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Berlin Brandenburg

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  • 1
    In: PLoS ONE, 2014, Vol.9(8)
    Description: The availability of high quality resources is an important factor driving community structure and reproductive mode of animals. Parthenogenetic reproduction prevails when resources are available in excess, whereas sexuality correlates with resource shortage. We investigated the effect of resource availability on the community structure of oribatid mites in a laboratory experiment. Availability of food resources was increased by addition of glucose to leaf litter and reduced by leaching of nutrients from leaf litter. Experimental systems were incubated at three different temperatures to establish different regimes of resource exploitation. Community structure of oribatids and numbers of eggs per female were measured over a period of ten months. We expected the density of oribatid mites to decline in the reduced litter quality treatment but to increase in the glucose treatment. Both effects were assumed to be more pronounced at higher temperatures. We hypothesized sexual species to be less affected than parthenogenetic species by reduced resource quality due to higher genetic diversity allowing more efficient exploitation of limited resources, but to be outnumbered by parthenogenetic species in case of resource addition due to faster reproduction. In contrast to our hypotheses, both sexual and parthenogenetic oribatid mite species responded similarly with their densities declining uniformly during incubation. The parthenogenetic Brachychthoniidae and Tectocepheus dominated early in the experiment but were replaced later by parthenogenetic Desmonomata and Rhysotritia . In parthenogenetic species the number of eggs per female increased during the experiment while the number of eggs in sexual females remained constant or decreased slightly; in general, egg numbers were higher in sexual than in parthenogenetic species. The results indicate that for sustaining oribatid mite populations other resources than litter and associated saprotrophic microorganisms are needed. They also indicate that there are two groups of parthenogenetically reproducing species: exploiters of easily available resources and consumers of leaf litter associated resources.
    Keywords: Research Article ; Biology And Life Sciences ; Ecology And Environmental Sciences
    E-ISSN: 1932-6203
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  • 2
    In: Oikos, October 2014, Vol.123(10), pp.1153-1156
    Description: To purchase or authenticate to the full-text of this article, please visit this link: http://onlinelibrary.wiley.com/doi/10.1111/oik.01768/abstract Byline: Ulrich Brose, Stefan Scheu ***** No abstract is available for this article. *****
    Keywords: Soil Structure;
    ISSN: 0030-1299
    E-ISSN: 1600-0706
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  • 3
    In: Oikos, October 2014, Vol.123(10), pp.1182-1191
    Description: Human impact on structure and functioning of ecosystems is rapidly increasing. Virtually all European forests are managed with major implications for diversity and structure of food webs. Centipedes (Chilopoda: Lithobiidae) are abundant arthropod predators in European temperate forest soils with a generalistic feeding behaviour. However, little is known on the variability in the prey spectrum of centipedes with land use and the responsible factors. Combining fatty acid (FA) analysis, which allows determination of the relative contribution of different prey to predator nutrition, and stable isotope analysis, providing insight into the trophic structure of decomposer food webs, we investigated variations in trophic niches of two dominant centipede species, and , in differently aged beech and spruce forests. FA composition of the two centipede species differed significantly with bacterial marker FAs being more abundant in as compared to . Differences were most pronounced in spruce as compared to beech forests. The results suggest that dense needle litter in coniferous forests may restrict prey availability to the larger and confine foraging to the litter surface whereas the smaller is able to also exploit prey of deeper litter layers. was significantly more enriched in N and C compared to suggesting that, compared to , the smaller occupies higher trophic levels and relies more on root derived carbon. The results indicate that trophic niches of centipedes vary in a species specific way between forest types with body size and habitat structure being major determinants of the variations in the prey spectrum. Combining techniques for delineating predator–prey interactions allowed insights into variations in trophic interrelationships and their driving forces in temperate forest soil food webs.
