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1.
An attempt is made to derive a measure for the degree of plant community organization, which would not be based on species co-occurrence and co-abundance. The use of the independent random distribution hypothesis (IRDH) is suggested for this purpose. The hypothesis is expected to be valid, if no deterministic phytosociological-structure-generating mechanism is present. If structural variability is used as a statistic for testing the hypothesis, deviances from the conditions of IRDH (species distributions are independent from each other, environmental gradients are lacking) will be attributable either to species interactions (smaller structural variability than expected), or to environmental heterogeneity (greater structural variability than expected). Structural variability is evaluated as the variance of species diversity, the indexN=exp(H') is used for measuring diversity. The precise measure of the degree of community organizationW is computed as the shift between two empirical distributions:D
* (VN) or Bootstrap distribution of variance of diversity in the community, andD
o (VN) or the random community variability distribution, which is evaluated after simulating the IRDH conditions.A satisfactory interpretation can be given to the results of evaluatingW for 11 data sets of 10 relevés each.Abbreviation IRDH
Independent random distribution hypothesis 相似文献
2.
The biomass allocation pattern in plants is known to depend on the below and above-ground resource availabilities. In a herbaceous
multi-species stand, it can be expected that the effects of nutrient and light availability on plants’ general space-use strategy
are fundamentally different. We hypothesized that nutrient status alters the amount of biomass produced per unit canopy volume
(biomass density), but not so much the biomass vertical distribution pattern. Changes in light availability, in contrast,
should affect the vertical distribution pattern of biomass but not biomass density. We were also interested in whether the
effect of resource manipulation on a plant’s space-use strategy depends on its basic morphological characteristics (growth
form).
The results from a four-year permanent plot experiment in a species-rich grassland, with fertilization and additional illumination
from mirrors applied to 40 × 40 cm plots, showed that our main hypothesis was correct. Fertilization significantly affected
biomass density above as well as below-ground, while additional illumination generally did not. Light addition altered the
vertical distribution pattern of above-ground biomass, which remained unaffected by the fertilizer treatment. 相似文献
3.
Gudmundsson KS Wang Z Daluge SM Johnson LC Hazen R Condreay LD McGuigan C 《Nucleosides, nucleotides & nucleic acids》2004,23(12):1929-1937
Synthesis of phosphoramidate protides of carbocyclic D- and L-2',3'-dideoxy-2',3'-didehydro-7-deazaadenosine by treatment of the nucleoside with phosphorochloridates in the presence of pyridine and t-BuMgCl is described. Several of these protides showed significantly improved antiviral potency over the parent nucleosides against both HIV and HBV. 相似文献
4.
A susceptibility gene for psoriatic arthritis maps to chromosome 16q: evidence for imprinting 总被引:8,自引:0,他引:8
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Karason A Gudjonsson JE Upmanyu R Antonsdottir AA Hauksson VB Runasdottir EH Jonsson HH Gudbjartsson DF Frigge ML Kong A Stefansson K Valdimarsson H Gulcher JR 《American journal of human genetics》2003,72(1):125-131
Several genetic loci have been reported for psoriasis, but none has been specifically linked to psoriatic arthritis (PsA), a condition that affects >10% of patients with psoriasis. A genetic component for PsA is suggested by segregation within families and high concordance among identical twins. We performed a linkage scan to map genes contributing to PsA. We identified 178 patients with PsA out of 906 patients who were included in our genetic study of psoriasis. Using a comprehensive genealogy database, we were able to connect 100 of these into 39 families. We genotyped the patients using a framework marker set of 1,000 microsatellite markers, with an average density of 3 cM, and performed multipoint, affected-only, allele-sharing linkage analysis using the Allegro program. On the basis of the initial results, we genotyped more markers for the most prominent loci. A linkage with a LOD score of 2.17 was observed on chromosome 16q. The linkage analysis, conditioned on paternal transmission to affected individuals, gave a LOD score of 4.19, whereas a LOD score of only 1.03 was observed when conditioned for maternal transmission. A suggestive locus on chromosome 16q has previously been implicated in psoriasis. Our data indicate that a gene at this locus may be involved in paternal transmission of PsA. 相似文献
5.
Saal K Sammelselg V Lõhmus A Kuusk E Raidaru G Rinken T Rinken A 《Biomolecular engineering》2002,19(2-6):195-199
Glucose oxidase (E.C 1.1.3.4) immobilized onto activated surface of mica was analyzed by enzymatic kinetics and visualization with atomic force microscopy (AFM). The activity of the immobilized enzyme decreased with the decrease of concentration of gamma-aminopropyltrimethoxysilane used for the first step of activation of mica, while AFM analysis showed similar homogeneous filling of the surface with the enzyme. The comparison of enzyme activity with its surface filling revealed that there has to be additional vertical structures, which cannot be visualized by the methods of AFM. The simultaneous decrease of the silanizing agent and the concentration of the enzyme led to molecular resolution for the enzyme on the surface of mica. This allows to propose the described method also for analyzing other surfaces of solid materials with coupled biomolecules. 相似文献
6.
