Home About us Contact
|
Home About us Contact | ||
|
|
||
Limited Period (limited + period)
Selected AbstractsInfluence of Temporal Scale of Sampling on Detection of Relationships between Invasive Plants and the Diversity Patterns of Plants and ButterfliesCONSERVATION BIOLOGY, Issue 6 2004RALPH MAC NALLY But monitoring is often neglected because it can be expensive and time-consuming. Accordingly, it is valuable to determine whether the temporal extent of sampling alters the validity of inferences about the response of diversity measures to environmental variables affected by restoration actions. Non-native species alter ecosystems in undesirable ways, frequently homogenizing flora and fauna and extirpating local populations of native species. In the Mojave Desert, invasion of salt-cedar (Tamarix ramosissima Ledeb.) and human efforts to eradicate salt-cedar have altered vegetation structure, vegetation composition, and some measures of faunal diversity. We examined whether similar inferences about relationships between plants and butterflies in the Muddy River drainage (Nevada, U.S.A.) could have been obtained by sampling less intensively (fewer visits per site over the same period of time) or less extensively (equal frequency of visits but over a more limited period of time). We also tested whether rank order of butterfly species with respect to occurrence rate (proportion of sites occupied) would be reflected accurately in temporal subsamples. Temporal subsampling did not lead to erroneous inferences about the relative importance of six vegetation-based predictor variables on the species richness of butterflies. Regardless of the temporal scale of sampling, the species composition of butterflies was more similar in sites with similar species composition of plants. The rank order of occurrence of butterfly species in the temporal subsamples was highly correlated with the rank order of species occurrence in the full data set. Thus, similar inferences about associations between vegetation and butterflies and about relative occurrence rates of individual species of butterflies could be obtained by less intensive or extensive temporal sampling. If compromises between temporal intensity and extent of sampling must be made, our results suggest that maximizing temporal extent will better capture variation in biotic interactions and species occurrence. Resumen:,El monitoreo es un componente importante de los esfuerzos de restauración y de manejo adoptivo. Pero el monitoreo a menudo es desatendido porque puede ser costoso y consume tiempo. En consecuencia, es valioso determinar si la extensión temporal del muestreo altera la validez de inferencias sobre la respuesta de medidas de diversidad a variables ambientales afectadas por acciones de restauración. Las especies no nativas alteran a los ecosistemas de manera indeseable, frecuentemente homogenizan la flora y fauna y extirpan poblaciones locales de especies nativas. En el Desierto Mojave, la invasión de Tamarix ramosissima Ledeb. y los esfuerzos humanos para erradicarla han alterado la estructura y composición de la vegetación y algunas medidas de diversidad de fauna. Examinamos si se podían obtener inferencias similares sobre las relaciones entre plantas y mariposas en la cuenca Muddy River (Nevada, E.U.A.) muestreando menos intensivamente (menos visitas por sitio en el mismo período de tiempo) o menos extensivamente (igual frecuencia de visitas pero sobre un período de tiempo más limitado). También probamos si el orden jerárquico de especies de mariposas con respecto a la tasa de ocurrencia (proporción de sitios ocupados) se reflejaba con precisión en las submuestras temporales. El submuestreo temporal no condujo a inferencias erróneas acerca de la importancia relativa de seis variables predictivas basadas en vegetación sobre la riqueza de especies de mariposas. A pesar de la escala temporal del muestreo, la composición de especies de mariposas fue más similar en sitios con composición de especies de plantas similar. El orden jerárquico de ocurrencia de especies de mariposas en las muestras subtemporales estuvo muy correlacionado con el orden jerárquico de ocurrencia de especies en todo el conjunto de datos. Por lo tanto, se pudieron obtener inferencias similares de las asociaciones entre vegetación y mariposas y de las tasas de ocurrencia relativa de especies individuales de mariposas con muestreo temporal menos intensivo o extensivo. Si se deben hacer compromisos entre la intensidad y extensión de muestreo temporal, nuestros resultados sugieren que la maximización de la extensión temporal capturará la variación en interacciones bióticas y ocurrencia de especies más adecuadamente. [source] Mismatch between the timing of oviposition and the seasonal optimum.ECOLOGICAL ENTOMOLOGY, Issue 3 2010The stochastic phenology of Mediterranean acorn weevils 1. The timing of reproduction is predicted to match the period of maximum food availability. In this sense, the case of many phytophagous insects in temperate regions is very illustrative, as their larvae usually depend on a resource only available for a limited period of time each year. 2. For 3 years the interactions between the weevil Curculio elephas and the Mediterranean Holm oak Quercus ilex were studied. Weevil larvae grow within the acorns, feeding on the cotyledons. The timing of oviposition will determine food availability for the larvae, as acorns stop growing once they are attacked. 