TY - JOUR A1 - Klauschies, Toni A1 - Coutinho, Renato Mendes A1 - Gaedke, Ursula T1 - A beta distribution-based moment closure enhances the reliability of trait-based aggregate models for natural populations and communities JF - Ecological modelling : international journal on ecological modelling and engineering and systems ecolog N2 - 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. KW - Moment closure KW - Normal and beta distribution KW - Skewed and peaked trait distributions KW - Fitness landscape and frequency-dependent selection KW - Eco-evolutionary dynamics KW - Modelling functional diversity Y1 - 2018 U6 - https://doi.org/10.1016/j.ecolmodel.2018.02.001 SN - 0304-3800 SN - 1872-7026 VL - 381 SP - 46 EP - 77 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Schmidtke, Andrea A1 - Gaedke, Ursula A1 - Weithoff, Guntram T1 - A mechanistic basis for underyielding in phytoplankton communities N2 - 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. Y1 - 2010 UR - http://www.esajournals.org/doi/full/10.1890/08-2370.1 SN - 0012-9658 ER - TY - JOUR A1 - Vasseur, David A1 - Gaedke, Ursula A1 - McCann, Kevin S. T1 - A seasonal alternation of coherent and compensatory dynamics occurs in phytoplankton N2 - 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. Y1 - 2005 ER - TY - JOUR A1 - Kath, Nadja J. A1 - Boit, Alice A1 - Guill, Christian A1 - Gaedke, Ursula T1 - Accounting for activity respiration results in realistic trophic transfer efficiencies in allometric trophic network (ATN) models JF - Theoretical ecology N2 - 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. KW - Food web KW - Trophic transfer efficiency KW - Allometric trophic network model KW - Allometry KW - Energy transfer KW - Activity respiration Y1 - 2018 U6 - https://doi.org/10.1007/s12080-018-0378-z SN - 1874-1738 SN - 1874-1746 VL - 11 IS - 4 SP - 453 EP - 463 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Boit, Alice A1 - Gaedke, Ursula T1 - Benchmarking successional progress in a quantitative food web JF - PLoS one N2 - 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. Y1 - 2014 U6 - https://doi.org/10.1371/journal.pone.0090404 SN - 1932-6203 VL - 9 IS - 2 PB - PLoS CY - San Fransisco ER - TY - JOUR A1 - Lischke, Betty A1 - Mehner, Thomas A1 - Hilt, Sabine A1 - Attermeyer, Katrin A1 - Brauns, Mario A1 - Brothers, Soren M. A1 - Grossart, Hans-Peter A1 - Koehler, Jan A1 - Scharnweber, Inga Kristin A1 - Gaedke, Ursula T1 - Benthic carbon is inefficiently transferred in the food webs of two eutrophic shallow lakes JF - Freshwater biology N2 - 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. KW - bacterial production KW - benthic food chain KW - pelagic food chain KW - quantitative food webs KW - trophic transfer efficiency Y1 - 2017 U6 - https://doi.org/10.1111/fwb.12979 SN - 0046-5070 SN - 1365-2427 VL - 62 SP - 1693 EP - 1706 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Coutinho, Renato Mendes A1 - Klauschies, Toni A1 - Gaedke, Ursula T1 - Bimodal trait distributions with large variances question the reliability of trait-based aggregate models JF - Theoretical ecology N2 - 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. KW - Fitness gradient KW - Communities as complex adaptive systems KW - Moment closure for trait-based aggregate model approaches KW - Multimodal trait distributions KW - Lumpiness in pattern formation and self-organization KW - Shape of trade-offs and stabilizing and disruptive selection Y1 - 2016 U6 - https://doi.org/10.1007/s12080-016-0297-9 SN - 1874-1738 SN - 1874-1746 VL - 9 SP - 389 EP - 408 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Gaedke, Ursula A1 - Ruhenstroth-Bauer, Miriam A1 - Wiegand, Ina A1 - Tirok, Katrin A1 - Aberle-Malzahn, Nicole A1 - Breithaupt, Petra A1 - Lengfellner, Kathrin A1 - Wohlers, Julia A1 - Sommer, Ulrich T1 - Biotic interactions may overrule direct climate effects on spring phytoplankton dynamics N2 - 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. Y1 - 2010 UR - http://www3.interscience.wiley.com/cgi-bin/issn?DESCRIPTOR=PRINTISSN&VALUE=1354-1013 U6 - https://doi.org/10.1111/j.1365-2486.2009.02009.x SN - 1354-1013 ER - TY - JOUR A1 - Mooij, Wolf M. A1 - Trolle, Dennis A1 - Jeppesen, Erik A1 - Arhonditsis, George B. A1 - Belolipetsky, Pavel V. A1 - Chitamwebwa, Deonatus B. R. A1 - Degermendzhy, Andrey G. A1 - DeAngelis, Donald L. A1 - Domis, Lisette Nicole de Senerpont A1 - Downing, Andrea S. A1 - Elliott, J. Alex A1 - Fragoso Jr, Carlos Ruberto A1 - Gaedke, Ursula A1 - Genova, Svetlana N. A1 - Gulati, Ramesh D. A1 - Håkanson, Lars A1 - Hamilton, David P. A1 - Hipsey, Matthew R. A1 - ‘t Hoen, Jochem A1 - Hülsmann, Stephan A1 - Los, F. Hans A1 - Makler-Pick, Vardit A1 - Petzoldt, Thomas A1 - Prokopkin, Igor G. A1 - Rinke, Karsten A1 - Schep, Sebastiaan A. A1 - Tominaga, Koji A1 - Van Dam, Anne A. A1 - Van Nes, Egbert H. A1 - Wells, Scott A. A1 - Janse, Jan H. T1 - Challenges and opportunities for integrating lake ecosystem modelling approaches JF - Aquatic ecology N2 - 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. KW - aquatic KW - food web dynamics KW - plankton KW - nutrients KW - spatial KW - lake KW - freshwater KW - marine KW - community KW - population KW - hydrology KW - eutrophication KW - global change KW - climate warming KW - fisheries KW - biodiversity KW - management KW - mitigation KW - adaptive processes KW - non-linear dynamics KW - analysis KW - bifurcation KW - understanding KW - prediction KW - model limitations KW - model integration Y1 - 2010 U6 - https://doi.org/10.1007/s10452-010-9339-3 SN - 1573-5125 SN - 1386-2588 VL - 44 SP - 633 EP - 667 PB - Springer Science + Business Media B.V. CY - Dordrecht ER - TY - JOUR A1 - Klauschies, Toni A1 - Bauer, Barbara A1 - Aberle-Malzahn, Nicole A1 - Sommer, Ulrich A1 - Gaedke, Ursula T1 - Climate change effects on phytoplankton depend on cell size and food web structure JF - Marine biology : international journal on life in oceans and coastal waters N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1007/s00227-012-1904-y SN - 0025-3162 VL - 159 IS - 11 SP - 2455 EP - 2478 PB - Springer CY - New York ER - TY - JOUR A1 - Weithoff, Guntram A1 - Rocha, Marcia R. A1 - Gaedke, Ursula T1 - Comparing seasonal dynamics of functional and taxonomic diversity reveals the driving forces underlying phytoplankton community structure JF - Freshwater biology N2 - 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. KW - algae KW - biodiversity KW - functional traits KW - seasonality KW - time series Y1 - 2015 U6 - https://doi.org/10.1111/fwb.12527 SN - 0046-5070 SN - 1365-2427 VL - 60 IS - 4 SP - 758 EP - 767 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Houlahan, Jeff E. A1 - Currie, David J. A1 - Cottenie, Karl A1 - Cumming, Graeme S. A1 - Ernest, S. K. Morgan A1 - Findlay, C. Scott A1 - Fuhlendorf, Samuel D. A1 - Gaedke, Ursula A1 - Legendre, Pierre A1 - Magnuson, John J. A1 - McArdle, Brian H. A1 - Muldavin, Esteban H. A1 - Noble, David A1 - Russell, Robert A1 - Stevens, Richard D. A1 - Willis, Trevor J. A1 - Woiwod, Ian P. A1 - Wondzell, Steve M. T1 - Compensatory dynamics are rare in natural ecological communities N2 - 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. Y1 - 2007 UR - http://www.pnas.org/ U6 - https://doi.org/10.1073/pnas.0603798104 SN - 0027-8424 ER - TY - JOUR A1 - Clegg, Mark R. A1 - Gaedke, Ursula A1 - Böhrer, Bertram A1 - Spijkerman, Elly T1 - Complementary ecophysiological strategies combine to facilitate survival in the hostile conditions of a deep chlorophyll maximum JF - Oecologia N2 - 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. KW - DCM KW - Photosynthesis KW - Growth KW - Behaviour KW - Phytoplankton Y1 - 2012 U6 - https://doi.org/10.1007/s00442-011-2225-4 SN - 0029-8549 VL - 169 IS - 3 SP - 609 EP - 622 PB - Springer CY - New York ER - TY - JOUR A1 - Massie, Thomas Michael A1 - Ryabov, Alexei A1 - Blasius, Bernd A1 - Weithoff, Guntram A1 - Gaedke, Ursula T1 - Complex transient dynamics of stage-structured populations in response to environmental changes JF - The American naturalist : a bi-monthly journal devoted to the advancement and correlation of the biological sciences N2 - 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. KW - chemostat experiments KW - Chlorella vulgaris KW - environmental changes KW - population dynamics KW - stage structure KW - transient dynamics Y1 - 2013 U6 - https://doi.org/10.1086/670590 SN - 0003-0147 SN - 1537-5323 VL - 182 IS - 1 SP - 103 EP - 119 PB - Univ. of Chicago Press CY - Chicago ER - TY - JOUR A1 - Ehrlich, Elias A1 - Gaedke, Ursula T1 - Coupled changes in traits and biomasses cascading through a tritrophic plankton food web JF - Limnology and oceanography N2 - 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. KW - community ecology KW - cyclops vicinus KW - dynamics KW - functional traits KW - lake KW - life-cycle KW - natural rotifer KW - phytoplankton KW - trophic cascades KW - zooplankton Y1 - 2020 U6 - https://doi.org/10.1002/lno.11466 SN - 0024-3590 SN - 1939-5590 VL - 65 IS - 10 SP - 2502 EP - 2514 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Raatz, Michael A1 - van Velzen, Ellen A1 - Gaedke, Ursula T1 - Co‐adaptation impacts the robustness of predator–prey dynamics against perturbations JF - Ecology and Evolution N2 - Global change threatens the maintenance of ecosystem functions that are shaped by the persistence and dynamics of populations. It has been shown that the persistence of species increases if they possess larger trait adaptability. Here, we investigate whether trait adaptability also affects the robustness of population dynamics of interacting species and thereby shapes the reliability of ecosystem functions that are driven by these dynamics. We model co‐adaptation in a predator–prey system as changes to predator offense and prey defense due to evolution or phenotypic plasticity. We investigate how trait adaptation affects the robustness of population dynamics against press perturbations to environmental parameters and against pulse perturbations targeting species abundances and their trait values. Robustness of population dynamics is characterized by resilience, elasticity, and resistance. In addition to employing established measures for resilience and elasticity against pulse perturbations (extinction probability and return time), we propose the warping distance as a new measure for resistance against press perturbations, which compares the shapes and amplitudes of pre‐ and post‐perturbation population dynamics. As expected, we find that the robustness of population dynamics depends on the speed of adaptation, but in nontrivial ways. Elasticity increases with speed of adaptation as the system returns more rapidly to the pre‐perturbation state. Resilience, in turn, is enhanced by intermediate speeds of adaptation, as here trait adaptation dampens biomass oscillations. The resistance of population dynamics strongly depends on the target of the press perturbation, preventing a simple relationship with the adaptation speed. In general, we find that low robustness often coincides with high amplitudes of population dynamics. Hence, amplitudes may indicate the robustness against perturbations also in other natural systems with similar dynamics. Our findings show that besides counteracting extinctions, trait adaptation indeed strongly affects the robustness of population dynamics against press and pulse perturbations. KW - disturbance KW - evolutionary rescue KW - population dynamics KW - stability KW - trait adaptation Y1 - 2019 U6 - https://doi.org/10.1002/ece3.5006 SN - 2045-7758 VL - 9 IS - 7 SP - 3823 EP - 3836 PB - John Wiley & Sons CY - Hoboken, NJ ER - TY - JOUR A1 - Gaedke, Ursula A1 - Straile, Dietmar T1 - Daphnids : Keystone species for the pelagic food web structure and energy flow ; a body size related analysis linking seasonal changes on the population and ecosystem level N2 - Seasonal changes of the impact of daphnids on the plankton biomass size distribution, the biomass within individual size ranges, the average predator-prey weight ratios, and the efficiency to transfer matter and energy from small to large organisms are analyzed in large and deep Lake Constance based on comprehensive long-term observations. A comparison of daphnid biomass and production with those of other herbivorous groups (i. e. ciliates, rotifers, herbivorous crustaceans) reveals that in early spring daphnids play a minor role in relative and absolute values as compared to small fast growing ciliates. During this time, small algae and ciliates dominate which gives rise to a decreasing Sheldon-type size spectrum, low predator-prey weight ratios, and a low transfer efficiency along the size gradient. Around June, daphnids reach maximum abundances and become keystone species for the shape of the biomass size distribution, the food web structure, and the energy flow. They accumulate biomass in their size range one order of magnitude above the average. The slope of the normalized biomass size spectrum is less negative and positively correlated with daphnid biomass if the latter exceeds about 200 mg C/m2. This indicates a more efficient transfer along the size gradient with high predator-prey weight ratios and high trophic transfer efficiencies. The coefficients of determination of regression lines fitted to size distributions decrease with daphnid abundance, i. e. the size spectra become more irregular when daphnids dominate. In midsummer, daphnids lose their dominance and coexist with other herbivores (especially ciliates) in a highly diverse plankton community. The latter gives rise to a relatively smooth and almost flat Sheldon-type size distribution, lower predator-prey weight ratios, and a slightly reduced transfer efficiency along the size gradient. In late spring/early summer, negative relationships are found between daphnid biomass and the biomasses in the size ranges of autotrophic picoplankton, small phytoplankton, heterotrophic flagellates, and small and medium sized ciliates (0.06 - 32 pg C and 100-30,000 pg C). In mid- and late summer or on annual average, hardly any of these relationships existed. This cannot solely be attributed to lower daphnid abundance but points also to a more diverse control of small plankton organisms including nutrient limitation in summer. Ciliates influence the slope and shape of the size distribution much less than daphnids although they are at least of equal importance as daphnids in respect to herbivory and related fluxes in Lake Constance on annual average. The findings on the impact of daphnids on the energy flow within the plankton food web derived from size distributions are compared to, and are consistent with results obtained by mass-balanced carbon flow diagrams. Y1 - 1998 ER - TY - JOUR A1 - Spijkerman, Elly A1 - Behrend, Hella A1 - Fach, Bettina A1 - Gaedke, Ursula T1 - Decreased phosphorus incorporation explains the negative effect of high iron concentrations in the green microalga Chlamydomonas acidophila JF - The science of the total environment : an international journal for scientific research into the environment and its relationship with man N2 - The green microalga Chlamydomonas acidophila is an important primary producer in very acidic lakes (pH 2.0-3.5), characterized by high concentrations of ferric iron (up to 1 g total Fe L-1) and low rates of primary production. It was previously suggested that these high iron concentrations result in high iron accumulation and inhibit photosynthesis in C. acidophila. To test this, the alga was grown in sterilized lake water and in medium with varying total iron concentrations under limiting and sufficient inorganic phosphorus (Pi) supply, because Pi is an important growth limiting nutrient in acidic waters. Photosynthesis and growth of C. acidophila as measured over 5 days were largely unaffected by high total iron concentrations and only decreased if free ionic Fe3+ concentrations exceeded 100 mg Fe3+ L-1. Although C. acidophila was relatively rich in iron (up to 5 mmol Fe: mol C), we found no evidence of iron toxicity. In contrast, a concentration of 260 mg total Fe L-1 (i.e. 15 mg free ionic Fe3+ L-1), which is common in many acidic lakes, reduced Pi-incorporation by 50% and will result in Pi-limited photosynthesis. The resulting Pi-limitation present at high iron and Pi concentrations was illustrated by elevated maximum Pi-uptake rates. No direct toxic effects of high iron were found, but unfavourable chemical Pi-speciation reduced growth of the acidophile alga. KW - Chlamydomonas KW - Ecotoxicology KW - Extreme environment KW - Iron toxicity KW - Phosphate limitation KW - Phytoplankton Y1 - 2018 U6 - https://doi.org/10.1016/j.scitotenv.2018.01.188 SN - 0048-9697 SN - 1879-1026 VL - 626 SP - 1342 EP - 1349 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - van Velzen, Ellen A1 - Gaedke, Ursula T1 - Disentangling eco-evolutionary dynamics of predator-prey coevolution: the case of antiphase cycles JF - Scientific reports N2 - The impact of rapid predator-prey coevolution on predator-prey dynamics remains poorly understood, as previous modelling studies have given rise to contradictory conclusions and predictions. Interpreting and reconciling these contradictions has been challenging due to the inherent complexity of model dynamics, defying mathematical analysis and mechanistic understanding. We develop a new approach here, based on the Geber method for deconstructing eco-evolutionary dynamics, for gaining such understanding. We apply this approach to a co-evolutionary predator-prey model to disentangle the processes leading to either antiphase or 1/4-lag cycles. Our analysis reveals how the predator-prey phase relationship is driven by the temporal synchronization between prey biomass and defense dynamics. We further show when and how prey biomass and trait dynamics become synchronized, resulting in antiphase cycles, allowing us to explain and reconcile previous modelling and empirical predictions. The successful application of our proposed approach provides an important step towards a comprehensive theory on eco-evolutionary feedbacks in predator-prey systems. Y1 - 2017 U6 - https://doi.org/10.1038/s41598-017-17019-4 SN - 2045-2322 VL - 7 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Bauer, Barbara A1 - Vos, Matthijs A1 - Klauschies, Toni A1 - Gaedke, Ursula T1 - Diversity, functional