Saevarsdottir S Ding B Steinsson K Grondal G Valdimarsson H Alfredsson L Klareskog L Padyukov L 《Arthritis research & therapy》2011,13(2):R65
Introduction
Previous studies have provided inconsistent results on whether variants in the MBL2 gene, coding for the complement-activating mannan-binding lectin (MBL) protein, associate with rheumatoid arthritis (RA). We re-evaluated this in context of the main environmental and genetic risk factors (smoking, HLA-DRB1 'shared epitope' (SE), PTPN22*620W), which predispose to rheumatoid factor (RF) and/or anti-citrullinated-protein antibody (ACPA)-positive RA. 相似文献7.
8.
Jacob F Ukegjini K Nixdorf S Ford CE Olivier J Caduff R Scurry JP Guertler R Hornung D Mueller R Fink DA Hacker NF Heinzelmann-Schwarz VA 《PloS one》2012,7(2):e31885
Background
Activation of the Wnt signaling pathway is implicated in aberrant cellular proliferation in various cancers. In 40% of endometrioid ovarian cancers, constitutive activation of the pathway is due to oncogenic mutations in β-catenin or other inactivating mutations in key negative regulators. Secreted frizzled-related protein 4 (SFRP4) has been proposed to have inhibitory activity through binding and sequestering Wnt ligands.Methodology/Principal Findings
We performed RT-qPCR and Western-blotting in primary cultures and ovarian cell lines for SFRP4 and its key downstream regulators activated β-catenin, β-catenin and GSK3β. SFRP4 was then examined by immunohistochemistry in a cohort of 721 patients and due to its proposed secretory function, in plasma, presenting the first ELISA for SFRP4. SFRP4 was most highly expressed in tubal epithelium and decreased with malignant transformation, both on RNA and on protein level, where it was even more profound in the membrane fraction (p<0.0001). SFRP4 was expressed on the protein level in all histotypes of ovarian cancer but was decreased from borderline tumors to cancers and with loss of cellular differentiation. Loss of membrane expression was an independent predictor of poor survival in ovarian cancer patients (p = 0.02 unadjusted; p = 0.089 adjusted), which increased the risk of a patient to die from this disease by the factor 1.8.Conclusions/Significance
Our results support a role for SFRP4 as a tumor suppressor gene in ovarian cancers via inhibition of the Wnt signaling pathway. This has not only predictive implications but could also facilitate a therapeutic role using epigenetic targets. 相似文献9.
10.
Lars Götzenberger Francesco de Bello Kari Anne Bråthen John Davison Anne Dubuis Antoine Guisan Jan Lepš Regina Lindborg Mari Moora Meelis Pärtel Loic Pellissier Julien Pottier Pascal Vittoz Kristjan Zobel Martin Zobel 《Biological reviews of the Cambridge Philosophical Society》2012,87(1):111-127
Understanding how communities of living organisms assemble has been a central question in ecology since the early days of the discipline. Disentangling the different processes involved in community assembly is not only interesting in itself but also crucial for an understanding of how communities will behave under future environmental scenarios. The traditional concept of assembly rules reflects the notion that species do not co‐occur randomly but are restricted in their co‐occurrence by interspecific competition. This concept can be redefined in a more general framework where the co‐occurrence of species is a product of chance, historical patterns of speciation and migration, dispersal, abiotic environmental factors, and biotic interactions, with none of these processes being mutually exclusive. Here we present a survey and meta‐analyses of 59 papers that compare observed patterns in plant communities with null models simulating random patterns of species assembly. According to the type of data under study and the different methods that are applied to detect community assembly, we distinguish four main types of approach in the published literature: species co‐occurrence, niche limitation, guild proportionality and limiting similarity. Results from our meta‐analyses suggest that non‐random co‐occurrence of plant species is not a widespread phenomenon. However, whether this finding reflects the individualistic nature of plant communities or is caused by methodological shortcomings associated with the studies considered cannot be discerned from the available metadata. We advocate that more thorough surveys be conducted using a set of standardized methods to test for the existence of assembly rules in data sets spanning larger biological and geographical scales than have been considered until now. We underpin this general advice with guidelines that should be considered in future assembly rules research. This will enable us to draw more accurate and general conclusions about the non‐random aspect of assembly in plant communities. 相似文献