Limiting Factor (limiting + factor)

Distribution by Scientific Domains
Distribution within Life Sciences

Kinds of Limiting Factor

  • main limiting factor
  • major limiting factor

  • Selected Abstracts

    Glacial refugia for summer-green trees in Europe and south-west Asia as proposed by ECHAM3 time-slice atmospheric model simulations

    Suzanne A. G. Leroy
    Abstract Aim, To generate maps of potential refugia for summer-green trees during the Last Glacial Maximum (LGM). Locations, Southern Europe and south-western Asia. Methods, Time-slice simulations of the atmospheric climate with the ECHAM3 model are used for the LGM. Limiting factors beyond which cool and warm groups of deciduous trees cannot grow (such as temperature in growing degree days, minimum monthly temperature and precipitation in summer) are chosen. A limited validation by fossil pollen and charcoal records from LGM sites was done. Results, Two sets of maps extending from Europe to the Caspian region for cool and warm summer-green trees are presented. Three criteria are combined using contour lines to indicate confidence levels. Small areas within the three southern peninsulas of Europe (Spain, Italy and Greece) are highlighted as possible refugia for summer-green trees. Further, areas that have remained poorly known are now proposed as refugia, including the Sakarya,Kerempe region in northern Turkey, the east coast of the Black Sea and the area south of the Caspian Sea. Main conclusions, The maps produced in this study could be used to facilitate better long-term management for the protection of European and south-western Asian biodiversity. [source]

    Prospective study of zonisamide therapy for refractory idiopathic epilepsy in dogs

    T. Von Klopmann
    Objectives: Investigation of the efficacy of zonisamide as an add-on therapy in dogs with refractory epilepsy. Methods: Thirteen dogs fulfilled the inclusion criteria of poor seizure control despite adequate serum levels of phenobarbital, potassium bromide or both. One further dog was treated with zonisamide as monotherapy because of severe blood dyscrasia due to phenobarbital treatment. Various seizure parameters were evaluated retrospectively for a four month period without zonisamide and prospectively for the same time period under zonisamide add-on therapy. The study time period was extended by up to 17 months to evaluate long-term outcome. Results: Data of 11 dogs could be evaluated: nine of them were responders. The median reduction of seizure frequency of all dogs on zonisamide add-on therapy was 70 per cent (range 14 to 100 per cent). Only transient central nervous system side effects were reported. No further increase of liver enzymes occurred. In three of the responder dogs, seizure control subsided after individual time periods (between 69 days and seven months). Clinical Significance: In dogs with refractory epilepsy, zonisamide may have a beneficial effect on seizure control. In three responder dogs, seizure activity relapsed possibly because of an induction of tolerance. Limiting factors are the high costs. [source]

    Limiting factors for reforestation of mine spoils from Galicia (Spain)

    F. A. Vega
    Abstract Mined areas are a continuing source of heavy metals and acidity that move off site in response to erosion. Revegetation of the mine tailings could limit the spread of these heavy metals and acidity. This study was conducted to evaluate, at four tailings on opencast mines of Galicia (Touro: copper mine; and Meirama: lignite mine, NW Spain), the chemical and physical soil quality indicators and limiting edaphic factors concerning forest production. Selected zones were: (1) The tailings formed by the waste materials from the depleted Touro mine; (2) the decantation site of deposited sludge coming from the copper extraction in the flotation stage; (3) and (4) tailings of 3 and 10 years old of the Meirama lignite mine. The main physical limitations of the mine soils are the low effective depth (<50,cm), high stoniness (>30,per,cent) and high porosity (>60,per,cent); which make them vulnerable to soil erosion and seriously interferes with the forest production. Soils coming from the decantation site of copper mine do not have physical limitations. The main chemical limitations of mine soils are their acidity (pH from 3·62 to 5·71), and aluminium saturation (>60,per,cent in copper mine soils, and >20,per,cent in lignite mine soils), low CECe (from 5·34 to 9·47,cmol(+),kg,1), organic carbon (from 0·47 to 7·52,mg,kg,1) and Ca2+ and Mg2+ contents, and imbalance between exchange bases. Mine soils coming from the decantation site of copper mine soils are strongly limited by the high Cu content (1218,mg,kg,1). Lime and organic amendments are the most important factors in providing a suitable medium for plant growth. Copyright © 2004 John Wiley & Sons, Ltd. [source]

    Continuous glucose monitoring and closed-loop systems

    DIABETIC MEDICINE, Issue 1 2006
    R. Hovorka
    Abstract Background The last two decades have witnessed unprecedented technological progress in the development of continuous glucose sensors, resulting in the first generation of commercial glucose monitors. This has fuelled the development of prototypes of a closed-loop system based on the combination of a continuous monitor, a control algorithm, and an insulin pump. Method A review of electromechanical closed-loop approaches is presented. This is followed by a review of existing prototypes and associated glucose sensors. A literature review was undertaken from 1960 to 2004. Results Two main approaches exist. The extracorporeal s.c.,s.c. approach employs subcutaneous glucose monitoring and subcutaneous insulin delivery. The implantable i.v.,i.p. approach adopts intravenous sampling and intraperitoneal insulin delivery. Feasibility of both solutions has been demonstrated in small-scale laboratory studies using either the classical proportional,integral,derivative controller or a model predictive controller. Performance in the home setting has yet to be demonstrated. Conclusions The glucose monitor remains the main limiting factor in the development of a commercially viable closed-loop system, as presently available monitors fail to demonstrate satisfactory characteristics in terms of reliability and/or accuracy. Regulatory issues are the second limiting factor. Closed-loop systems are likely to be used first by health-care professionals in controlled environments such as intensive care units. [source]

