networks, Kalman filters and fuzzy logic. Thereafter, we zoom in, as an in-depth example, on the multi-decadal development and application of the lake ecosystem model PCLake and related models (PCLake Metamodel, Lake Shira Model, IPH-TRIM3D-PCLake). In the discussion, we argue that while the historical development of each approach and model is understandable given its 'leading principle', there are many opportunities for combining approaches. We take the point of view that a single 'right' approach does not exist and should not be strived for. Instead, multiple modelling approaches, applied concurrently to a given problem, can help develop an integrative view on the functioning of lake ecosystems. We end with a set of specific recommendations that may be of help in the further development of lake ecosystem models.}, language = {en} } @article{MooijTrolleJeppesenetal.2010, author = {Mooij, Wolf M. and Trolle, Dennis and Jeppesen, Erik and Arhonditsis, George B. and Belolipetsky, Pavel V. and Chitamwebwa, Deonatus B. R. and Degermendzhy, Andrey G. and DeAngelis, Donald L. and Domis, Lisette Nicole de Senerpont and Downing, Andrea S. and Elliott, J. Alex and Fragoso Jr, Carlos Ruberto and Gaedke, Ursula and Genova, Svetlana N. and Gulati, Ramesh D. and H{\aa}kanson, Lars and Hamilton, David P. and Hipsey, Matthew R. and 't Hoen, Jochem and H{\"u}lsmann, Stephan and Los, F. Hans and Makler-Pick, Vardit and Petzoldt, Thomas and Prokopkin, Igor G. and Rinke, Karsten and Schep, Sebastiaan A. and Tominaga, Koji and Van Dam, Anne A. and Van Nes, Egbert H. and Wells, Scott A. and Janse, Jan H.}, title = {Challenges and opportunities for integrating lake ecosystem modelling approaches}, series = {Aquatic ecology}, volume = {44}, journal = {Aquatic ecology}, publisher = {Springer Science + Business Media B.V.}, address = {Dordrecht}, issn = {1573-5125}, doi = {10.1007/s10452-010-9339-3}, pages = {633 -- 667}, year = {2010}, abstract = {A large number and wide variety of lake ecosystem models have been developed and published during the past four decades. We identify two challenges for making further progress in this field. One such challenge is to avoid developing more models largely following the concept of others ('reinventing the wheel'). The other challenge is to avoid focusing on only one type of model, while ignoring new and diverse approaches that have become available ('having tunnel vision'). In this paper, we aim at improving the awareness of existing models and knowledge of concurrent approaches in lake ecosystem modelling, without covering all possible model tools and avenues. First, we present a broad variety of modelling approaches. To illustrate these approaches, we give brief descriptions of rather arbitrarily selected sets of specific models. We deal with static models (steady state and regression models), complex dynamic models (CAEDYM, CE-QUAL-W2, Delft 3D-ECO, LakeMab, LakeWeb, MyLake, PCLake, PROTECH, SALMO), structurally dynamic models and minimal dynamic models. We also discuss a group of approaches that could all be classified as individual based: super-individual models (Piscator, Charisma), physiologically structured models, stage-structured models and traitbased models. We briefly mention genetic algorithms, neural networks, Kalman filters and fuzzy logic. Thereafter, we zoom in, as an in-depth example, on the multi-decadal development and application of the lake ecosystem model PCLake and related models (PCLake Metamodel, Lake Shira Model, IPH-TRIM3D-PCLake). In the discussion, we argue that while the historical development of each approach and model is understandable given its 'leading principle', there are many opportunities for combining approaches. We take the point of view that a single 'right' approach does not exist and should not be strived for. Instead, multiple modelling approaches, applied concurrently to a given problem, can help develop an integrative view on the functioning of lake ecosystems. We end with a set of specific recommendations that may be of help in the further development of lake ecosystem models.