    Keywords: Forest Soils – Analysis ; Fatty Acids – Analysis;
    ISSN: 0030-1299
    E-ISSN: 1600-0706
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  • 4
    Language: English
    In: Soil Biology and Biochemistry, Feb, 2014, Vol.69, p.38(8)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.soilbio.2013.10.034 Byline: Kathleen Lemanski, Stefan Scheu Abstract: In permanent grassland the influence of NPK fertilizer addition and sward composition (proportion of plant functional groups) on soil microorganisms and the incorporation of.sup.13C labelled glucose into microbial tissue were studied for 52 weeks. Microbial biomass was analysed by chloroform fumigation-extraction (CFE), soil microbial community structure by phospholipid fatty acids (PLFAs) and incorporation of labelled glucose into microorganisms by gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS)..sup.13C incorporation into PLFA biomarkers suggested that after two and six weeks fungi most efficiently captured glucose C compared to later sampling dates, whereas in bacteria it remained at a similar level for 52 weeks, suggesting that microbial residues are processed predominantly by bacteria not by fungi. Further the fungal-to-bacterial atom percent excess ratio of PLFA concentrations after two and six weeks exceeded one, indicating that in relative terms initially fungi are more efficient in capturing low molecular weight C compounds entering the soil in pulses than bacteria. NPK fertilizer decreased soil microbial biomass and changed microbial community structure but did not affect the fungal-to-bacterial PLFA ratio. In fertilized swards the fungal-to-bacterial.sup.13C ratio increased, while bacterial.sup.13C incorporation remained at the same level, suggesting that NPK fertilizer addition increases the efficiency of resource capture by fungi. Sward composition little affected microbial community composition and glucose C incorporation. Author Affiliation: J.F. Blumenbach Institute of Zoology and Anthropology, Georg August University Gottingen, Berliner Stra[sz]e 28, 37073 Gottingen, Germany Article History: Received 14 May 2013; Revised 11 October 2013; Accepted 14 October 2013
    Keywords: Fertilizers -- Analysis ; Glucose Metabolism -- Analysis ; Fatty Acids -- Analysis ; Soil Microbiology -- Analysis ; Bacteria -- Analysis ; Glucose -- Analysis
    ISSN: 0038-0717
    Source: Cengage Learning, Inc.
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  • 5
    Language: English
    In: Oecologia, 2014, Vol.176(2), pp.487-496
    Description: Roots and root-derived C compounds are increasingly recognised as important resources for soil animal food webs. We used 13 C-labelled glucose as a model C compound representing root exudates to follow the incorporation of root-derived C into the soil animal food web of a temperate grassland over a period of 52 weeks. We investigated variations in glucose C incorporation with fertilizer addition and sward composition, i.e. variations in plant functional groups. The approach allowed the differentiation of trophic chains based on primary decomposers feeding on litter and phytophagous species feeding on roots (i.e. not incorporating glucose C) from those based on secondary decomposers feeding on microorganisms (thereby assimilating glucose C). Each of the studied soil animal species incorporated glucose C, indicating that the majority of grassland soil animal species rely on microorganisms as food resources with microorganisms being fuelled by root exudates. However, incorporation of glucose C into soil animal species varied markedly with species identity, suggesting that detritivorous microarthropods complement each other in channelling microbial C through soil food webs. Fertilizer addition markedly reduced the concentration of glucose C in most soil animal species as well as the absolute transfer of glucose C into oribatid mites as major secondary decomposers. The results suggest that fertilizer addition shifts the basis of the decomposer food web towards the use of unlabelled resources, presumably roots, i.e. towards a herbivore system, thereby lessening the link between microorganisms and microbial grazers and hampering the propagation of microbial C to higher trophic levels.
    Keywords: Soil arthropods ; Trophic interactions ; Stable isotopes ; Rhizodeposition ; Root exudates
    ISSN: 0029-8549
    E-ISSN: 1432-1939
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  • 6
    Language: English
    In: Oecologia, 2012, Vol.170(4), pp.1067-1076
    Description: The structure and functioning of decomposer systems heavily relies on soil moisture. However, this has been primarily studied in temperate ecosystems; little is known about how soil moisture affects the microfaunal food web in tropical regions. This lack of knowledge is surprising, since the microfaunal food web controls major ecosystem processes. To evaluate the role of precipitation in the structure of soil food web components (i.e., microorganisms and testate amoebae), we excluded water input by rain in montane rainforests at different altitudes in Ecuador. Rain exclusion strongly reduced microbial biomass and respiration by about 50 %, and fungal biomass by 23 %. In testate amoebae, rain exclusion decreased the density of live cells by 91 % and caused a shift in species composition at each of the altitudes studied, with ergosterol concentrations, microbial biomass, and water content explaining 25 % of the variation in species data. The results document that reduced precipitation negatively affects soil microorganisms, but that the response of testate amoebae markedly exceeds that of bacteria and fungi. This suggests that, in addition to food, low precipitation directly affects the community structure of testate amoebae, with the effect being more pronounced at lower altitudes. Overall, the results show that microorganisms and testate amoebae rapidly respond to a reduction in precipitation, with testate amoebae—representatives of higher trophic levels—being more sensitive. The results imply that precipitation and soil moisture in tropical rainforests are the main factors regulating decomposition and nutrient turnover.
