@misc{ChorusSpijkerman2020, author = {Chorus, Ingrid and Spijkerman, Elly}, title = {What Colin Reynolds could tell us about nutrient limitation, N:P ratios and eutrophication control}, series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1}, issn = {1866-8372}, doi = {10.25932/publishup-54197}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-541979}, pages = {19}, year = {2020}, abstract = {Colin Reynolds exquisitely consolidated our understanding of driving forces shaping phytoplankton communities and those setting the upper limit to biomass yield, with limitation typically shifting from light in winter to phosphorus in spring. Nonetheless, co-limitation is frequently postulated from enhanced growth responses to enrichments with both N and P or from N:P ranging around the Redfield ratio, concluding a need to reduce both N and P in order to mitigate eutrophication. Here, we review the current understanding of limitation through N and P and of co-limitation. We conclude that Reynolds is still correct: (i) Liebig's law of the minimum holds and reducing P is sufficient, provided concentrations achieved are low enough; (ii) analyses of nutrient limitation need to exclude evidently non-limiting situations, i.e. where soluble P exceeds 3-10 mu g/l, dissolved N exceeds 100-130 mu g/l and total P and N support high biomass levels with self-shading causing light limitation; (iii) additionally decreasing N to limiting concentrations may be useful in specific situations (e.g. shallow waterbodies with high internal P and pronounced denitrification); (iv) management decisions require local, situation-specific assessments. The value of research on stoichiometry and co-limitation lies in promoting our understanding of phytoplankton ecophysiology and community ecology.}, language = {en} } @article{ChorusSpijkerman2020, author = {Chorus, Ingrid and Spijkerman, Elly}, title = {What Colin Reynolds could tell us about nutrient limitation, N:P ratios and eutrophication control}, series = {Hydrobiologia : acta hydrobiologica, hydrographica, limnologica et protistologica}, volume = {848}, journal = {Hydrobiologia : acta hydrobiologica, hydrographica, limnologica et protistologica}, number = {1}, publisher = {Springer Nature}, address = {Berlin}, issn = {0018-8158}, doi = {10.1007/s10750-020-04377-w}, pages = {95 -- 111}, year = {2020}, abstract = {Colin Reynolds exquisitely consolidated our understanding of driving forces shaping phytoplankton communities and those setting the upper limit to biomass yield, with limitation typically shifting from light in winter to phosphorus in spring. Nonetheless, co-limitation is frequently postulated from enhanced growth responses to enrichments with both N and P or from N:P ranging around the Redfield ratio, concluding a need to reduce both N and P in order to mitigate eutrophication. Here, we review the current understanding of limitation through N and P and of co-limitation. We conclude that Reynolds is still correct: (i) Liebig's law of the minimum holds and reducing P is sufficient, provided concentrations achieved are low enough; (ii) analyses of nutrient limitation need to exclude evidently non-limiting situations, i.e. where soluble P exceeds 3-10 mu g/l, dissolved N exceeds 100-130 mu g/l and total P and N support high biomass levels with self-shading causing light limitation; (iii) additionally decreasing N to limiting concentrations may be useful in specific situations (e.g. shallow waterbodies with high internal P and pronounced denitrification); (iv) management decisions require local, situation-specific assessments. The value of research on stoichiometry and co-limitation lies in promoting our understanding of phytoplankton ecophysiology and community ecology.}, language = {en} } @article{KoussoroplisPincebourdeWacker2017, author = {Koussoroplis, Apostolos-Manuel and Pincebourde, Sylvain and Wacker, Alexander}, title = {Understanding and predicting physiological performance of organisms in fluctuating and multifactorial environments}, series = {Ecological monographs : a publication of the Ecological Society of America.}, volume = {87}, journal = {Ecological monographs : a publication of the Ecological Society of America.}, publisher = {Wiley}, address = {Hoboken}, issn = {0012-9615}, doi = {10.1002/ecm.1247}, pages = {178 -- 197}, year = {2017}, abstract = {Understanding how variance in environmental factors affects physiological performance, population growth, and persistence is central in ecology. Despite recent interest in the effects of variance in single biological drivers, such as temperature, we have lacked a comprehensive framework for predicting how the variances and covariances between multiple environmental factors will affect physiological rates. Here, we integrate current theory on variance effects with co-limitation theory into a single unified conceptual framework that has general applicability. We show how the framework can be applied (1) to generate mathematically tractable predictions of the physiological effects of multiple fluctuating co-limiting factors, (2) to understand how each co-limiting factor contributes to these effects, and (3) to detect mechanisms such as acclimation or physiological stress when they are at play. We show that the statistical covariance of co-limiting factors, which has not been considered before, can be a strong driver of physiological performance in various ecological contexts. Our framework can provide powerful insights on how the global change-induced shifts in multiple environmental factors affect the physiological performance of organisms.