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41.
Chi Xu Milena Holmgren Egbert H. Van Nes Marina Hirota F. Stuart Chapin III Marten Scheffer 《PloS one》2015,10(11)
Publicly available remote sensing products have boosted science in many ways. The openness of these data sources suggests high reproducibility. However, as we show here, results may be specific to versions of the data products that can become unavailable as new versions are posted. We focus on remotely-sensed tree cover. Recent studies have used this public resource to detect multi-modality in tree cover in the tropical and boreal biomes. Such patterns suggest alternative stable states separated by critical tipping points. This has important implications for the potential response of these ecosystems to global climate change. For the boreal region, four distinct ecosystem states (i.e., treeless, sparse and dense woodland, and boreal forest) were previously identified by using the Collection 3 data of MODIS Vegetation Continuous Fields (VCF). Since then, the MODIS VCF product has been updated to Collection 5; and a Landsat VCF product of global tree cover at a fine spatial resolution of 30 meters has been developed. Here we compare these different remote-sensing products of tree cover to show that identification of alternative stable states in the boreal biome partly depends on the data source used. The updated MODIS data and the newer Landsat data consistently demonstrate three distinct modes around similar tree-cover values. Our analysis suggests that the boreal region has three modes: one sparsely vegetated state (treeless), one distinct ‘savanna-like’ state and one forest state, which could be alternative stable states. Our analysis illustrates that qualitative outcomes of studies may change fundamentally as new versions of remote sensing products are used. Scientific reproducibility thus requires that old versions remain publicly available. 相似文献
42.
Marten Michaelis Oliver Gralla Thomas Behrends Marcus Scharpf Tobias Endermann Eddy Rijntjes Nicole Pietschmann Birgit Hollenbach Lutz Schomburg 《Biochemical and biophysical research communications》2014
Hepatically-derived selenoprotein P (SePP) transports selenium (Se) via blood to other tissues including the testes. Male Sepp-knockout mice are infertile. SePP-mediated Se transport to Sertoli cells is needed for supporting biosynthesis of the selenoenzyme glutathione peroxidase-4 (GPX4) in spermatozoa. GPX4 becomes a structural component of sperm midpiece during sperm maturation, and its expression correlates to semen quality. We tested whether SePP is also present in seminal plasma, potentially correlating to fertility parameters. Semen quality was assessed by sperm density, morphology and motility. SePP was measured by an immunoluminometric assay, and trace elements were determined by X-ray fluorescence spectroscopy. SePP levels were considerably lower in seminal plasma as compared to serum (0.4 ± 0.1 mg/l vs. 3.5 ± 1.0 mg/l); Se concentrations showed a similar but less pronounced difference (48.9 ± 20.7 μg/l vs. 106.7 ± 17.3 μg/l). Se and Zn correlated positively in seminal fluid but not in serum. Seminal plasma SePP concentrations were independent of serum SePP concentrations, but correlated positively to sperm density and fraction of vital sperm. SePP concentrations in seminal plasma of vasectomized men were similar to controls indicating that accessory sex glands are a testes-independent source of SePP. This notion was corroborated by histochemical analyses localizing SePP in epithelial cells of seminal vesicles. We conclude that SePP is not only involved in Se transport to testes supporting GPX4 biosynthesis but it also becomes secreted into seminal plasma, likely important to protect sperm during storage, genital tract passage and final journey. 相似文献
43.
Marius Priebe Marten Bernhardt Christoph Blum Marco Tarantola Eberhard Bodenschatz Tim Salditt 《Biophysical journal》2014,107(11):2662-2673
We have performed scanning x-ray nanobeam diffraction experiments on single cells of the amoeba Dictyostelium discoideum. Cells have been investigated in 1), freeze-dried, 2), frozen-hydrated (vitrified), and 3), initially alive states. The spatially resolved small-angle x-ray scattering signal shows characteristic streaklike patterns in reciprocal space, which we attribute to fiber bundles of the actomyosin network. From the intensity distributions, an anisotropy parameter can be derived that indicates pronounced local variations within the cell. In addition to nanobeam small-angle x-ray scattering, we have evaluated the x-ray differential phase contrast in view of the projected electron density. Different experimental aspects of the x-ray experiment, sample preparation, and data analysis are discussed. Finally, the x-ray results are correlated with optical microscopy (differential phase contrast and confocal microscopy of mutant strains with fluorescently labeled actin and myosin II), which have been carried out in live and fixed states, including optical microscopy under cryogenic conditions. 相似文献
44.