    Keywords: Rain exclusion ; Testate amoebae ; Ergosterol ; Microbial biomass ; Food web
    ISSN: 0029-8549
    E-ISSN: 1432-1939
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  • 7
    In: Oikos, October 2014, Vol.123(10), pp.1224-1233
    Description: Soil systems maintain important ecosystem processes crucial for plant life and food production. Especially agricultural systems are strongly affected by climate change due to low vegetation cover associated with high temperatures and drought. Nevertheless, the response of soil systems to climate change is little explored. We used microcosms with a simplified soil community to address effects of climate change using independent temperature and dryness gradients and addressed their effects on top–down control and litter decomposition. The community consisted of maize litter as a basal resource, fungi, springtails and as top predators mites and centipedes. As the body‐size structure is of high importance for communities, we included differently‐sized springtails and predator species. After seven weeks, the experiment was terminated, and the impact of climate change on direct feeding interactions and indirect effects across trophic levels was analysed. With increasing temperature and dryness, consumption rates increased, thereby amplifying the negative influence of consumer populations on their resources. Hence, these climate‐change variables increased the top–down control of 1) predators (mainly mites) on springtails and 2) fungi on litter decomposition. In addition, we found that the climate‐change variables strengthened trophic cascades from predators on fungi whose density was thus increasingly decoupled from top–down control by their springtail consumers. Their increased decomposition rates are of high importance for carbon cycling and may result in accelerated nutrient turnover. In conclusion, our results suggest that climate change may strongly influence the structure and functioning of soil systems by strengthening consumption rates and trophic cascades, which will have far reaching consequences for the nutrient turnover and productivity of agricultural ecosystems.
    Keywords: Climate Change – Environmental Aspects ; Droughts – Environmental Aspects ; Agricultural Ecology – Environmental Aspects ; Ecosystems – Environmental Aspects;
    ISSN: 0030-1299
    E-ISSN: 1600-0706
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  • 8
    Language: English
    In: Oikos, Oct, 2012, Vol.121, p.1649(7)
    Description: To purchase or authenticate to the full-text of this article, please visit this link: http://onlinelibrary.wiley.com/doi/10.1111/j.1600-0706.2011.20073.x/abstract Byline: Dennis Lummer(1), Stefan Scheu(1), Olaf Butenschoen(1) Synergistic effects on decomposition in litter mixtures have been suggested to be due to the transfer of nitrogen from N-rich to N-poor species. However, the dominant pathway and the underlying mechanisms remain to be elucidated. We conducted an experiment to investigate and quantify the control mechanisms for nitrogen transfer between two litter species of contrasting nitrogen status (.sub.15N labeled and unlabeled Fagus sylvatica and Fraxinus excelsior) in presence and absence of micro-arthropods. We found that .sub.15N was predominantly transferred actively aboveground by saprotrophic fungi, rather than belowground or passively by leaching. However, litter decomposition remained unaffected by N-dynamics and was poorly affected by micro-arthropods, suggesting that synergistic effects in litter mixtures depend on complex environmental interrelationships. Remarkably, more .sub.15N was transferred from N-poor beech than N-rich ash litter. Moreover, the low transfer of .sub.15N from ash litter was insensitive to destination species whereas the transfer of .sub.15N from labeled beech litter to unlabeled beech was significantly greater than the amount of .sub.15N transferred to unlabeled ash suggesting that processes of nitrogen transfer fundamentally differ between litter species of different nitrogen status. Microbial analyses suggest that nitrogen of N-rich litter is entirely controlled by bacteria that hamper nitrogen capture of microbes in the environment supporting the source-theory. In contrast, nitrogen of N-poor fungal dominated litter is less protected and transferable depending on the nitrogen status and the transfer capacity of the microbial community of the co-occurring litter species supporting the gradient-theory. Thus, our results challenge the traditional view regarding the role of N-rich litter in decomposing litter mixtures. We rather suggest that N-rich litter is only a poor nitrogen source, whereas N-poor litter, can act as an important nitrogen source in litter mixtures. Consequently both absolute and relative differences in initial litter C/N ratios of co-occurring litter species need to be considered for understanding nitrogen dynamics in decomposing litter mixtures. Author Affiliation: (1)J. F. Blumenbach Inst. of Zoology and Anthropology, Georg-August-Univ. Gottingen, Berliner Str. 28, DE-37073 Gottingen, Germany Correspondence: O. Butenschoen, J. F. Blumenbach Inst. of Zoology and Anthropology, Georg-August-Univ. Gottingen, Berliner Str. 28, DE-37073 Gottingen, Germany. E-mail: obutens@gwdg.de Paper manuscript accepted 13 October 2011
    ISSN: 0030-1299
    Source: Cengage Learning, Inc.