}, language = {en} } @article{KoussoroplisWacker2016, author = {Koussoroplis, Apostolos-Manuel and Wacker, Alexander}, title = {Covariance modulates the effect of joint temperature and food variance on ectotherm life-history traits}, series = {Ecology letters}, volume = {19}, journal = {Ecology letters}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {1461-023X}, doi = {10.1111/ele.12546}, pages = {143 -- 152}, year = {2016}, abstract = {Understanding animal performance in heterogeneous or variable environments is a central question in ecology. We combine modelling and experiments to test how temperature and food availability variance jointly affect life-history traits of ectotherms. The model predicts that as mean temperatures move away from the ectotherm's thermal optimum, the effect size of joint thermal and food variance should become increasingly sensitive to their covariance. Below the thermal optimum, performance should be positively correlated with food-temperature covariance and the opposite is predicted above it. At lower temperatures, covariance should determine whether food and temperature variance increases or decreases performance compared to constant conditions. Somewhat stronger than predicted, the covariance effect below the thermal optimum was confirmed experimentally on an aquatic ectotherm (Daphnia magna) exposed to diurnal food and temperature variance with different amounts of covariance. Our findings have important implications for understanding ectotherm responses to climate-driven alterations of thermal mean and variance.}, language = {en} } @misc{AcevedoFallahReichetal.2017, author = {Acevedo, Walter and Fallah, Bijan and Reich, Sebastian and Cubasch, Ulrich}, title = {Assimilation of pseudo-tree-ring-width observations into an atmospheric general circulation model}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe}, number = {627}, issn = {1866-8372}, doi = {10.25932/publishup-41874}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-418743}, pages = {545 -- 557}, year = {2017}, abstract = {Paleoclimate data assimilation (DA) is a promising technique to systematically combine the information from climate model simulations and proxy records. Here, we investigate the assimilation of tree-ring-width (TRW) chronologies into an atmospheric global climate model using ensemble Kalman filter (EnKF) techniques and a process-based tree-growth forward model as an observation operator. Our results, within a perfect-model experiment setting, indicate that the "online DA" approach did not outperform the "off-line" one, despite its considerable additional implementation complexity. On the other hand, it was observed that the nonlinear response of tree growth to surface temperature and soil moisture does deteriorate the operation of the time-averaged EnKF methodology. Moreover, for the first time we show that this skill loss appears significantly sensitive to the structure of the growth rate function, used to represent the principle of limiting factors (PLF) within the forward model. In general, our experiments showed that the error reduction achieved by assimilating pseudo-TRW chronologies is modulated by the magnitude of the yearly internal variability in themodel. This result might help the dendrochronology community to optimize their sampling efforts.}, language = {en} } @article{LukasWacker2014, author = {Lukas, Marcus and Wacker, Alexander}, title = {Constraints by oxygen and food quality on carbon pathway regulation: a co-limitation study with an aquatic key herbivore}, series = {Ecology : a publication of the Ecological Society of America}, volume = {95}, journal = {Ecology : a publication of the Ecological Society of America}, number = {11}, publisher = {Wiley}, address = {Washington}, issn = {0012-9658}, pages = {3068 -- 3079}, year = {2014}, abstract = {In food webs, herbivores are often constrained by low food quality in terms of mineral and biochemical limitations, which in aquatic ecosystems can co-occur with limited oxygen conditions. As low food quality implies that carbon (C) is available in excess, and therefore a regulation to get rid of excess C is crucial for the performance of consumers, we examined the C pathways (ingestion, feces release, excretion, and respiration) of a planktonic key herbivore (Daphnia magna). We tested whether consumer C pathways increase due to mineral (phosphorus, P) or biochemical (cholesterol and fatty acid) limitations and how these regulations vary when in addition oxygen is low. Under such conditions, at least the capability of the upregulation of respiration may be restricted. Furthermore, we discussed the potential role of the oxygen-transporting protein hemoglobin (Hb) in the regulation of C budgets. Different food quality constraints led to certain C regulation patterns to increase the removal of excess dietary C: P-limited D. magna increased excretion and respiration, while cholesterol-limited Daphnia in addition upregulated the release of feces. In contrast, the regulative effort was low and only feces release increased when D. magna was limited by a long-chain polyunsaturated fatty acid (eicosapentaenoic acid, EPA). Co-limiting oxygen did not always impact the discharge of excess C. We found the food-quality-induced upregulation of respiration was still present at low oxygen. In contrast, higher excretion of excess C was diminished at low oxygen supply. Besides the effect that the Hb concentration increased under low oxygen, our results indicate a low food-quality-induced increase in the Hb content of the animals. Overall, C budgeting is phenotypically plastic towards different (co-) limiting scenarios. These trigger specific regulation responses that could be the result of evolutionary adaptations.}, language = {en} }