Cytochrome bd is a terminal quinol:O2 oxidoreductase of respiratory chains of many bacteria. It contains three hemes, b558, b595, and d. The role of heme b595 remains obscure. A CO photolysis/recombination study of the membranes of Escherichia coli containing either wild type cytochrome bd or inactive E445A mutant was performed using nanosecond absorption spectroscopy. We compared photoinduced changes of heme d-CO complex in one-electron-reduced, two-electron-reduced, and fully reduced states of cytochromes bd. The line shape of spectra of photodissociation of one-electron-reduced and two-electron-reduced enzymes is strikingly different from that of the fully reduced enzyme. The difference demonstrates that in the fully reduced enzyme photolysis of CO from heme d perturbs ferrous heme b595 causing loss of an absorption band centered at 435 nm, thus supporting interactions between heme b595 and heme d in the di-heme oxygen-reducing site, in agreement with previous works. Photolyzed CO recombines with the fully reduced enzyme monoexponentially with τ ∼ 12 μs, whereas recombination of CO with one-electron-reduced cytochrome bd shows three kinetic phases, with τ ∼ 14 ns, 14 μs, and 280 μs. The spectra of the absorption changes associated with these components are different in line shape. The 14 ns phase, absent in the fully reduced enzyme, reflects geminate recombination of CO with part of heme d. The 14-μs component reflects bimolecular recombination of CO with heme d and electron backflow from heme d to hemes b in ∼ 4% of the enzyme population. The final, 280-μs component, reflects return of the electron from hemes b to heme d and bimolecular recombination of CO in that population. The fact that even in the two-electron-reduced enzyme, a nanosecond geminate recombination is observed, suggests that namely the redox state of heme b595, and not that of heme b558, controls the pathway(s) by which CO migrates between heme d and the medium. 相似文献
45.
Gaia Luziatelli Marten Sørensen Ida Theilade Per Mølgaard 《Journal of ethnobiology and ethnomedicine》2010,6(1):1-23
Background
The Asháninka Native Community Bajo Quimiriki, District Pichanaki, Junín, Peru, is located only 4 km from a larger urban area and is dissected by a major road. Therefore the loss of traditional knowledge is a main concern of the local headman and inhabitants. The present study assesses the state of traditional medicinal plant knowledge in the community and compares the local pharmacopoeia with the one from a related ethnic group.Methods
Fieldwork was conducted between July and September 2007. Data were collected through semi-structured interviews, collection of medicinal plants in the homegardens, forest walks, a walk along the river banks, participant observation, informal conversation, cross check through voucher specimens and a focus group interview with children.Results
Four-hundred and two medicinal plants, mainly herbs, were indicated by the informants. The most important families in terms of taxa were Asteraceae, Araceae, Rubiaceae, Euphorbiaceae, Solanaceae and Piperaceae. Eighty-four percent of the medicinal plants were wild and 63% were collected from the forest. Exotics accounted to only 2% of the medicinal plants. Problems related to the dermal system, digestive system, and cultural belief system represented 57% of all the medicinal applications. Some traditional healers received non-indigenous customers, using their knowledge as a source of income. Age and gender were significantly correlated to medicinal plant knowledge. Children knew the medicinal plants almost exclusively by their Spanish names. Sixteen percent of the medicinal plants found in this community were also reported among the Yanesha of the Pasco Region.Conclusions
Despite the vicinity to a city, knowledge on medicinal plants and cultural beliefs are still abundant in this Asháninka Native Community and the medicinal plants are still available in the surroundings. Nevertheless, the use of Spanish names for the medicinal plants and the shift of healing practices towards a source of income with mainly non-indigenous customers, are signs of acculturation. Future studies on quantification of the use of medicinal plants, dynamics of transmission of ethno-medicinal knowledge to the young generations and comparison with available pharmacological data on the most promising medicinal plants are suggested. 相似文献46.