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  • 9
    In: Ecology Letters, May 2012, Vol.15(5), pp.468-474
    Description: To authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1461-0248.2012.01759.x Byline: Joachim Becker (1), Nico Eisenhauer (2), Stefan Scheu (1), Alexandre Jousset (1*) Keywords: Allelopathy; biodiversity; ecosystem functioning; interference competition; Pseudomonas fluorescens; rhizosphere Abstract: Ecology Letters (2012) 15: 468-474 Abstract Biodiversity is a major determinant of ecosystem functioning. Species-rich communities often use resources more efficiently thereby improving community performance. However, high competition within diverse communities may also reduce community functioning. We manipulated the genotypic diversity of Pseudomonas fluorescens communities, a plant mutualistic species inhibiting pathogens. We measured antagonistic interactions in vitro, and related these interactions to bacterial community productivity (root colonisation) and ecosystem service (host plant protection). Antagonistic interactions increased disproportionally with species richness. Mutual poisoning between competitors lead to a 'negative complementarity effect', causing a decrease in bacterial density by up to 98% in diverse communities and a complete loss of plant protection. The results emphasize that antagonistic interactions may determine community functioning and cause negative biodiversity-ecosystem functioning relationships. Interference competition may thus be an additional key for predicting the dynamics and performance of natural assemblages and needs to be implemented in future biodiversity models. Author Affiliation: (1)J.F. Blumenbach Institute for Zoology and Anthropology, Georg August University Gottingen, Berliner Str. 28, 37073 Gottingen, Germany (2)University of Minnesota, Department of Forest Resources, 1530 Cleveland Ave. N., St. Paul, MN 55108, USA Article History: Editor, Gregor Fussmann Manuscript received 26 December 2011 First decision made 27 January 2012 Manuscript accepted 8 February 2012 Article note: (*) E-mail: ajousse@gwdg.de
    Keywords: Allelopathy ; Biodiversity ; Ecosystem Functioning ; Interference Competition ; Pseudomonas Fluorescens ; Rhizosphere
    ISSN: 1461-023X
    E-ISSN: 1461-0248
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  • 10
    In: Ecology Letters, May 2012, Vol.15(5), pp.436-443
    Description: To authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1461-0248.2012.01750.x Byline: Florian Dirk Schneider (1,2*), Stefan Scheu (1), Ulrich Brose (1) Keywords: Allometry; body size; biodiversity-ecosystem functioning; food web; identity effects; interaction strength; intraguild predation; predator-prey interactions; species traits; trophic cascade Abstract: Ecology Letters (2012) 15: 436-443 Abstract Understanding effects of species loss in complex food webs with multiple trophic levels is complicated by the idiosyncrasy of the predator effects on lower trophic levels: direct and indirect effects intermingle and may increase, decrease or not affect ecosystem functioning. We introduce a reductionist approach explaining a predator's trophic effect only by empirically well-founded body-mass constraints on abundance, diet breadth and feeding strength. We demonstrate that this mechanistic concept successfully explains the positive, negative and neutral net effects of predators on decomposers in a litter microcosm experiment. This approach offers a new perspective on the interplay of complex interactions within food webs and is easily extendable to include phylogenetic and other body-mass independent traits. We anticipate that allometry will substantially improve our understanding of idiosyncratic predator effects in experiments and the consequences of predator loss in natural ecosystems. Author Affiliation: (1)Georg August University Gottingen, J.F. Blumenbach Institute of Zoology and Anthropology, Berliner Str. 28, 37073 Gottingen, Germany (2)Technische Universitat Darmstadt, Institute of Zoology, Schnittspahnstr. 10, 64287 Darmstadt, Germany Article History: Editor, Giulio De Leo Manuscript received 10 November 2011 First decision made 8 December 2011 Second decision made 27 December 2011 Third decision made 16 January 2012 Manuscript accepted 31 January 2012 Article note: (*) E-mail: f_schneider@bio.tu-darmstadt.de
    Keywords: Allometry ; Body Size ; Biodiversity–Ecosystem Functioning ; Food Web ; Identity Effects ; Interaction Strength ; Intraguild Predation ; Predator–Prey Interactions ; Species Traits ; Trophic Cascade
    ISSN: 1461-023X
    E-ISSN: 1461-0248
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