@article{BuschKlausPenoneetal.2017, author = {Busch, Verena and Klaus, Valentin H. and Penone, Caterina and Sch{\"a}fer, Deborah and Boch, Steffen and Prati, Daniel and M{\"u}ller, J{\"o}rg and Socher, Stephanie A. and Niinemets, {\"U}lo and Penuelas, Josep and H{\"o}lzel, Norbert and Fischer, Markus and Kleinebecker, Till}, title = {Nutrient stoichiometry and land use rather than species richness determine plant functional diversity}, series = {Ecology and evolution}, volume = {8}, journal = {Ecology and evolution}, number = {1}, publisher = {Wiley}, address = {Hoboken}, issn = {2045-7758}, doi = {10.1002/ece3.3609}, pages = {601 -- 616}, year = {2017}, abstract = {Plant functional traits reflect individual and community ecological strategies. They allow the detection of directional changes in community dynamics and ecosystemic processes, being an additional tool to assess biodiversity than species richness. Analysis of functional patterns in plant communities provides mechanistic insight into biodiversity alterations due to anthropogenic activity. Although studies have consi-dered of either anthropogenic management or nutrient availability on functional traits in temperate grasslands, studies combining effects of both drivers are scarce. Here, we assessed the impacts of management intensity (fertilization, mowing, grazing), nutrient stoichiometry (C, N, P, K), and vegetation composition on community-weighted means (CWMs) and functional diversity (Rao's Q) from seven plant traits in 150 grasslands in three regions in Germany, using data of 6 years. Land use and nutrient stoichiometry accounted for larger proportions of model variance of CWM and Rao's Q than species richness and productivity. Grazing affected all analyzed trait groups; fertilization and mowing only impacted generative traits. Grazing was clearly associated with nutrient retention strategies, that is, investing in durable structures and production of fewer, less variable seed. Phenological variability was increased. Fertilization and mowing decreased seed number/mass variability, indicating competition-related effects. Impacts of nutrient stoichiometry on trait syndromes varied. Nutrient limitation (large N:P, C:N ratios) promoted species with conservative strategies, that is, investment in durable plant structures rather than fast growth, fewer seed, and delayed flowering onset. In contrast to seed mass, leaf-economics variability was reduced under P shortage. Species diversity was positively associated with the variability of generative traits. Synthesis. Here, land use, nutrient availability, species richness, and plant functional strategies have been shown to interact complexly, driving community composition, and vegetation responses to management intensity. We suggest that deeper understanding of underlying mechanisms shaping community assembly and biodiversity will require analyzing all these parameters.}, language = {en} } @article{KoussoroplisSchaelickeRaatzetal.2019, author = {Koussoroplis, Apostolos-Manuel and Sch{\"a}licke, Svenja and Raatz, Michael and Bach, Moritz and Wacker, Alexander}, title = {Feeding in the frequency domain}, series = {Ecology letters}, volume = {22}, journal = {Ecology letters}, number = {7}, publisher = {Wiley}, address = {Hoboken}, issn = {1461-023X}, doi = {10.1111/ele.13267}, pages = {1104 -- 1114}, year = {2019}, abstract = {Theory predicts that resource variability hinders consumer performance. How this effect depends on the temporal structure of resource fluctuations encountered by individuals remains poorly understood. Combining modelling and growth experiments with Daphnia magna, we decompose the complexity of resource fluctuations and test the effect of resource variance, supply peak timing (i.e. phase) and co-limiting resource covariance along a gradient from high to low frequencies reflecting fine- to coarse-grained environments. Our results show that resource storage can buffer growth at high frequencies, but yields a sensitivity of growth to resource peak timing at lower ones. When two resources covary, negative covariance causes stronger growth depression at low frequencies. However, negative covariance might be beneficial at intermediate frequencies, an effect that can be explained by digestive acclimation. Our study provides a mechanistic basis for understanding how alterations of the environmental grain size affect consumers experiencing variable nutritional quality in nature.