similarity, and top-down control drive synchronization and the reliability of ecosystem function JF - The American naturalist : a bi-monthly journal devoted to the advancement and correlation of the biological sciences N2 - 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. KW - biodiversity KW - ecosystem services KW - population dynamics KW - predator-prey system KW - species richness KW - synchrony Y1 - 2014 U6 - https://doi.org/10.1086/674906 SN - 0003-0147 SN - 1537-5323 VL - 183 IS - 3 SP - 394 EP - 409 PB - Univ. of Chicago Press CY - Chicago ER - TY - JOUR A1 - Rossberg, Axel G. A1 - Gaedke, Ursula A1 - Kratina, Pavel T1 - Dome patterns in pelagic size spectra reveal strong trophic cascades JF - Nature Communications N2 - In ecological communities, especially the pelagic zones of aquatic ecosystems, certain bodysize ranges are often over-represented compared to others. Community size spectra, the distributions of community biomass over the logarithmic body-mass axis, tend to exhibit regularly spaced local maxima, called "domes", separated by steep troughs. Contrasting established theory, we explain these dome patterns as manifestations of top-down trophic cascades along aquatic food chains. Compiling high quality size-spectrum data and comparing these with a size-spectrum model introduced in this study, we test this theory and develop a detailed picture of the mechanisms by which bottom-up and top-down effects interact to generate dome patterns. Results imply that strong top-down trophic cascades are common in freshwater communities, much more than hitherto demonstrated, and may arise in nutrient rich marine systems as well. Transferring insights from the general theory of nonlinear pattern formation to domes patterns, we provide new interpretations of past lake-manipulation experiments. Y1 - 2019 U6 - https://doi.org/10.1038/s41467-019-12289-0 SN - 2041-1723 VL - 10 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Mehner, Thomas A1 - Lischke, Betty A1 - Scharnweber, Inga Kristin A1 - Attermeyer, Katrin A1 - Brothers, Soren A1 - Gaedke, Ursula A1 - Hilt, Sabine A1 - Brucet, Sandra T1 - Empirical correspondence between trophic transfer efficiency in freshwater food webs and the slope of their size spectra JF - Ecology : a publication of the Ecological Society of America N2 - The density of organisms declines with size, because larger organisms need more energy than smaller ones and energetic losses occur when larger organisms feed on smaller ones. A potential expression of density-size distributions are Normalized Biomass Size Spectra (NBSS), which plot the logarithm of biomass independent of taxonomy within bins of logarithmic organismal size, divided by the bin width. Theoretically, the NBSS slope of multi-trophic communities is exactly - 1.0 if the trophic transfer efficiency (TTE, ratio of production rates between adjacent trophic levels) is 10% and the predator-prey mass ratio (PPMR) is fixed at 10(4). Here we provide evidence from four multi-trophic lake food webs that empirically estimated TTEs correspond to empirically estimated slopes of the respective community NBSS. Each of the NBSS considered pelagic and benthic organisms spanning size ranges from bacteria to fish, all sampled over three seasons in 1 yr. The four NBSS slopes were significantly steeper than -1.0 (range -1.14 to -1.19, with 95% CIs excluding -1). The corresponding average TTEs were substantially lower than 10% in each of the four food webs (range 1.0% to 3.6%, mean 1.85%). The overall slope merging all biomass-size data pairs from the four systems (-1.17) was almost identical to the slope predicted from the arithmetic mean TTE of the four food webs (-1.18) assuming a constant PPMR of 10(4). Accordingly, our empirical data confirm the theoretically predicted quantitative relationship between TTE and the slope of the biomass-size distribution. Furthermore, we show that benthic and pelagic organisms can be merged into a community NBSS, but future studies have yet to explore potential differences in habitat-specific TTEs and PPMRs. We suggest that community NBSS may provide valuable information on the structure of food webs and their energetic pathways, and can result in improved accuracy of TTE-estimates. KW - energetic equivalence rule KW - metabolic theory of ecology KW - multi-trophic communities KW - normalized biomass size spectra KW - pelagic and benthic lake habitats KW - size of organisms Y1 - 2018 U6 - https://doi.org/10.1002/ecy.2347 SN - 0012-9658 SN - 1939-9170 VL - 99 IS - 6 SP - 1463 EP - 1472 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Perkins, Daniel M. A1 - Perna, Andrea A1 - Adrian, Rita A1 - Cermeno, Pedro A1 - Gaedke, Ursula A1 - Huete-Ortega, Maria A1 - White, Ethan P. A1 - Yvon-Durocher, Gabriel T1 - Energetic equivalence underpins the size structure of tree and phytoplankton communities JF - Nature Communications N2 - The size structure of autotroph communities - the relative abundance of small vs. large individuals - shapes the functioning of ecosystems. Whether common mechanisms underpin the size structure of unicellular and multicellular autotrophs is, however, unknown. Using a global data compilation, we show that individual body masses in tree and phytoplankton communities follow power-law distributions and that the average exponents of these individual size distributions (ISD) differ. Phytoplankton communities are characterized by an average ISD exponent consistent with three-quarter-power scaling of metabolism with body mass and equivalence in energy use among mass classes. Tree communities deviate from this pattern in a manner consistent with equivalence in energy use among diameter size classes. Our findings suggest that whilst universal metabolic constraints ultimately underlie the emergent size structure of autotroph communities, divergent aspects of body size (volumetric vs. linear dimensions) shape the ecological outcome of metabolic scaling in forest vs. pelagic ecosystems. Y1 - 2019 U6 - https://doi.org/10.1038/s41467-018-08039-3 SN - 2041-1723 VL - 10 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Lischke, Betty A1 - Hilt, Sabine A1 - Janse, Jan H. A1 - Kuiper, Jan J. A1 - Mehner, Thomas A1 - Mooij, Wolf M. A1 - Gaedke, Ursula T1 - Enhanced input of terrestrial particulate organic matter reduces the resilience of the clear-water state of shallow lakes: A model study JF - Ecosystems N2 - The amount of terrestrial particulate organic matter (t-POM) entering lakes is predicted to increase as a result of climate change. This may especially alter the structure and functioning of ecosystems in small, shallow lakes which can rapidly shift from a clear-water, macrophyte-dominated into a turbid, phytoplankton-dominated state. We used the integrative ecosystem model PCLake to predict how rising t-POM inputs affect the resilience of the clear-water state. PCLake links a pelagic and benthic food chain with abiotic components by a number of direct and indirect effects. We focused on three pathways (zoobenthos, zooplankton, light availability) by which elevated t-POM inputs (with and without additional nutrients) may modify the critical nutrient loading thresholds at which a clear-water lake becomes turbid and vice versa. Our model results show that (1) increased zoobenthos biomass due to the enhanced food availability results in more benthivorous fish which reduce light availability due to bioturbation, (2) zooplankton biomass does not change, but suspended t-POM reduces the consumption of autochthonous particulate organic matter which increases the turbidity, and (3) the suspended t-POM reduces the light availability for submerged macrophytes. Therefore, light availability is the key process that is indirectly or directly changed by t-POM input. This strikingly resembles the deteriorating effect of terrestrial dissolved organic matter on the light climate of lakes. In all scenarios, the resilience of the clear-water state is reduced thus making the turbid state more likely at a given nutrient loading. Therefore, our study suggests that rising t-POM input can add to the effects of climate warming making reductions in nutrient loadings even more urgent. KW - climate change KW - PCLake KW - bistability KW - alternative stable states KW - critical nutrient loading KW - ecosystem modeling KW - allochthony KW - t-POM Y1 - 2014 U6 - https://doi.org/10.1007/s10021-014-9747-7 SN - 1432-9840 SN - 1435-0629 VL - 17 IS - 4 SP - 616 EP - 626 PB - Springer CY - New York ER - TY - JOUR A1 - Massie, Thomas Michael A1 - Weithoff, Guntram A1 - Kucklaender, Nina A1 - Gaedke, Ursula A1 - Blasius, Bernd T1 - Enhanced Moran effect by spatial variation in environmental autocorrelation JF - Nature Communications N2 - Spatial correlations in environmental stochasticity can synchronize populations over wide areas, a phenomenon known as the Moran effect. The Moran effect has been confirmed in field, laboratory and theoretical investigations. Little is known, however, about the Moran effect in a common ecological case, when environmental variation is temporally autocorrelated and this autocorrelation varies spatially. Here we perform chemostat experiments to investigate the temporal response of independent phytoplankton populations to autocorrelated stochastic forcing. In contrast to naive expectation, two populations without direct coupling can be more strongly correlated than their environmental forcing (enhanced Moran effect), if the stochastic variations differ in their autocorrelation. Our experimental findings are in agreement with numerical simulations and analytical calculations. The enhanced Moran effect is robust to changes in population dynamics, noise spectra and different measures of correlation-suggesting that noise-induced synchrony may play a larger role for population dynamics than previously thought. Y1 - 2015 U6 - https://doi.org/10.1038/ncomms6993 SN - 2041-1723 VL - 6 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Rosenbaum, Benjamin A1 - Raatz, Michael A1 - Weithoff, Guntram A1 - Fussmann, Gregor F. A1 - Gaedke, Ursula T1 - Estimating parameters from multiple time series of population dynamics using bayesian inference JF - Frontiers in ecology and evolution N2 - Empirical time series of interacting entities, e.g., species abundances, are highly useful to study ecological mechanisms. Mathematical models are valuable tools to further elucidate those mechanisms and underlying processes. However, obtaining an agreement between model predictions and experimental observations remains a demanding task. As models always abstract from reality one parameter often summarizes several properties. Parameter measurements are performed in additional experiments independent of the ones delivering the time series. Transferring these parameter values to different settings may result in incorrect parametrizations. On top of that, the properties of organisms and thus the respective parameter values may vary considerably. These issues limit the use of a priori model parametrizations. In this study, we present a method suited for a direct estimation of model parameters and their variability from experimental time series data. We combine numerical simulations of a continuous-time dynamical population model with Bayesian inference, using a hierarchical framework that allows for variability of individual parameters. The method is applied to a comprehensive set of time series from a laboratory predator-prey system that features both steady states and cyclic population dynamics. Our model predictions are able to reproduce both steady states and cyclic dynamics of the data. Additionally to the direct estimates of the parameter values, the Bayesian approach also provides their uncertainties. We found that fitting cyclic population dynamics, which contain more information on the process rates than steady states, yields more precise parameter estimates. We detected significant variability among parameters of different time series and identified the variation in the maximum growth rate of the prey as a source for the transition from steady states to cyclic dynamics. By lending more flexibility to the model, our approach facilitates parametrizations and shows more easily which patterns in time series can be explained also by simple models. Applying Bayesian inference and dynamical population models in conjunction may help to quantify the profound variability in organismal properties in nature. KW - Bayesian inference KW - chemostat experiments KW - ordinary differential equation KW - parameter estimation KW - population dynamics KW - predator prey KW - time series analysis KW - trait variability Y1 - 2019 U6 - https://doi.org/10.3389/fevo.2018.00234 SN - 2296-701X VL - 6 PB - Frontiers Research Foundation CY - Lausanne ER - TY - JOUR A1 - Spindler, Joris A1 - Gaedke, Ursula T1 - Estimating production in plankton food webs from biomass size spectra and allometric relationships Y1 - 2000 ER - TY - JOUR A1 - Coloma, Sebastian A1 - Gaedke, Ursula A1 - Sivonen, Kaarina A1 - Hiltunen, Teppo T1 - Frequency of virus-resistant hosts determines experimental community dynamics JF - Ecology : a publication of the Ecological Society of America N2 - Parasites, such as bacterial viruses (phages), can have large effects on host populations both at the ecological and evolutionary levels. In the case of cyanobacteria, phages can reduce primary production and infected hosts release intracellular nutrients influencing planktonic food web structure, community dynamics, and biogeochemical cycles. Cyanophages may be of great importance in aquatic food webs during large cyanobacterial blooms unless the host population becomes resistant to phage infection. The consequences on plankton community dynamics of the evolution of phage resistance in bloom forming cyanobacterial populations are still poorly studied. Here, we examined the effect of different frequencies of a phage-resistant genotype within a filamentous nitrogen-fixing Nodularia spumigena population on an experimental plankton community. Three Nodularia populations with different initial frequencies (0%, 5%, and 50%) of phage-resistant genotypes were inoculated in separate treatments with the phage 2AV2, the green alga Chlorella vulgaris, and the rotifer Brachionus plicatilis, which formed the experimental plankton community subjected to either nitrogen-limited or nitrogen-rich conditions. We found that the frequency of the phage-resistant Nodularia genotype determined experimental community dynamics. Cyanobacterial populations with a high frequency (50%) of the phage-resistant genotype dominated the cultures despite the presence of phages, retaining most of the intracellular nitrogen in the plankton community. In contrast, populations with low frequencies (0% and 5%) of the phage-resistant genotype were lysed and reduced to extinction by the phage, transferring the intracellular nitrogen held by Nodularia to Chlorella and rotifers, and allowing Chlorella to dominate the communities and rotifers to survive. This study shows that even though phages represent minuscule biomass, they can have key effects on community composition and eco-evolutionary feedbacks in plankton communities. KW - cyanobacteria KW - eco-evolutionary feedbacks KW - experimental evolution KW - host-parasite interaction KW - phage resistance KW - predator-prey interaction Y1 - 2018 U6 - https://doi.org/10.1002/ecy.2554 SN - 0012-9658 SN - 1939-9170 VL - 100 IS - 1 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Gaedke, Ursula T1 - Functional and taxonomical properties of the phytoplankton community : interannual variability and response to re-oligotrophication N2 - In large and deep Lake Constance, total phosphorus concentrations during winter mixing (TPmix) were reduced by a factor of three (> 80 to ca. 30 ;g/l) from about 1979 to 1993. This resulted in an amplification and lengthening of phosphorus (P) depleted conditions throughout the season and water column. The response of the phytoplankton community depended on the time of the year and the level of aggregation under consideration. Total phytoplankton biomass quantified in terms of algal biovolume or chlorophyll concentrations decreased in summer, i. e. during the period of most severe P depletion, to about half of the original values during the first decade. In subsequent years, summer chlorophyll concentrations remained at this lower level whereas total biovolume increased again despite further decreases of TPmix. Average algal biomass in spring and autumn fluctuated without a distinct relationship to TPmix although P was depleted below the detection level during parts of these time intervals in recent years. This moderate response by community level parameters is attributed to changes in the temporal and internal organization of the algal community. Population dynamics and the relative importance of various taxonomical and functional groups such as mixotrophs and less-edible forms clearly changed in spring and summer. The renewed increase in algal biovolume in summer is mostly caused by species which are able to exploit additional P sources. For example, Dinobryon is an evidently mixotrophic organism which ingests P rich bacteria, its strongest competitors for soluble reactive phosphorus (SRP). Ceratium hirundinella might be migrating between the euphotic zone and deeper, P enriched water layers under suitable hydrodynamical conditions. At the level of genera and higher taxa, consistent trends in respect to TPmix were observed in spring and summer mostly indicating an adaptation to more oligotrophic conditions. In contrast, the functional group of well-edible algae showed little interannual variability and did not change in absolute numbers. This suggests that, in contrast to less-edible algae, well-edible forms are more strongly under top-down than bottom-up control, and that the nutritional basis of most herbivores changed less than it would be expected from the decrease in total algal biomass. Y1 - 1998 ER - TY - JOUR A1 - Wojcik, Laurie Anne A1 - Ceulemans, Ruben A1 - Gaedke, Ursula T1 - Functional diversity buffers the effects of a pulse perturbation on the dynamics of tritrophic food webs JF - Ecology and Evolution N2 - Biodiversity decline causes a loss of functional diversity, which threatens ecosystems through a dangerous feedback loop: This loss may hamper ecosystems’ ability to buffer