3. Acorn temporal growing patterns did not change between years and food availability for larvae was at its highest in October, when temperature was still suitable for larval development. However, oviposition phenology did change between years. In 2002 females oviposited later, larvae grew within larger acorns, and their body mass was significantly higher than in 2003 or 2004, when females oviposited into early acorns. 4. Thus, weevils do not always adjust oviposition to the best possible feeding conditions for their offspring. Rather, they seem to maximise their own lifetime fitness, ovipositing as soon as they emerge in late summer. Emergence, in turn, depends strongly on stochastic events such as summer storms in the Mediterranean region. 5. Under a climate change perspective, the trend towards higher August rainfall recorded in our study area may alter oviposition phenology, with the subsequent cascade effects on weevil body size and fitness [source] Examining the Impact of Opportunity Bursaries on the Financial Circumstances and Attitudes of Undergraduate Students in EnglandHIGHER EDUCATION QUARTERLY, Issue 2 2009Anne West Notwithstanding the expansion of higher education across the OECD, there continues to be concern about the levels of participation amongst those from disadvantaged backgrounds. In response to this, a new form of financial support for students from low-income families, the ,opportunity bursary', was introduced for a limited period in England from 2001/02. Surveys of two cohorts of opportunity-bursary applicants were carried out and these suggested possible psychological, behavioural and economic impacts. Fewer opportunity-bursary recipients than non-recipients reported that part-time work had interfered with their studies and more reported that the bursary had made them less worried about meeting the costs of going to university. There was some evidence that the scheme led to increased retention in the first year of university study; it also appeared to lead to lower levels of debt, in particular bank overdrafts or credit card debt. [source] Performance assessment of a GCM land surface scheme using a fine-scale calibrated hydrological model: an evaluation of MOSES for the Nile BasinHYDROLOGICAL PROCESSES, Issue 11 2009Mohamed Ezzat Elshamy Abstract Land surface schemes (LSSs) represent the interface between land surface and the atmosphere in general circulation models (GCMs). Errors in LSS-simulated heat and moisture fluxes can result from inadequate representation of hydrological features and the derivation of effective surface parameters for large heterogeneous GCM gridboxes from small-scale observations. Previous assessments of LSS performance have generally compared simulated heat and moisture fluxes to observations over a defined experimental domain for a limited period. A different approach has been evaluated in this study, which uses a fine-resolution calibrated hydrological model of the study basin to provide a quasi-observed runoff series for direct comparison with simulated runoff from a selected LSS at GCM scale. The approach is tested on two GCM gridboxes covering two contrasting regions within the Nile Basin. Performance is mixed; output from the LSS is generally compatible with that of the fine-resolution model for one gridbox while it cannot reproduce the runoff dynamics for the other. The results also demonstrate the high sensitivity of runoff and evapotranspiration to radiation and precipitation inputs and show the importance of subtle issues such as temporal disaggregation of climatic inputs. We conclude that the use of a fine-resolution calibrated model to evaluate a LSS has several advantages, can be generalized to other areas to improve the performance of global models and provides useful data that can be used to constrain LSS parameterizations. Copyright © 2009 John Wiley & Sons, Ltd. [source] The Role of Support Networks in the Initial Stages of Integration: The Case of West African Newcomers in the NetherlandsINTERNATIONAL MIGRATION, Issue 2 2010Magali Chelpi-den Hamer This study focuses on the role of support networks in West African migration to the Netherlands. The authors examine the interactions of non-State support groups with West African newcomers and explore the nature, scope and function of support. What type of support networks do respondents rely on, under which circumstances, and for how long? What is the scope of support? Is it to be taken for granted? What alternatives are there for those left out of the loop? The findings suggest that support is mainly punctual, in response to a specific need, and for a limited period of time. It is not to be taken for granted, as support groups have limited capacities, and protect themselves from excessive demands. They play a significant role in providing assistance to migrants, yet this role should not be overestimated. [source] Seasonal Dynamics of Picocyanobacteria and Picoeukaryotes in a Large Shallow Lake (Lake Balaton, Hungary)INTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 1 2006Andrea Mózes Abstract The abundance and composition of autotrophic picoplankton (APP) were studied between February 2003 and March 2004 in Lake Balaton. Water samples were taken fortnightly in the eutrophic western basin and mesotrophic eastern basin. Our study, which took more than one year, revealed pronounced seasonal pattern of the picoplankton abundance and composition. According to our results there were three types of picoplankton in Lake Balaton: 1. Phycoerythrin-rich coccoid cyanobacteria (PE), dominant summer picoplankters in the mesotrophic lake area; 2. Phycocyanin-rich cyanobacteria (PC), the most abundant summer picoplankters in the eutrophic lake area; 3. Picoeukaryotes, dominant winter picoplankters in the whole lake. The observed abundance of picoeukaryotes (3 × 105 cells ml,1) was one of the highest ever found. Our study confirms that in Lake Balaton the colonial autotrophic picoplankton (colonial APP) become dominant in summer in the nutrient limited period. We have found strong negative relationship between the concentrations of available nitrogen forms (NH4,N, NO3,N, urea-N) and the colonial APP abundance. