Key Approach (key + approach)

Distribution by Scientific Domains

Selected Abstracts

The interpretation, assessment and conservation of ecological communities

David A. Keith
Summary Ecological communities are assemblages of species that occur together in space and time. Their properties include composition, structure, habitat, distribution, biological interactions and ecosystem functions. The community concept has a central role in conservation planning, and is a key approach for biodiversity conservation above the species level. The relatively recent application of risk assessment and regulatory systems to conservation of ecological communities has highlighted a number of challenges related to intrinsic uncertainties in the definition, diagnosis and assessment of ecological communities. In this review, I aim to elucidate some key conceptual issues essential to the interpretation of communities. Effective description, diagnosis and assessment of communities rests on an understanding of community theory in relation to environmental gradients and ecosystem dynamics. Continuum and discrete models can both contribute to interpretation of communities for conservation. Different sources of uncertainty are inherent in the key properties that characterize communities. Although some of these are reducible, remaining uncertainty must be incorporated into assessments and decision-making processes for conservation. Protocols for assessing extinction risks of communities address rates of decline in distribution, size of distribution and rates of decline in ecological functions. Some protocols assess these factors in a manner that may be inconsistent with equivalent methods for assessing species. Communities may be viewed in a framework that distinguishes thematic, spatial and temporal scales. These scales influence the outcomes of risk assessment, the benefits and limitations of maps and how well communities perform their function in conservation planning. When applied effectively, ecological communities can be powerful tools for delivering cost-effective outcomes for land-use planning and biodiversity conservation. [source]

Assigning Escherichia coli strains to phylogenetic groups: multi-locus sequence typing versus the PCR triplex method

David M. Gordon
Summary It is well recognized that Escherichia coli consists of a number of distinct phylo-groups and that strains of the different phylo-groups vary in their ecological niches, life-history characteristics and propensity to cause disease. Consequently, much can be learnt by assigning a strain of E. coli to one of the recognized phylo-groups. A triplex PCR-based method that enables strains of E. coli to be assigned to a phylo-group using a dichotomous key approach based on the presence or absence of two genes (chuA and yjaA) and an anonymous DNA fragment (TSPE4.C2) has been developed. However, the accuracy with which this method assigns strains to their correct phylo-group has not been adequately evaluated. Consequently, 662 strains of E. coli were characterized using a multi-locus sequence typing approach. Unsupervised population assignment algorithms were used to assign strains to phylo-groups based on the multi-locus sequence typing data. The analyses revealed that 85,90% of E. coli strains can be assigned to a phylo-group and that 80,85% of the phylo-group memberships assigned using the Clermont method are correct. However, the accuracy with which strains are assigned to the correct phylo-group depends on their Clermont genotype. For example, strains yielding a Clermont genotype consistent with phylo-groups B1 and B2 are assigned correctly 95% of the time. Strains failing to yield any PCR products using the Clermont method are seldom members of phylo-group A and strains with such a genotype should not be assigned to a phylo-group. [source]

Slope traversal controls for planetary exploration rover on sandy terrain

Genya Ishigami
In this paper, two control approaches are presented for exploration rovers traversing sandy-sloped terrain. One of the proposed controls is a model-based feed-forward control using a characteristic diagram, called a thrust-cornering characteristic diagram. It consists of various characteristic curves of wheel forces for varied wheel slip conditions. An appropriate steering maneuver for slope traversal can be found using the diagram with slope traversal criteria. The other control is a sensor-based feedback control. A key approach to this feedback control is to compensate for three types of slip, namely, the vehicle sideslip and longitudinal/lateral slips of a wheel. The feedback control calculates both steering and driving maneuvers that can compensate for these slips and also allow the rover to successfully traverse a sandy slope. The performances of these two control approaches are confirmed in slope traversal experiments using a four-wheeled rover test bed. The proposed controls are verified by quantitative evaluations of distance and orientation errors. Through the experiment, it was found that the two controls have advantages and disadvantages, and the possibility of merging the model-based control and the sensor-based control is discussed. 2009 Wiley Periodicals, Inc. [source]

Managing ecosystem services: what do we need to know about their ecology?

Claire Kremen
Abstract Human domination of the biosphere has greatly altered ecosystems, often overwhelming their capacity to provide ecosystem services critical to our survival. Yet ecological understanding of ecosystem services is quite limited. Previous work maps the supply and demand for services, assesses threats to them, and estimates economic values, but does not measure the underlying role of biodiversity in providing services. In contrast, experimental studies of biodiversity,function examine communities whose structures often differ markedly from those providing services in real landscapes. A bridge is needed between these two approaches. To develop this research agenda, I discuss critical questions and key approaches in four areas: (1) identifying the important ,ecosystem service providers'; (2) determining the various aspects of community structure that influence function in real landscapes, especially compensatory community responses that stabilize function, or non-random extinction sequences that rapidly erode it; (3) assessing key environmental factors influencing provision of services, and (4) measuring the spatio-temporal scale over which providers and services operate. I show how this research agenda can assist in developing environmental policy and natural resource management plans. [source]

Prevention of hepatocellular carcinoma complicating chronic hepatitis C

Yoshiyuki Ueno
Abstract Chronic hepatitis C virus (HCV) infection accounts for most cases of hepatocellular carcinoma (HCC) in Japan and is the second major cause in many other countries. Development of HCC takes a considerable time after onset of HCV infection, between 20,40 years in most cases, and usually develops after cirrhosis is established. Although only a minority of HCV infections reach this stage, the high prevalence of chronic HCV infection in many countries (1,3%) is such that HCC related to HCV infection poses a significant public health issue 20,50 years after the onset of HCV epidemics. Due to advances in testing, and accessibility of clean, disposable medical apparatus including syringes and needles, and particularly screening of donor blood for anti-HCV and by nucleic acid testing, new cases of HCV infection have decreased in most countries, except for continued transmission by injection drug users (IDU). A key difference between HBV and HCV infection is that HCV can be eradicated by effective antiviral treatment. Sustained eradication of HCV reverses hepatic fibrosis, thereby preventing progression to cirrhosis and risk of HCC. Further, it has been well demonstrated that interferon-based antiviral therapy suppresses development of HCC in high-risk patients, particularly when sustained viral response (SVR) is obtained. In summary, the two key approaches to prevent development of HCV-related HCC are primary prevention of HCV infection (adequate programs to screen donor blood, universal precautions to stop medical transmission of blood-borne viruses, curbing transmission by IDU) and potent antiviral therapy of chronic HCV infection. [source]