}, language = {en} } @book{GaedkeWickham2004, author = {Gaedke, Ursula and Wickham, Steve}, title = {Ciliate dynamics in response to changing biotic and abiotic conditions in a large, deep lake (L. Constance)}, issn = {0948-3055}, year = {2004}, abstract = {During 1987-1998, the ciliates and their prey and predator communities in large, deep, mesotrophic Lake Constance were intensively studied as it underwent re-oligotrophication. Ciliate biomass exhibited the bimodal seasonal distribution typical for meso-eutrophic lakes, with high biomass in spring and summer and low biomass in winter and during the clear-water phase. Cluster analysis produced nine groups of temporally co-occurring ciliate morphotypes with potentially similar ecological characteristics. The clusters exhibited a larger seasonality than found in the size distribution, showing that similarly-sized ciliates had seasonally compensatory dynamics. Ciliate biomass declined by approx. 30 \% during the 12 years of study, i.e. considerably less than daphnids (and total phosphorus). This yielded a significant increase in the ratio between summer ciliate and daphnid biomass as re-oligotrophication progressed, in contrast to previous studies. Few indications for a mechanistic link between phosphorus concentrations (which declined threefold during the study period) and ciliate biomass or community composition via group-specific food concentrations were found. The relative contribution of three of the nine clusters changed as re-oligotrophication progressed. Ciliate size distribution was related to reoligotrophication and daphnid biomass in summer. The smallest and largest ciliates gained in importance when daphnids decreased whereas large ciliates declined. Overall, summer daphnid biomas had a greater predictive power for attributes of the ciliate community than the other factors studied (phosphorus, prey biomass, copepod biomass). The extent of bottom-up and top-down control of ciliates appeared to be time and group specific. Overall, the ciliate community exhibited remarkably recurrent seasonal patterns despite major alternations in abiotic and biotic conditions.}, 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{WeithoffRochaGaedke2015, author = {Weithoff, Guntram and Rocha, Marcia R. and Gaedke, Ursula}, title = {Comparing seasonal dynamics of functional and taxonomic diversity reveals the driving forces underlying phytoplankton community structure}, series = {Freshwater biology}, volume = {60}, journal = {Freshwater biology}, number = {4}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0046-5070}, doi = {10.1111/fwb.12527}, pages = {758 -- 767}, year = {2015}, abstract = {In most biodiversity studies, taxonomic diversity is the measure for the multiplicity of species and is often considered to represent functional diversity. However, trends in taxonomic diversity and functional diversity may differ, for example, when many functionally similar but taxonomically different species co-occur in a community. The differences between these diversity measures are of particular interest in diversity research for understanding diversity patterns and their underlying mechanisms. We analysed a temporally highly resolved 20-year time series of lake phytoplankton to determine whether taxonomic diversity and functional diversity exhibit similar or contrasting seasonal patterns. We also calculated the functional mean of the community in n-dimensional trait space for each sampling day to gain further insights into the seasonal dynamics of the functional properties of the community. We found an overall weak positive relationship between taxonomic diversity and functional diversity with a distinct seasonal pattern. The two diversity measures showed synchronous behaviour from early spring to mid-summer and a more complex and diverging relationship from autumn to late winter. The functional mean of the community exhibited a recurrent annual pattern with the most prominent changes before and after the clear-water phase. From late autumn to winter, the functional mean of the community and functional diversity were relatively constant while taxonomic diversity declined, suggesting competitive exclusion during this period. A further decline in taxonomic diversity concomitant with increasing functional diversity in late winter to early spring is seen as a result of niche diversification together with competitive exclusion. Under these conditions, several different sets of traits are suitable to thrive, but within one set of functional traits only one, or very few, morphotypes can persist. Taxonomic diversity alone is a weak descriptor of trait diversity in phytoplankton. However, the combined analysis of taxonomic diversity and functional diversity, along with the functional mean of the community, allows for deeper insights into temporal patterns of community assembly and niche diversification.