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Poor Predictor (poor + predictor)
Selected AbstractsUsefulness and Limitation of Dobutamine Stress Echocardiography to Predict Acute Response to Cardiac Resynchronization TherapyECHOCARDIOGRAPHY, Issue 1 2010F.R.C.P.C., Mario Sénéchal M.D. Background: It has been hypothesized that a long-term response to cardiac resynchronization therapy (CRT) could correlate with myocardial viability in patients with left ventricular (LV) dysfunction. Contractile reserve and viability in the region of the pacing lead have not been investigated in regard to acute response after CRT. Methods: Fifty-one consecutive patients with advanced heart failure, LV ejection fraction , 35%, QRS duration > 120 ms, and intraventricular asynchronism , 50 ms were prospectively included. The week before CRT implantation, the presence of viability was evaluated using dobutamine stress echocardiography. Acute responders were defined as a ,15% increase in LV stroke volume. Results: The average of viable segments was 5.8 ± 1.9 in responders and 3.9 ± 3 in nonresponders (P = 0.03). Viability in the region of the pacing lead had an excellent sensitivity (96%), but a low specificity (56%) to predict acute response to CRT. Mitral regurgitation (MR) was reduced in 21 patients (84%) with acute response. The presence of MR was a poor predictor of response (sensibility 93% and specificity 17%). However, combining the presence of MR and viability in the region of the pacing lead yields a sensibility (89%) and a specificity (70%) to predict acute response to CRT. Conclusion: Myocardial viability is an important factor influencing acute hemodynamic response to CRT. In acute responders, significant MR reduction is frequent. The combined presence of MR and viability in the region of the pacing lead predicts acute response to CRT with the best accuracy. (Echocardiography 2010;27:50-57) [source] An ecological law and its macroecological consequences as revealed by studies of relationships between host densities and parasite prevalenceECOGRAPHY, Issue 3 2001Per ArnebergArticle first published online: 30 JUN 200 Epidemiological models predict a positive relationship between host population density and abundance of macroparasites. Here I test these by a comparative study. I used data on communities of four groups of parasites inhabiting the gastrointestinal tract of mammals, nematodes of the orders Oxyurida, Ascarida, Enoplida and Spirurida, respectively. The data came from 44 mammalian species and represent examination of 16 886 individual hosts. I studied average prevalence of all nematodes within an order in a host species, a measure of community level abundance, and considered the potential confounding effects of host body weight, fecundity, age at maturity and diet. Host population density was positively correlated with parasite prevalence within the order Oxyurida, where all species have direct life cycles. Considering the effects of other variables did not change this. This supports the assumption that parasite transmission rate generally is a positive function of host population density. It also strengthens the hypothesis that host densities generally act as important determinants of species richness among directly transmitted parasites and suggests that negative influence of such parasites on host population growth rate increase with increasing host population density among host species. Within the other three nematode orders, where a substantial number of the species have indirect life cycles, no relationships between prevalence and host population density were seen. Again, considering the effects of other variables did not affect this conclusion. This suggests that host population density is a poor predictor of species richness of indirectly transmitted parasites and that effects of such parasites on host population dynamics do not scale with host densities among species of hosts. [source] AN EXACT FORM OF THE BREEDER'S EQUATION FOR THE EVOLUTION OF A QUANTITATIVE TRAIT UNDER NATURAL SELECTIONEVOLUTION, Issue 11 2005John S. Heywood Abstract Starting with the Price equation, I show that the total evolutionary change in mean phenotype that occurs in the presence of fitness variation can be partitioned exactly into five components representing logically distinct processes. One component is the linear response to selection, as represented by the breeder's equation of quantitative genetics, but with heritability defined as the linear regression coefficient of mean offspring phenotype on parent phenotype. The other components are identified as constitutive transmission bias, two types of induced transmission bias, and a spurious response to selection caused by a covariance between parental fitness and offspring phenotype that cannot be predicted from parental phenotypes. The partitioning can be accomplished in two ways, one with heritability measured before (in the absence of) selection, and the other with heritability measured after (in the presence of) selection. Measuring heritability after selection, though unconventional, yields a representation for the linear response to selection that is most consistent with Darwinian evolution by natural selection because the response to selection is determined by the reproductive features of the selected group, not of the parent population as a whole. The analysis of an explicitly Mendelian model shows that the relative contributions of the five terms to the total evolutionary change depends on the level of organization (gene, individual, or mated pair) at which the parent population is divided into phenotypes, with each frame of reference providing unique insight. It is shown that all five components of phenotypic evolution will generally have nonzero values as a result of various combinations of the normal features of Mendelian populations, including biparental sex, allelic dominance, inbreeding, epistasis, linkage disequilibrium, and environmental covariances between traits. Additive genetic variance can be a poor predictor of the adaptive response to selection in these models. The narrow-sense heritability s,2A/s,2P should be viewed as an approximation to the offspring-parent linear regression rather than the other way around. [source] VICARIANCE AND DISPERSAL ACROSS BAJA CALIFORNIA IN DISJUNCT MARINE FISH POPULATIONSEVOLUTION, Issue 7 2003Giacomo Bernardi Abstract., Population disjunctions, as a first step toward complete