environmental changes, leading to further biodiversity losses. In this context, the increasing frequency of human-induced excessive loading of nutrients causes major problems in aquatic systems. Previous studies investigating how functional diversity influences the response of food webs to disturbances have mainly considered systems with at most two functionally diverse trophic levels. We investigated the effects of functional diversity on the robustness, that is, resistance, resilience, and elasticity, using a tritrophic—and thus more realistic—plankton food web model. We compared a non-adaptive food chain with no diversity within the individual trophic levels to a more diverse food web with three adaptive trophic levels. The species fitness differences were balanced through trade-offs between defense/growth rate for prey and selectivity/half-saturation constant for predators. We showed that the resistance, resilience, and elasticity of tritrophic food webs decreased with larger perturbation sizes and depended on the state of the system when the perturbation occurred. Importantly, we found that a more diverse food web was generally more resistant and resilient but its elasticity was context-dependent. Particularly, functional diversity reduced the probability of a regime shift toward a non-desirable alternative state. The basal-intermediate interaction consistently determined the robustness against a nutrient pulse despite the complex influence of the shape and type of the dynamical attractors. This relationship was strongly influenced by the diversity present and the third trophic level. Overall, using a food web model of realistic complexity, this study confirms the destructive potential of the positive feedback loop between biodiversity loss and robustness, by uncovering mechanisms leading to a decrease in resistance, resilience, and potentially elasticity as functional diversity declines. KW - functional diversity KW - nutrient spike KW - pulse perturbation KW - regime shift KW - robustness KW - tritrophic food web Y1 - 2021 U6 - https://doi.org/10.1002/ece3.8214 SN - 2045-7758 N1 - Wojcik and Ceulemans shared first authorship. VL - 11 IS - 22 SP - 15639 EP - 15663 PB - John Wiley & Sons, Inc. CY - Hoboken (New Jersey) ER - TY - JOUR A1 - Rocha, Marcia R. A1 - Gaedke, Ursula A1 - Vasseur, David A. T1 - Functionally similar species have similar dynamics JF - The journal of ecology N2 - 1. Improving the mechanistic basis of biodiversity-ecosystem function relationships requires a better understanding of how functional traits drive the dynamics of populations. For example, environmental disturbances or grazing may increase synchronization of functionally similar species, whereas functionally different species may show independent dynamics, because of different responses to the environment. Competition for resources, on the other hand, may yield a wide range of dynamic patterns among competitors and lead functionally similar and different species to display synchronized to compensatory dynamics. The mixed effect of these forces will influence the temporal fluctuations of populations and, thus, the variability of aggregate community properties. 2. To search for a relationship between functional and dynamics similarity, we studied the relationship between functional trait similarity and temporal dynamics similarity for 36 morphotypes of phytoplankton using long-term high-frequency measurements. 3. Our results show that functionally similar morphotypes exhibit dynamics that are more synchronized than those of functionally dissimilar ones. Functionally dissimilar morphotypes predominantly display independent temporal dynamics. This pattern is especially strong when short time-scales are considered. 4. Negative correlations are present among both functionally similar and dissimilar phytoplankton morphotypes, but are rarer and weaker than positive ones over all temporal scales. 5. Synthesis. We demonstrate that diversity in functional traits decreases community variability and ecosystem-level properties by decoupling the dynamics of individual morphotypes. KW - compensatory dynamics KW - competition KW - environmental forcing KW - functional diversity KW - functional traits KW - grazing KW - phytoplankton KW - plant population and community dynamics KW - synchrony KW - temporal dynamics Y1 - 2011 U6 - https://doi.org/10.1111/j.1365-2745.2011.01893.x SN - 0022-0477 VL - 99 IS - 6 SP - 1453 EP - 1459 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Seifert, Linda I. A1 - de Castro, Francisco A1 - Marquart, Arnim A1 - Gaedke, Ursula A1 - Weithoff, Guntram A1 - Vos, Matthijs T1 - Heated relations: temperature-mediated shifts in consumption across trophic levels JF - PLoS one N2 - A rise in temperature will intensify the feeding links involving ectotherms in food webs. However, it is unclear how the effects will quantitatively differ between the plant-herbivore and herbivore-carnivore interface. To test how warming could differentially affect rates of herbivory and carnivory, we studied trophic interaction strength in a food chain comprised of green algae, herbivorous rotifers and carnivorous rotifers at 10, 15, 20 and 25 degrees C. We found significant warming-induced changes in feeding by both herbivorous and carnivorous rotifers, but these responses occurred at different parts of the entire temperature gradient. The strongest response of the per capita herbivore's ingestion rate occurred due to an increase in temperature from 15 to 20 degrees C (1.9 fold: from 834 to 1611 algal cells per h(-1)) and of the per capita carnivore's ingestion rate from 20 to 25 degrees C (1.6 fold: from 1.5 to 2.5 prey h(-1)). Handling time, an important component of a consumer's functional response, significantly decreased from 15 to 20 degrees C in herbivorous rotifers. In contrast, it decreased from 20 to 25 degrees C in carnivorous rotifers. Attack rates significantly and strongly increased from 10 to 25 degrees C in the herbivorous animals, but not at all in the carnivores. Our results exemplify how the relative forces of top-down control exerted by herbivores and carnivores may strongly shift under global warming. But warming, and its magnitude, are not the only issue: If our results would prove to be representative, shifts in ectotherm interactions will quantitatively differ when a 5 degrees C increase starts out from a low, intermediate or high initial temperature. This would imply that warming could have different effects on the relative forces of carnivory and herbivory in habitats differing in average temperature, as would exist at different altitudes and latitudes. Y1 - 2014 U6 - https://doi.org/10.1371/journal.pone.0095046 SN - 1932-6203 VL - 9 IS - 5 PB - PLoS CY - San Fransisco ER - TY - JOUR A1 - Raatz, Michael A1 - Gaedke, Ursula A1 - Wacker, Alexander T1 - High food quality of prey lowers its risk of extinction JF - Oikos N2 - The mineral and biochemical food quality of prey may limit predator production. This well-studied direct bottom-up effect is especially prominent for herbivore-plant interactions. Low-quality prey species, particularly when defended, are generally considered to be less prone to predator-driven extinction. Undefended high-quality prey species sustain high predator production thereby potentially increasing their own extinction risk. The food quality of primary producers is highly species-specific. In communities of competing prey species, predators thus may supplement their diets of low-quality prey with high-quality prey, leading to indirect horizontal interactions between prey species of different food quality. We explore how these predator-mediated indirect interactions affect species coexistence in a general predator-prey model that is parametrized for an experimental algae-rotifer system. To cover a broad range of three essential functional traits that shape many plant-herbivore interactions we consider differences in 1) the food quality of the prey species, 2) their competitive ability for nutrient uptake and 3) their defence against predation. As expected, low food quality of prey can, similarly to defence, provide protection against extinction by predation. Counterintuitively, our simulations demonstrate that being of high food quality also prevents extinction of that prey species and additionally promotes coexistence with a competing, low-quality prey. The persistence of the high-quality prey enables a high conversion efficiency and control of the low-quality prey by the predator and allows for re-allocation of nutrients to the high-quality competitor. Our results show that high food quality is not necessarily detrimental for a prey species but instead can protect against extinction and promote species richness and functional biodiversity. Y1 - 2017 U6 - https://doi.org/10.1111/oik.03863 SN - 0030-1299 SN - 1600-0706 VL - 126 SP - 1501 EP - 1510 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Bauer, Barbara A1 - Sommer, Ulrich A1 - Gaedke, Ursula T1 - High predictability of spring phytoplankton biomass in mesocosms at the species, functional group and community level JF - Freshwater biology N2 - 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. KW - divergence KW - hierarchical level KW - mesocosms KW - predictability KW - replicates Y1 - 2013 U6 - https://doi.org/10.1111/j.1365-2427.2012.02780.x SN - 0046-5070 VL - 58 IS - 3 SP - 588 EP - 596 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Spijkerman, Elly A1 - de Castro, Francisco A1 - Gaedke, Ursula T1 - Independent Colimitation for Carbon Dioxide and Inorganic Phosphorus JF - PLoS one N2 - Simultaneous limitation of plant growth by two or more nutrients is increasingly acknowledged as a common phenomenon in nature, but its cellular mechanisms are far from understood. We investigated the uptake kinetics of CO(2) and phosphorus of the algae Chlamydomonas acidophila in response to growth at limiting conditions of CO(2) and phosphorus. In addition, we fitted the data to four different Monod-type models: one assuming Liebigs Law of the minimum, one assuming that the affinity for the uptake of one nutrient is not influenced by the supply of the other (independent colimitation) and two where the uptake affinity for one nutrient depends on the supply of the other (dependent colimitation). In addition we asked whether the physiological response under colimitation differs from that under single nutrient limitation. We found no negative correlation between the affinities for uptake of the two nutrients, thereby rejecting a dependent colimitation. Kinetic data were supported by a better model fit assuming independent uptake of colimiting nutrients than when assuming Liebigs Law of the minimum or a dependent colimitation. Results show that cell nutrient homeostasis regulated nutrient acquisition which resulted in a trade-off in the maximum uptake rates of CO(2) and phosphorus, possibly driven by space limitation on the cell membrane for porters for the different nutrients. Hence, the response to colimitation deviated from that to a single nutrient limitation. In conclusion, responses to single nutrient limitation cannot be extrapolated to situations where multiple nutrients are limiting, which calls for colimitation experiments and models to properly predict growth responses to a changing natural environment. These deviations from single nutrient limitation response under colimiting conditions and independent colimitation may also hold for other nutrients in algae and in higher plants. Y1 - 2011 U6 - https://doi.org/10.1371/journal.pone.0028219 SN - 1932-6203 VL - 6 IS - 12 PB - PLoS CY - San Fransisco ER - TY - JOUR A1 - van Velzen, Ellen A1 - Thieser, Tamara A1 - Berendonk, Thomas U. A1 - Weitere, Markus A1 - Gaedke, Ursula T1 - Inducible defense destabilizes predator–prey dynamics BT - the importance of multiple predators JF - Oikos N2 - Phenotypic plasticity in prey can have a dramatic impact on predator-prey dynamics, e.g. by inducible defense against temporally varying levels of predation. Previous work has overwhelmingly shown that this effect is stabilizing: inducible defenses dampen the amplitudes of population oscillations or eliminate them altogether. However, such studies have neglected scenarios where being protected against one predator increases vulnerability to another (incompatible defense). Here we develop a model for such a scenario, using two distinct prey phenotypes and two predator species. Each prey phenotype is defended against one of the predators, and vulnerable to the other. In strong contrast with previous studies on the dynamic effects of plasticity involving a single predator, we find that increasing the level of plasticity consistently destabilizes the system, as measured by the amplitude of oscillations and the coefficients of variation of both total prey and total predator biomasses. We explain this unexpected and seemingly counterintuitive result by showing that plasticity causes synchronization between the two prey phenotypes (and, through this, between the predators), thus increasing the temporal variability in biomass dynamics. These results challenge the common view that plasticity should always have a stabilizing effect on biomass dynamics: adding a single predator-prey interaction to an established model structure gives rise to a system where different mechanisms may be at play, leading to dramatically different outcomes. KW - phenotypic plasticity KW - inducible defense KW - stability KW - synchronization KW - predator-prey dynamics Y1 - 2018 U6 - https://doi.org/10.1111/oik.04868 SN - 0030-1299 SN - 1600-0706 VL - 127 IS - 11 SP - 1551 EP - 1562 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Tittel, Jörg A1 - Bissinger, Vera A1 - Gaedke, Ursula A1 - Kamjunke, Norbert T1 - Inorganic carbon limitation and mixotrophic growth in Chlamydomonas from an acidic mining lake N2 - Plankton communities in acidic mining lakes (pH 2.5-3.3) are species-poor because they face extreme environmental conditions, e.g. 150 mg l(-1) Fe2++Fe3+. We investigated the growth characteristics of the dominant pigmented species, the flagellate Chlamydomonas acidophila, in semi-continuous culture experiments under in situ conditions. The following hypotheses were tested: (1) Low inorganic carbon (IC) concentrations in the epilimnion (e.g. 0.3 mg l(-1)) arising from the low pH limit phototrophic growth (H-1); (2) the additional use of dissolved organic carbon (mixotrophy) leads to higher growth rates under IC-limitation (H-2), and (3) phagotrophy is not relevant (H-3). H- 1 was supported as the culture experiments, in situ PAR and IC concentrations indicated that IC potentially limited phototrophic growth in the mixed surface layers. H-2 was also supported: mixotrophic growth always exceeded pure phototrophic growth even when photosynthesis was saturated. Dark growth in filtered lake water illuminated prior to inoculation provided evidence that Chlamydomonas was able to use the natural DOC. The alga did not grow on bacteria, thus confirming H-3. Chlamydomonas exhibited a remarkable resistance to starvation in the dark. The compensation light intensity (ca. 20 mu mol photons m(-2) s(-1)) and the maximum phototrophic growth (1.50 d(-1)) fell within the range of algae from non-acidic waters. Overall, Chlamydomonas, a typical r-strategist in circum-neutral systems, showed characteristics of a K-strategist in the stable, acidic lake environment in achieving moderate growth rates and minimizing metabolic losses. (c) 2005 Elsevier GmbH. All rights reserved Y1 - 2005 SN - 1434-4610 ER - TY - JOUR A1 - Tirok, Katrin A1 - Gaedke, Ursula T1 - Internally driven alternation of functional traits in a multispecies predator-prey system N2 - The individual functional traits of different species play a key role for ecosystem function in aquatic and terrestrial systems. We modeled a multispecies predator-prey system with functionally different predator and prey species based on observations of the community dynamics of ciliates and their algal prey in Lake Constance. The model accounted for differences in predator feeding preferences and prey susceptibility to predation, and for the respective trade-offs. A low food demand of the predator was connected to a high food selectivity, and a high growth rate of the prey was connected to a high vulnerability to grazing. The data and the model did not show standard uniform predator- prey cycles, but revealed both complex dynamics and a coexistence of predator and prey at high biomass levels. These dynamics resulted from internally driven alternations in species densities and involved compensatory dynamics between functionally different species. Functional diversity allowed for ongoing adaptation of the predator and prey communities to changing environmental conditions such as food composition and grazing pressure. The trade-offs determined whether compensatory or synchronous dynamics occurred which influence the variability at the community level. Compensatory dynamics were promoted by a joint carrying capacity linking the different prey species which is particularly relevant at high prey biomasses, i.e., when grazers are less efficient. In contrast, synchronization was enhanced by the coupling of the different predator and prey species via common feeding links, e.g., by a high grazing pressure of a nonselective predator. The communities had to be functionally diverse in terms of their trade-offs and their traits to yield compensatory dynamics. Rather similar predator species tended to cycle synchronously, whereas profoundly different species did not coexist. Compensatory dynamics at the community level thus required intermediately strong tradeoffs for functional traits in both predators and their prey. Y1 - 2010 UR - http://esapubs.org/esapubs/journals/ecology.htm U6 - https://doi.org/10.1890/09-1052.1 SN - 0012-9658 ER - TY - JOUR A1 - Gaedke, Ursula A1 - Hochstädter, Silke A1 - Straile, Dietmar T1 - Interplay between energy limitation and nutritional deficiency: Empirical data and food web models N2 - Due to differences in the biochemical composition of autotrophs and their grazers, food quality can strongly influence herbivore population dynamics. Under nutrient depleted conditions the carbon to nutrient ratios of autotrophs can increase to such an extent that consumers become nutrient rather than energy limited. Estimating the importance