    Evaluation of the Left Ventricular Function with Tissue Tracking and Tissue Doppler Echocardiography in Pediatric Malignancy Survivors after Anthracycline Therapy

    ECHOCARDIOGRAPHY, Issue 8 2008
    it Karakurt M.D.
    Although the anthracyclines have gained widespread use in the treatment of childhood hematological malignancies and solid tumors, cardiotoxicity is the major limiting factor in the use of anthracyclines. The aim of this study was to assess the mitral annular displacement by tissue tracking in pediatric malignancy survivors who had been treated with anthracycline groups chemotheraphy and compare with the tissue Doppler and conventional two dimensional measurements and Doppler indices. In this study, 32 pediatric malignancy survivors and 22 healthy children were assessed with 2D, colour-coded echocardiography. Left ventricular ejection fraction, fractional shortening, stroke volume, cardiac output, cardiac index and diastolic functions were measured. All subjects were assessed with tissue Doppler echocardiography, mitral annular displacements, and also with tissue tracking method. We detected that peak velocity of the early rapid filling on tissue Doppler (E,) was lower (p < 0.05) and the ratio of early peak velocity of rapid filling on pulse Doppler to tissue Doppler (E/E,) values were statistically higher in patient group than control group (p < 0.05). Myocardial performance index values were also higher in patient group than the control group (p < 0.01). It appears that MPI is a useful echocardiograghic method than tissue tracking of mitral annular displacement in patients with pediatric cancer survivors who had subclinical diastolic dysfunction. [source]

    Sphagnum under pressure: towards an ecohydrological approach to examining Sphagnum productivity

    ECOHYDROLOGY, Issue 4 2008
    D. K. Thompson
    Abstract The genus Sphagnum is the key peat-forming bryophyte in boreal ecosystems. Relying entirely on passive capillary action for water transport, soil moisture is often the limiting factor in Sphagnum production, and hence peat accumulation. While several hydrological models of peat physics and peatland water movement exist, these models do not readily interface with observations and models of peatland carbon accumulation. A conflict of approaches exists, where hydrological studies primarily utilize variables such as hydraulic head, while ecological models of Sphagnum growth adopt the coarse hydrological variables of water table (WT), volumetric water content (VWC) or gravimetric water content (WC). This review examines the potential of soil pressure head as a measurement to link the hydrological and ecological functioning of Sphagnum in peatlands. The non-vascular structure of Sphagnum mosses and the reliance on external capillary transport of water in the mosses make them an ideal candidate for this approach. The main advantage of pressure head is the ability to mechanistically link plot-scale hydrology to cellular-scale water requirements and carbon exchange. Measurement of pressure head may improve photosynthetic process representation in the next generation of peatland models. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    Prey protein influences growth and decoration building in the orb web spider Argiope keyserlingi

    Abstract. 1. Protein is important for a foraging animal to consume, as it promotes growth and enhances survival, particularly in web-building spiders, which need to invest considerable protein into web building and may trade-off growth for web investment. 2. The influence of dietary protein uptake on growth and web investment was tested in the orb web spider Argiope keyserlingi, by feeding them flies reared on three different media: (1) high protein, (2) low protein, and (3) standard (control) media. There was a negative correlation between protein and energy content of the flies across treatments; flies reared on the high protein media had the highest protein, but lowest energy, while flies reared on the low protein media had the lowest protein but highest energy. 3. It was found that silk investment and web architecture in A. keyserlingi was not affected by diet. Growth and decoration building were both enhanced when spiders were fed a high protein diet. 4. It was concluded that protein intake, rather than energy, influenced both growth and decoration building because: (1) protein intake enhances growth in other animals, (2) protein is essential for silk synthesis, especially aciniform silk, and (3) protein is a limiting factor actively sought by foraging animals in natural environments. [source]

    Mechanical innovation in the industrial revolution: the case of plough design

    Liam Brunt
    Variations in levels of embodied technology generated variations in English plough prices in 1770. Using plough prices as a quality index, this article explains size and daily output of plough teams. It shows that variations in plough technology were due to technological change,not static optimization,and village plough technology was influenced by neighbouring villages. But technological advance was not constrained on the demand size: farmers purchased the best ploughs available. Rather, local supply of technology was the limiting factor. Technological change, urbanization, and information networks are rejected as explanations of local supply of technology. The key factor was market density. [source]

    ESCI award lecture: from a little mouse to rationale medicine for bone loss

    A. Leibbrandt
    Abstract Completion of the human genome is one of the many significant milestones in the new era of systems biology. The current phase of genomic studies is focused upon parsing this new found genetic data with respect to scientific interest, and economic and health impact applications. As the sequences are now available and whole genome single nucleotide polymorphism maps for multiple human diseases will be available with the advent of modern genomics, the big challenge is to determine the function of these genes in the context of the entire organism. The emphasis is therefore on functional genomic analysis that represents the new front-line and limiting factor for realizing potential benefits of genome-based science. Defined gene targeting has been proven to be particularly useful as loss of expression mutants can reveal essential functions of molecules and the pathogenesis of disease. Using gene-targeted mice, my group has over the years identified genes that control heart and lung functions [1,5]; apoptosis [6,9]; lymphocyte activation [10,14]; cancer [15,17]; pain [18]; diabetes [19]; fertility [20] or wound healing [21]. In this study, I would like to review our work on RANKL in more detail. [source]

    Expression of PRiMA in the mouse brain: membrane anchoring and accumulation of ,tailed' acetylcholinesterase