allopatry, present an interesting situation to study incipient speciation. The geological formation of the Baja California Peninsula currently divides 19 species of fish into disjunct populations that are found on its Pacific Coast and in the northern part of the Gulf of California (also called the Sea of Cortez), but are absent from the Cape (Cabo San Lucas) region. We studied the genetic makeup of disjunct populations for 12 of these 19 fish species. Phylogeographic patterns for the 12 species can be separated into two major classes: a first group (eight species) showed reciprocal monophyly and high genetic divergence between disjunct populations. A second group (four species) displayed what appeared to be panmictic populations. Population structure between Pacific Coast populations, across the Punta Eugenia biogeographic boundary, was also evaluated. While dispersal potential (inferred by pelagic larval duration) was a poor predictor of population structure between Gulf of California and Pacific populations, we found that population genetic subdivision along the Pacific Coast at Punta Eugenia was always positively correlated with differentiation between Pacific and Gulf of California populations. Vicariant events, ongoing gene flow, and ecological characteristics played essential roles in shaping the population structures observed in this study. [source] Can grazing response of herbaceous plants be predicted from simple vegetative traits?JOURNAL OF APPLIED ECOLOGY, Issue 3 2001Sandra Díaz Summary 1,Range management is based on the response of plant species and communities to grazing intensity. The identification of easily measured plant functional traits that consistently predict grazing response in a wide spectrum of rangelands would be a major advance. 2,Sets of species from temperate subhumid upland grasslands of Argentina and Israel, grazed by cattle, were analysed to find out whether: (i) plants with contrasting grazing responses differed in terms of easily measured vegetative and life-history traits; (ii) their grazing response could be predicted from those traits; (iii) these patterns differed between the two countries. Leaf mass, area, specific area (SLA) and toughness were measured on 83 Argentine and 19 Israeli species. Species were classified by grazing response (grazing-susceptible or grazing-resistant) and plant height (< or > 40 cm) as well as by life history (annual or perennial) and taxonomy (monocotyledon or dicotyledon). 3,Similar plant traits were associated with a specific response to grazing in both Argentina and Israel. Grazing-resistant species were shorter in height, and had smaller, more tender, leaves, with higher SLA than grazing-susceptible species. Grazing resistance was associated with both avoidance traits (small height and leaf size) and tolerance traits (high SLA). Leaf toughness did not contribute to grazing resistance and may be related to selection for canopy dominance. 4,Plant height was the best single predictor of grazing response, followed by leaf mass. The best prediction of species grazing response was achieved by combining plant height, life history and leaf mass. SLA was a comparatively poor predictor of grazing response. 5,The ranges of plant traits, and some correlation patterns between them, differed markedly between species sets from Argentina and Israel. However, the significant relationships between plant traits and grazing response were maintained. 6,The results of this exploratory study suggest that prediction of grazing responses on the basis of easily measured plant traits is feasible and consistent between similar grazing systems in different regions. The results challenge the precept that intense cattle grazing necessarily favours species with tough, unpalatable, leaves. [source] Soil N dynamics in relation to leaf litter quality and soil fertility in north-western Patagonian forestsJOURNAL OF ECOLOGY, Issue 2 2003Patricia Satti Summary 1We examined the relationships among soil N dynamics, soil chemistry and leaf litter quality in 28 forest stands dominated by conifers, woody broad-leaf deciduous species or broad-leaf evergreens. Potential net N mineralization, net nitrification and microbial biomass N were used as indicators of soil N dynamics; pH, organic C, total N, exchangeable cations and extractable P as indicators of soil chemistry and N concentration, lignin concentration, C : N ratio and lignin : N ratio in senescent leaves as indicators of leaf litter quality. N dynamics were assessed in two consecutive years with contrasting precipitation. 2Net N mineralization was lower in stands of the three conifers and one of three broad-leaf evergreen species than in stands of the other six broad-leaf species (40,77 vs. 87,250 mg N kg,1 after 16-week incubations) and higher in the wetter year. 3The proportion of N nitrified was high beneath most species regardless of mineralization rates, soil N fertility and leaf litter quality, and was significantly higher for the wetter year. Ammonium was the predominant form of N in three sites affected by seasonal waterlogging and in two sites the predominant form changed from ammonium in the drier year to nitrate during the wetter year, probably due to differences in soil texture affecting soil moisture. 4Net N mineralization was linearly related to microbial biomass N, implying that the microbial activity per biomass unit was quite similar beneath all species. Constant microbial biomass during the wetter year suggested that as mineralization/nitrification increased, there was a higher potential risk of N losses. 