of this effect in situ in pelagic food webs is complicated by the omnivory of many consumers and rapid nutrient recycling. Isolated predator-prey studies inadequately represent this interaction, instead an ecosystem perspective is required. We used seven years of data from large, deep Lake Constance to develop seasonally resolved flux models of the pelagic food web and analyze the balance between energetic and nutrient constraints. The carbon (C) and phosphorus (P) flows were simultaneously quantified and balanced. C represented food quantity/energy. P was taken as a surrogate of food quality, because algal C:P ratios exceeded the threshold above which P limitation of herbivores is predicted by stoichiometric theory throughout summer and autumn. Primary production exceeded bacterial C production by a factor of 3 but autotrophs and bacteria took up approximately equal amounts of P during summer and autumn. As a consequence the C and P supply of suspension-feeding zooplankton was decoupled: Consumer C demands were largely met by phytoplankton whereas P was mostly obtained from bacteria and their protist predators. The degree of consumer P deficiency varied according to supplementation of their algal diet with P-enriched bacteria or bacterivores. This favored the occurrence of omnivores, i.e. organisms that minimized P deficiencies at the cost of enhanced energy limitation. In contrast with previous perceptions, P remineralization during P depleted summer conditions was dominated by bacterivorous flagellates, carnivorous crustaceans and fish, which fed on prey with an elemental composition similar to their own, whereas herbivores contributed only 30% of P cycling despite their large biomass and C production. Our results suggested a co- limitation of predominantly herbivorous consumers by C and P and a mutual dependence of the two types of deficiency at the individual and system level. This pattern is not specific to pelagic systems but appears to be applicable across ecosystem types. Y1 - 2002 ER - TY - JOUR A1 - Flöder, Sabine A1 - Yong, Joanne A1 - Klauschies, Toni A1 - Gaedke, Ursula A1 - Poprick, Tobias A1 - Brinkhoff, Thorsten A1 - Moorthi, Stefanie T1 - Intraspecific trait variation alters the outcome of competition in freshwater ciliates JF - Ecology and evolution N2 - Trait variation among heterospecific and conspecific organisms may substantially affect community and food web dynamics. While the relevance of competition and feeding traits have been widely studied for different consumer species, studies on intraspecific differences are more scarce, partly owing to difficulties in distinguishing different clones of the same species. Here, we investigate how intraspecific trait variation affects the competition between the freshwater ciliates Euplotes octocarinatus and Coleps hirtus in a nitrogen-limited chemostat system. The ciliates competed for the microalgae Cryptomonas sp. (Cry) and Navicula pelliculosa (Nav), and the bacteria present in the cultures over a period of 33 days. We used monoclonal Euplotes and three different Coleps clones (Col 1, Col 2, and Col 3) in the experiment that could be distinguished by a newly developed rDNA-based molecular assay based on the internal transcribed spacer (ITS) regions. While Euplotes feeds on Cry and on bacteria, the Coleps clones cannot survive on bacteria alone but feed on both Cry and Nav with clone-specific rates. Experimental treatments comprised two-species mixtures of Euplotes and one or all of the three different Coleps clones, respectively. We found intraspecific variation in the traits "selectivity" and "maximum ingestion rate" for the different algae to significantly affect the competitive outcome between the two ciliate species. As Nav quickly escaped top-down control and likely reached a state of low food quality, ciliate competition was strongly determined by the preference of different Coleps clones for Cry as opposed to feeding on Nav. In addition, the ability of Euplotes to use bacteria as an alternative food source strengthened its persistence once Cry was depleted. Hence, trait variation at both trophic levels codetermined the population dynamics and the outcome of species competition. KW - ciliate predators KW - intraspecific trait variation KW - microalgal resource KW - predator trait variation KW - predator-prey systems KW - resource competition Y1 - 2021 U6 - https://doi.org/10.1002/ece3.7828 SN - 2045-7758 VL - 11 IS - 15 SP - 10225 EP - 10243 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Weithoff, Guntram A1 - Moser, Michael A1 - Kamjunke, Norbert A1 - Gaedke, Ursula A1 - Weisse, Thomas T1 - Lake morphometry and wind exposure may shape the plankton community structure in acidic mining lakes N2 - Acidic mining lakes (pH <3) are specific habitats exhibiting particular chemical and biological characteristics. The species richness is low and mixotrophy and omnivory are common features of the plankton food web in such lakes. The plankton community structure of mining lakes of different morphometry and mixing type but similar chemical characteristics (Lake 130, Germany and Lake Langau, Austria) was investigated. The focus was laid on the species composition, the trophic relationship between the phago-mixotrophic flagellate Ochromonas sp. and bacteria and the formation of a deep chlorophyll maximum along a vertical pH-gradient. The shallow wind-exposed Lake 130 exhibited a higher species richness than Lake Langau. This increase in species richness was made up mainly by mero-planktic species, suggesting a strong benthic/littoral - pelagic coupling. Based on the field data from both lakes, a nonlinear, negative relation between bacteria and Ochromonas biomass was found, suggesting that at an Ochromonas biomass below 50 mu g CL-1. the grazing pressure on bacteria is low and with increasing Ochromonas biomass bacteria decline. Furthermore, in Lake Langau, a prominent deep chlorophyll maximum was found with chlorophyll concentrations ca. 50 times higher than in the epilimnion which was build up by the euglenophyte Lepocinclis sp. We conclude that lake morphometry, and specific abiotic characteristics such as mixing behaviour influence the community structure in these mining lakes. Y1 - 2010 UR - http://www.sciencedirect.com/science/journal/00759511 U6 - https://doi.org/10.1016/j.limno.2009.11.002 SN - 0075-9511 ER - TY - JOUR A1 - Lischke, Betty A1 - Weithoff, Guntram A1 - Wickham, Stephen A. A1 - Attermeyer, Katrin A1 - Großart, Hans-Peter A1 - Scharnweber, Inga Kristin A1 - Hilt, Sabine A1 - Gaedke, Ursula T1 - Large biomass of small feeders: ciliates may dominate herbivory in eutrophic lakes JF - Journal of plankton research N2 - The importance of ciliates as herbivores and in biogeochemical cycles is increasingly recognized. An opportunity to observe the potential consequences of zooplankton dominated by ciliates arose when winter fish kills resulted in strong suppression of crustaceans by young planktivorous fish in two shallow lakes. On an annual average, ciliates made up 38-76% of the total zooplankton biomass in both lakes during two subsequent years. Consequently, ciliate biomass and their estimated grazing potential were extremely high compared with other lakes of various trophic states and depths. Grazing estimates based on abundance and size suggest that ciliates should have cleared the water column of small (<5 mu m) and intermediate (5-50 mu m) sized phytoplankton more than once a day. Especially, small feeders within the ciliates were important, likely exerting a strong top-down control on small phytoplankton. Particle-attached bacteria were presumably strongly suppressed by intermediate-sized ciliate feeders. In contrast to other lakes, large phytoplankton was proportionately very abundant. The phytoplankton community had a high evenness, which may be attributed to the feeding by numerous fast growing and selective ciliate species. Our study highlights ciliates as an important trophic link and adds to the growing awareness of the role of winter processes for plankton dynamics. KW - phytoplankton KW - crustaceans KW - rotifers KW - filtration rate KW - winter fish kill Y1 - 2016 U6 - https://doi.org/10.1093/plankt/fbv102 SN - 0142-7873 SN - 1464-3774 VL - 38 SP - 2 EP - 15 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Mittler, Udo A1 - Blasius, Bernd A1 - Gaedke, Ursula A1 - Ryabov, Alexey B. T1 - Length-volume relationship of lake phytoplankton JF - Limnology and Oceanography: Methods N2 - The shapes of phytoplankton units (unicellular organisms and colonies) are extremely diverse, and no unique relationship exists between their volume, V, and longest linear dimension, L. However, an approximate scaling between these parameters can be found because the shape variations within each size class are constrained by cell physiology, grazing pressure, and optimality of resource acquisition. To determine this scaling and to test for its seasonal and interannual variation under changing environmental conditions, we performed weighted regression analysis of time-dependent length-volume relations of the phytoplankton community in large deep Lake Constance from 1979 to 1999. We show that despite a large variability in species composition, the V(L) relationship can be approximated as a power law, V similar to L-alpha, with a scaling exponent alpha = 3 for small cells (L < 25 mu m) and alpha = 1.7 if the fitting is performed over the entire length range, including individual cells and colonies. The best description is provided by a transitional power function describing a regime change from a scaling exponent of 3 for small cells to an exponent of 0.4 in the range of large phytoplankton. Testing different weighted fitting approaches we show that remarkably the best prediction of the total community biovolume from measurements of L and cell density is obtained when the regression is weighted with the squares of species abundances. Our approach should also be applicable to other systems and allows converting phytoplankton length distributions (e.g., obtained with automatic monitoring such as flow cytometry) into distributions of biovolume and biovolume-related phytoplankton traits. Y1 - 2018 U6 - https://doi.org/10.1002/lom3.10296 SN - 1541-5856 VL - 17 IS - 1 SP - 58 EP - 68 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Spijkerman, Elly A1 - Bissinger, Vera A1 - Gaedke, Ursula T1 - Low potassium and inorganic carbon concentrations influence a possible phosphorus limitation in Chlamydomonas acidophila N2 - Chlamydomonas acidophila, a dominant phytoplankton species in the very acidic Lake 111 (pH 2.7) situated in Germany, faces low concentrations of inorganic phosphorus (P-i), inorganic carbon (C-i) and potassium (K+) in its environment, which may lead to a complex colimitation by these nutrients. We performed laboratory and field investigations to test for P-i limitation and its dependence on C-i and K+ concentrations. The minimum cell quota for phosphorus (Q(0)) and phosphatase enzyme activity were similar to those for neutrophilic algae, despite the low pH and high concentrations of iron and aluminium, indicating no extra metabolic costs or inhibition of enzymes by the extreme environment. The threshold concentration of soluble reactive phosphorus for growth (SRPt), the algal C:P ratio and the alkaline phosphatase enzyme activity all suggested a moderate P-i limitation of C. acidophila in Lake 111. SRPt and Q(0) were higher at low CO2 and K+ concentrations in culture, showing a relationship between C-i and P-i acquisition. Furthermore, SRPt and Q(0) were higher under K+/P-i-colimiting conditions than under P-i-limiting conditions alone, suggesting that K+ concentrations influence P-i limitation in C. acidophila as well. Our results show that a limitation by one macronutrient requires consideration of the availability of the others as their uptake mechanisms depend on each other. Notwithstanding these interactions, C-i or K+ concentrations had no clear influence on the P-i limitation of C. acidophila in Lake 111. Y1 - 2007 UR - http://www.tandfonline.com/doi/full/10.1080/09670260701529596 U6 - https://doi.org/10.1080/09670260701529596 ER - TY - JOUR A1 - Weithoff, Guntram A1 - Gaedke, Ursula T1 - Mean functional traits of lake phytoplankton reflect seasonal and inter-annual changes in nutrients, climate and herbivory JF - Journal of plankton research N2 - Trait-based approaches have become increasingly successful in community ecology. They assume that the distribution of functional traits within communities responds in a predictable way to alterations in environmental forcing and that strong forcing may accelerate such trait changes. We used high frequency measurements of phytoplankton to test these assumptions. We analyzed the seasonal and long-term dynamics of the community trait mean within a multi-dimensional trait space under alternating multifactorial environmental conditions. The community trait mean exhibited a distinct recurrent annual pattern that reflected minor changes in climate, herbivory and nutrients. Independent of early spring conditions, the community trait mean was repeatedly driven into a narrow confined area in the trait space under pronounced herbivory during the clear water phase. The speed of movement was highest at the onset and the relaxation of such strong unidirectional forcing. Thus, our data support the conceptual framework of trait-based ecology that alterations in environmental conditions are systematically tracked by adjustments in the dominant functional trait values and that the speed of trait changes depends on the kind and intensity of the selection pressure. Our approach provides a sensitive tool to detect small functional differences in the community related to subtle differences in forcing. KW - phytoplankton KW - temporal dynamics KW - climate KW - trait distribution KW - Lake Constance KW - functional traits Y1 - 2017 U6 - https://doi.org/10.1093/plankt/fbw072 SN - 0142-7873 SN - 1464-3774 VL - 39 SP - 509 EP - 517 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Boit, Alice A1 - Martinez, Neo D. A1 - Williams, Richard J. A1 - Gaedke, Ursula T1 - Mechanistic theory and modelling of complex food-web dynamics in Lake Constance JF - Ecology letters N2 - Mechanistic understanding of consumer-resource dynamics is critical to predicting the effects of global change on ecosystem structure, function and services. Such understanding is severely limited by mechanistic models inability to reproduce the dynamics of multiple populations interacting in the field. We surpass this limitation here by extending general consumer-resource network theory to the complex dynamics of a specific ecosystem comprised by the seasonal biomass and production patterns in a pelagic food web of a large, well-studied lake. We parameterised our allometric trophic network model of 24 guilds and 107 feeding relationships using the lakes food web structure, initial spring biomasses and body-masses. Adding activity respiration, the detrital loop, minimal abiotic forcing, prey resistance and several empirically observed rates substantially increased the model's fit to the observed seasonal dynamics and the size-abundance distribution. This process illuminates a promising approach towards improving food-web theory and dynamic models of specific habitats. KW - Allometric Trophic Network model KW - community ecology KW - food web KW - multi-trophic dynamics KW - seasonal plankton succession Y1 - 2012 U6 - https://doi.org/10.1111/j.1461-0248.2012.01777.x SN - 1461-023X VL - 15 IS - 6 SP - 594 EP - 602 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Hart, D. A1 - Stone, L. A1 - Stern, A. A1 - Straile, Dietmar A1 - Gaedke, Ursula T1 - Methods for balancing ecosystem flux charts : new techniques and software Y1 - 1997 ER - TY - JOUR A1 - Tittel, Jörg A1 - Bissinger, Vera A1 - Zippel, Barbara A1 - Gaedke, Ursula A1 - Bell, Elanor M. A1 - Lorke, Andreas A1 - Kamjunke, Norbert T1 - Mixotrophs combine resource use to outcompete specialists: Implications for aquatic food webs N2 - The majority of species can be grouped into those relying solely on photosynthesis (phototrophy) or those relying solely on the assimilation of organic substances (heterotrophy) to meet their requirements for energy and carbon. However, a special life history trait exists in which organisms combine both phototrophy and heterotrophy. Such 'mixotrophy' is a widespread phenomenon in aquatic habitats and is observed in many protozoan and metazoan organisms. The strategy requires investment in both photosynthetic and heterotrophic cellular apparatus, but the benefits must outweigh these costs. In accordance with the mechanistic resource competition theory, laboratory experiments revealed that pigmented mixotrophs combined light and prey as substitutable resources. Thereby, they reduced prey abundance below the critical food concentration of competing specialist grazers [Rothhaupt, K. O. (1996) Ecology 77, 716-724]. Here, we demonstrate for the first time the important consequences of this strategy for an aquatic community. In the illuminated surface strata of a lake, mixotrophs reduced prey abundance so steeply that grazers from higher trophic levels, consuming both the mixotrophs and their prey, could not persist. Thus, the mixotrophs escaped from both competition and grazing, and remained dominant. Furthermore, the mixotrophs structured the prey abundance along the vertical light gradient creating low densities near the surface and a pronounced maximum of their algal prey at depth. Such deep algal accumulations are typical features of nutrient poor aquatic habitats, previously explained by resource availability. We hypothesize instead that the mixotrophic grazing strategy is responsible for deep algal accumulations in many aquatic environments. Y1 - 2003 UR - www.pnas.org/cgi/doi/10.1073/pnas.2130696100 ER - TY - JOUR A1 - Filip, Joanna A1 - Bauer, Barbara A1 - Hillebrand, Helmut A1 - Beniermann, Anna A1 - Gaedke, Ursula A1 - Moorthi, Stefanie D. T1 - Multitrophic diversity effects depend on consumer specialization and species-specific growth and grazing rates JF - Oikos N2 - 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. Y1 - 2014 U6 - https://doi.org/10.1111/oik.01219 SN - 0030-1299 SN - 1600-0706 VL - 123 IS - 8 SP - 912 EP - 922 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Hairston, Nelson