    Noël A. Perrier
    Abstract We analysed the expression of PRiMA (proline-rich membrane anchor), the membrane anchor of acetylcholinesterase (AChE), by in situ hybridization in the mouse brain. We compared the pattern of PRiMA transcripts with that of AChE transcripts, as well as those of choline acetyltransferase and M1 muscarinic receptors which are considered pre- and postsynaptic cholinergic markers. We also analysed cholinesterase activity and its molecular forms in several brain structures. The results suggest that PRiMA expression is predominantly or exclusively related to the cholinergic system and that anchoring of cholinesterases to cell membranes by PRiMA represents a limiting factor for production of the AChE tailed splice variant (AChET),PRiMA complex, which represents the major AChE component in the brain. This enzyme species is mostly associated with cholinergic neurons because the pattern of PRiMA mRNA expression largely coincides with that of ChAT. We also show that, in both mouse and human, PRiMA proteins exist as two alternative splice variants which differ in their cytoplasmic regions. [source]

    Complementation of NADPH oxidase in p67-phox-deficient CGD patients

    FEBS JOURNAL, Issue 4 2000
    p67-phox/p40-phox interaction
    Chronic granulomatous disease (CGD) is due to a functional defect of the O2, generating NADPH oxidase of phagocytes. Epstein,Barr-virus-immortalized B lymphocytes express all the constituents of oxidase with activity 100 times less than that of neutrophils. As in neutrophils, oxidase activity of Epstein,Barr-virus-immortalized B lymphocytes was shown to be defective in the different forms of CGD; these cells were used as a model for the complementation studies of two p67-phox-deficient CGD patients. Reconstitution of oxidase activity was performed in vitro by using a heterologous cell-free assay consisting of membrane-suspended or solubilized and purified cytochrome b558 that was associated with cytosol or with the isolated cytosolic-activating factors (p67-phox, p47-phox, p40-phox) from healthy or CGD patients. In p67-phox-deficient CGD patients, two cytosolic factors are deficient or missing: p67-phox and p40-phox. Not more than 20% of oxidase activity was recovered by complementing the cytosol of p67-phox-deficient patients with recombinant p67-phox. On the contrary, a complete restoration of oxidase activity was observed when, instead of cytosol, the cytosolic factors were added in the cell-free assay after isolation in combination with cytochrome b558 purified from neutrophil membrane. Moreover, the simultaneous addition of recombinant p67-phox and recombinant p40-phox reversed the previous complementation in a p40-phox dose-dependent process. These results suggest that in the reconstitution of oxidase activity, p67-phox is the limiting factor; the efficiency of complementation depends on the membrane tissue and the cytosolic environment. In vitro, the transition from the resting to the activated state of oxidase, which results from assembling, requires the dissociation of p40-phox from p67-phox for efficient oxidase activity. In the process, p40-phox could function as a negative regulatory factor and stabilize the resting state. [source]

    Controlling Photoactivity in Ultrathin Hematite Films for Solar Water-Splitting

    Florian Le Formal
    Abstract A promising route to increase the performance of hematite (,-Fe2O3) photoelectrodes for solar hydrogen production through water-splitting is to use an extremely thin layer of this visible light absorber on a nanostructured scaffold. However, the typically poor performance of ultrathin (ca. 20,nm) films of hematite has been the limiting factor in implementing this approach. Here, the surprising effect of a substrate pretreatment using tetraethoxysilicate (TEOS) is reported; it results in drastic improvements in the photoperformance of 12.5,nm thick films of hematite. These films exhibit a water oxidation photocurrent onset potential at 1.1,V versus the reversible hydrogen electrode (vs. RHE) and a plateau current of 0.63,mA cm,2 at 1.5,V vs. RHE under standard illumination conditions, representing the highest reported performance for ultrathin hematite films. In contrast, almost no photoactivity is observed for the photoanode with the same amount of hematite on an untreated substrate. A detailed study of the effects of the TEOS treatment shows that a monolayer of SiOx is formed, which acts to change the hematite nucleation and growth mechanism, increases its crystallinity, reduces the concentration of carrier trapping states of the ultrathin films, and suggests its further application to quantum-dot and extremely-thin-absorber (ETA)-type solar cells. [source]

    Drought changes phosphorus and potassium accumulation patterns in an evergreen Mediterranean forest

    FUNCTIONAL ECOLOGY, Issue 2 2007
    Summary 1Climate models predict more extreme weather in Mediterranean ecosystems, with more frequent drought periods and torrential rainfall. These expected changes may affect major process in ecosystems such as mineral cycling. However, there is a lack of experimental data regarding the effects of prolonged drought on nutrient cycling and content in Mediterranean ecosystems. 2A 6-year drought manipulation experiment was conducted in a Quercus ilex Mediterranean forest. The aim was to investigate the effects of drought conditions expected to occur over the coming decades, on the contents and concentrations of phosphorus (P) and potassium (K) in stand biomass, and P and K content and availability in soils. 3Drought (an average reduction of 15% in soil moisture) increased P leaf concentration by 18·2% and reduced P wood and root concentrations (30·9% and 39·8%, respectively) in the dominant tree species Quercus ilex, suggesting a process of mobilization of P from wood towards leaves. The decrease in P wood concentrations in Quercus ilex, together with a decrease in forest biomass growth, led to an overall decrease (by approximately one-third) of the total P content in above-ground biomass. In control plots, the total P content in the above-ground biomass increased 54 kg ha,1 from 1999 to 2005, whereas in drought plots there was no increase in P levels in above-ground biomass. Drought had no effects on either K above-ground contents or concentrations. 4Drought increased total soil soluble P by increasing soil soluble organic P, which is the soil soluble P not directly available to plant capture. Drought reduced the ratio of soil soluble inorganic P : soil soluble organic P by 50% showing a decrease of inorganic P release from P bound to organic matter. Drought increased by 10% the total K content in the soil, but reduced the soil soluble K by 20·4%. 5Drought led to diminished plant uptake of mineral nutrients and to greater recalcitrance of minerals in soil. This will lead to a reduction in P and K in the ecosystem, due to losses in P and K through leaching and erosion, if the heavy rainfalls predicted by IPCC (Intergovernmental Panel on Climate Change) models occur. As P is currently a limiting factor in many Mediterranean terrestrial ecosystems, and given that P and K are necessary for high water-use efficiency and stomata control, the negative effects of drought on P and K content in the ecosystem may well have additional indirect negative effects on plant fitness. [source]