5Although the litter lignin : N ratio allowed differentiation of soil N dynamics between broad-leaf species and conifers, its constant value (23,28) in all broad-leaf species made it a poor predictor of the differences found within this group. Across all sites and between broad-leaf species, soil N dynamics were best explained by a combination of leaf litter lignin and soil chemistry indicators, particularly soil total N for net N mineralization and net nitrification, and soil organic C for microbial biomass N. [source] Thrombin generation time is a novel parameter for monitoring enoxaparin therapy in patients with end-stage renal diseaseJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 2 2006D. F. BROPHY Summary.,Background:,Patients with end-stage renal disease (ESRD) who receive enoxaparin are at increased risk for adverse bleeding episodes. This phenomenon appears to occur despite judicious monitoring of antifactor Xa (aFXa) activity. Better monitoring parameters are needed to quantify the anticoagulant effects of enoxaparin in the ESRD population. Objectives:,The objective of this study was to determine the utility of using thrombin generation time (TGT), platelet contractile force (PCF) and clot elastic modulus (CEM) to monitor the degree of anticoagulation in ESRD subjects, and to compare these results to aFXa activity, the current gold-standard monitoring parameter. Methods:,Eight healthy volunteers without renal dysfunction and eight ESRD subjects were enrolled into this study. Subjects received a single dose of enoxaparin 1 mg kg,1 subcutaneously, and blood samples were obtained for the determination of aFXa activity, TGT, PCF and CEM at baseline, 4, 8, and 12 h postdose. Results:,Baseline, 4, 8, and 12-h aFXa activity concentrations were not different between groups. However, the corresponding TGT at 8 and 12 h was significantly prolonged in the ESRD group (P = 0.04, and P = 0.008, respectively). The 4-h peak TGT trended toward significance (P = 0.06). There were no differences in PCF or CEM across time. Conclusions:,These data suggest that the parameter aFXa activity is a poor predictor of the anticoagulant effect of enoxaparin in patients with ESRD. Thrombin generation time appears to be more sensitive to the antithrombotic effects of enoxaparin in this population. Further large-scale trials are needed to corroborate these data. [source] Antithrombotic Effect of Enoxaparin in Clinically Healthy Cats: A Venous Stasis ModelJOURNAL OF VETERINARY INTERNAL MEDICINE, Issue 1 2010C.M. Van De Wiele Background: Systemic arterial thromboembolic events are a serious complication of cardiac disease in cats. Objectives: To determine if enoxaparin induces an antithrombotic effect in cats at a dosage of 1 mg/kg SC q12h and if this antithrombotic effect is predicted by anti-Xa activity. Animals: Fourteen clinically healthy cats were divided into 3 groups: control (4 cats), treated and assessed at 4 hours (5 cats), and treated and assessed at 12 hours (5 cats). Methods: A venous stasis model was used and the extent of thrombus formation estimated by measuring thrombus weight and accretion of 125I-fibrinogen. Plasma anti-Xa activity was measured in treated cats. Results: There was a significant reduction in thrombus formation in the 4 h group compared with control (median weight, 0.000 versus 0.565 mg/mm, P < .01; median %125I-fibrinogen accretion, 0.0 versus 42.0%, P < .01). There was a reduction in thrombus formation in the 12 h group (median weight, 0.006 mg/mm, P= .09; median %125I-fibrinogen accretion, 3.83%, P= .09) but this reduction was not significant. The median percent thrombus inhibition for treated cats was 100.0% at 4 hours and 91.4% at 12 hours. Plasma anti-Xa activity was not significantly correlated with thrombus formation. Conclusions and Clinical Importance: This pilot study demonstrates that enoxaparin, when administered at a dosage of 1 mg/kg SC q12h, produces an antithrombotic effect in a venous statsis model in clinically healthy cats. Furthermore, this study demonstrates that anti-Xa activity is a poor predictor of enoxaparin's antithrombotic effect. [source] Determinants of Lesion Sizes and Tissue Temperatures During Catheter CryoablationPACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 5 2007MARK A. WOOD M.D. Background:Factors which influence lesion size from catheter-based cryoablation have not been well described. This study describes factors which influence lesion size during catheter cryoablation. Methods and Results:Cryoablation was delivered to porcine left ventricular myocardium in a saline bath using 4- or 8-mm electrode catheters. Ablation was delivered with the electrodes either vertical or horizontal to the tissue and both with and without superfusate flow over the electrode. The effect of electrode contact pressure was tested. Lesion dimensions were measured. All experiments were duplicated to measure tissue temperatures at 1-, 2-, 3-, and 5-mm deep to the ablation electrode. The 8-mm electrode produced lower tissue temperatures and larger lesion volumes when compared with the 4-mm electrode (all P < 0.05). Superfusate flow slowed the rate of tissue cooling, markedly warmed tissue temperatures, and reduced lesion volume when compared with no flow conditions. By linear regression modeling, lesion sizes and tissue temperatures were related to the presence of superfusate flow, electrode orientation, contact pressure and electrode size, or catheter refrigerant flow rate (r2 for models = 0.90,0.96, all P < 0.001). Electrode temperature predicted lesion size or tissue temperatures only when analyzed independent of electrode size or refrigerant flow rate. Conclusions:Lesion sizes and tissue temperatures during catheter cryoablation are related to convective warming, electrode orientation, electrode contact pressure, and any of the following: electrode size, catheter refrigerant flow rate or electrode temperature. However, electrode temperature may be a poor predictor of lesion size and tissue temperature for a given catheter size. [source] The effects of droperidol and ondansetron on dispersion of myocardial repolarization in childrenPEDIATRIC ANESTHESIA, Issue 10 2010DISHA MEHTA BSc Summary Objectives:, To compare the effects of droperidol and ondansetron on electrocardiographic indices of myocardial repolarization in children. Aim:, To refine understanding of the torsadogenic risk to children exposed to anti-emetic prophylaxis in the perioperative period. Background:, QT interval prolongation is associated with torsades des pointes (TdP), but is a poor predictor of drug torsadogenicity. Susceptibility to TdP arises from increased transmural dispersion of repolarization (TDR) across the myocardial wall, rather than QT interval prolongation per se. TDR can be measured on the electrocardiogram as the time interval between the peak and end of the T wave (Tp-e). Tp-e may therefore provide a readily available, noninvasive assay of drug torsadogenicity. The perioperative period is one of high risk for TdP in children with or at risk of long QT syndromes. Droperidol and ondansetron are two drugs commonly administered perioperatively, for prophylaxis of nausea and vomiting, which can prolong the QT interval. This study investigated their effects on myocardial repolarization. Methods:, One hundred and eight ASA1-2 