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1.
元江干热河谷山地五百年来植被变迁探讨 总被引:15,自引:2,他引:13
元江河谷是云南省最干热地区之一,在海拔800—900米以下的山地上广泛分布着稀树灌草丛。根据《元江府志》(1714年编纂)、《元江州志》(1826年编纂)、《元江志稿》(1922年编篡)及对现存植被的考察,本文探讨了元江干热河谷山地五百年来植被的变迁。 元江县森林复盖率的减少与人口的增加有密切关系,十七世纪中期以前,森林复盖率在75%以上,十八、十九世纪时为70%左右,1958年为61.5%,1975年为27.3%,至1982年则为19.3%。研究表明,在十九世纪以前,这个地区分布的主要植被是热带季雨林,甚而热带季节雨林,以后热带稀树灌草丛则迅速发展。植被的历史变化与土壤流失密切相关。植物群落的演变是由以乔木树种为优势演变为以灌木种类为优势,再演变为以多年生草木植物为优势,而最后则成为裸地。本文也讨论了这个地区植被恢复的方法。 相似文献
2.
F. Kocourek J. Havelka J. Bernkov V. Jaro
ik 《Entomologia Experimentalis et Applicata》1994,71(1):59-64
Thermal requirements for development and life table statistics ofAphis gossypii Glover (Homoptera, Aphididae) were determined over a range of constant temperatures from 10 to 30°C. The lower development
threshold and the sum of effective temperatures were 6.9°C and 90.1°C, respectively, for preimaginal development, and 5.8°C
and 113.6°C from birth to the onset of reproduction. Mean total fecundity ranged from 36 larvae per female at 10°C to 76 larvae
at 30°C. On a time scale of days, net reproductive rate (R
o
) increased with increasing temperature while generation time (T) decreased causing the intrinsic rate of increase (r
m
) to increase linearly from 0.115 to 0.465. On a day-degree scaler
m
only varied from 0.019 to 0.028 because the growth ofR
o
was compensated by an increase inT with increase in temperature. The nearly constantr
m
in terms of day-degrees, over a wide range of temperatures, greatly simplifies the prediction of future population numbers
ofA. gossypii. 相似文献
3.
We investigated the possible role of prostaglandins produced by COX-2 in the immunosuppression observed during Trypanosoma cruzi infection. Con-A-stimulated splenocytes isolated from mice on days 5, 10, and 15 of infection released large amounts of PGE2 and this release was inhibited by the treatment of animals with sodium salicylate or meloxicam. The treatment of the animals with these drugs enhanced the release of IL-2 by splenocytes from T. cruzi-infected animals and significantly reduced the blood parasitemia and delayed the mortality of the infected mice. Furthermore, the release of TNF-alpha, IFN-gamma, IL-4, and IL-10 by Con-A-stimulated splenocytes obtained from infected mice on days 5, 10, and 15 of the infection was significantly inhibited by treatment of the animals with salicylate or meloxicam. In conclusion, the results suggest that the prostaglandins produced mainly by COX-2 mediate the immunosuppression observed in the acute phase of T. cruzi infection. 相似文献
4.
Predicting population dynamics of weed biological control agents: science or gazing into crystal balls? 总被引:1,自引:0,他引:1
Abstract Various factors can influence the population dynamics of phytophages post introduction, of which climate is fundamental. Here we present an approach, using a mechanistic modelling package (CLIMEX), that at least enables one to make predictions of likely dynamics based on climate alone. As biological control programs will have minimal funding for basic work (particularly on population dynamics), we show how predictions can be made using a species geographical distribution, relative abundance across its range, seasonal phenology and laboratory rearing data. Many of these data sets are more likely to be available than long-term population data, and some can be incorporated into the exploratory phase of a biocontrol program. Although models are likely to be more robust the more information is available, useful models can be developed using information on species distribution alone. The fitted model estimates a species average response to climate, and can be used to predict likely geographical distribution if introduced, where the agent is likely to be more abundant (i.e. good locations) and more importantly for interpretation of release success, the likely variation in abundance over time due to intra- and inter-year climate variability. The latter will be useful in predicting both the seasonal and long-term impacts of the potential biocontrol agent on the target weed. We believe this tool may not only aid in the agent selection process, but also in the design of release strategies, and for interpretation of post-introduction dynamics and impacts. More importantly we are making testable predictions. If biological control is to become more of a science making and testing such hypothesis will be a key component. 相似文献
5.