}, language = {en} } @article{WackerMarzetzSpijkerman2015, author = {Wacker, Alexander and Marzetz, Vanessa and Spijkerman, Elly}, title = {Interspecific competition in phytoplankton drives the availability of essential mineral and biochemical nutrients}, series = {Ecology : a publication of the Ecological Society of America}, volume = {96}, journal = {Ecology : a publication of the Ecological Society of America}, number = {9}, publisher = {Wiley}, address = {Washington}, issn = {0012-9658}, doi = {10.1890/14-1915.1}, pages = {2467 -- 2477}, year = {2015}, abstract = {The underlying mechanisms and consequences of competition and diversity are central themes in ecology. A higher diversity of primary producers often results in higher resource use efficiency in aquatic and terrestrial ecosystems. This may result in more food for consumers on one hand, while, on the other hand, it can also result in a decreased food quality for consumers; higher biomass combined with the same availability of the limiting compound directly reduces the dietary proportion of the limiting compound. Here we tested whether and how interspecific competition in phytoplankton communities leads to changes in resource use efficiency and cellular concentrations of nutrients and fatty acids. The measured particulate carbon : phosphorus ratios (C:P) and fatty acid concentrations in the communities were compared to the theoretically expected ratios and concentrations of measurements on simultaneously running monocultures. With interspecific competition, phytoplankton communities had higher concentrations of the monounsaturated fatty acid oleic acid and also much higher concentrations of the ecologically and physiologically relevant long-chain polyunsaturated fatty acid eicosapentaenoic acid than expected concentrations based on monocultures. Such higher availability of essential fatty acids may contribute to the positive relationship between phytoplankton diversity and zooplankton growth, and may compensate limitations by mineral nutrients in higher trophic levels.}, language = {en} } @article{ZimmermannZimmermannTurneretal.2014, author = {Zimmermann, Beate and Zimmermann, Alexander and Turner, Benjamin L. and Francke, Till and Elsenbeer, Helmut}, title = {Connectivity of overland flow by drainage network expansion in a rain forest catchment}, series = {Water resources research}, volume = {50}, journal = {Water resources research}, number = {2}, publisher = {American Geophysical Union}, address = {Washington}, issn = {0043-1397}, doi = {10.1002/2012WR012660}, pages = {1457 -- 1473}, year = {2014}, abstract = {Soils in various places of the Panama Canal Watershed feature a low saturated hydraulic conductivity (K-s) at shallow depth, which promotes overland-flow generation and associated flashy catchment responses. In undisturbed forests of these areas, overland flow is concentrated in flow lines that extend the channel network and provide hydrological connectivity between hillslopes and streams. To understand the dynamics of overland-flow connectivity, as well as the impact of connectivity on catchment response, we studied an undisturbed headwater catchment by monitoring overland-flow occurrence in all flow lines and discharge, suspended sediment, and total phosphorus at the catchment outlet. We find that connectivity is strongly influenced by seasonal variation in antecedent wetness and can develop even under light rainfall conditions. Connectivity increased rapidly as rainfall frequency increased, eventually leading to full connectivity and surficial drainage of entire hillslopes. Connectivity was nonlinearly related to catchment response. However, additional information on factors such as overland-flow volume would be required to constrain relationships between connectivity, stormflow, and the export of suspended sediment and phosphorus. The effort to monitor those factors would be substantial, so we advocate applying the established links between rain event characteristics, drainage network expansion by flow lines, and catchment response for predictive modeling and catchment classification in forests of the Panama Canal Watershed and in similar regions elsewhere.}, 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} } @article{PiephoMartinCreuzburgWacker2012, author = {Piepho, Maike and Martin-Creuzburg, Dominik and Wacker, Alexander}, title = {Phytoplankton sterol contents vary with temperature, phosphorus and silicate supply a study on three freshwater species}, series = {European journal of phycology}, volume = {47}, journal = {European journal of phycology}, number = {2}, publisher = {Routledge, Taylor \& Francis Group}, address = {Abingdon}, issn = {0967-0262}, doi = {10.1080/09670262.2012.665484}, pages = {138 -- 145}, year = {2012}, abstract = {The understanding of environmentally induced changes in the biochemical composition of phytoplankton species is of great importance in both physiological studies and ecological food web research. In extensive laboratory experiments we tested the influence of two different temperatures (10 degrees C and 25 degrees C) and a phosphorus supply gradient