children undergoing elective day-case surgery were randomized to receive droperidol, ondansetron, both or neither. Pre- and post-administration 12-lead electrocardiogram (ECGs) were recorded. QT and Tp-e intervals were measured and compared within and between groups, for the primary endpoint of a 25 ms change in Tp-e. Results:, Eighty children completed the study. There were no demographic or baseline ECG differences between groups. QT intervals lengthened by 10,17 ms after allocated treatments, with no between-group differences. Values remained within normal limits for all groups. Tp-e intervals increased by 0,7 ms, with no between-group differences. There were no instances of dysrhythmia. Conclusions:, Droperidol and ondansetron, in therapeutic anti-emetic doses, produce equivalent, clinically insignificant QT prolongation and negligible Tp-e prolongation, suggesting that neither is torsadogenic in healthy children at these doses. [source] Serum ferritin underestimates liver iron concentration in transfusion independent thalassemia patients as compared to regularly transfused thalassemia and sickle cell patientsPEDIATRIC BLOOD & CANCER, Issue 3 2007Zahra Pakbaz MD Abstract Serum ferritin (SF) and liver iron concentration (LIC), as measured by SQUID biosusceptometry, were assessed in a convenience sample of transfusion independent thalassemia patients (nTx-Thal, n,=,26), regularly transfused thalassemia (Tx-Thal, n,=,89), or sickle cell patients (SCD, n,=,45) to investigate the severity of iron overload and the relationship between SF and LIC in nTx-Thal compared to SCD and Tx-Thal. SF correlated with LIC (RS,=,0.53, P,<,0.001), but was found to be a poor predictor for LIC. SF was significantly lower (P,<,0.001) in nTx-Thal patients than in other groups, despite similar LIC values. The SF-to-LIC ratio was significantly lower in nTx-Thal compared to Tx-Thal and SCD patients (median of 0.32, 0.87, and 1.2, respectively: P,<,0.001). Due to underestimation of LIC by ferritin levels, chelation treatment may be delayed or misdirected in patients with thalassemia intermedia. Pediatr Blood Cancer 2007;49:329,332. © 2007 Wiley-Liss, Inc. [source] Seed production in fens and fen meadows along a disturbance gradientAPPLIED VEGETATION SCIENCE, Issue 3 2009A. Klimkowska Abstract Question: The seed production in several wetland communities across Europe was investigated and differences in seed output in relation to disturbance intensity were tested. The relationship between the vegetation composition and the seed production profile was examined and the results are discussed in relation to restoration. Location: Poland, Germany and the Netherlands. Methods: The seed production in various plant communities was estimated, based on field counts. In addition, records from available databases were used for missing data. Multivariate methods were used to characterize the vegetation and seed production. Communities were grouped according to level of disturbance and tested for differences in seed production. Similarity between vegetation composition and seed profile was examined using the Sørensen index and Spearman correlation coefficient. Results: It was found that the seed production of the studied communities is large, variable and in general increasing with disturbance intensity. The estimated median seed production was ca. 24 × 103 seeds m,2 in fens, 167 × 103 in fen meadows and 556 × 103 seeds m,2 in degraded meadows. The majority of seeds was produced by just a few species. The similarity between the vegetation composition and the seed production profile was low (similarity 52%, correlation coefficient 0.42, P<0.05) and slightly increased with disturbance intensity. Conclusions: Increased disturbance enhances seed production at the community level. The composition of the vegetation is a poor predictor of the seed output. It is estimated that the number of seeds transferred with hay is much lower than the seed production in fens and fen meadows. [source] Recognising and responding to outbreaks of hepatitis A associated with child day-care centresAUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH, Issue 6 2001Jeffrey N. Hanna Objectives: To assess the appropriateness of a protocol for recognising and responding to outbreaks of hepatitis A in child day-care centres and to determine if measles-mumps-rubella (MMR) vaccine was given too soon following the administration of normal human immunoglobulin (NIGH) to young children to control the outbreaks. Design: Prospective surveillance to recognise cases of hepatitis A associated with, and outbreaks of hepatitis A in, day-care centres. Main outcome measures: The percentage of initial (,sentinel') cases of hepatitis A associated with day-care centres that were subsequently recognised as also being 'index' cases of outbreaks of hepatitis A in the centres, and the number of children 9,13 months of age when given NIGH who were subsequently given MMR less than three months later. Results: Only 18 (16%) of the 114 sentinel day-care associated cases of hepatitis A were also index cases of outbreaks of hepatitis A in their respective centres. A total of 105 cases of hepatitis A were associated with the 18 outbreak centres; NIGH was administered to 928 (78%) of the attendee children, and to 105 (82%) of the susceptible staff, at the 18 centres. Three of the five children 9,13 months of age when given NIGH were given MMR less that three months later. Conclusions: Although outbreaks of hepatitis A were common events in day-care centres in north Queensland during the two-year study period, a single case of hepatitis A associated with a centre was a poor predictor of an outbreak within that centre. Precautions must be taken to ensure that live vaccines are not administered to young children too soon after NIGH. [source] Power frequency magnetic fields and risk of childhood leukaemia: Misclassification of exposure from the use of the ,distance from power line' exposure surrogateBIOELECTROMAGNETICS, Issue 3 2009Myron Maslanyj Abstract A recent study examining the relationship between distance to nearby power lines and childhood cancer risk re-opened the debate about which exposure metrics are appropriate for power frequency magnetic field investigations. Using data from two large population-based UK and German studies we demonstrate that distance to power lines is a comparatively poor predictor of measured residential magnetic fields. Even at proximities