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The influence of the particle size distribution on fluidized bed hydrodynamics using high-throughput experimentationAICHE JOURNAL, Issue 8 2009Renske Beetstra Abstract The goal of the described project is to design mixtures of particles with optimal fluidization properties. Using high-throughput experimentation, a novel approach to study hydrodynamics in fluidized beds, the relevant properties can be obtained in a limited period of time. This approach is demonstrated by assessing the influence of particle size distribution on fluidized bed hydrodynamics of Geldart A powders. By manipulating the width of the particle size distribution of alumina powder, the bubble diameter is reduced up to 40%. The addition of fines to a given particle size distribution also decreases the bubble diameter up to 40%, whereas the addition of coarse particles hardly influences the bubble size. At low gas velocities, the bubble size was found to increase with fines addition or increasing standard deviation. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Single Mothers, Welfare, and Incentives to WorkLABOUR, Issue 3 2008Libertad González The reform aimed at encouraging participation by allowing eligible single parents to accumulate welfare benefits and labor earnings for a limited period of time. The analysis shows that eligible single mothers were significantly more likely to work after the reform. During the same period, the employment rate of married mothers with young children did not experience a significant change, suggesting that at least part of the increase among single mothers was a consequence of the reform. [source] Antitubercular potential of plants: A brief account of some important moleculesMEDICINAL RESEARCH REVIEWS, Issue 4 2010Arvind S. Negi Abstract Mycobacterium tuberculosis is the most lethal pathogen causing tuberculosis in human. After the discovery of antitubercular drugs pyrazinamide, rifampicin, isoniazid, streptomycin, and ethambutol (PRISE), the disease was controlled for a limited period. However, over the course of their usage, the pathogen acquired resistance and evolved into multi-drug resistant, single-drug resistant, and extensive drug resistant forms. A good number of plant secondary metabolites are reported to have antitubercular activity comparable to the existing antitubercular drugs or sometimes even better in potency. A well-defined strategy is required to exploit these phytomolecules as antitubercular drugs. This review gives concise up-to-date information regarding the chemistry and pharmacology of plant-based leads and some insight into their structure,activity relationship. © 2009 Wiley Periodicals, Inc. Med Res Rev, 30, No. 4, 603,645, 2010 [source] Transitory real-time property rights and exchange intellectual propertyTHE JOURNAL OF FUTURES MARKETS, Issue 9 2003Robert I. Webb American exchanges own the price quotations they generate. Access to real-time price information is highly valued by most market participants. This enables exchanges to exact royalties from the sale of such market information. In this sense, an exchange's ownership of its price quotations is akin to owning a property right in a perishable commodity (i.e., fresh market price quotations) that is most valuable for only a transitory or limited period of time. The implications of exchange ownership of price data extend beyond financial markets. Recently, Woodard (2000) has noted that some internet auction operators have asserted ownership over the prices they generate. This study reviews the legal origin and nature of the property right to price quotations generated on U.S. futures exchanges and assesses whether exchange ownership should be transitory. The legal basis for transitory real-time (real and personal) property rights is discussed and the economic implications are considered. © 2003 Wiley Periodicals, Inc. Jrl Fut Mark 23:891,913, 2003 [source] Changes in frigate tuna populations on the south coast of Sri Lanka: evidence of the shifting baseline syndrome from analysis of fisher observationsAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 2 2010A. J. Venkatachalam Abstract 1.This study examines changes in frigate tuna populations in southern Sri Lanka, based on reports from fishers in three age classes. Significantly higher values for best day's catch and largest specimen ever caught were obtained by older fishers than younger ones. Values were also significantly higher during early years, providing clear evidence of a decrease in the resource over time (1951,2007). 2.Older fishers reported best catches further inshore and in shallower waters which, on becoming depleted, forced younger generations to fish in less exploited areas further offshore. Heavy harvesting is also evident from the significantly greater number of sites reported by older fishers as being depleted, compared with observations of younger fishers. 