on the sterol concentrations of the three freshwater phytoplankton species Scenedesmus quadricauda, Cryptomonas ovata and Cyclotella meneghiniana. The diatom C. meneghiniana was additionally exposed to a silicate gradient. In two separate experiments we analysed (1) possible interactive effects of temperature and phosphorus supply and (2) the effect of four phosphorus levels and three silicate levels on algal sterol concentrations. We observed that sterol concentrations were higher at 25 degrees C than at 10 degrees C in S. quadricauda and C. meneghiniana, but were not affected by temperature in C. ovata. Interactive effects of temperature and phosphorus supply on sterol concentrations were found in C. meneghiniana. This presumably was due to the bioconversion of one sterol (24-methylenecholesterol) into another (22-dihydrobrassicasterol). Increasing phosphorus supply resulted in species-specific effects on sterol concentrations, viz. an optimum curve response in S. quadricauda, a saturation curve response in C. meneghiniana and no change in sterol concentration in C. ovata. Effects of silicate supply on the sterols of C. meneghiniana equalled the effects of phosphorus supply. Albeit we did not observe a general trend in the three phytoplankton species tested, we conclude that sterol concentrations of phytoplankton are strongly affected by temperature and nutrient supply. Interactive effects point out the importance of taking into account more than just one environmental factor when assessing the effects of environmentally induced changes on phytoplankton sterol concentrations.}, language = {en} } @article{IslamSchaeublinWenketal.2012, author = {Islam, Khan M. Shaiful and Schaeublin, H. and Wenk, C. and Wanner, Michael and Liesegang, Annette}, title = {Effect of dietary citric acid on the performance and mineral metabolism of broiler}, series = {Journal of animal physiology and animal nutrition}, volume = {96}, journal = {Journal of animal physiology and animal nutrition}, number = {5}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0931-2439}, doi = {10.1111/j.1439-0396.2011.01225.x}, pages = {808 -- 817}, year = {2012}, abstract = {The objective of this study was to investigate the effect of dietary citric acid (CA) on the performance and mineral metabolism of broiler chicks. A total of 1720 Ross PM3 broiler chicks (days old) were randomly assigned to four groups (430 in each) and reared for a period of 35 days. The diets of groups 1, 2, 3 and 4 were supplemented with 0\%, 0.25\%, 0.75\% or 1.25\% CA by weight respectively. Feed and faeces samples were collected weekly and analysed for acid insoluble ash, calcium (Ca), phosphorus (P) and magnesium (Mg). The pH was measured in feed and faeces. At the age of 28 days, 10 birds from each group were slaughtered; tibiae were collected from each bird for the determination of bone mineral density, total ash, Ca, P, Mg and bone-breaking strength, and blood was collected for the measurement of osteocalcin, serum CrossLaps (R), Ca, P, Mg and 1,25(OH)(2)Vit-D in serum. After finishing the trial on day 37, all chicks were slaughtered by using the approved procedure. Birds that were fed CA diets were heavier (average body weights of 2030, 2079 and 2086 g in the 0.25\%, 0.75\% and 1.25\% CA groups, respectively, relative to the control birds (1986 g). Feed conversion efficiency (weight gain in g per kg of feed intake) was also higher in birds of the CA-fed groups (582, 595 and 587 g/kg feed intake for 0.25\%, 0.75\% and 1.25\% CA respectively), relative to the control birds (565 g/kg feed intake). The digestibility of Ca, P and Mg increased in the CA-fed groups, especially for the diets supplemented with 0.25\% and 0.75\% CA. Support for finding was also indicated in the results of the analysis of the tibia. At slaughter, the birds had higher carcass weights and higher graded carcasses in the groups that were fed the CA diets. The estimated profit margin was highest for birds fed the diet containing 0.25\% CA. Birds of the 0.75\% CA group were found to have the second highest estimated profit margin. Addition of CA up to a level of 1.25\% of the diet increased performance, feed conversion efficiency, carcass weight and carcass quality, but only in numerical terms. The addition of CA up to 0.75\% significantly increased the digestibility of macro minerals, bone ash content, bone mineral density and bone strength of the broiler chicks. It may, therefore, be concluded that the addition of 0.75\% CA in a standard diet is suitable for growth, carcass traits, macromineral digestibility and bone mineral density of broiler chicks.