47.
We have used quartz Ca2+-sensitive microelectrodes (CASMs) in large voltage-clamped snail neurones to investigate the inward spread of Ca2+ after a brief depolarisation. Both steady state and [Ca2+]i transients changed with depth of penetration. When the CASM tip was within 20 microm of the far side of the cell the [Ca2+]i transient time to peak was 4.4+/-0.5s, rising to 14.7+/-0.7s at a distance of 80 microm. We estimate that the Ca2+ transients travelled centripetally at an average speed of 6 microm2 s(-1) and decreased in size by half over a distance of about 45 microm. Cyclopiazonic acid had little effect on the size and time to peak of Ca2+ transients but slowed their recovery significantly. This suggests that the endoplasmic reticulum curtails rather than reinforces the transients. Injecting the calcium buffer BAPTA made the Ca2+ transients more uniform in size and increased their times to peak and rates of recovery near the membrane. We have developed a computational model for the transients, which includes diffusion, uptake and Ca2+ extrusion. Good fits were obtained with a rather large apparent diffusion coefficient of about 90+/-20 microm2 s(-1).This may assist fast recovery by extrusion. 相似文献
48.
Vasilis Dakos Stephen R. Carpenter Egbert H. van Nes Marten Scheffer 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2015,370(1659)
In the vicinity of tipping points—or more precisely bifurcation points—ecosystems recover slowly from small perturbations. Such slowness may be interpreted as a sign of low resilience in the sense that the ecosystem could easily be tipped through a critical transition into a contrasting state. Indicators of this phenomenon of ‘critical slowing down (CSD)’ include a rise in temporal correlation and variance. Such indicators of CSD can provide an early warning signal of a nearby tipping point. Or, they may offer a possibility to rank reefs, lakes or other ecosystems according to their resilience. The fact that CSD may happen across a wide range of complex ecosystems close to tipping points implies a powerful generality. However, indicators of CSD are not manifested in all cases where regime shifts occur. This is because not all regime shifts are associated with tipping points. Here, we review the exploding literature about this issue to provide guidance on what to expect and what not to expect when it comes to the CSD-based early warning signals for critical transitions. 相似文献
49.
50.
Global trade will accelerate plant invasions in emerging economies under climate change 总被引:1,自引:0,他引:1 下载免费PDF全文
Hanno Seebens Franz Essl Wayne Dawson Nicol Fuentes Dietmar Moser Jan Pergl Petr Pyšek Mark van Kleunen Ewald Weber Marten Winter Bernd Blasius 《Global Change Biology》2015,21(11):4128-4140
Trade plays a key role in the spread of alien species and has arguably contributed to the recent enormous acceleration of biological invasions, thus homogenizing biotas worldwide. Combining data on 60‐year trends of bilateral trade, as well as on biodiversity and climate, we modeled the global spread of plant species among 147 countries. The model results were compared with a recently compiled unique global data set on numbers of naturalized alien vascular plant species representing the most comprehensive collection of naturalized plant distributions currently available. The model identifies major source regions, introduction routes, and hot spots of plant invasions that agree well with observed naturalized plant numbers. In contrast to common knowledge, we show that the ‘imperialist dogma,’ stating that Europe has been a net exporter of naturalized plants since colonial times, does not hold for the past 60 years, when more naturalized plants were being imported to than exported from Europe. Our results highlight that the current distribution of naturalized plants is best predicted by socioeconomic activities 20 years ago. We took advantage of the observed time lag and used trade developments until recent times to predict naturalized plant trajectories for the next two decades. This shows that particularly strong increases in naturalized plant numbers are expected in the next 20 years for emerging economies in megadiverse regions. The interaction with predicted future climate change will increase invasions in northern temperate countries and reduce them in tropical and (sub)tropical regions, yet not by enough to cancel out the trade‐related increase. 相似文献