of 50 m or less, the positive predictive value of having a household measurement over 0.2 µT was only 19.4%. Clearly using distance from power lines, without taking account of other variables such as load, results in a poor proxy of residential magnetic field exposure. We conclude that such high levels of exposure misclassification render the findings from studies that rely on distance alone uninterpretable. Bioelectromagnetics 30:183,188, 2009. © 2008 Wiley-Liss, Inc. [source] The predictive value of serum 1,5-anhydro-D-glucitol in pregnancies at increased risk of gestational diabetes mellitus and gestational impaired glucose toleranceBJOG : AN INTERNATIONAL JOURNAL OF OBSTETRICS & GYNAECOLOGY, Issue 7 2001Wing-Hung Tam The objective of the study was to determine the efficacy of 1,5-anhydro-D-glucitol (1,5 AG) for the prediction of gestational diabetes and gestational impaired glucose tolerance (GIGT). One hundred and eighty-five pregnant women with epidemiological risk factors of gestational diabetes or GIGT underwent 75 g oral glucose tolerance test and plasma 1,5 AG assay at 26 to 28 weeks of gestation. There was no significant difference in plasma 1,5 AG either before or after an oral glucose load. The area under the receiver operator characteristic curve for 1,5 AG was only 0.485 which implies that 1,5 AG is a poor predictor of GIGT or gestational diabetes. [source] The use of renal scintigraphy in assessing the potential for recovery in the obstructed renal tract in childrenBJU INTERNATIONAL, Issue 9 2001A. Thompson Objective To assess the value of renal scintigraphy with 99mTc-dimercaptosuccinic acid (DMSA) in predicting functional recovery after the surgical relief of obstructed kidneys in children. Patients and methods Forty-three children underwent surgery to relieve upper urinary tract obstruction; 37 had pelvi-ureteric junction obstruction and six had vesico-ureteric junction obstruction. The indication for surgery was a combination of an obstructed renogram with symptoms of either pain or pyelonephritis. Most children (41) had < 40% function on the affected side before surgery, with just two having hyperfunction (> 55%). In all patients intravenous urography before surgery showed hydronephrosis, and a micturating cystogram was used to exclude coexisting reflux in the presence of an associated megaureter. Diuretic renography (using 99mTc-mercaptoacetyl triglycine or 123I-hippuran) and DMSA scintigraphy were both carried out before surgery and the renography repeated 6 months afterward. Results The renographic drainage curves improved from obstructed to unobstructed or ,dilated unobstructed' on all postoperative studies. Regression analysis showed that preoperative DMSA scan was an excellent predictor of outcome (P < 0.001) whilst the preoperative renogram was a relatively poor predictor of the functional result. In four patients where the initial renographic function was < 10%, DMSA scintigraphy predicted correctly the capacity for recovery in three and the inability to improve in the fourth. Conclusion Before surgery, DMSA scintigraphy in children with upper urinary tract obstruction is a more useful estimate of probable long-term renal function than value from diuresis renography. If there is doubt about the desirability of reconstructive surgery, a DMSA scan may eliminate the need for more invasive methods of estimating recovery, e.g. a period of nephrostomy drainage. [source] Six-minute walk test is a poor predictor of maximum oxygen uptake in childrenACTA PAEDIATRICA, Issue 7 2010T Takken No abstract is available for this article. [source] Non-explanatory equilibria: An extremely simple game with (mostly) unattainable fixed pointsCOMPLEXITY, Issue 4 2002Joshua M. Epstein Abstract Equilibrium analysis pervades mathematical social science. This paper calls into question the explanatory significance of equilibrium by offering an extremely simple game, most of whose equilibria are unattainable in principle from any of its initial conditions. Moreover, the number of computation steps required to reach those (few) equilibria that are attainable is shown to grow exponentially with the number of players,making long-run equilibrium a poor predictor of the game's observed state. The paper also poses a number of combinatorially challenging problems raised by the game. © 2002 Wiley Periodicals, Inc. [source] Stream communities across a rural,urban landscape gradientDIVERSITY AND DISTRIBUTIONS, Issue 4 2006Mark C. Urban ABSTRACT Rapid urbanization throughout the world is expected to cause extensive loss of biodiversity in the upcoming decades. Disturbances associated with urbanization frequently operate over multiple spatial scales such that local species extirpations have been attributed both to localized habitat degradation and to regional changes in land use. Urbanization also may shape stream communities by restricting species dispersal within and among stream reaches. In this patch-dynamics view, anthropogenic disturbances and isolation jointly reduce stream biodiversity in urbanizing landscapes. We evaluated predictions of stream invertebrate community composition and abundance based on variation in environmental conditions at five distinct spatial scales: stream habitats, reaches, riparian corridors and watersheds and their spatial location within the larger three-river basin. Despite strong associations between biodiversity loss and human density in this study, local stream habitat and stream reach conditions were poor predictors of community patterns. Instead, local community diversity and abundance were more accurately predicted by riparian vegetation and watershed landscape structure. Spatial coordinates associated with instream distances provided better predictions of stream communities than any of the environmental data sets. Together, results suggest that urbanization in the study region was associated with reduced stream invertebrate diversity through the alteration of landscape vegetation structure and patch connectivity. These findings suggest that maintaining and restoring watershed vegetation corridors in urban landscapes will aid efforts to conserve freshwater biodiversity. [source] Polymorphism in the sperm ultrastructure among four species of lizards in the genus Tupinambis (Squamata: Teiidae)ACTA ZOOLOGICA, Issue 4 2002L. Tavares-Bastos Abstract We describe, for the first time, the ultrastructure of the spermatozoa of four species of the genus