    Phase transitions and heat conduction in post-glacial rebound

    M. E. Tamisiea
    Summary We have developed a method for including phase boundary conditions into post-glacial rebound models that allows for conduction of latent heat away from the boundary. This method returns the chemical boundary results if latent heat conducts away from the phase boundary too slowly to allow the transition to proceed, as is commonly argued. This is not necessarily the case, however. For example, the secular change of the geoid and the vertical uplift rates for phase boundaries with latent heat conduction can differ from the chemical boundary results by up to 10 and 15 per cent, respectively. When modelling the phase transition, we consider two scenarios: the latent heat is released either at a narrow boundary that separates the two phases or over a thick mixed region of the two phases. In the case where the phase transition occurs over a thick enough region (5,10 km), the final results are close to the results obtained by considering a phase boundary that ignores the release of latent heat completely. This thick boundary formulation also suggest that the phase boundaries could respond nearly instantaneously, changing both the elastic load and body Love numbers. However, we have not considered kinetics, the energetics of the mechanisms of the phase transitions, in this formulation. This work suggests a greater knowledge of the kinetics near equilibrium phase transitions is required. A naive calculation indicates that the kinetics will not be a significant factor for post-glacial rebound but will be a limiting factor for earth tides. [source]

    Experimental evidence for the attenuating effect of SOM protection on temperature sensitivity of SOM decomposition

    GLOBAL CHANGE BIOLOGY, Issue 10 2010
    Abstract The ability to predict C cycle responses to temperature changes depends on the accurate representation of temperature sensitivity (Q10) of soil organic matter (SOM) decomposition in C models for different C pools and soil depths. Theoretically, Q10 of SOM decomposition is determined by SOM quality and availability (referred to here as SOM protection). Here, we focus on the role of SOM protection in attenuating the intrinsic, SOM quality dependent Q10. To assess the separate effects of SOM quality and protection, we incubated topsoil and subsoil samples characterized by differences in SOM protection under optimum moisture conditions at 25 °C and 35 °C. Although lower SOM quality in the subsoil should lead to a higher Q10 according to kinetic theory, we observed a much lower overall temperature response in subsoil compared with the topsoil. Q10 values determined for respired SOM fractions of decreasing lability within the topsoil increased from 1.9 for the most labile to 3.8 for the least labile respired SOM, whereas corresponding Q10 values for the subsoil did not show this trend (Q10 between 1.4 and 0.9). These results indicate the existence of a limiting factor that attenuates the intrinsic effect of SOM quality on Q10 in the subsoil. A parallel incubation experiment of 13C-labeled plant material added to top- and subsoil showed that decomposition of an unprotected C substrate of equal quality responds similarly to temperature changes in top- and subsoil. This further confirms that the attenuating effect on Q10 in the subsoil originates from SOM protection rather than from microbial properties or other nutrient limitations. In conclusion, we found experimental evidence that SOM protection can attenuate the intrinsic Q10 of SOM decomposition. [source]

    Simulating soil-water movement under a hedgerow surrounding a bottomland reveals the importance of transpiration in water balance

    Z. Thomas
    Abstract The objective of this study was to quantify components of the water balance related to root-water uptake in the soil below a hedgerow. At this local scale, a two-dimensional (2D) flow domain in the x,z plane 6 m long and 1·55 m deep was considered. An attempt was made to estimate transpiration using a simulation model. The SWMS-2D model was modified and used to simulate temporally and spatially heterogeneous boundary conditions. A function with a variable spatial distribution of root-water uptake was considered, and model calibration was performed by adjusting this root-water uptake distribution. Observed data from a previous field study were compared against model predictions. During the validation step, satisfactory agreement was obtained, as the difference between observed and modelled pressure head values was less than 50 cm for 80% of the study data. Hedge transpiration capacity is a significant component of soil-water balance in the summer, when predicted transpiration reaches about 5·6 mm day,1. One of the most important findings is that hedge transpiration is nearly twice that of a forest canopy. In addition, soil-water content is significantly different whether downslope or upslope depending on the root-water uptake. The high transpiration rate was mainly due to the presence of a shallow water table below the hedgerow trees. Soil-water content was not a limiting factor for transpiration in this context, as it could be in one with a much deeper water table. Hedgerow tree transpiration exerts a strong impact not only on water content within the vadose zone but also on the water-table profile along the transect. Results obtained at the local scale reveal that the global impact of hedges at the catchment scale has been underestimated in the past. Transpiration rate exerts a major influence on water balance at both the seasonal and annual scales for watersheds with a dense network of hedgerows. Copyright © 2007 John Wiley & Sons, Ltd. [source]