G. A1 - Holtmeier, C. L. A1 - Lampert, W. A1 - Weider, L. J. A1 - Post, D. M. A1 - Fischer, J. M. A1 - Caceres, C. E. A1 - Fox, J. A. A1 - Gaedke, Ursula T1 - Natural selection for grazer resistance to toxic cyanobacteria: Evolution of phenotypic plasticity? Y1 - 2001 ER - TY - JOUR A1 - Ehrlich, Elias A1 - Gaedke, Ursula T1 - Not attackable or not crackable BT - How pre-and post-attack defenses with different competition costs affect prey coexistence and population dynamics JF - Ecology and Evolution N2 - It is well-known that prey species often face trade-offs between defense against predation and competitiveness, enabling predator-mediated coexistence. However, we lack an understanding of how the large variety of different defense traits with different competition costs affects coexistence and population dynamics. Our study focusses on two general defense mechanisms, that is, pre-attack (e.g., camouflage)and post-attack defenses (e.g., weaponry) that act at different phases of the predator—prey interaction. We consider a food web model with one predator, two prey types and one resource. One prey type is undefended, while the other one is pre-or post-attack defended paying costs either by a higher half-saturation constant for resource uptake or a lower maximum growth rate. We show that post-attack defenses promote prey coexistence and stabilize the population dynamics more strongly than pre-attack defenses by interfering with the predator’s functional response: Because the predator spends time handling “noncrackable” prey, the undefended prey is indirectly facilitated. A high half-saturation constant as defense costs promotes coexistence more and stabilizes the dynamics less than a low maximum growth rate. The former imposes high costs at low resource concentrations but allows for temporally high growth rates at predator-induced resource peaks preventing the extinction of the defended prey. We evaluate the effects of the different defense mechanisms and costs on coexistence under different enrichment levels in order to vary the importance of bottom-up and top-down control of the prey community. KW - coexistence KW - competition–defense trade‐off KW - defense against predation KW - functional response KW - indirect facilitation KW - predator–prey cycles Y1 - 2018 U6 - https://doi.org/10.1002/ece3.4145 SN - 2045-7758 VL - 8 IS - 13 SP - 6625 EP - 6637 PB - Wiley ER - TY - JOUR A1 - Kamjunke, Norbert A1 - Gaedke, Ursula T1 - Phosphorus gain by bacterivory promotes the mixotrophic flagellate Dinobryon spp. during re-oligotrophication N2 - Bacterivory by mixotrophic flagellates may contribute to their nutrient supply, providing a competitive advantage in oligotrophic waters. We hypothesized an increase in Dinobryon biomass during the re-oligotrophication process in the large and deep Lake Constance. To estimate whether bacterivory contributed substantially to the flagellates' phosphorus supply, we determined ingestion rates. Dinobryon biomass increased with decreasing total phosphorus concentrations in the lake over a period of 17 years (P = 0.0005). The promotion of Dinobryon biomass during re-oligotrophication may be explained by the increasing light availability due to the decreasing biomass of other phytoplankton yielding a release from competition. The date of the Dinobryon abundance maximum shifted to earlier time points in the year, probably because a smaller phosphorus pool was depleted more quickly. Ingestion rates of Dinobryon ranged between 0.5 and 13 bacteria cell(-1) h(-1) (0.2-5.4 fg C pg C-1 h(-1)), and clearance rates varied between 0.2 and 3.2 nL cell(-1) h(-1) (4-78 pL pg C-1 h(-1)), leading to bacterial losses of up to 30% day(-1) of bacterial standing stock. The ingestion of bacteria covered 77% of the phosphorus need of the flagellate during the period of maximum growth in 1996 (net growth rate 0.34 day(-1)), and it fully covered the need at all other times. Y1 - 2007 UR - http://plankt.oxfordjournals.org/ U6 - https://doi.org/10.1093/plankt/fb1054 SN - 0142-7873 ER - TY - JOUR A1 - Häse, C. A1 - Gaedke, Ursula A1 - Beese, B. A1 - Seifried, A. A1 - Tilzer, M. T1 - Phytoplankton response to reoligotrophication in large and deep Lake Constance : Photosynthetic activity and chlorophyll concentration N2 - In Lake Constance, phytoplankton productivity, together with parameters relevant for the production process, was assessed year-round at about 500 dates between 1980 and 1995/1996. During this period, the concentration of total phosphorus during winter circulation decreased from more than 80 to 22 ;g/l as a consequence of sewage diversion and waste water treatment within the catchment area. By contrast, annual photosynthetic rates remained virtually unchanged for about 10 more years following phosphorus decline (mean value 288 " 21 g C m-2 a-1), and thereafter decreased only by about 25 % until 1996. The aim of this study is to analyze factors responsible for this pronounced resilience. Y1 - 1998 ER - TY - JOUR A1 - Schmidtke, Andrea A1 - Rottstock, Tanja A1 - Gaedke, Ursula A1 - Fischer, Markus T1 - Plant community diversity and composition affect individual plant performance N2 - Effects of plant community diversity on ecosystem processes have recently received major attention. In contrast, effects of species richness and functional richness on individual plant performance, and their magnitude relative to effects of community composition, have been largely neglected. Therefore, we examined height, aboveground biomass, and inflorescence production of individual plants of all species present in 82 large plots of the Jena Experiment, a large grassland biodiversity experiment in Germany. These plots differed in species richness (1-60), functional richness (1-4), and community composition. On average, in more species-rich communities, plant individuals grew taller, but weighed less, were less likely to flower, and had fewer inflorescences. In plots containing legumes, non-legumes were higher and weighed more than in plots without legumes. In plots containing grasses, non-grasses were less likely to flower than in plots without grasses. This indicates that legumes positively and grasses negatively affected the performance of other species. Species richness and functional richness effects differed systematically between functional groups. The magnitude of the increase in plant height with increasing species richness was greatest in grasses and was progressively smaller in legumes, small herbs, and tall herbs. Individual aboveground biomass responses to increasing species richness also differed among functional groups and were positive for legumes, less pronouncedly positive for grasses, negative for small herbs, and more pronouncedly negative for tall herbs. Moreover, these effects of species richness differed strongly between species within these functional groups. We conclude that individual plant performance largely depends on the diversity of the surrounding community, and that the direction and magnitude of the effects of species richness and functional richness differs largely between species. Our study suggests that diversity of the surrounding community needs to be taken into account when interpreting drivers of the performance of individual plants. Y1 - 2010 UR - http://www.springerlink.com/content/067x6r4n36w12184/fulltext.html U6 - https://doi.org/10.1007/s00442-010-1688-z SN - 0029-8549 ER - TY - JOUR A1 - Tirok, Katrin A1 - Bauer, Barbara A1 - Wirtz, Kai A1 - Gaedke, Ursula T1 - Predator-Prey Dynamics Driven by Feedback between Functionally Diverse Trophic Levels JF - PLoS one N2 - Neglecting the naturally existing functional diversity of communities and the resulting potential to respond to altered conditions may strongly reduce the realism and predictive power of ecological models. We therefore propose and study a predator-prey model that describes mutual feedback via species shifts in both predator and prey, using a dynamic trait approach. Species compositions of the two trophic levels were described by mean functional traits-prey edibility and predator food-selectivity- and functional diversities by the variances. Altered edibility triggered shifts in food-selectivity so that consumers continuously respond to the present prey composition, and vice versa. This trait-mediated feedback mechanism resulted in a complex dynamic behavior with ongoing oscillations in the mean trait values, reflecting continuous reorganization of the trophic levels. The feedback was only possible if sufficient functional diversity was present in both trophic levels. Functional diversity was internally maintained on the prey level as no niche existed in our system, which was ideal under any composition of the predator level due to the trade-offs between edibility, growth and carrying capacity. The predators were only subject to one trade-off between food-selectivity and grazing ability and in the absence of immigration, one predator type became abundant, i.e., functional diversity declined to zero. In the lack of functional diversity the system showed the same dynamics as conventional models of predator-prey interactions ignoring the potential for shifts in species composition. This way, our study identified the crucial role of trade-offs and their shape in physiological and ecological traits for preserving diversity. Y1 - 2011 U6 - https://doi.org/10.1371/journal.pone.0027357 SN - 1932-6203 VL - 6 IS - 11 PB - PLoS CY - San Fransisco ER - TY - JOUR A1 - Sperfeld, Erik A1 - Schmidtke, Andrea A1 - Gaedke, Ursula A1 - Weithoff, Guntram T1 - Productivity, herbivory, and species traits rather than diversity influence invasibility of experimental phytoplankton communities N2 - Biological invasions are a major threat to natural biodiversity; hence, understanding the mechanisms underlying invasibility (i.e., the susceptibility of a community to invasions by new species) is crucial. Invasibility of a resident community may be affected by a complex but hitherto hardly understood interplay of (1) productivity of the habitat, (2) diversity, (3) herbivory, and (4) the characteristics of both invasive and resident species. Using experimental phytoplankton microcosms, we investigated the effect of nutrient supply and species diversity on the invasibility of resident communities for two functionally different invaders in the presence or absence of an herbivore. With increasing nutrient supply, increased herbivore abundance indicated enhanced phytoplankton biomass production, and the invasion success of both invaders showed a unimodal pattern. At low nutrient supply (i.e., low influence of herbivory), the invasibility depended mainly on the competitive abilities of the invaders, whereas at high nutrient supply, the susceptibility to herbivory dominated. This resulted in different optimum nutrient levels for invasion success of the two species due to their individual functional traits. To test the effect of diversity on invasibility, a species richness gradient was generated by random selection from a resident species pool at an intermediate nutrient level. Invasibility was not affected by species richness; instead, it was driven by the functional traits of the resident and/or invasive species mediated by herbivore density. Overall, herbivory was the driving factor for invasibility of phytoplankton communities, which implies that other factors affecting the intensity of herbivory (e.g., productivity or edibility of primary producers) indirectly influence invasions. Y1 - 2010 UR - http://springerlink.metapress.com/content/100458/ U6 - https://doi.org/10.1007/s00442-010-1594-4 SN - 0029-8549 ER - TY - JOUR A1 - Velzen, Ellen van A1 - Gaedke, Ursula A1 - Klauschies, Toni T1 - Quantifying the capacity for contemporary trait changes to drive intermittent predator-prey cycles JF - Ecological monographs : a publication of the Ecological Society of America N2 - A large and growing body of theory has demonstrated how the presence of trait variation in prey or predator populations may affect the amplitude and phase of predator-prey cycles. Less attention has been given to so-called intermittent cycles, in which predator-prey oscillations recurrently disappear and re-appear, despite such dynamics being observed in empirical systems and modeling studies. A comprehensive understanding of the conditions under which trait changes may drive intermittent predator-prey dynamics, as well as their potential ecological implications, is therefore missing. Here we provide a first systematic analysis of the eco-evolutionary conditions that may give rise to intermittent predator-prey cycles, investigating 16 models that incorporate different types of trait variation within prey, predators, or both. Our results show that intermittent dynamics often arise through predator-prey coevolution, but only very rarely when only one trophic level can adapt. Additionally, the frequency of intermittent cycles depends on the source of trait variation (genetic variation or phenotypic plasticity) and the genetic architecture (Mendelian or quantitative traits), with intermittency occurring most commonly through Mendelian evolution, and very rarely through phenotypic plasticity. Further analysis identified three necessary conditions for when trait variation can drive intermittent cycles. First, the intrinsic stability of the predator-prey system must depend on the traits of prey, predators, or both. Second, there must be a mechanism causing the recurrent alternation between stable and unstable states, leading to a "trait" cycle superimposed on the population dynamics. Finally, these trait dynamics must be significantly slower than the predator-prey cycles. We show how these conditions explain all the abovementioned patterns. We further show an important unexpected consequence of these necessary conditions: they are most easily met when intraspecific trait variation is at high risk of being lost. As trait diversity is positively associated with ecosystem functioning, this can have potentially severe negative consequences. This novel result highlights the importance of identifying and understanding intermittent cycles in theoretical studies and natural systems. The new approach for detecting and quantifying intermittency we develop here will be instrumental in enabling future study. KW - eco-evolutionary feedbacks KW - ecosystem functioning KW - intraspecific trait KW - variation KW - population cycles KW - predator-prey dynamics KW - trait dynamics Y1 - 2022 U6 - https://doi.org/10.1002/ecm.1505 SN - 1557-7015 SN - 0012-9615 VL - 92 IS - 2 PB - Wiley CY - New York ER - TY - JOUR A1 - Li, Xiaoxiao A1 - Yang, Wei A1 - Sun, Tao A1 - Gaedke, Ursula T1 - Quantitative food web structure and ecosystem functions in a warm-temperate seagrass bed JF - Marine biology : international journal on life in oceans and coastal waters N2 - Seagrass beds are important habitats in coastal areas but increasingly decline in area and quality, thus conservation measures are urgently needed. Quantitative food webs, describing the biomass distribution and energy fluxes among trophic groups, reveal structural and functional aspects of ecosystems. Their knowledge can improve ecological conservation. For the recently discovered large warm-temperate seagrass (Zostera japonica) habitat in China's Yellow River Delta wetland, we used delta C-13 and delta N-15 measurements and a Bayesian isotope mixing model to construct its food web diagram with quantitative estimations of consumer diet compositions, comprising detritus and 14 living trophic groups from primary producers to fish. We then estimated the quantitative food web fluxes based on biomass measurements and calculated corresponding ecosystem functions. Pelagic producers were significantly C-13-depleted compared to benthic sources. Consumers (except zooplankton) were increasingly C-13-depleted with increasing trophic positions even though the consumed benthic production surpassed the pelagic one. Bivalves dominated consumer biomasses and fluxes and were the first to connect the pelagic and benthic pathways, whereas zooplankton and gastropods were specialized on the two pathways, respectively. We found flat biomass and production pyramids indicating low trophic transfer efficiencies. Generally, the energetic structure of the quantitative food web was consistent with the stable isotope analysis, and the estimated net primary production and most estimated production to biomass ratios of the trophic groups fell within literature ranges. This study provides a systematical understanding of the quantitative trophic ecology of a seagrass bed and facilitates synergistic knowledge on management, conservation, and restoration. Y1 - 2021 U6 - https://doi.org/10.1007/s00227-021-03878-z SN - 0025-3162 SN - 1432-1793 VL - 168 IS - 5 PB - Springer CY - Berlin ; Heidelberg ER - TY - JOUR A1 - Tirok, Katrin A1 - Gaedke, Ursula T1 - Regulation of planktonic ciliate dynamics and functional composition during spring in Lake Constance N2 - Protozoans are among the most important grazers of phytoplankton and remineralizers of nutrients in marine and freshwater ecosystems, but less is known about the regulation of their population dynamics. We analyzed a 12 yr data set of ciliate biomass and species composition in large, deep Lake Constance to understand the factors influencing ciliate spring development. The start of ciliate net growth in spring was closely linked to that of edible algae, chlorophyll a and the vertical mixing intensity, but independent of water temperature. During ciliate spring growth, the relative contribution of ciliated interception feeders was positively related to that of cryptomonads, whereas the relative contribution of filter feeders correlated positively with that of non-cryptomonads. The duration of ciliate dominance in spring was largely controlled by the highly variable onset of the phytoplankton bloom, as the termination of the ciliate bloom was less variable. During years with an extended spring bloom of algae and ciliates, internally forced species shifts were observed in both communities. Interception feeders alternated with filter feeders in their relative importance as did cryptomonads and non-cryptomonads. Extended spring blooms were observed when vertical mixing intensity was low at low temperatures during early spring, which will become less likely under the