Tupinambis (Squamata, Teiidae). We identified seven polymorphic characters within this genus: the presence and shape of the perforatorial base plate, the presence of the epinuclear lucent zone, the presence of a unilateral ridge in the acrosome, the presence of a central density within the proximal centriole, the number of mitochondria and dense-bodies sets, and the shape of mitochondria. We analysed the evolution of the seven polymorphic characters by mapping them onto a current phylogeny of the species of Tupinambis, using the teiids Ameiva ameiva and Cnemidophorus sexlineatus as outgroups. Our results indicate that sperm ultrastucture characters, although of great value for phylogeny at higher taxonomic levels in reptiles and other groups, are poor predictors of phylogeny when considering the species of Tupinambis studied here. We failed to identify evidences that homoplasy in sperm ultrastructure among the species of Tupinambis is due to convergent adaptation, suggesting that the polymorphism may be selectively neutral in this group. [source] The globalized, generous welfare state: Possibility or oxymoron?EUROPEAN JOURNAL OF POLITICAL RESEARCH, Issue 3 2002Cynthia Kite Arguments about the incompatibility of globalization and generous welfare spending have given way to more nuanced analyses of how domestic-level institutions mediate the impact of globalization. This article discusses and compares two models , the labour-partisan politics model and the labour-monetary politics model , that identify national-level institutions that are said to make it possible for states to combine generous welfare spending and good economic performance. The empirical analysis shows that the labour-monetary politics model performs better for the period 1973,1989. However, institutional conditions that existed during these years are shown to be rather poor predictors of economic performance in the 1990s. The article goes on to discuss what this suggests for the continued viability of generous welfare spending and argues that while globalization might undermine some institutional settings conducive to continued generosity, there is evidence that other ones remain viable. [source] Site reoccupation in fragmented landscapes: testing predictions of metapopulation theoryJOURNAL OF ANIMAL ECOLOGY, Issue 2 2001Ralph S. Hames Summary 1,Populations of formerly continuously distributed species subdivided by habitat fragmentation may show distributions in space and time that are consistent with predictions of metapopulation theory. Local extinctions and recolonizations should result in the most fragmented sites being infrequently occupied and the least fragmented sites being continuously occupied by sensitive species. The probability of extinction is predicted to be negatively correlated with patch size and the amount of habitat in the landscape. Conversely, recolonization is predicted to be negatively correlated with the isolation of the patch, and positively correlated with the amount of habitat in the landscape. 2,Data from a 3-year study of the effect of fragmentation were used to test whether these predictions from metapopulation theory apply to populations of the long-distance migrant forest bird Piranga olivacea (Scarlet Tanager) in fragmented North American landscapes. 3,Principal components analysis was used to derive a composite measure of fragmentation. This measure was used in a logistic regression as a predictor of the number of years that territorial males would occupy a site, given that it was occupied at least once. More fragmented sites were more likely to be occupied only once; the least fragmented sites were more likely to be occupied in all three years. Data on fragmentation were necessary, but not sufficient, to predict site reoccupation, and were poor predictors at medium levels of fragmentation. 4,The univariate measures of fragmentation (patch size and isolation, proportion of forest, and forest/non-forest edge), were also used in logistic regressions to predict the separate probabilities of local extinction or recolonization. Local extinctions were negatively correlated with patch size and amount of forest in the landscape, as predicted. Recolonizations were negatively correlated with isolation of the patch as predicted, and surprisingly, also with the amount of edge in the landscape. This suggests that stochasticity may drive extinctions, but that habitat selection may play an important role in recolonization. 5,Demographic data are usually required to establish the suitability of habitat to support persistent populations, but multiple-year distributional data can provide information on habitat quality far above that obtained from single-year studies. [source] Survival of common goldeneye Bucephala clangula ducklings in relation to weather, timing of breeding, brood size, and female conditionJOURNAL OF AVIAN BIOLOGY, Issue 2 2007Antti Paasivaara The survival of common goldeneye Bucephala clangula ducklings during their first week of life was studied in relation to hatching date, brood size, female condition, and weather (temperature and precipitation) during the first week post-hatch by using data from radio-marked females and their broods. Also, age-specific variation in the survival of the young was determined until fledging (over 50 d of age). Survival was lowest in the first week after hatching. Hatching date, brood size, and first week temperature and precipitation were poor predictors of duckling survival during the first week after nest exodus. Instead, the ducklings of females in a better body condition survived better in their first week of life. The results suggest that weather does not have a direct effect on downy ducklings' survival, but the condition of the female seems to be an important determinant of the survival of common goldeneye ducklings. [source] Relationships Between Bone Mineral Density and Incident Vertebral Fracture Risk with Raloxifene Therapy,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 1 2002Somnath Sarkar Ph.D. Abstract Although low absolute values of bone mineral density (BMD) predict increased fracture risk in osteoporosis, it is not certain how well increases in BMD with antiresorptive therapy predict observed reductions in fracture risk. This work examines the relationships between changes in BMD after 1 year or 3 years of raloxifene or placebo therapy and the risk for new vertebral fractures at 3 years. In the Multiple Outcomes of