    Hydrology as a policy-relevant science

    Kuniyoshi Takeuchi
    Abstract Water is now a global political agenda and water science is part of it. The United Nations Millennium Development Goals (MDGs) in 2000, the World Summit on Sustainable Development in 2002, the 3rd World Water Forum and Ministerial Conference in Kyoto in 2003 and the G8 Summit in Evian in 2003 were all concerned about urgent global water issues and call for international scientific research collaboration. Hydrology is responding to such political commitments with various scientific initiatives that include the International Association of Hydrological Sciences (IAHS) Predictions in Ungauged Basins (PUB), the Global Energy and Water Circulation Experiments (GEWEX) Coordinated Enhanced Observation Period (CEOP), and the Global Water Systems Project (GWSP). These initiatives will play key roles in the implementation of the new intergovernmental project, Global Earth Observing System of Systems, under preparation by Global Observation Summits from 2003 to 2005. In order to achieve the MDGs, hydrological science has to play a major role supporting policy makers by overcoming methodological obstacles and providing the necessary information. This paper emphasizes that: the availability of ground measurements is a limiting factor that prevents the full use of scientific knowledge; hydrology has to integrate and downscale the various global information into local-scale information useful for river basin management; as the availability of professional personnel is in critical short supply, in addition to funds needed, to achieve the MDGs any scientific research should always accompany capacity-building programmes to close the science divide between developed and developing nations. Copyright © 2004 John Wiley & Sons, Ltd. [source]

    Reconstruction of a 1436-year soil moisture and vegetation water use history based on tree-ring widths from Qilian junipers in northeastern Qaidam Basin, northwestern China

    Zhi-Yong Yin
    Abstract Tree-ring widths have been used widely in studies of environmental changes and reconstructions of past climate. Eleven tree-ring chronologies of approximately 800,1500 years long were developed from Qilian junipers (Sabina przewalskii Kom.) for northeastern Qaidam Basin, along the margin of the Qinghai,Tibetan Plateau. Previous studies have revealed that water usage stress is the most limiting factor for tree growth in the study region. To evaluate the impact of the combined effects of temperature and precipitation changes over time, we performed water balance modelling using 1955,2002 meteorological data. We found that the tree-ring widths were strongly correlated with variables representing soil moisture conditions obtained from the water balance model. Specifically we considered actual evapotranspiration (AE) to represent the combined effect of water use demand and moisture availability, deficit as the difference between potential evapotranspiration (PE) and AE to represent the severity of water use stress, and relative soil moisture as the measure of moisture availability. For certain individual monthly and seasonal combinations, the tree-ring chronologies explained up to 80% of the variation in the soil moisture variables in regression analysis, indicating very good potential for reconstruction of regional soil moisture conditions in the past. These soil moisture variables outperformed precipitation and Palmer's drought severity index in most cases. We reconstructed the soil moisture conditions from 566 AD to 2001, which revealed major dry and wet periods and a general trend toward a wetter condition during the most recent 300 years. By comparing with other proxies in the region, we concluded that the moisture conditions reconstructed from tree-ring widths very well reflected the climate variability at the interannual and interdecadal scales. Copyright © 2007 Royal Meteorological Society [source]

    Absorption kinetics of oxygen scavengers

    Gaurav Tewari
    The oxygen (O2) absorption kinetics of six commercial O2 scavengers were studied. The scavengers were placed in bags which were filled with 240 mL of air, 4.5 L N2 + 15 mL of air, or 3.5 L CO2 + 9 mL of air. The O2 concentration in each bag was measured at hourly intervals for 8 h. The effects of variability among individual scavengers, initial O2 concentrations of 20% or 500 ppm (0.05%), temperatures of 25, 12, 2 or ,1.5 °C, and scavenger capacity on the O2 absorption rate were determined. In addition, the effect of placing scavengers within over-wrapped trays within bags, was examined. Rates of O2 absorption varied by factors of up to 2 between individual O2 scavengers of the same type, but rates of absorption by groups of four scavengers of the same type were similar. Low temperatures gave longer O2 half-life when compared with those at higher temperatures, e.g. O2 half-lives of 7.1 and 1.0 h at ,1.5 and 25 °C, respectively, were obtained for one scavenger type. Shorter O2 half-lives were obtained in air than in N2 atmospheres at the same temperature, e.g. O2 half-lives of 1.0 and 3.3 h in air and N2 at 25 °C, respectively, were obtained for one scavenger type. The O2 absorption reactions were of first order for both high and low initial O2 concentrations. However, O2 concentration was the primary limiting factor for O2 absorption in atmospheres having O2 concentration of 500 ppm because of the dominance of diffusion. Scavengers, when placed within over-wrapped trays within bags had up to 12 times longer O2 half-lives, indicating that the O2 permeable film acts as an O2 barrier when pack atmosphere has low O2 concentrations. To obtain consistent and reproducible results, it is recommended that multiple scavengers be used in a packaging system. The appropriate number should be based on scavenger type, desired O2 absorption rate, storage temperature, and pack atmosphere (air/N2/CO2). [source]

    Life-long protein malnutrition in the rat (Rattus norvegicus) results in altered patterns of craniofacial growth and smaller individuals

    JOURNAL OF ANATOMY, Issue 6 2006
    Shannon L. Lobe
    Abstract Dietary protein is a limiting factor in mammalian growth, significantly affecting the non-linear trajectories of skeletal growth. Young females may be particularly vulnerable to protein malnutrition if the restriction is not lifted before they become reproductive. With such early malnutrition, limited amino acids would be partitioned between two physiological objectives, successful reproduction vs. continued growth. Thus, the consequences of protein malnutrition could affect more than one generation. However, few studies have quantified these cross-generational effects. Our objective was to test for differences in skeletal growth in a second generation of malnourished rats compared with rats malnourished only post-weaning, the first generation and with controls. In this longitudinal study we modelled the growth of 22 craniofacial measurements with the logistic Gompertz equation, and tested for differences in the equation's parameters among the diet groups. The female offspring of post-weaning malnourished dams did not catch up in size to the first generation or to controls, although certain aspects of their craniofacial skeleton were less affected than others. The second generation's growth trajectories resembled the longer and slower growth of the first malnourished generation. There was a complex interaction between developmental processes and early nutritional environment, which affected variation of adult size. [source]