anticipated climate change scenarios. The termination of the ciliate spring bloom occurred prior to a reduction in food concentration and mostly also prior to the mass development of daphnids alone, but coincided with increased grazing by various predators together, such as rotifers, copepods and daphnids in late May/early June. Y1 - 2007 UR - http://www.int-res.com/articles/ame2007/49/a049p087.pdf U6 - https://doi.org/10.3354/Ame01127 ER - TY - JOUR A1 - Muhl, Rika M. W. A1 - Roelke, Daniel L. A1 - Zohary, Tamar A1 - Moustaka-Gouni, Maria A1 - Sommer, Ulrich A1 - Borics, Gabor A1 - Gaedke, Ursula A1 - Withrow, Frances G. A1 - Bhattacharyya, Joydeb T1 - Resisting annihilation BT - relationships between functional trait dissimilarity, assemblage competitive power and allelopathy JF - Ecology letters N2 - 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. KW - Allelopathy KW - exploitative competition KW - interference competition KW - intransitivity KW - lumpy coexistence KW - neutrality KW - species supersaturated assemblages Y1 - 2018 U6 - https://doi.org/10.1111/ele.13109 SN - 1461-023X SN - 1461-0248 VL - 21 IS - 9 SP - 1390 EP - 1400 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Kamjunke, Norbert A1 - Straile, Dietmar A1 - Gaedke, Ursula T1 - Response of heterotrophic bacteria, autotrophic picoplankton and heterotrophic nanoflagellates to re- oligotrophication N2 - We investigated the response of the microbial components of the pelagic food web to re-oligotrophication of large, deep Lake Constance where total phosphorus concentrations during mixing decreased from a maximum of 2.81 mu mol L- 1 in 1979 via 1.87 mu mol L-1 in 1987 to 0.26 mu mol L-1 in 2007. Measurements of heterotrophic bacteria, autotrophic picoplankton (APP) and heterotrophic nanoflagellates (HNF) in 2006 and 2007 were compared to values from 1987 to 1997. We hypothesized that the biomass and seasonal variability of all groups will decrease under more oligotrophic conditions due to reduced resource availability, particularly for APP and HNF but less for the competitively stronger bacteria. Average bacterial biomass between spring and autumn was unrelated to phosphorus, whereas the ratio of bacterial biomass to chlorophyll a concentration increased with decreasing trophy due to declining chlorophyll concentrations. In contrast, a unimodal relationship was found between APP and phosphorus with low biomass at low and high phosphorus concentrations and maximum biomass in between. Average HNF biomass decreased strongly by a factor of 10-30 with decreasing trophy, and chlorophyll-specific HNF biomass was unimodally related to phosphorus. The relative seasonal biomass variability did not change for any group during re-oligotrophication. To conclude, HNF responded much more strongly and bacteria less so than chlorophyll concentrations to oligotrophication, whereas APP exhibited a more complex pattern. Y1 - 2009 UR - http://plankt.oxfordjournals.org/ U6 - https://doi.org/10.1093/plankt/fbp037 SN - 0142-7873 ER - TY - JOUR A1 - Weyhenmeyer, G. A. A1 - Adrian, Rita A1 - Gaedke, Ursula A1 - Livingstone, D. M. A1 - Maberly, Stephen C. T1 - Response of phytoplankton in European lakes to a change in the North Atlantic Oscillation Y1 - 2002 SN - 0368-0770 ER - TY - JOUR A1 - van Velzen, Ellen A1 - Gaedke, Ursula T1 - Reversed predator-prey cycles are driven by the amplitude of prey oscillations JF - Ecology and evolution N2 - Ecoevolutionary feedbacks in predator-prey systems have been shown to qualitatively alter predator-prey dynamics. As a striking example, defense-offense coevolution can reverse predator-prey cycles, so predator peaks precede prey peaks rather than vice versa. However, this has only rarely been shown in either model studies or empirical systems. Here, we investigate whether this rarity is a fundamental feature of reversed cycles by exploring under which conditions they should be found. For this, we first identify potential conditions and parameter ranges most likely to result in reversed cycles by developing a new measure, the effective prey biomass, which combines prey biomass with prey and predator traits, and represents the prey biomass as perceived by the predator. We show that predator dynamics always follow the dynamics of the effective prey biomass with a classic 1/4-phase lag. From this key insight, it follows that in reversed cycles (i.e., -lag), the dynamics of the actual and the effective prey biomass must be in antiphase with each other, that is, the effective prey biomass must be highest when actual prey biomass is lowest, and vice versa. Based on this, we predict that reversed cycles should be found mainly when oscillations in actual prey biomass are small and thus have limited impact on the dynamics of the effective prey biomass, which are mainly driven by trait changes. We then confirm this prediction using numerical simulations of a coevolutionary predator-prey system, varying the amplitude of the oscillations in prey biomass: Reversed cycles are consistently associated with regions of parameter space leading to small-amplitude prey oscillations, offering a specific and highly testable prediction for conditions under which reversed cycles should occur in natural systems. KW - coevolution KW - ecoevolutionary dynamics KW - predator-prey dynamics KW - top-down control Y1 - 2018 U6 - https://doi.org/10.1002/ece3.4184 SN - 2045-7758 VL - 8 IS - 12 SP - 6317 EP - 6329 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Gaedke, Ursula A1 - Weisse, Thomas T1 - Seasonal and interannual variability of picocyanobacteria in Lake Constance (1987 - 1996) N2 - The ecology of chroococcoid picocyanobacteria was studied from 1987 to 1997 in large, deep, mesotrophic Lake Constance in relation to various abiotic and biotic factors that may influence their population dynamics. Picocyanobacteria dominated the autotrophic picoplankton (APP) numerically in this lake at all depths and times. Their abundances did not respond unequivocally to the decline of winterly phosphorus concentrations by a factor of 2.5 during the decade of investigation. They showed a recurrent seasonal pattern with peaks in spring and late summer, interspersed by a pronounced minimum during and after the clear-water phase around June. The magnitude, timing, and number of peaks and troughs which varied interannually, could in part be related to weather conditions or the impact of other plankton groups. Larger phytoplankton and picocyanobacteria exhibited a distinct and predictable response to the vertical mixing intensity during early spring. Except for 1993, picocyanobacteria and larger phytoplankton decreased simultaneously during the mass development of daphnids in late May or June which gave rise to the clear-water phase. As the daphnid development depends more strongly on surface water temperature than on vertical mixing intensity an early onset of stratification may imply a longer spring development which contributed to a higher seasonal average of picocyanobacterial abundances in 1989-1991. The decline in picocyanobacteria around the clear-water phase was often more pronounced and lasted longer than did the decline in larger algae. The rate of decrease may be related to daphnid abundance, however, no such relationship existed in respect to its duration. Summer peaks of picocyanobacteria were recorded despite the presence of relatively high densities of daphnids. We conclude that with the exception of the clear- water phase, grazing control by nano- and microzooplankton may be more important for controlling picocyanobacterial numbers than is grazing by daphnids. Picocyanobacteria declined in autumn prior to or concomitant with larger algae without any obvious relationship to phytoplankton biovolume or the extent of vertical mixing within the uppermost 20 m. The as yet unexplained variation in the population dynamics of picocyanobacteria points to the significance of species- specific protist grazing and to shifts in picocyanobacterial species composition which should be tackled in future studies. Y1 - 1998 ER - TY - JOUR A1 - Rocha, Marcia R. A1 - Vasseur, David A. A1 - Gaedke, Ursula T1 - Seasonal variations alter the impact of functional traits on plankton dynamics JF - PLoS one N2 - Gaining understanding of food-web processes often requires a simplified representation of natural diversity. One such simplification can be based on functional traits, as functionally similar species may provide a similar contribution to ecosystem level-processes. However, understanding how similarity in functional traits actually translates into similar contributions to ecosystem-level properties remains a challenge due to the complex ways in which traits can influence species' dynamics. Moreover, in many communities, seasonality alters the abiotic and biotic forcing regime, causing ongoing changes to patterns of species' dominance; groups of species do not stay intact but are rather continuously subjected to changes throughout the year. Using long-term high frequency measurements of phytoplankton in Lake Constance, we investigated the effect of seasonal changes on the relationship between functional similarity and temporal dynamics similarity of 36 morphotypes, and the relative contribution of different functional traits during the different parts of the year. Our results revealed seasonal differences in the overall degree of synchronization of morphotypes' temporal dynamics and how combinations of functional traits influence the relationship between functional trait similarity and temporal dynamics similarity, showing that different forcing regimes change how species cope with their environment based on their functional traits. Moreover, we show that the individual functional traits matter at different periods of the year indicating that species which are dynamically similar at certain parts of the year may not be at others. The differential strength of the overall and individual impact of functional traits on species' temporal dynamics makes the cohesion of a pair of functionally similar species dependent on the different forcing. Hence, simplifying food webs based solely on functional traits may not provide consistent estimates of functional groups over all seasons. Y1 - 2012 U6 - https://doi.org/10.1371/journal.pone.0051257 SN - 1932-6203 VL - 7 IS - 12 PB - PLoS CY - San Fransisco ER - TY - JOUR A1 - Bengfort, Michael A1 - van Velzen, Ellen A1 - Gaedke, Ursula T1 - Slight phenotypic variation in predators and prey causes complex predator-prey oscillations JF - Ecological Complexity N2 - Predator-prey oscillations are expected to show a 1/4-phase lag between predator and prey. However, observed dynamics of natural or experimental predator-prey systems are often more complex. A striking but hardly studied example are sudden interruptions of classic 1/4-lag cycles with periods of antiphase oscillations, or periods without any regular predator-prey oscillations. These interruptions occur for a limited time before the system reverts to regular 1/4-lag oscillations, thus yielding intermittent cycles. Reasons for this behaviour are often difficult to reveal in experimental systems. Here we test the hypothesis that such complex dynamical behaviour may result from minor trait variation and trait adaptation in both the prey and predator, causing recurrent small changes in attack rates that may be hard to capture by empirical measurements. Using a model structure where the degree of trait variation in the predator can be explicitly controlled, we show that a very limited amount of adaptation resulting in 10-15% temporal variation in attack rates is already sufficient to generate these intermittent dynamics. Such minor variation may be present in experimental predator-prey systems, and may explain disruptions in regular 1/4-lag oscillations. KW - Predator-prey cycles KW - Phase relationships KW - Intermittent cycles KW - Adaptive traits KW - Eco-evolutionary dynamics KW - Complex dynamics Y1 - 2017 U6 - https://doi.org/10.1016/j.ecocom.2017.06.003 SN - 1476-945X SN - 1476-9840 VL - 31 SP - 115 EP - 124 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Gaedke, Ursula T1 - Spectral analysis unmasks synchronous and compensatory dynamics in plankton communities Y1 - 2007 ER - TY - JOUR A1 - Spijkerman, Elly A1 - Barua, Deepak A1 - Gerloff-Elias, Antje A1 - Gaedke, Ursula A1 - Heckathorn, S. A. T1 - Stress responses and metal tolerance of Chlamydomonas acidophila in metal-enriched lake water and artificial medium N2 - Chlamydomonas acidophila faces high heavy-metal concentrations in acidic mining lakes, where it is a dominant phytoplankton species. To investigate the importance of metals to C. acidophila in these lakes, we examined the response of growth, photosynthesis, cell structure, heat-shock protein (Hsp) accumulation, and metal adsorption after incubation in metal-rich lake water and artificial growth medium enriched with metals (Fe, Zn). Incubation in both metal-rich lake water and medium caused large decreases in photosystem II function (though no differences among lakes), but no decrease in growth rate (except for medium + Fe). Concentrations of small Hsps were higher in algae incubated in metal-rich lake- water than in metal-enriched medium, whereas Hsp60 and Hsp70A were either less or equally expressed. Cellular Zn and Fe contents were lower, and metals adsorbed to the cell surface were higher, in lake-water-incubated algae than in medium- grown cells. The results indicate that high Zn or Fe levels are likely not the main or only contributor to the low primary production in mining lakes, and multiple adaptations of C. acidophila (e.g., high Hsp levels, decreased metal accumulation) increase its tolerance to metals and permit survival under such adverse environmental conditions. Supposedly, the main stress factor present in the lake water is an interaction between low P and high Fe concentrations. Y1 - 2007 UR - http://www.springerlink.com/content/p7273234p8255263/ U6 - https://doi.org/10.1007/s00792-007-0067-0 ER - TY - JOUR A1 - Kamjunke, Norbert A1 - Gaedke, Ursula A1 - Tittel, Jörg A1 - Weithoff, Guntram A1 - Bell, Elanor M. T1 - Strong vertical differences in the plankton composition of an extremely acidic lake N2 - Vertical differences in food web structure were examined in an extremely acidic, iron-rich mining lake in Germany (Lake 111; pH 2.6, total Fe 150mg L-1) during the period of stratification. We tested whether or not the seasonal variation of the plankton composition is less pronounced than the differences observed over depth. The lake was strongly stratified in summer, and concentrations of dissolved organic carbon and inorganic carbon were consistently low in the epilimnion but high in the hypolimnion. Oxygen concentrations declined in the hypolimnion but were always above 2mg L-1. Light attenuation did not change over depth and time and was governed by dissolved ferric iron. The plankton consisted mainly of single-celled and filamentous bacteria, the two mixotrophic flagellates Chlamydomonas sp. and Ochromonas sp., the two rotifer species Elosa worallii and Cephalodella hoodi, and Heliozoa as top predators. We observed very few ciliates and rhizopods, and no heterotrophic flagellates, crustaceans or fish. Ochromonas sp., bacterial filaments, Elosa and Heliozoa dominated in the epilimnion whereas Chlamydomonas sp., single-celled bacteria and Cephalodella dominated in the hypolimnion. Single-celled bacteria were controlled by Ochromonas sp. whereas the lack of large consumers favoured a high proportion of bacterial filaments. The primarily phototrophic Chlamydomas sp. was limited by light and CO2 and may have been reduced due to grazing by Ochromonas sp. in the epilimnion. The distribution of the primarily phagotrophic Ochromonas sp. and of the animals seemed to be controlled by prey availability. Differences in the plankton composition were much higher between the epilimnion and hypolimnion than within a particular stratum over time. The food web in Lake 111 was extremely species-poor enabling no functional redundancy. This was attributed to the direct exclusion of species by the harsh environmental conditions and presumably enforced by competitive exclusion. The latter was promoted by the low diversity at the first trophic level which, in turn, was attributed to relatively stable growth conditions and the independence of resource availability (inorganic carbon and light) from algal density. Ecological theory suggests that low functional redundancy promotes low stability in ecosystem processes which was not supported by our data. Y1 - 2004 ER - TY - JOUR A1 - Bell, Elanor M. A1 - Weithoff, Guntram A1 - Gaedke, Ursula T1 - Temporal dynamics and growth of Actinophrys sol (Sarcodina: Heliozoa), the top predator in an extremely acidic lake N2 - 1. The in situ abundance, biomass and mean cell volume of Actinophrys sol (Sarcodina: Heliozoa), the top predator in an extremely acidic German mining lake (Lake 111; pH 2.65), were determined over three consecutive years (spring to autumn, 2001-03). 2. Actinophrys sol exhibited pronounced temporal and vertical patterns in abundance, biomass and mean cell volume. Increasing from very low spring densities, maxima in abundance and biomass were observed in late June/early July and September. The highest mean abundance recorded during the study was 7 x 10(3) Heliozoa L-1. Heliozoan abundance and biomass were higher in the epilimnion than in the hypolimnion. Actinophrys sol cells from this acidic lake were smaller than individuals of the same species found in other aquatic systems. 3. We determined the growth rate of A. sol using all potential prey items available in, and isolated and cultured from, Lake 111. Prey items included: single-celled and filamentous bacteria of unknown taxonomic affinity, the mixotrophic flagellates Chlamydomonas acidophila and Ochromonas sp., the ciliate Oxytricha sp. and the rotifers Elosa worallii and Cephalodella hoodi. Actinophrys sol fed over a wide-size spectrum from bacteria to metazoans. Positive growth was not supported by all naturally available prey. Actinophrys sol neither increased in cell number (k) nor biomass (k(b)) when starved, with low concentrations of single-celled bacteria or with the alga Ochromonas sp. Positive growth was achieved with single- celled bacteria (k = 0.22 +/- 0.02 d(-1); k(b) = -0.06 +/- 0.02 d(-1)) and filamentous bacteria (k = 0.52 +/- < 0.01 d(- 1); k(b) = 0.66 d(-1)) at concentrations greater than observed in situ, and the alga C. acidophila (up to k = 0.43 +/- 0.03 d(-1); k(b) = 0.44 +/- 0.04 d(-1)), the ciliate Oxytricha sp. (k = 0.34 +/- 0.01 d(-1)) and in mixed cultures containing rotifers and C. acidophila (k = 0.23 +/- 0.02-0.32 +/- 0.02 d(-1); maximum k(b) = 0.42 +/- 0.05 d(-1)). The individual- and biomass-based growth of A. sol was highest when filamentous bacteria were provided. 