}, language = {en} } @article{HoulahanCurrieCottenieetal.2007, author = {Houlahan, Jeff E. and Currie, David J. and Cottenie, Karl and Cumming, Graeme S. and Ernest, S. K. Morgan and Findlay, C. Scott and Fuhlendorf, Samuel D. and Gaedke, Ursula and Legendre, Pierre and Magnuson, John J. and McArdle, Brian H. and Muldavin, Esteban H. and Noble, David and Russell, Robert and Stevens, Richard D. and Willis, Trevor J. and Woiwod, Ian P. and Wondzell, Steve M.}, title = {Compensatory dynamics are rare in natural ecological communities}, issn = {0027-8424}, doi = {10.1073/pnas.0603798104}, year = {2007}, abstract = {In population ecology, there has been a fundamental controversy about the relative importance of competition- driven (density-dependent) population regulation vs. abiotic influences such as temperature and precipitation. The same issue arises at the community level; are population sizes driven primarily by changes in the abundances of cooccurring competitors (i.e., compensatory dynamics), or do most species have a common response to environmental factors? Competitive interactions have had a central place in ecological theory, dating back to Gleason, Volterra, Hutchison and MacArthur, and, more recently, Hubbell's influential unified neutral theory of biodiversity and biogeography. If competitive interactions are important in driving year-to-year fluctuations in abundance, then changes in the abundance of one species should generally be accompanied by compensatory changes in the abundances of others. Thus, one necessary consequence of strong compensatory forces is that, on average, species within communities will covary negatively. Here we use measures of community covariance to assess the prevalence of negative covariance in 41 natural communities comprising different taxa at a range of spatial scales. We found that species in natural communities tended to covary positively rather than negatively, the opposite of what would be expected if compensatory dynamics were important. These findings suggest that abiotic factors such as temperature and precipitation are more important than competitive interactions in driving year-to-year fluctuations in species abundance within communities.}, language = {en} } @article{CleggGaedkeBoehreretal.2012, author = {Clegg, Mark R. and Gaedke, Ursula and B{\"o}hrer, Bertram and Spijkerman, Elly}, title = {Complementary ecophysiological strategies combine to facilitate survival in the hostile conditions of a deep chlorophyll maximum}, series = {Oecologia}, volume = {169}, journal = {Oecologia}, number = {3}, publisher = {Springer}, address = {New York}, issn = {0029-8549}, doi = {10.1007/s00442-011-2225-4}, pages = {609 -- 622}, year = {2012}, abstract = {In the deep, cooler layers of clear, nutrient-poor, stratified water bodies, phytoplankton often accumulate to form a thin band or "deep chlorophyll maximum" (DCM) of ecological importance. Under such conditions, these photosynthetic microorganisms may be close to their physiological compensation points and to the boundaries of their ecological tolerance. To grow and survive any resulting energy limitation, DCM species are thought to exhibit highly specialised or flexible acclimation strategies. In this study, we investigated several of the adaptable ecophysiological strategies potentially employed by one such species, Chlamydomonas acidophila: a motile, unicellular, phytoplanktonic flagellate that often dominates the DCM in stratified, acidic lakes. Physiological and behavioural responses were measured in laboratory experiments and were subsequently related to field observations. Results showed moderate light compensation points for photosynthesis and growth at 22A degrees C, relatively low maintenance costs, a behavioural preference for low to moderate light, and a decreased compensation point for photosynthesis at 8A degrees C. Even though this flagellated alga exhibited a physiologically mediated diel vertical migration in the field, migrating upwards slightly during the day, the ambient light reaching the DCM was below compensation points, and so calculations of daily net photosynthetic gain showed that survival by purely autotrophic means was not possible. Results suggested that strategies such as low-light acclimation, small-scale directed movements towards light, a capacity for mixotrophic growth, acclimation to low temperature, in situ exposure to low O-2, high CO2 and high P concentrations, and an avoidance of predation, could combine to help overcome this energetic dilemma and explain the occurrence of the DCM. Therefore, corroborating the deceptive ecophysiological complexity of this and similar organisms, only a suite of complementary strategies can facilitate the survival of C. acidophila in this DCM.