    Computing simplifications for non-additive genetic models

    L. R. Schaeffer
    Summary A limiting factor in the analysis of non-additive genetic models has been the ability to compute the inverses of non-additive genetic covariance matrices for large populations. Also, the order of the equations was equal to the number of animals times the number of non-additive genetic effects that were included in the model. This paper describes a computing algorithm that avoids the inverses of the non-additive genetic covariance matrices and keeps the size of the equations to be the same as any animal model with only additive genetic effects. Quadratic forms for the non-additive genetic variances could also be computed without the inverses of the non-additive genetic covariance matrices. Zusammenfassung In der Analyse von nicht additiven genetischen Modellen war der limitierende Faktor die Fähigkeit Inversen der Matrizen nicht additiver genetischer Kovarianzen in großen Populationen zu berechnen. Auch die Reihenfolge der Gleichungen war gleich zu der Anzahl der Tiere mal der Anzahl der nicht additiven genetischen Effekte, die im Model berücksichtigt wurden. Diese Veröffentlichung beschreibt einen Berechnungsalgorithmus, der die Umkehrung der Matrizen nicht additiver genetischer Kovarianzen umgeht und die Gleichungen auf der selben Größe hält wie ein Tiermodel mit additiven genetischen Effekten. Auch quadratische Formen für nicht additive genetische Kovarianzen können ohne die Umkehrung der Matrizen nicht additiver genetischer Kovarianzen berechnet werden. [source]

    Can the limited marsupium space be a limiting factor for Syngnathus abaster females?

    Insights from a population with size-assortative mating
    Summary 1Some syngnathid species show varying degrees of sex role reversal aside from male pregnancy, with females competing for access to mates and sometimes presenting conspicuous secondary sexual characters. Among other variables, brooding space constraints are usually considered a key element in female reproductive success, contributing strongly to the observed morphological and behavioural sexual differences. Nevertheless, a close relationship between sex role reversal and male brooding space limitation has not yet been accurately demonstrated in field studies. 2The present work, conducted over two consecutive breeding seasons in a wild population of the sex role-reversed pipefish Syngnathus abaster, simultaneously analysed egg number and occupied space, as well as the free area in the male's marsupium. The number of eggs that would fit in the observed unoccupied space was estimated. 3Contrary to what would be expected, given the marked sexual dimorphism observed in the population studied, where females were larger and more colourful, male brooding space did not appear to limit female reproduction as neither large nor small individuals presented a fully occupied pouch. Interestingly, the largest unoccupied areas of marsupium were found in the larger individuals, although they received more and larger eggs. Laboratory data also showed that larger females lay larger eggs. 4Together, these results suggest the existence of assortative mating, which may result from: (i) the reluctance of larger males (which tend not to receive small eggs usually laid by small females) to mate with lower quality females, even at the expense of a smaller number of offspring; or (ii) female,female competition, which might strongly reduce the hypothesis of a small female mating with a large male. The potential impact of temperature on reproduction and population dynamics is also discussed in the light of ongoing climatic changes. [source]

    The role of competition in adaptive radiation: a field study on sequentially ovipositing host-specific seed predators

    Laurence Després
    Summary 1We propose an alternative model to the host-shifting model of sympatric speciation in plant,insect systems. The role of competition in driving ecological adaptive radiation was evaluated in a seed predator exploiting a single host-plant species. Sympatric speciation may occur through disruptive selection on oviposition timing if this shift decreases competition among larvae feeding on seeds. 2The globeflower fly Chiastocheta presents a unique case of adaptive radiation, with at least six sister species co-developing in fruits of Trollius europaeus. These species all feed on seeds, and differ in their oviposition timing, one species ovipositing in 1-day-old flowers (early species), while all the other species sequentially oviposit throughout the flower life span (late species). We evaluated the impact of conspecific and heterospecific larvae on larval installation success, and on larval fresh mass and area, for early and late species, in natural conditions. 3None of the three larval traits measured was correlated with fruit size, and no fruit lost all seeds to predation, suggesting that seed availability was not a limiting factor for larval development. 4Our results show strong intraspecific competition among early larvae for larval installation, and among late larvae for larval mass. By contrast, larval competition between species was weak. These results are consistent with the hypothesis that shifts in oviposition promoted rapid radiation in globeflower flies by lowering competition among larvae. [source]

    Raptor predation and population limitation in red grouse

    Simon J. Thirgood
    Summary 1.,We assessed the impact of predation by hen harriers and peregrine falcons on a red grouse population in southern Scotland during 1992,98. Grouse density in April, July and October declined during this time, coincident with an increase in the numbers of breeding harriers and peregrines. 2.,Winter losses of grouse between October and April averaged 33% and were density-dependent. Raptors were the cause of about 70% of winter mortality and they killed about 30% of the grouse present in October. We were unable to determine whether winter mortality in raptors was additive to other losses. 3.,Summer losses of adult grouse between April and July averaged 30% and were density-dependent. Raptors were the cause of more than 90% of the early summer mortality of adult grouse. Summer losses of grouse chicks between May and July averaged 45% and were not density-dependent. Harriers killed about 28% of grouse chicks by late July and about 37% by the end of August. Summer raptor predation on adult grouse and chicks appeared to be largely additive to other losses and we estimated that it reduced autumn grouse densities by about 50%. 4.,A model combining the estimated reduction in autumn grouse density caused by raptors with the observed density dependence in winter loss predicted that, in the absence of raptors for 2 years, grouse density in spring would be 1·9 times greater, and grouse density in autumn 3·9 times greater, than in the presence of raptors. The model suggested that raptor predation prevented the grouse population from increasing and was thus a limiting factor. [source]