4. Existing quantitative carbon flux models for the Lake 111 food web can be updated in light of our results. Actinophrys sol are omnivorous predators supported by a mixed diet of filamentous bacteria and C. acidophila in the epilimnion. Heliozoa are important components in the planktonic food webs of 'extreme' environments Y1 - 2006 UR - http://www3.interscience.wiley.com/cgi-bin/issn?DESCRIPTOR=PRINTISSN&VALUE=0046-5070 U6 - https://doi.org/10.1111/j.1365-2427.2006.01561.x SN - 0046-5070 ER - TY - JOUR A1 - Kath, Nadja Jeanette A1 - Gaedke, Ursula A1 - van Velzen, Ellen T1 - The double-edged sword of inducible defences: costs and benefits of maladaptive switching from the individual to the community level JF - Scientific Reports N2 - Phenotypic plasticity can increase individual fitness when environmental conditions change over time. Inducible defences are a striking example, allowing species to react to fluctuating predation pressure by only expressing their costly defended phenotype under high predation risk. Previous theoretical investigations have focused on how this affects predator–prey dynamics, but the impact on competitive outcomes and broader community dynamics has received less attention. Here we use a small food web model, consisting of two competing plastic autotrophic species exploited by a shared consumer, to study how the speed of inducible defences across three trade-off constellations affects autotroph coexistence, biomasses across trophic levels, and temporal variability. Contrary to the intuitive idea that faster adaptation increases autotroph fitness, we found that higher switching rates reduced individual fitness as it consistently provoked more maladaptive switching towards undefended phenotypes under high predation pressure. This had an unexpected positive impact on the consumer, increasing consumer biomass and lowering total autotroph biomass. Additionally, maladaptive switching strongly reduced autotroph coexistence through an emerging source-sink dynamic between defended and undefended phenotypes. The striking impact of maladaptive switching on species and food web dynamics indicates that this mechanism may be of more critical importance than previously recognized. Y1 - 2022 U6 - https://doi.org/10.1038/s41598-022-13895-7 SN - 2045-2322 VL - 12 SP - 1 EP - 14 PB - Springer Nature CY - London ER - TY - JOUR A1 - Kath, Nadja Jeanette A1 - Gaedke, Ursula A1 - van Velzen, Ellen T1 - The double-edged sword of inducible defences: costs and benefits of maladaptive switching from the individual to the community level JF - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Phenotypic plasticity can increase individual fitness when environmental conditions change over time. Inducible defences are a striking example, allowing species to react to fluctuating predation pressure by only expressing their costly defended phenotype under high predation risk. Previous theoretical investigations have focused on how this affects predator–prey dynamics, but the impact on competitive outcomes and broader community dynamics has received less attention. Here we use a small food web model, consisting of two competing plastic autotrophic species exploited by a shared consumer, to study how the speed of inducible defences across three trade-off constellations affects autotroph coexistence, biomasses across trophic levels, and temporal variability. Contrary to the intuitive idea that faster adaptation increases autotroph fitness, we found that higher switching rates reduced individual fitness as it consistently provoked more maladaptive switching towards undefended phenotypes under high predation pressure. This had an unexpected positive impact on the consumer, increasing consumer biomass and lowering total autotroph biomass. Additionally, maladaptive switching strongly reduced autotroph coexistence through an emerging source-sink dynamic between defended and undefended phenotypes. The striking impact of maladaptive switching on species and food web dynamics indicates that this mechanism may be of more critical importance than previously recognized. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1288 Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-572006 SN - 1866-8372 IS - 1288 ER - TY - JOUR A1 - Tirok, Katrin A1 - Gaedke, Ursula T1 - The effect of irradiance, vertical mixing and temperature on spring phytoplankton dynamics under climate change : long-term observations and model analysis N2 - Spring algal development in deep temperate lakes is thought to be strongly influenced by surface irradiance, vertical mixing and temperature, all of which are expected to be altered by climate change. Based on long-term data from Lake Constance, we investigated the individual and combined effects of these variables on algal dynamics using descriptive statistics, multiple regression models and a processoriented dynamic simulation model. The latter considered edible and less-edible algae and was forced by observed or anticipated irradiance, temperature and vertical mixing intensity. Unexpectedly, irradiance often dominated algal net growth rather than vertical mixing for the following reason: algal dynamics depended on algal net losses from the euphotic layer to larger depth due to vertical mixing. These losses strongly depended on the vertical algal gradient which, in turn, was determined by the mixing intensity during the previous days, thereby introducing a memory effect. This observation implied that during intense mixing that had already reduced the vertical algal gradient, net losses due to mixing were small. Consequently, even in deep Lake Constance, the reduction in primary production due to low light was often more influential than the net losses due to mixing. In the regression model, the dynamics of small, fast-growing algae was best explained by vertical mixing intensity and global irradiance, whereas those of larger algae were best explained by their biomass 1 week earlier. The simulation model additionally revealed that even in late winter grazing may represent an important loss factor during calm periods when losses due to mixing are small. The importance of losses by mixing and grazing changed rapidly as it depended on the variable mixing intensity. Higher temperature, lower global irradiance and enhanced mixing generated lower algal biomass and primary production in the dynamic simulation model. This suggests that potential consequences of climate change may partly counteract each other. Y1 - 2007 UR - http://www.springerlink.com/content/p450177134590p61/ U6 - https://doi.org/10.1007/s00442-006-0547-4 ER - TY - JOUR A1 - Ceulemans, Ruben A1 - Gaedke, Ursula A1 - Klauschies, Toni A1 - Guill, Christian T1 - The effects of functional diversity on biomass production, variability, and resilience of ecosystem functions in a tritrophic system JF - Scientific Reports N2 - Diverse communities can adjust their trait composition to altered environmental conditions, which may strongly influence their dynamics. Previous studies of trait-based models mainly considered only one or two trophic levels, whereas most natural system are at least tritrophic. Therefore, we investigated how the addition of trait variation to each trophic level influences population and community dynamics in a tritrophic model. Examining the phase relationships between species of adjacent trophic levels informs about the strength of top-down or bottom-up control in non-steadystate situations. Phase relationships within a trophic level highlight compensatory dynamical patterns between functionally different species, which are responsible for dampening the community temporal variability. Furthermore, even without trait variation, our tritrophic model always exhibits regions with two alternative states with either weak or strong nutrient exploitation, and correspondingly low or high biomass production at the top level. However, adding trait variation increased the basin of attraction of the high-production state, and decreased the likelihood of a critical transition from the high- to the lowproduction state with no apparent early warning signals. Hence, our study shows that trait variation enhances resource use efficiency, production, stability, and resilience of entire food webs. KW - early-warning signals KW - top-down control KW - community ecology KW - regime shifts KW - food webs KW - compensatory dynamics KW - consumer diversity KW - metabolic theory KW - rapid evolution KW - stable states Y1 - 2019 U6 - https://doi.org/10.1038/s41598-019-43974-1 SN - 2045-2322 VL - 9 PB - Macmillan Publishers Limited CY - London ER - TY - JOUR A1 - Weithoff, Guntram A1 - Walz, Norbert A1 - Gaedke, Ursula T1 - The intermediate disturbance hypothesis : species diversity or functional diversity N2 - Phytoplankton dynamics in a shallow eutrophic lake were investigated over a 3-year period with respect to environmental forces which drive species composition and diversity. Diversity was calculated on the basis of species as well as on the basis of their functional properties (the C-R-S-concept). Stratification and water column mixing had a strong impact on phytoplankton composition. Application of a similarity-diversity model revealed that a high diversity was a transient non-stable state, whereas drastic changes or long-lasting stable environmental conditions are characterized by low diversity. This effect was more pronounced when the diversity was calculated on the basis of the phytoplankton species functional properties. Thus, this functional approach supports the intermediate disturbance hypothesis from field data. Y1 - 2001 ER - TY - JOUR A1 - Pennekamp, Frank A1 - Iles, Alison C. A1 - Garland, Joshua A1 - Brennan, Georgina A1 - Brose, Ulrich A1 - Gaedke, Ursula A1 - Jacob, Ute A1 - Kratina, Pavel A1 - Matthews, Blake A1 - Munch, Stephan A1 - Novak, Mark A1 - Palamara, Gian Marco A1 - Rall, Bjorn C. A1 - Rosenbaum, Benjamin A1 - Tabi, Andrea A1 - Ward, Colette A1 - Williams, Richard A1 - Ye, Hao A1 - Petchey, Owen L. T1 - The intrinsic predictability of ecological time series and its potential to guide forecasting JF - Ecological monographs : a publication of the Ecological Society of America. KW - empirical dynamic modelling KW - forecasting KW - information theory KW - permutation entropy KW - population dynamics KW - time series analysis Y1 - 2019 U6 - https://doi.org/10.1002/ecm.1359 SN - 0012-9615 SN - 1557-7015 VL - 89 IS - 2 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Gaedke, Ursula T1 - The response of the pelagic community of a large and deep lake (L. Constance) to reoligotrophication : evidence for scale-dependent hierarchical patterns N2 - Large (472 km2) and deep (zmean=101 m) Lake Constance is undergoing re-oligotrophication. Total phosphorus during winter mixing (TPmix) decreased from >80 during 1975-1981 to 22 ;g/l in 1996. Average summer values of secchi and euphotic depth increased significantly from 4.5 to 6.5 m and from 10.5 to 13 m, respectively. The algal species composition changed and, during summer, total algal biomass decreased by 50 % and primary production by 25 %. Standing stocks of well-edible algae, rotifers, and herbivorous and carnivorous crustaceans did not exhibit a trend with TPmix, whereas their species compositions or egg-ratios were partially altered. The age-at-capture of planktivorous whitefish increased slightly. I tested the hypotheses that (1) changes should first be observed at the level of individuals or within species (altering e. g. C:P or egg-ratios) prior to changes within communities (affecting e. g. the taxonomic composition) and at the community level (affecting e. g. total biomass or production). This would imply that it is more appropriate to conceptualize step-wise responses along a hierarchical gradient of increasing aggregation as suggested by hierarchy theory, rather than simultaneous changes at all hierarchical levels. (2) Responses become dampened along the food chain and with increasing body size, i. e. bottom-up control is most important for autotrophs. All communities studied (phytoplankton, crustaceans, fish) reacted at the individual level (e. g. by changes of (re)production rates), and/or within the community (e. g. altered taxonomic composition) whereas changes of bulk parameters of the entire community were restricted to phytoplankton. Hence, the first hypothesis is partially supported by the observed reactions and demands further testing. The second hypothesis is clearly supported by our data when comparing autotrophs and consumers, but not when comparing crustaceans and fish. The testing of these hypotheses is complicated by the large differences in size and, consequently, in reaction times of pelagic organisms on the one hand and the rather fixed time scale of limnological research on the other hand. The different time scales imply a selective perception of the various potential responses of the differently sized organisms as the time scales of the responses depend on body size and the level of aggregation. For example, we are more likely to establish physiological or behaviourial changes of fish, and taxonomical or biomass changes of phytoplankton. Acknowledging the scale dependence and level of aggregation is also crucial for cross-system comparisons. Y1 - 1998 ER - TY - JOUR A1 - Huber, Veronika A1 - Gaedke, Ursula T1 - The role of predation for seasonal variability patterns among phytoplankton and ciliates N2 - Investigating the mechanisms which underlie the biomass fluctuations of populations and communities is important to better understand the processes which buffer community biomass in a variable environment. Based on long- term data of plankton biomass in Lake Constance (Bodensee), this study aims at explaining the different degree of synchrony among populations observed within two freshwater plankton groups, phytoplankton and ciliates. Established measures of temporal variability such as the variance ratio and cross-correlation coefficients were combined with first- order autoregressive models that allow estimating species interactions from time-series data. We found that predation was an important driver of the observed seasonal variability patterns in phytoplankton and ciliates, and that competitive interactions only played a subordinate role. In Lake Constance copepods and cladocerans, two major invertebrate predator groups, focus their grazing pressure at different times of the season. Model results suggested that compensatory dynamics detected in phytoplankton originate from the differential vulnerability of species to either one of these two predator groups. For ciliates model results advocated that synchrony among species occurs because ciliates tend to be vulnerable to both predator groups. Our findings underline the necessity of extending studies of community variability to multiple trophic levels because accounting for predator-prey interactions may often be more important than accounting for competitive interactions at one trophic level Y1 - 2006 UR - http://www3.interscience.wiley.com/cgi-bin/issn?DESCRIPTOR=PRINTISSN&VALUE=0030-1299 U6 - https://doi.org/10.1111/j.2006.0030-1299.14753.x SN - 0030-1299 ER - TY - JOUR A1 - Ehrlich, Elias A1 - Kath, Nadja Jeanette A1 - Gaedke, Ursula T1 - The shape of a defense-growth trade-off governs seasonal trait dynamics in natural phytoplankton JF - The ISME journal N2 - Theory predicts that trade-offs, quantifying costs of functional trait adjustments, crucially affect community trait adaptation to altered environmental conditions, but empirical verification is scarce. We evaluated trait dynamics (antipredator defense, maximum growth rate, and phosphate affinity) of a lake phytoplankton community in a seasonally changing environment, using literature trait data and 21 years of species-resolved high-frequency biomass measurements. The trait data indicated a concave defense-growth trade-off, promoting fast-growing species with intermediate defense. With seasonally increasing grazing pressure, the community shifted toward higher defense levels at the cost of lower growth rates along the trade-off curve, while phosphate affinity explained some deviations from it. We discuss how low fitness differences of species, inferred from model simulations, in concert with stabilizing mechanisms, e.g., arising from further trait dimensions, may lead to the observed phytoplankton diversity. In conclusion, quantifying trade-offs is key for predictions of community trait adaptation and biodiversity under environmental change. KW - coexistence KW - community ecology KW - diversity KW - evolution KW - fitness KW - functional traits KW - lake KW - maintenance KW - mechanisms KW - plankton Y1 - 2020 U6 - https://doi.org/10.1038/s41396-020-0619-1 SN - 1751-7362 SN - 1751-7370 VL - 14 IS - 6 SP - 1451 EP - 1462 PB - Nature Publishing Group CY - London ER - TY - JOUR A1 - Ceulemans, Ruben A1 - Guill, Christian A1 - Gaedke, Ursula T1 - Top predators govern multitrophic diversity effects in tritrophic food webs JF - Ecology : a publication of the Ecological Society of America N2 - 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. KW - food-web efficiency KW - functional diversity KW - machine learning KW - nutrient KW - exploitation KW - production KW - random forest KW - temporal variability KW - top KW - predator KW - trait diversity Y1 - 2021 U6 - https://doi.org/10.1002/ecy.3379 SN - 0012-9658 SN - 1939-9170 VL - 102 IS - 7 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Klauschies, Toni A1 - Vasseur, David A. A1 - Gaedke, Ursula T1 - Trait adaptation promotes species coexistence in diverse predator and prey communities JF - Ecology and evolution N2 - Species can adjust their traits in response to selection which may strongly influence species coexistence. Nevertheless, current theory mainly assumes distinct and time-invariant trait values. We examined the combined effects of