}, language = {en} } @article{MassieRyabovBlasiusetal.2013, author = {Massie, Thomas Michael and Ryabov, Alexei and Blasius, Bernd and Weithoff, Guntram and Gaedke, Ursula}, title = {Complex transient dynamics of stage-structured populations in response to environmental changes}, series = {The American naturalist : a bi-monthly journal devoted to the advancement and correlation of the biological sciences}, volume = {182}, journal = {The American naturalist : a bi-monthly journal devoted to the advancement and correlation of the biological sciences}, number = {1}, publisher = {Univ. of Chicago Press}, address = {Chicago}, issn = {0003-0147}, doi = {10.1086/670590}, pages = {103 -- 119}, year = {2013}, abstract = {Stage structures of populations can have a profound influence on their dynamics. However, not much is known about the transient dynamics that follow a disturbance in such systems. Here we combined chemostat experiments with dynamical modeling to study the response of the phytoplankton species Chlorella vulgaris to press perturbations. From an initially stable steady state, we altered either the concentration or dilution rate of a growth-limiting resource. This disturbance induced a complex transient response-characterized by the possible onset of oscillations-before population numbers relaxed to a new steady state. Thus, cell numbers could initially change in the opposite direction of the long-term change. We present quantitative indexes to characterize the transients and to show that the dynamic response is dependent on the degree of synchronization among life stages, which itself depends on the state of the population before perturbation. That is, we show how identical future steady states can be approached via different transients depending on the initial population structure. Our experimental results are supported by a size-structured model that accounts for interplay between cell-cycle and population-level processes and that includes resource-dependent variability in cell size. Our results should be relevant to other populations with a stage structure including organisms of higher order.}, language = {en} } @article{HiltWankeScharnweberetal.2015, author = {Hilt, Sabine and Wanke, Thomas and Scharnweber, Inga Kristin and Brauns, Mario and Syvaranta, Jari and Brothers, Soren M. and Gaedke, Ursula and K{\"o}hler, Jan and Lischke, Betty and Mehner, Thomas}, title = {Contrasting response of two shallow eutrophic cold temperate lakes to a partial winterkill of fish}, series = {Hydrobiologia : acta hydrobiologica, hydrographica, limnologica et protistologica}, volume = {749}, journal = {Hydrobiologia : acta hydrobiologica, hydrographica, limnologica et protistologica}, number = {1}, publisher = {Springer}, address = {Dordrecht}, issn = {0018-8158}, doi = {10.1007/s10750-014-2143-7}, pages = {31 -- 42}, year = {2015}, abstract = {Food-web effects of winterkill are difficult to predict as the enhanced mortality of planktivorous fish may be counterbalanced by an even higher mortality of piscivores. We hypothesised that a winterkill in a clear and a turbid shallow lake would equalise their fish community composition, but seasonal plankton successions would differ between lakes. After a partial winterkill, we observed a reduction of fish biomass by 16 and 43\% in a clear-water and a turbid small temperate lake, respectively. Fish biomass and piscivore shares (5\% of fish biomass) were similar in both lakes after this winterkill, but young-of-the-year (YOY) abundances were higher in the turbid lake. Top-down control by crustaceans was only partly responsible for low phytoplankton biomass at the end of May following the winterkill in both lakes. Summer phytoplankton biomass remained low in the clear-water lake despite high abundances of YOY fish (mainly roach). In contrast, the crustacean biomass of the turbid lake was reduced in summer by a high YOY abundance (sunbleak and roach), leading to a strong increase in phytoplankton biomass. The YOY abundance of fish in shallow eutrophic lakes may thus be more important for their summer phytoplankton development after winterkill than the relative abundance of piscivores.}, language = {en} }