}, language = {en} } @article{KlausHoelzelBochetal.2013, author = {Klaus, Valentin H. and H{\"o}lzel, Norbert and Boch, Steffen and M{\"u}ller, Jorg and Socher, Stephanie A. and Prati, Daniel and Fischer, Markus and Kleinebecker, Till}, title = {Direct and indirect associations between plant species richness and productivity in grasslands regional differences preclude simple generalization of productivity-biodiversity relationships}, series = {Preslia : the journal of the Czech Botanical Society}, volume = {85}, journal = {Preslia : the journal of the Czech Botanical Society}, number = {2}, publisher = {Czech Botanical Soc.}, address = {Praha}, issn = {0032-7786}, pages = {97 -- 112}, year = {2013}, abstract = {Plant species richness of permanent grasslands has often been found to be significantly associated with productivity. Concentrations of nutrients in biomass can give further insight into these productivity-plant species richness relationships, e.g. by reflecting land use or soil characteristics. However, the consistency of such relationships across different regions has rarely been taken into account, which might significantly compromise our potential for generalization. We recorded plant species richness and measured above-ground biomass and concentrations of nutrients in biomass in 295 grasslands in three regions in Germany that differ in soil and climatic conditions. Structural equation modelling revealed that nutrient concentrations were mostly indirectly associated with plant species richness via biomass production. However, negative associations between the concentrations of different nutrients and biomass and plant species richness differed considerably among regions. While in two regions, more than 40\% of the variation in plant species richness could be attributed to variation in biomass, K, P. and to some degree also N concentrations, in the third region only 15\% of the variation could be explained in this way. Generally, highest plant species richness was recorded in grasslands where N and P were co-limiting plant growth, in contrast to N or K (co-) limitation. But again, this pattern was not recorded in the third region. While for two regions land-use intensity and especially the application of fertilizers are suggested to be the main drivers causing the observed negative associations with productivity, in the third region the little variance accounted for, low species richness and weak relationships implied that former intensive grassland management, ongoing mineralization of peat and fluctuating water levels in fen grasslands have overruled effects of current land-use intensity and productivity. Finally, we conclude that regional replication is of major importance for studies seeking general insights into productivity-diversity relationships.}, language = {en} } @article{NeillCoeRiskinetal.2013, author = {Neill, Christopher and Coe, Michael T. and Riskin, Shelby H. and Krusche, Alex V. and Elsenbeer, Helmut and Macedo, Marcia N. and McHorney, Richard and Lefebvre, Paul and Davidson, Eric A. and Scheffler, Raphael and Figueira, Adelaine Michela e Silva and Porder, Stephen and Deegan, Linda A.}, title = {Watershed responses to Amazon soya bean cropland expansion and intensification}, series = {Philosophical transactions of the Royal Society of London : B, Biological sciences}, volume = {368}, journal = {Philosophical transactions of the Royal Society of London : B, Biological sciences}, number = {1619}, publisher = {Royal Society}, address = {London}, issn = {0962-8436}, doi = {10.1098/rstb.2012.0425}, pages = {7}, year = {2013}, abstract = {The expansion and intensification of soya bean agriculture in southeastern Amazonia can alter watershed hydrology and biogeochemistry by changing the land cover, water balance and nutrient inputs. Several new insights on the responses of watershed hydrology and biogeochemistry to deforestation in Mato Grosso have emerged from recent intensive field campaigns in this region. Because of reduced evapotranspiration, total water export increases threefold to fourfold in soya bean watersheds compared with forest. However, the deep and highly permeable soils on the broad plateaus on which much of the soya bean cultivation has expanded buffer small soya bean watersheds against increased stormflows. Concentrations of nitrate and phosphate do not differ between forest or soya bean watersheds because fixation of phosphorus fertilizer by iron and aluminium oxides and anion exchange of nitrate in deep soils restrict nutrient movement. Despite resistance to biogeochemical change, streams in soya bean watersheds have higher temperatures caused by impoundments and reduction of bordering riparian forest. In larger rivers, increased water flow, current velocities and sediment flux following deforestation can reshape stream morphology, suggesting that cumulative impacts of deforestation in small watersheds will occur at larger scales.}, language = {en} }