Tatiane Katsue Furuya Patrícia Natália Oliveira da Silva Spencer Luiz Marques Payão Lucas Trevizani Rasmussen Roger Willian de Labio Paulo Henrique Ferreira Bertolucci Ianna Lacerda Sampaio Braga Elizabeth Suchi Chen Gustavo Turecki Naguib Mechawar Jonathan Mill Marília de Arruda Cardoso Smith 《Neurochemistry international》2012
Alzheimer’s Disease (AD) is a neurodegenerative disorder and the most common cause of dementia among the elderly. Efforts have been made to understand the genetic and epigenetic mechanisms involved in the development of this disease. As SORL1 (sortilin-related receptor) and SIRT1 (sirtuin 1) genes have been linked to AD pathogenesis, we aimed to investigate their mRNA expression and promoter DNA methylation in post mortem brain tissues (entorhinal and auditory cortices and hippocampus) from healthy elderly subjects and AD patients. We also evaluated these levels in peripheral blood leukocytes from young, healthy elderly and AD patients, investigating whether there was an effect of age on these profiles. The comparative CT method by Real Time PCR and MALDI-TOF mass spectrometry were used to analyze gene expression and DNA methylation, respectively. SORL1 gene was differently expressed in the peripheral blood leukocytes and might act as a marker of aging in this tissue. Furthermore, we found that SORL1 promoter DNA methylation might act as one of the mechanisms responsible for the differences in expression observed between blood and brain for both healthy elderly and AD patients groups. The impact of these studied genes on AD pathogenesis remains to be better clarified. 相似文献
6.
7.
Summary . In medical research, there is great interest in developing methods for combining biomarkers. We argue that selection of markers should also be considered in the process. Traditional model/variable selection procedures ignore the underlying uncertainty after model selection. In this work, we propose a novel model-combining algorithm for classification in biomarker studies. It works by considering weighted combinations of various logistic regression models; five different weighting schemes are considered in the article. The weights and algorithm are justified using decision theory and risk-bound results. Simulation studies are performed to assess the finite-sample properties of the proposed model-combining method. It is illustrated with an application to data from an immunohistochemical study in prostate cancer. 相似文献
8.
M. DODD 《The Annals of applied biology》1991,119(3):521-531
In field trials at eight sites throughout the UK the mean thermal time requirement for navy beans from sowing to harvest for a standard cultivar, Marcus, was 2069 Ontario Heat Units (OHU). Low level plastic covers increased the range of warm environments at one site and gave a mean thermal time required of 2098 OHU. Analysis of daily air temperatures from six weather stations throughout the UK over a 29 year period, showed a 14 day possible planting period on the south coast of England, but gave a high probability of crop failure in Scotland. Maps of England and Wales indicating the probability of achieving 2000 OHU were produced from 5 km grid point temperatures. Less than 2% of the land had more than a 60% chance of receiving 2000 OHU under the present climate, however this area increased to 70% with a mean temperature rise of 1.5°C. Although 2000 OHU is often used as the thermal time requirement of navy beans, these trials showed that it may be more accurate to use the higher figure of 2087 OHU from sowing to harvest, and restrict the use of 2000 OHU to the period between emergence and harvest. When the map was redrawn using 2087 OHU and current climate, no parts of England and Wales showed a reasonable chance of growing the present cultivars of navy beans. 相似文献
9.
10.
Thanthrige Thiunuwan Priyathilaka Don Anushka Sandaruwan Elvitigala Ilson Whang Bong-Soo Lim Hyung-Bok Jeong Sang-Yeob Yeo Cheol Young Choi Jehee Lee 《Gene》2014
Toll-like receptors (TLRs) are a large family of pattern recognition receptors, which are involved in triggering host immune responses against various pathogens by detecting their evolutionarily conserved pathogen associated molecular patterns (PAMPs). TLR21 is a non-mammalian type TLR, which recognizes unmethylated CpG DNA, and is considered as a functional homolog of mammalian TLR9. In this study, we attempted to identify and characterize a novel TLR21 counterpart from rock bream (Oplegnathus fasciatus) designated as RbTLR21, at molecular level. The complete coding sequence of RbTLR21 was 2919 bp in length, which encodes a polypeptide of 973 amino acids with a predicted molecular mass of 112 kDa and a theoretical isoelectric point of 8.6. The structure of the deduced RbTLR21 protein is similar to that of the members of typical TLR family, and includes the ectodomain, which consists of 16 leucine rich repeats (LRRs), a transmembrane domain, and a cytoplasmic Toll/interleukin-1 receptor (TIR) domain. According to the pairwise sequence analysis data, RbTLR21 was homologous to that of the orange-spotted grouper (Epinephelus coioides) with 76.9% amino acid identity. Furthermore, our phylogenetic analysis revealed that RbTLR21 is closely related to E. coioides TLR21. The RbTLR21 was ubiquitously expressed in all the tissues tested, but the highest expression was found in spleen. Additionally, upon stimulation with Streptococcus iniae, rock bream iridovirus (RBIV), and Edwardsiella tarda, RbTLR21 mRNA was significantly up-regulated in spleen tissues. Collectively, our findings suggest that RbTLR21 is indeed an ortholog of the TLR21 family and may be important in mounting host immune responses against pathogenic infections. 相似文献