    Earlywood vessel size of oak as a potential proxy for spring precipitation in mesic sites

    Patrick Fonti
    Abstract Aim, In this study, we evaluate the importance of the mean earlywood vessel size of oaks as a potential proxy for climate in mesic areas. Location, The study was conducted in Switzerland at three forest sites dominated by oak (Quercus petraea and Q. pubescens). The three sites were in different climatic zones, varying mainly in terms of precipitation regime. Methods, Three 50-year-long site chronologies of mean earlywood vessel size and tree-ring widths were obtained at each site and related to monthly meteorological records in order to identify the main variables controlling growth. The responses of mean vessel size to climate were compared with those of the width variables to evaluate the potential climatic information recorded by the earlywood vessels. Results, The results show that the mean vessel size has a different and stronger response to climate than ring-width variables, although its common signal and year-to-year variability are lower. This response is better in particular at mesic sites, where it is linked to precipitation during spring, i.e. at the time of vessel formation, and is probably related to the occurrence of only a few processes controlling vessel growth, whereas radial increment is controlled by multiple and varying factors. Main conclusions, The mean earlywood vessel size of oak appears to be a promising proxy for future climate reconstructions of mesic sites, where radial growth is not controlled by a single limiting factor. [source]

    Climatic limits for the present distribution of beech (Fagus L.) species in the world

    Jingyun Fang
    Abstract Aim, Beech (Fagus L., Fagaceae) species are representative trees of temperate deciduous broadleaf forests in the Northern Hemisphere. We focus on the distributional limits of beech species, in particular on identifying climatic factors associated with their present range limits. Location, Beech species occur in East Asia, Europe and West Asia, and North America. We collated information on both the southern and northern range limits and the lower and upper elevational limits for beech species in each region. Methods, In total, 292 lower/southern limit and 310 upper/northern limit sites with available climatic data for all 11 extant beech species were collected by reviewing the literature, and 13 climatic variables were estimated for each site from climate normals at nearby stations. We used principal components analysis (PCA) to detect climatic variables most strongly associated with the distribution of beech species and to compare the climatic spaces for the different beech species. Results, Statistics for thermal and moisture climatic conditions at the lower/southern and upper/northern limits of all world beech species are presented. The first two PCA components accounted for 70% and 68% of the overall variance in lower/southern and upper/northern range limits, respectively. The first PCA axis represented a thermal gradient, and the second a moisture gradient associated with the world-wide distribution pattern of beech species. Among thermal variables, growing season warmth was most important for beech distribution, but winter low temperature (coldness and mean temperature for the coldest month) and climatic continentality were also coupled with beech occurrence. The moisture gradient, indicated by precipitation and moisture indices, showed regional differences. American beech had the widest thermal range, Japanese beeches the most narrow; European beeches occurred in the driest climate, Japanese beeches the most humid. Climatic spaces for Chinese beech species were between those of American and European species. Main conclusions, The distributional limits of beech species were primarily associated with thermal factors, but moisture regime also played a role. There were some regional differences in the climatic correlates of distribution. The growing season temperature regime was most important in explaining distribution of Chinese beeches, whilst their northward distribution was mainly limited by shortage of precipitation. In Japan, distribution limits of beech species were correlated with summer temperature, but the local dominance of beech was likely to be dependent on snowfall and winter low temperature. High summer temperature was probably a limiting factor for southward extension of American beech, while growing season warmth seemed critical for its northward distribution. Although the present distribution of beech species corresponded well to the contemporary climate in most areas, climatic factors could not account for some distributions, e. g., that of F. mexicana compared to its close relative F. grandifolia. It is likely that historical factors play a secondary role in determining the present distribution of beech species. The lack of F. grandifolia on the island of Newfoundland, Canada, may be due to inadequate growing season warmth. Similarly, the northerly distribution of beech in Britain has not reached its potential limit, perhaps due to insufficient time since deglaciation to expand its range. [source]

    Bioclimatic perspectives in the distribution of Quercus ithaburensis Decne. subspecies in Turkey and in the Levant

    Jean-Marc Dufour-Dror
    Abstract Aim, To define the bioclimatic tolerance ranges of the two Tabor oak subspecies. Prior to this definition, and considering the confusion in the literature regarding the Tabor oak subspecies geography, a reassessment of their present distribution is proposed. Location, Turkey and the Levant. Methods, The bioclimatic tolerance range of each subspecies was characterized by four parameters: (1) the humidity category (Q2), (2) the winter variant (m) , the two basic variables used in Emberger's method for the definition of Mediterranean bioclimates, (3) the length of the dry season (LDS) and (4) its severity, expressed by the dry season water deficit (DSWD). The reference to the last two variables in the definition of bioclimatic tolerance ranges of Mediterranean species has so far never been considered. The concept of bioclimatic niche, based on the reference to these four parameters, is proposed and discussed. Results, The reassessment of the Tabor oak subspecies distribution shows that their extents of occurrence do not overlap and are significantly distant. The comparison between the characteristics of each subspecies bioclimatic niche has highlighted three major differences: (1) The bioclimatic niche of the subspecies macrolepis is characterized by a great heterogeneity as it includes up to 10 distinct bioclimate types, whereas only four types have been found in the bioclimatic niche of the subspecies ithaburensis. (2) A 10 °C gap has been found between the winter variants of both bioclimatic niches. (3) The third major difference relates to the dry season characteristics: the bioclimatic niche of the subspecies ithaburensis is characterized by an LDS 40,75% longer than it is in the bioclimatic niche of the subspecies macrolepis. Moreover, and surprisingly, although the most arid humidity categories are found in the bioclimatic niche of the subspecies macrolepis, the bioclimatic niche of the subspecies ithaburensis is characterized by a significantly more severe dry season as the DSWD is 36,180% greater than in the bioclimatic niche of the subspecies macrolepis. It is suggested that the duration and the severity of the dry season is a major limiting factor in the spatial distribution of the subspecies macrolepis. Main conclusions, The reference to the duration (LDS) and severity (DSWS) of the dry season is essential when defining the bioclimatic niche of Mediterranean species. [source]