3.These findings contrast markedly with catch and catch per effort patterns from statistics for frigate tuna and bullet tuna (combined) in southern Sri Lanka (1994,2004). No stock decline is evident, and at least one report in the early 1990s advocated increasing exploitation rates by 40% to maximize yields. 4.Although not a primary research objective, fisher observations on frigate tuna populations were also analysed to help evaluate possible effects of the 2004 tsunami. Most fishers reported post-tsunami decline, but mainly from a larger new generation of fishers, rather than extra boats provided by aid money or (direct or indirect) biophysical impacts from the tsunami. 5.Reliance on fishery statistics, especially for mixed species and over a limited period, can be risky and easily mask true stock status. Evidence of harvesting effects on frigate tuna in southern Sri Lanka is evident using questionnaire data over a longer time scale. 6.This study provides another compelling case of the ,shifting baseline syndrome', whereby fishers of different ages have altered perceptions/experiences of their environment. This may be its first reported occurrence in Sri Lanka. Traditional knowledge from this and similar surveys may provide national fishery management with valuable insights and help improve conservation prospects for frigate tuna and other marine resources. Copyright © 2009 John Wiley & Sons, Ltd. [source] Resolving the differences in plant burial responsesAUSTRAL ECOLOGY, Issue 1 2010MATTHEW E. GILBERT Abstract Burial is one of the major factors influencing plant ecology in deserts and coastal areas. Consequently, many studies have measured the responses of dune plants to sand burial. However, there remains little agreement about the mechanisms and characteristics constituting the burial response of plants. In particular, stimulation of growth has been reported as the most common plant burial response; however, stimulation has not been reported consistently among studies. Here, a literature survey showed that the depth of burial relative to the height of the plant determined whether the growth of a species was stimulated by burial. Growth stimulation was limited to shallow burial depths, while burial depths greater than the height of the plant consistently resulted in reduced growth. As studies used widely differing burial depths or units of growth measurement, the variation in reported stimulation of plant growth can be partly attributed to differences in experimental procedure. The stimulation of growth in many species was accompanied by an increase in photosynthesis over a limited period and by a shift in biomass allocation from root to shoot. Most plants demonstrated stimulated growth (up to 200%) in response to shallow burial indicating that some burial response mechanisms are general to many species. However, a few specialist dune species displayed a much greater ability to respond to burial (up to 700% stimulation of plant mass). Although allocation shifts and increased photosynthesis have been shown to be associated with dune plant burial response, there remains a need for field measurements that focus on the diversity of mechanisms underlying plant response to burial. [source] An Introduction to Simulation and Visualization of Biological Systems at Multiple Scales: A Summer Training Program for Interdisciplinary ResearchBIOTECHNOLOGY PROGRESS, Issue 1 2006Rajan Munshi Advances in biomedical research require a new generation of researchers having a strong background in both the life and physical sciences and a knowledge of computational, mathematical, and engineering tools for tackling biological problems. The NIH-NSF Bioengineering and Bioinformatics Summer Institute at the University of Pittsburgh (BBSI @ Pitt;www.ccbb.pitt.edu/bbsi) is a multi-institutional 10-week summer program hosted by the University of Pittsburgh, Duquesne University, the Pittsburgh Supercomputing Center, and Carnegie Mellon University, and is one of nine Institutes throughout the nation currently participating in the NIH-NSF program. Each BBSI focuses on a different area; the BBSI @ Pitt, entitled "Simulation and Computer Visualization of Biological Systems at Multiple Scales", focuses on computational and mathematical approaches to understanding the complex machinery of molecular-to-cellular systems at three levels, namely, molecular, subcellular (microphysiological), and cellular. We present here an overview of the BBSI@Pitt, the objectives and focus of the program, and a description of the didactic training activities that distinguish it from other traditional summer research programs. Furthermore, we also report several challenges that have been identified in implementing such an interdisciplinary program that brings together students from diverse academic programs for a limited period of time. These challenges notwithstanding, presenting an integrative view of molecular-to-system analytical models has introduced these students to the field of computational biology and has allowed them to make an informed decision regarding their future career prospects. [source] State of the art and recommendationsKangaroo mother care: application in a high-tech environmentACTA PAEDIATRICA, Issue 6 2010KH Nyqvist Abstract Since Kangaroo Mother Care (KMC) was developed in Colombia in the 1970s, two trends in clinical application emerged. In low income settings, the original KMC model is implemented. This consists of continuous (24 h/day, 7 days/week) and prolonged mother/parent,infant skin-to-skin contact; early discharge with the