Raloxifene Evaluation (MORE) trial, 7705 postmenopausal women with osteoporosis were randomized to placebo or raloxifene 60 mg/day or 120 mg/day. Relationships between baseline BMD and changes in BMD from baseline with the risk of new vertebral fractures were analyzed in this cohort using logistic regression models with the raloxifene doses pooled. As has been observed in other populations, women with the lowest baseline lumbar spine or femoral neck BMD in the MORE cohort had the greatest risk for vertebral fractures. Furthermore, for any percentage change, either increase or decrease in femoral neck or lumbar spine BMD at 1 year or 3 years, raloxifene-treated patients had a statistically significantly lower vertebral fracture risk compared with placebo-treated patients. The decrease in fracture risk with raloxifene was similar across the range of percentage change in femoral neck BMD observed at 3 years; patients receiving raloxifene had a 36% lower risk of vertebral fracture compared with those receiving placebo. At any percentage change in femoral neck and lumbar spine BMD observed at 1 year, raloxifene treatment decreased the risks of new vertebral fractures at 3 years by 38% and 41%, respectively. The logistic regression model showed that the percentage changes in BMD with raloxifene treatment accounted for 4% of the observed vertebral fracture risk reduction, and the other 96% of the risk reduction remains unexplained. The present data show that the measured BMD changes observed with raloxifene therapy are poor predictors of vertebral fracture risk reduction with raloxifene therapy. [source] Global patterns in plant heightJOURNAL OF ECOLOGY, Issue 5 2009Angela T. Moles Summary 1. ,Plant height is a central part of plant ecological strategy. It is strongly correlated with life span, seed mass and time to maturity, and is a major determinant of a species' ability to compete for light. Plant height is also related to critical ecosystem variables such as animal diversity and carbon storage capacity. However, remarkably little is known about global patterns in plant height. Here, we use maximum height data for 7084 plant Species × Site combinations to provide the first global, cross-species quantification of the latitudinal gradient in plant height. 2. ,The mean maximum height of species growing within 15° of the equator (7.8 m) was 29 times greater than the height of species between 60° and 75° N (27 cm), and 31 times greater than the height of species between 45° and 60° S (25 cm). There was no evidence that the latitudinal gradient in plant height was different in the northern hemisphere than in the southern hemisphere (P = 0.29). A 2.4-fold drop in plant height at the edge of the tropics (P = 0.006) supports the idea that there might be a switch in plant strategy between temperate and tropical zones. 3. ,We investigated 22 environmental variables to determine which factors underlie the latitudinal gradient in plant height. We found that species with a wide range of height strategies were present in cold, dry, low productivity systems, but there was a noticeable lack of very short species in wetter, warmer, more productive sites. Variables that capture information about growing conditions during the harsh times of the year were relatively poor predictors of height. The best model for global patterns in plant height included only one term: precipitation in the wettest month (R2 = 0.256). 4. ,Synthesis. We found a remarkably steep relationship between latitude and height, indicating a major difference in plant strategy between high and low latitude systems. We also provide new, surprising information about the correlations between plant height and environmental variables. [source] Growth properties of 16 non-pioneer rain forest tree species differing in sapling architectureJOURNAL OF ECOLOGY, Issue 5 2009Masahiro Aiba Summary 1.,Sapling architecture may be an important determinant of performance traits, such as light interception and height growth, but few studies have examined the direct relationship between sapling architecture and growth properties. To study this relationship and the potential for strategic diversification, we analysed the growth properties in saplings of 16 Bornean tree species that differ in architecture. 2.,Annual net production significantly differed amongst species and was positively correlated with total above-ground dry mass, total leaf area and crown area. In contrast, the net assimilation rate was weakly but negatively correlated with these architectural traits. The net assimilation rate was virtually independent of leaf size and specific leaf area. Relationships between sapling architecture and relative growth rate in mass were weak. 3.,The relative growth rate in height did not significantly differ amongst species, although their total dry mass, a proxy for extension cost, varied fourfold across species for a given sapling height. This is because the proportional increase in net production with total dry mass, which is based on a larger total leaf area and larger crown area, cancelled out the higher extension cost. All architectural traits, including leaf size and specific leaf area, failed to predict height growth rate. 4.,Synthesis. Relative growth rates in both mass and height were relatively independent of sapling architecture. Of the architectural traits, leaf size, specific leaf area and stem diameter were poor predictors of growth properties, even though they were considered functionally important. These results clearly reject the classic hypothesis that architectural variation leads to a trade-off between height growth and light interception, at least for the species that are under shaded conditions. However, functional variation ranging from species with high net production and low net assimilation rates (in saplings of equal height) to species with the opposite traits, which was accompanied by architectural variation in total dry mass and related size factors, may be important for the coexistence of these tree species. The possibility that small total dry mass may be advantageous in height growth under well-lit conditions should be examined in future studies. [source] Predictors of plant phenology in a diverse high-latitude alpine landscape: growth forms and topographyJOURNAL OF VEGETATION SCIENCE, Issue 5 2009Marianne Iversen Abstract Question: Different plant growth forms may have distinctly different functioning in ecosystems. Association