the range and the speed of trait adaptation on species coexistence using an innovative multispecies predator–prey model. It allows for temporal trait changes of all predator and prey species and thus simultaneous coadaptation within and among trophic levels. We show that very small or slow trait adaptation did not facilitate coexistence because the stabilizing niche differences were not sufficient to offset the fitness differences. In contrast, sufficiently large and fast trait adaptation jointly promoted stable or neutrally stable species coexistence. Continuous trait adjustments in response to selection enabled a temporally variable convergence and divergence of species traits; that is, species became temporally more similar (neutral theory) or dissimilar (niche theory) depending on the selection pressure, resulting over time in a balance between niche differences stabilizing coexistence and fitness differences promoting competitive exclusion. Furthermore, coadaptation allowed prey and predator species to cluster into different functional groups. This equalized the fitness of similar species while maintaining sufficient niche differences among functionally different species delaying or preventing competitive exclusion. In contrast to pre- vious studies, the emergent feedback between biomass and trait dynamics enabled supersaturated coexistence for a broad range of potential trait adaptation and parameters. We conclude that accounting for trait adaptation may explain stable and supersaturated species coexistence for a broad range of environmental conditions in natural systems when the absence of such adaptive changes would preclude it. Small trait changes, coincident with those that may occur within many natural populations, greatly enlarged the number of coexisting species. KW - Coadaptation KW - equalizing and stabilizing mechanisms KW - maintenance of functional diversity KW - niche and fitness differences KW - supersaturated species coexistence KW - trait convergence and divergence Y1 - 2016 U6 - https://doi.org/10.1002/ece3.2172 SN - 2045-7758 PB - John Wiley & Sons, Inc. ER - TY - JOUR A1 - Klauschies, Toni A1 - Vasseur, David A. A1 - Gaedke, Ursula T1 - Trait adaptation promotes species coexistence in diverse predator and prey communities JF - Ecology and evolution N2 - Species can adjust their traits in response to selection which may strongly influence species coexistence. Nevertheless, current theory mainly assumes distinct and time-invariant trait values. We examined the combined effects of the range and the speed of trait adaptation on species coexistence using an innovative multispecies predator-prey model. It allows for temporal trait changes of all predator and prey species and thus simultaneous coadaptation within and among trophic levels. We show that very small or slow trait adaptation did not facilitate coexistence because the stabilizing niche differences were not sufficient to offset the fitness differences. In contrast, sufficiently large and fast trait adaptation jointly promoted stable or neutrally stable species coexistence. Continuous trait adjustments in response to selection enabled a temporally variable convergence and divergence of species traits; that is, species became temporally more similar (neutral theory) or dissimilar (niche theory) depending on the selection pressure, resulting over time in a balance between niche differences stabilizing coexistence and fitness differences promoting competitive exclusion. Furthermore, coadaptation allowed prey and predator species to cluster into different functional groups. This equalized the fitness of similar species while maintaining sufficient niche differences among functionally different species delaying or preventing competitive exclusion. In contrast to previous studies, the emergent feedback between biomass and trait dynamics enabled supersaturated coexistence for a broad range of potential trait adaptation and parameters. We conclude that accounting for trait adaptation may explain stable and supersaturated species coexistence for a broad range of environmental conditions in natural systems when the absence of such adaptive changes would preclude it. Small trait changes, coincident with those that may occur within many natural populations, greatly enlarged the number of coexisting species. KW - Coadaptation KW - equalizing and stabilizing mechanisms KW - maintenance of functional diversity KW - niche and fitness differences KW - supersaturated species coexistence KW - trait convergence and divergence Y1 - 2016 U6 - https://doi.org/10.1002/ece3.2172 SN - 2045-7758 VL - 6 SP - 4141 EP - 4159 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Ehrlich, Elias A1 - Becks, Lutz A1 - Gaedke, Ursula T1 - Trait-fitness relationships determine how trade-off shapes affect species coexistence JF - Ecology : a publication of the Ecological Society of America N2 - Trade-offs between functional traits are ubiquitous in nature and can promote species coexistence depending on their shape. Classic theory predicts that convex trade-offs facilitate coexistence of specialized species with extreme trait values (extreme species) while concave trade-offs promote species with intermediate trait values (intermediate species). We show here that this prediction becomes insufficient when the traits translate non-linearly into fitness which frequently occurs in nature, e.g., an increasing length of spines reduces grazing losses only up to a certain threshold resulting in a saturating or sigmoid trait-fitness function. We present a novel, general approach to evaluate the effect of different trade-off shapes on species coexistence. We compare the trade-off curve to the invasion boundary of an intermediate species invading the two extreme species. At this boundary, the invasion fitness is zero. Thus, it separates trait combinations where invasion is or is not possible. The invasion boundary is calculated based on measurable trait-fitness relationships. If at least one of these relationships is not linear, the invasion boundary becomes non-linear, implying that convex and concave trade-offs not necessarily lead to different coexistence patterns. Therefore, we suggest a new ecological classification of trade-offs into extreme-favoring and intermediate-favoring which differs from a purely mathematical description of their shape. We apply our approach to a well-established model of an empirical predator-prey system with competing prey types facing a trade-off between edibility and half-saturation constant for nutrient uptake. We show that the survival of the intermediate prey depends on the convexity of the trade-off. Overall, our approach provides a general tool to make a priori predictions on the outcome of competition among species facing a common trade-off in dependence of the shape of the trade-off and the shape of the trait-fitness relationships. KW - coexistence KW - competition KW - fitness KW - functional traits KW - invasion boundary KW - neutrality KW - predator-prey model KW - shape KW - trade-offs Y1 - 2017 U6 - https://doi.org/10.1002/ecy.2047 SN - 0012-9658 SN - 1939-9170 VL - 98 SP - 3188 EP - 3198 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Hartwich, Melanie A1 - Straile, Dietmar A1 - Gaedke, Ursula A1 - Wacker, Alexander T1 - Use of ciliate and phytoplankton taxonomic composition for the estimation of eicosapentaenoic acid concentration in lakes JF - Freshwater biology N2 - 1. The polyunsaturated fatty acid eicosapentaenoic acid (EPA) plays an important role in aquatic food webs, in particular at the primary producerconsumer interface where keystone species such as daphnids may be constrained by its dietary availability. Such constraints and their seasonal and interannual changes may be detected by continuous measurements of EPA concentrations. However, such EPA measurements became common only during the last two decades, whereas long-term data sets on plankton biomass are available for many well-studied lakes. Here, we test whether it is possible to estimate EPA concentrations from abiotic variables (light and temperature) and the biomass of prey organisms (e.g. ciliates, diatoms and cryptophytes) that potentially provide EPA for consumers. 2. We used multiple linear regression to relate size- and taxonomically resolved plankton biomass data and measurements of temperature and light intensity to directly measured EPA concentrations in Lake Constance during a whole year. First, we tested the predictability of EPA concentrations from the biomass of EPA-rich organisms (diatoms, cryptophytes and ciliates). Secondly, we included the variables mean temperature and mean light intensity over the sampling depth (020 m) and depth (08 and 820 m) as factors in our model to check for large-scale seasonal- and depth-dependent effects on EPA concentrations. In a third step, we included the deviations of light and temperature from mean values in our model to allow for their potential influence on the biochemical composition of plankton organisms. We used the Akaike Information Criterion to determine the best models. 3. All approaches supported our proposition that the biomasses of specific plankton groups are variables from which seston EPA concentrations can be derived. The importance of ciliates as an EPA source in the seston was emphasised by their high weight in our models, although ciliates are neglected in most studies that link fatty acids to seston taxonomic composition. The large-scale seasonal variability of light intensity and its interaction with diatom biomass were significant predictors of EPA concentrations. The deviation of temperature from mean values, accounting for a depth-dependent effect on EPA concentrations, and its interaction with ciliate biomass were also variables with high predictive power. 4. The best models from the first and second approaches were validated with measurements of EPA concentrations from another year (1997). The estimation with the best model including only biomass explained 80%, and the best model from the second approach including mean temperature and depth explained 87% of the variability in EPA concentrations in 1997. 5. We show that it is possible to predict EPA concentrations reliably from plankton biomass, while the inclusion of abiotic factors led to results that were only partly consistent with expectations from laboratory studies. Our approach of including biotic predictors should be transferable to other systems and allow checking for biochemical constraints on primary consumers. KW - ciliates KW - diatoms KW - eicosapentaenoic acid KW - light KW - temperature Y1 - 2012 U6 - https://doi.org/10.1111/j.1365-2427.2012.02799.x SN - 0046-5070 VL - 57 IS - 7 SP - 1385 EP - 1398 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Rocha, Marcia R. A1 - Vasseur, David A. A1 - Hayn, Michael A1 - Holschneider, Matthias A1 - Gaedke, Ursula T1 - Variability patterns differ between standing stock and process rates JF - Oikos N2 - Standing stocks are typically easier to measure than process rates such as production. Hence, stocks are often used as indicators of ecosystem functions although the latter are generally more strongly related to rates than to stocks. The regulation of stocks and rates and thus their variability over time may differ, as stocks constitute the net result of production and losses. Based on long-term high frequency measurements in a large, deep lake we explore the variability patterns in primary and bacterial production and relate them to those of the corresponding standing stocks, i.e. chlorophyll concentration, phytoplankton and bacterial biomass. We employ different methods (coefficient of variation, spline fitting and spectral analysis) which complement each other for assessing the variability present in the plankton data, at different temporal scales. In phytoplankton, we found that the overall variability of primary production is dominated by fluctuations at low frequencies, such as the annual, whereas in stocks and chlorophyll in particular, higher frequencies contribute substantially to the overall variance. This suggests that using standing stocks instead of rate measures leads to an under- or overestimation of food shortage for consumers during distinct periods of the year. The range of annual variation in bacterial production is 8 times greater than biomass, showing that the variability of bacterial activity (e.g. oxygen consumption, remineralisation) would be underestimated if biomass is used. The P/B ratios were variable and although clear trends are present in both bacteria and phytoplankton, no systematic relationship between stock and rate measures were found for the two groups. Hence, standing stock and process rate measures exhibit different variability patterns and care is needed when interpreting the mechanisms and implications of the variability encountered. Y1 - 2011 U6 - https://doi.org/10.1111/j.1600-0706.2010.18786.x SN - 0030-1299 VL - 120 IS - 1 SP - 17 EP - 25 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Aberle-Malzahn, Nicole A1 - Bauer, Barbara A1 - Lewandowska, A. A1 - Gaedke, Ursula A1 - Sommer, U. T1 - Warming induces shifts in microzooplankton phenology and reduces time-lags between phytoplankton and protozoan production JF - Marine biology : international journal on life in oceans and coastal waters N2 - Indoor mesocosm experiments were conducted to test for potential climate change effects on the spring succession of Baltic Sea plankton. Two different temperature (Delta 0 A degrees C and Delta 6 A degrees C) and three light scenarios (62, 57 and 49 % of the natural surface light intensity on sunny days), mimicking increasing cloudiness as predicted for warmer winters in the Baltic Sea region, were simulated. By combining experimental and modeling approaches, we were able to test for a potential dietary mismatch between phytoplankton and zooplankton. Two general predator-prey models, one representing the community as a tri-trophic food chain and one as a 5-guild food web were applied to test for the consequences of different temperature sensitivities of heterotrophic components of the plankton. During the experiments, we observed reduced time-lags between the peaks of phytoplankton and protozoan biomass in response to warming. Microzooplankton peak biomass was reached by 2.5 day A degrees C-1 earlier and occurred almost synchronously with biomass peaks of phytoplankton in the warm mesocosms (Delta 6 A degrees C). The peak magnitudes of microzooplankton biomass remained unaffected by temperature, and growth rates of microzooplankton were higher at Delta 6 A degrees C (mu(a dagger 0 A degrees C) = 0.12 day(-1) and mu(a dagger 6 A degrees C) = 0.25 day(-1)). Furthermore, warming induced a shift in microzooplankton phenology leading to a faster species turnover and a shorter window of microzooplankton occurrence. Moderate differences in the light levels had no significant effect on the time-lags between autotrophic and heterotrophic biomass and on the timing, biomass maxima and growth rate of microzooplankton biomass. Both models predicted reduced time-lags between the biomass peaks of phytoplankton and its predators (both microzooplankton and copepods) with warming. The reduction of time-lags increased with increasing Q(10) values of copepods and protozoans in the tritrophic food chain. Indirect trophic effects modified this pattern in the 5-guild food web. Our study shows that instead of a mismatch, warming might lead to a stronger match between protist grazers and their prey altering in turn the transfer of matter and energy toward higher trophic levels. Y1 - 2012 U6 - https://doi.org/10.1007/s00227-012-1947-0 SN - 0025-3162 VL - 159 IS - 11 SP - 2441 EP - 2453 PB - Springer CY - New York ER - TY - JOUR A1 - Mehner, T. A1 - Attermeyer, Katrin A1 - Brauns, Mario A1 - Brothers, Soren M. A1 - Diekmann, J. A1 - Gaedke, Ursula A1 - Grossart, Hans-Peter A1 - Koehler, J. A1 - Lischke, Betty A1 - Meyer, N. A1 - Scharnweber, Inga Kristin A1 - Syvaranta, J. A1 - Vanni, M. J. A1 - Hilt, S. T1 - Weak Response of Animal Allochthony and Production to Enhanced Supply of Terrestrial Leaf Litter in Nutrient-Rich Lakes JF - Ecosystems N2 - Ecosystems are generally linked via fluxes of nutrients and energy across their boundaries. For example, freshwater ecosystems in temperate regions may receive significant inputs of terrestrially derived carbon via autumnal leaf litter. This terrestrial particulate organic carbon (POC) is hypothesized to subsidize animal production in lakes, but direct evidence is still lacking. We divided two small eutrophic lakes each into two sections and added isotopically distinct maize litter to the treatment sections to simulate increased terrestrial POC inputs via leaf litter in autumn. We quantified the reliance of aquatic consumers on terrestrial resources (allochthony) in the year subsequent to POC additions by applying mixing models of stable isotopes. We also estimated lake-wide carbon (C) balances to calculate the C flow to the production of the major aquatic consumer groups: benthic macroinvertebrates, crustacean zooplankton, and fish. The sum of secondary production of crustaceans and benthic macroinvertebrates supported by terrestrial POC was higher in the treatment sections of both lakes. In contrast, total secondary and tertiary production (supported by both autochthonous and allochthonous C) was higher in the reference than in the treatment sections of both lakes. Average aquatic consumer allochthony per lake section was 27-40%, although terrestrial POC contributed less than about 10% to total organic C supply to the lakes. The production of aquatic consumers incorporated less than 5% of the total organic C supply in both lakes, indicating a low ecological efficiency. We suggest that the consumption of terrestrial POC by aquatic consumers facilitates a strong coupling with the terrestrial environment. However, the high autochthonous production and the large pool of autochthonous detritus in these nutrient-rich lakes make terrestrial POC quantitatively unimportant for the C flows within food webs. KW - stable isotopes KW - terrestrial subsidy KW - carbon budget KW - ecological efficiency KW - benthic food web KW - pelagic food web Y1 - 2016 U6 - https://doi.org/10.1007/s10021-015-9933-2 SN - 1432-9840 SN - 1435-0629 VL - 19 SP - 311 EP - 325 PB - Springer CY - New York ER -