    Trade Credit Terms Offered by Small Firms: Survey Evidence and Empirical Analysis

    Nicholas Wilson
    Trade credit has been shown to be an important source of short-term finance for smaller firms but small firms are also suppliers of trade credit. There is little empirical evidence on the credit granting decisions of small firms. Previous empirical work (Petersen and Rajan, 1997; and Ng, Smith and Smith, 1999) has focused on credit granting and investment in accounts receivable in larger firms. In this paper we look at the influences on credit granting for the smallest firms, using a sample of firms with an average of 10 employees. As in previous studies we find that product and demand characteristics influence credit terms. Moreover, we find evidence that firm size affects credit extension choices directly by setting limits on the possibilities for economies of scale, but it also impacts indirectly by affecting the firm's access to finance and its bargaining strength vis-à-vis suppliers. The dominant position of larger customers in bargaining with small suppliers constrains the impact of other factors on the firm's choice of credit terms. Small firms are also under pressure to conform to industry norms, although lack of resources can be a limiting factor. Constrained firms may make use of two-part terms in an attempt to improve their cashflow. [source]

    Control of human articular chondrocyte differentiation by reduced oxygen tension

    Christopher L. Murphy
    Cell number is often a limiting factor in studies of chondrocyte physiology, particularly for human investigations. Chondrocytes can be readily proliferated in monolayer culture, however, differentiated phenotype is soon lost. We therefore endeavored to restore normal phenotype to human chondrocytes after serial passage in monolayer culture by manipulating cell morphology and oxygen tension towards the in vivo state. Third passage cells were encapsulated in alginate and exposed to either 20% or more physiologic 5% oxygen tensions. To assess cell phenotype, gene expression was measured using TaqMan real-time PCR. Encapsulated, primary chondrocytes cultured in 20% oxygen were used as a positive reference. Passaged human chondrocytes were fibroblastic in appearance and had lost normal phenotype as evidenced by a decrease in expression of collagen II, aggrecan, and sox9 genes of 66, 6, and 14 fold, respectively; with concomitant high expression of type I collagen (22 fold increase). A partial regaining of the differentiated phenotype was observed by encapsulation in 20% oxygen; however, even after 4 weeks, collagen II gene expression was not fully restored. Collagen II and aggrecan expression were increased, on average, 3 fold, in 5% oxygen tension compared to 20% cultures. Furthermore, matrix glycosaminoglycan (GAG) levels were significantly increased in reduced oxygen. In fact, after 4 weeks in 5% oxygen, encapsulated third passage cells had collagen II expression fully regained and aggrecan and sox9 levels actually exceeding primary cell levels in 20% oxygen. Our results show that the phenotype of serially passaged human articular chondrocytes is more fully restored by combining encapsulation with culture in more physiological levels of oxygen. Sox9, an essential transcription factor for chondrocyte differentiation is strongly implicated in this process since its expression was upregulated almost 27 fold. These findings have implications for the optimal conditions for the in vitro culture of chondrocytes. © 2004 Wiley-Liss, Inc. [source]

    Factors affecting the distribution patterns of zebra and wildebeest in a resource-stressed environment

    Rosemary Groom
    Abstract Understanding the spatial dynamics of landscape use by free-ranging herbivores is integral for successful ecosystem management. We used binary logistic regression analyses to determine the relative importance of biotic, abiotic and human factors in influencing the distribution (presence/absence) of wild grazers on two Maasai ranches in Kenya's Amboseli-Tsavo ecosystem. Both ranches had low grass biomass and suffered from regular droughts. We found that grazers consistently located themselves where grass biomass was highest, usually irrespective of grass quality, suggesting that forage quantity may be the limiting factor where grass biomass is generally low. The availability of surface water had no significant effect on the likelihood of grazers being present, even in the dry season. Résumé La bonne compréhension de la dynamique spatiale de l'utilisation du paysage par les herbivores qui paissent en liberté fait partie intégrante de la gestion réussie d'un écosystème. Nous avons employé des analyses de régression logistique binaire pour déterminer l'importance relative des facteurs biotiques, abiotiques et humains dans l'influence sur la distribution (présence/absence) d'herbivores sauvages sur deux ranches masaï de l'écosystème Amboseli-Tsavo, au Kenya. Les deux ranches avaient une faible biomasse herbeuse et souffraient de sécheresses régulières. Nous avons découvert que les herbivores brouteurs se trouvaient de façon constante là où la biomasse herbeuse était la plus grande, sans tenir compte, d'habitude, de la qualité de l'herbe; ceci suggère que la quantité de fourrage pourrait être le facteur imitant là où la biomasse herbeuse est généralement faible. La disponibilité de l'eau de surface n'avait pas d'effet significatif sur la probabilité de la présence des herbivores, même en saison sèche. [source]