infant in the kangaroo position; (ideally) exclusive breastfeeding; and, adequate follow-up. In affluent settings, intermittent KMC with sessions of one or a few hours skin-to-skin contact for a limited period is common. As a result of the increasing evidence of the benefits of KMC for both infants and families in all intensive care settings, KMC in a high-tech environment was chosen as the topic for the first European Conference on KMC, and the clinical implementation of the KMC model in all types of settings was discussed at the 7th International Workshop on KMC. Kangaroo Mother Care protocols in high-tech Neonatal Intensive Care Units (NICU) should specify criteria for initiation, kangaroo position, transfer to/from KMC, transport in kangaroo position, kangaroo nutrition, parents' role, modification of the NICU environment, performance of care in KMC, and KMC in case of infant instability. Conclusion:, Implementation of the original KMC method, with continuous skin-to-skin contact whenever possible, is recommended for application in high-tech environments, although scientific evaluation should continue. [source] Are transient environmental agents involved in the cause of primary biliary cirrhosis?HEPATOLOGY, Issue 4 2009Evidence from space, time clustering analysis The cause of primary biliary cirrhosis (PBC) is unclear. Both genetic and environmental factors are likely to contribute. Some studies have suggested that one or more infectious agents may be involved. To examine whether infections may contribute to the cause of PBC, we have analyzed for space,time clustering using population-based data from northeast England over a defined period (1987,2003). Space,time clustering is observed when excess cases of a disease are found within limited geographical areas at limited periods of time. If present, it is suggestive of the involvement of one or more environmental components in the cause of a disease and is especially supportive of infections. A second-order procedure based on K -functions was used to test for global space,time clustering using residential addresses at the time of diagnosis. The Knox method determined the spatiotemporal range over which global clustering was strongest. K -function tests were repeated using nearest neighbor thresholds to adjust for variations in population density. Individual space,time clusters were identified using Kulldorff's scan statistic. Analysis of 1015 cases showed highly statistically significant space,time clustering (P < 0.001). Clustering was most marked for cases diagnosed within 1,4 months of one another. A number of specific space,time clusters were identified. In conclusion, these novel results suggest that transient environmental agents may play a role in the cause of PBC. (HEPATOLOGY 2009.) [source] Cellular lifespan and senescence signaling in embryonic stem cellsAGING CELL, Issue 6 2004Takumi Miura Summary Most mammalian cells when placed in culture will undergo a limited number of cell divisions before entering an unresponsive non-proliferating state termed senescence. However, several pathways that are activated singly or in concert can allow cells to bypass senescence at least for limited periods. These include the telomerase pathway required to maintain telomere ends, the p53 and Rb pathways required to direct senescence in response to DNA damage, telomere shortening and mitogenic signals, and the insulin-like growth factor , Akt pathway that may regulate lifespan and cell proliferation. In this review, we summarize recent findings related to these pathways in embryonic stem (ES) cells and suggest that ES cells are immortal because these pathways are tightly regulated. [source] Developments in the application of photography to ecological monitoring, with reference to algal bedsAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 2 2001Jean-Paul A. Ducrotoy Abstract 1.,The potential for using photographic methods in ecological monitoring of intertidal rocky shores was investigated at two scales: the scale of a bay, and at sampling quadrat level. 2.,The macroalgal beds at Selwicks Bay, Flamborough Head (north Humberside Coast, England) were used as a case study. 3.,At each station on three 90 m transects, a photograph was taken of a 50 cm2 quadrat. These images were analysed using SigmaScanÔ to measure the cover of algal species. These data were highly correlated with field data collected using a grid quadrat. 4.,Ground techniques were developed for drawing a scaled overhead map of the bay. The potential for a quantitative survey of the extent of the algal beds using cliff top photographs was investigated. The photographs were merged, and rectified using Arc/InfoÔ (a Geographical Information System package) to produce scaled overhead images of the bay. 5.,The two complementary methods developed are suitable for involving amateur naturalists into field-data collection. They were also designed to meet long-term statutory monitoring requirements. They are quick, so are well suited to intertidal areas where field sampling windows are limited. In long-term monitoring strategies, the use of photography produces interactive permanent records of the sample area for back reference. Reporting on the conservation status of sites of European interest could be greatly facilitated by such techniques. 6.,There are obvious applications for overseas monitoring and base-line surveys, which demand large data sets to be collected in limited periods of time. Copyright © 2001 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||