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 - TY - JOUR A1 - Seifert, Linda I. A1 - Weithoff, Guntram A1 - Gaedke, Ursula A1 - Vos, Matthijs T1 - Warming-induced changes in predation, extinction and invasion in an ectotherm food web JF - Oecologia N2 - Climate change will alter the forces of predation and competition in temperate ectotherm food webs. This may increase local extinction rates, change the fate of invasions and impede species reintroductions into communities. Invasion success could be modulated by traits (e.g., defenses) and adaptations to climate. We studied how different temperatures affect the time until extinction of species, using bitrophic and tritrophic planktonic food webs to evaluate the relative importance of predatory overexploitation and competitive exclusion, at 15 and 25 A degrees C. In addition, we tested how inclusion of a subtropical as opposed to a temperate strain in this model food web affects times until extinction. Further, we studied the invasion success of the temperate rotifer Brachionus calyciflorus into the planktonic food web at 15 and 25 A degrees C on five consecutive introduction dates, during which the relative forces of predation and competition differed. A higher temperature dramatically shortened times until extinction of all herbivore species due to carnivorous overexploitation in tritrophic systems. Surprisingly, warming did not increase rates of competitive exclusion among the tested herbivore species in bitrophic communities. Including a subtropical herbivore strain reduced top-down control by the carnivore at high temperature. Invasion attempts of temperate B. calyciflorus into the food web always succeeded at 15 A degrees C, but consistently failed at 25 A degrees C due to voracious overexploitation by the carnivore. Pre-induction of defenses (spines) in B. calyciflorus before the invasion attempt did not change its invasion success at the high temperature. We conclude that high temperatures may promote local extinctions in temperate ectotherms and reduce their chances of successful recovery. KW - Community dynamics KW - Freshwater ecosystem KW - Global warming KW - Species range shift KW - Trophic interactions Y1 - 2015 U6 - https://doi.org/10.1007/s00442-014-3211-4 SN - 0029-8549 SN - 1432-1939 VL - 178 IS - 2 SP - 485 EP - 496 PB - Springer CY - New York 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 - 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 - 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 - Mehner, Thomas A1 - Attermeyer, Katrin A1 - Brauns, Mario A1 - Brothers, Soren A1 - Hilt, Sabine A1 - Scharnweber, Kristin A1 - Dorst, Renee Minavan A1 - Vanni, Michael J. A1 - Gaedke, Ursula T1 - Trophic transfer efficiency in lakes JF - Ecosystems N2 - Trophic transfer efficiency (TTE) is usually calculated as the ratio of production rates between two consecutive trophic levels. Although seemingly simple, TTE estimates from lakes are rare. In our review, we explore the processes and structures that must be understood for a proper lake TTE estimate. We briefly discuss measurements of production rates and trophic positions and mention how ecological efficiencies, nutrients (N, P) and other compounds (fatty acids) affect energy transfer between trophic levels and hence TTE. Furthermore, we elucidate how TTE estimates are linked with size-based approaches according to the Metabolic Theory of Ecology, and how food-web models can be applied to study TTE in lakes. Subsequently, we explore temporal and spatial heterogeneity of production and TTE in lakes, with a particular focus on the links between benthic and pelagic habitats and between the lake and the terrestrial environment. We provide an overview of TTE estimates from lakes found in the published literature. Finally, we present two alternative approaches to estimating TTE. First, TTE can be seen as a mechanistic quantity informing about the energy and matter flow between producer and consumer groups. This approach is informative with respect to food-web structure, but requires enormous amounts of data. The greatest uncertainty comes from the proper consideration of basal production to estimate TTE of omnivorous organisms. An alternative approach is estimating food-chain and food-web efficiencies, by comparing the heterotrophic production of single consumer levels or the total sum of all heterotrophic production including that of heterotrophic bacteria to the total sum of primary production. We close the review by pointing to a few research questions that would benefit from more frequent and standardized estimates of TTE in lakes. KW - stoichiometry KW - production rates KW - trophic position KW - fatty acids KW - land-water coupling KW - food-web models Y1 - 2022 U6 - https://doi.org/10.1007/s10021-022-00776-3 SN - 1432-9840 SN - 1435-0629 VL - 25 IS - 8 SP - 1628 EP - 1652 PB - Springer CY - New York 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - Gaedke, Ursula T1 - The impact of weather conditions on the seasonal plankton development N2 - Long-term measurements (1979-1994) of meteorological parameters and of algal and crustacean biomass were used in conjunction with a comprehensive hydrodynamic model to evaluate the impact of weather conditions on plankton dynamics in a large, deep, temperate lake (Upper Lake Constance), and to identify potential causal mechanisms. The natural variability of weather conditions, including the exceptionally mild winters during the late eighties, allowed us the investigation of the covariation of meteorological parameters such as irradiance, air temperature, and wind with vernal algal and crustacean population growth. Crustacean zooplankton responded strongly to differences in surface water temperature, but not to mixing depth or algal biomass. Clear relationships between changes of algal biomass and meteorological factors were only found during the rare occasions when acted together to favour or hamper algal development. Otherwise, the impact of meterological conditions on the physical conditions which were most likely conducive to phytoplankton development, could not be followed by this simple approach. This problem was overcome with a one-dimensional hydrodynamic turbulent exchange model driven by the meteorological boundary conditions at the water surface. It was used to simulate the development of the vernal density stratification and to investigate the relationships between meteorological conditions and exchange rates from the euphotic to the aphotic zone. The beginning of the spring algal bloom was shown to depend on the stabilization of the upper part of the water column. As soon as mixing below 20 m was inhibited, confining the algae to the euphotic zone for prolonged periods of time, substantial increases in algal standing stock occurred consistently. In contrast, during periods when high vertical mixing rates were computed with the model no substantial increases of algal biomass were found. This tight coupling between the estimates of vertical mixing intensity and observed algal development, combined with knowledge about the impact of individual meteorological factors on mixing, enabled predictions about the response of algae to different weather conditions during spring. Y1 - 1998 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 - 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 - 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 -