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 - 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 - Gaedke, Ursula A1 - Klauschies, Toni T1 - Analyzing the shape of observed trait distributions enables a data-based moment closure of aggregate models JF - Limnology and Oceanography: Methods N2 - The shape of trait distributions may inform about the selective forces that structure ecological communities. Here, we present a new moment-based approach to classify the shape of observed biomass-weighted trait distributions into normal, peaked, skewed, or bimodal that facilitates spatio-temporal and cross-system comparisons. Our observed phytoplankton trait distributions exhibited substantial variance and were mostly skewed or bimodal rather than normal. Additionally, mean, variance, skewness und kurtosis were strongly correlated. This is in conflict with trait-based aggregate models that often assume normally distributed trait values and small variances. Given these discrepancies between our data and general model assumptions we used the observed trait distributions to test how well different aggregate models with first- or second-order approximations and different types of moment closure predict the biomass, mean trait, and trait variance dynamics using weakly or moderately nonlinear fitness functions. For weakly non-linear fitness functions aggregate models with a second-order approximation and a data-based moment closure that relied on the observed correlations between skewness and mean, and kurtosis and variance predicted biomass and often also mean trait changes fairly well and better than models with first-order approximations or a normal-based moment closure. In contrast, none of the models reflected the changes of the trait variances reliably. Aggregate model performance was often also poor for moderately nonlinear fitness functions. This questions a general applicability of the normal-based approach, in particular for predicting variance dynamics determining the speed of trait changes and maintenance of biodiversity. We evaluate in detail how and why better approximations can be obtained. Y1 - 2018 U6 - https://doi.org/10.1002/lom3.10218 SN - 1541-5856 VL - 15 SP - 979 EP - 994 PB - Wiley CY - Hoboken 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 - 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 - Seiler, Claudia A1 - van Velzen, Ellen A1 - Neu, Thomas R. A1 - Gaedke, Ursula A1 - Berendonk, Thomas U. A1 - Weitere, Markus T1 - Grazing resistance of bacterial biofilms: a matter of predators’ feeding trait JF - FEMS microbiology ecology N2 - Biofilm formation in bacteria is considered to be one strategy to avoid protozoan grazing. However, this assumption is largely based on experiments with suspension-feeding protozoans. Here we test the hypothesis that grazing resistance depends on both the grazers’ feeding trait and the bacterial phenotype, rather than being a general characteristic of bacterial biofilms. We combined batch experiments with mathematical modelling, considering the bacterium Pseudomonas putida and either a suspension-feeding (i.e. the ciliate Paramecium tetraurelia) or a surface-feeding grazer (i.e. the amoeba Acanthamoeba castellanii). We find that both plankton and biofilm phenotypes were consumed, when exposed to their specialised grazer, whereas the other phenotype remained grazing-resistant. This was consistently shown in two experiments (starting with either only planktonic bacteria or with additional pre-grown biofilms) and matches model predictions. In the experiments, the plankton feeder strongly stimulated the biofilm biomass. This stimulation of the resistant prey phenotype was not predicted by the model and it was not observed for the biofilm feeders, suggesting the existence of additional mechanisms that stimulate biofilm formation besides selective feeding. Overall, our results confirm our hypothesis that grazing resistance is a matter of the grazers’ trait (i.e. feeding type) rather than a biofilm-specific property. KW - protozoa KW - biofilm KW - plankton KW - predator-prey model KW - grazing defence KW - feeding trait Y1 - 2017 U6 - https://doi.org/10.1093/femsec/fix112 SN - 0168-6496 SN - 1574-6941 VL - 93 PB - Oxford Univ. Press CY - Oxford 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 - 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 -