of phenological patterns with growth form will therefore help elucidate the role of phenology in an ecosystem. We ask whether growth forms of common vascular plants differ in terms of vegetative and flowering phenology, and if such phenological differences are consistent across environmental gradients caused by landscape-scale topography. Location: A high-latitude alpine landscape in Finnmark County, Norway (70°N). Methods: We assessed vegetative and flowering phenology repeatedly in five growth forms represented by 11 common vascular plant species across an altitudinal gradient and among differing slope aspects. Results: Species phenology clustered well according to growth form, and growth form strongly explained variation in both flowering and vegetative phenology. Altitude and aspect were poor predictors of phenological variation. Vegetative phenology of the growth forms, ranked from slowest to fastest, was in the order evergreen shrubs Stress tolerance abilities and competitive responses in a watering and fertilization field experimentJOURNAL OF VEGETATION SCIENCE, Issue 6 2005P. Liancourt Abstract Question: Do water gradients produce patterns of responses to stress and competition similar to those induced by nutrient gradients? Location: French Alps. Methods: We established a split-plot design in a calcareous grassland, with watering and fertilization as main plot treatments and competition as subplot treatment. We followed individual and competitive responses of transplants of the three potential dominant grass species: Bromus erectus, Brachypodium rupestre and Arrhenatherum elatius, in all plots during two growing seasons. Changes in natural relative abundances of the three grass species were also monitored. Results: The growth and the relative abundance of A. elatius were primarily stimulated by nutrient addition and those of B. rupestre by water addition, whereas B. erectus decreased in abundance and had a very low flexibility with enhanced resource supply. Competition intensity increased for all species with both watering and fertilization and the ranking in competitive responses did not change with treatments: A. elatius > B. rupestre > B. erectus. Conclusions: Patterns of dominance were efficiently explained by stress tolerance abilities and competitive responses for dry and poor sites, and wet and rich sites for B. erectus and A. elatius respectively, whereas competitive responses were poor predictors of dominance for B. rupestre in wet and nutrient-poor sites. Further studies are needed to assess the potential role of other processes, such as increasing competitive effect on light with increasing age as well as interference, to explain the dominance of this conservative competitor type of species in wet and nutrient-poor sites. [source] More plant biomass results in more offspring production in annuals, or does it?OIKOS, Issue 9 2008Marina S. Neytcheva Competitive ability in plants has been previously measured almost exclusively in terms of traits related to growth (biomass) or plant size. In this study, however, we used a multi-species competition experiment with six annuals to measure relative competitive ability in terms of reproductive output, i.e. the number of offspring produced for the next generation. Under greenhouse conditions, plants of each species were started in pots from germinating seeds and were grown singly (free of competition) and at high density in both monocultures and in mixtures with all study species. Several traits traditionally regarded as determinants of competitive ability in plants were recorded for each species grown singly, including: seed mass, germination time, early growth rate and potential plant size (biomass and height). Under competition, several traits were recorded as indicators of relative performance in both monocultures and mixtures, including: biomass of survivors, total number of survivors, number of reproductive survivors, and reproductive output (total seed production) of the survivors. As expected, species that grew to a larger biomass in isolation had higher seed production in isolation. However, none of the traditional plant growth/size-related traits, measured either in isolation or under competition, could predict between species variation in reproductive output under competition in either monocultures or mixtures. In mixtures, 97% of this variation in reproductive output could be explained by between-species variation in the number of reproductive survivors. The results indicate that traits measured on plants grown singly may be poor predictors of reproductive output under competition, and that species' rank order of competitive ability in terms of the biomass of survivors may bear no relationship to their rank order in terms of the number of offspring produced by these survivors. This has important implications for the interpretation of mechanisms of species coexistence and community assembly within vegetation. [source] Determinants of preferred intertidal feeding habitat for Eastern Curlew: A study at two spatial scalesAUSTRAL ECOLOGY, Issue 2 2007PAUL G. FINN Abstract Broadscale habitat use by Eastern Curlews (Numenius madagascariensis) in their non-breeding range in eastern Australia was assessed using low tide surveys on feeding grounds, where 60 skilled volunteers made repeated counts of the birds on intertidal flats, across 41% (9500 ha) of the intertidal habitat within Moreton Bay, Australia. We analysed 32 defined sections of intertidal flat, of roughly equal area (mostly 200,400 ha), which varied greatly in their curlew density (2,47 birds per 100 ha) and also in substrate and other environmental features. Sites with the least resistant substrates had densities three times those with the most resistant substrates. Of 10 environmental characteristics measured for each site, substrate resistance was the best predictor of curlew density (r2 = 0.45). Characteristics that were poor predictors included distance to the nearest roost, level of human disturbance and distance to urban settlement. For a finer-scale assessment, microhabitat use and feeding behaviour were recorded during low tide within 12 intertidal flats, which varied in size (23,97 ha), substrate, topography and other features. Across all flats, curlews strongly preferred to feed relatively close (0,50 m) to the low-water line. They fed on a variety of substrates (including sand, sandy-mud, mud and seagrass) in broadly similar proportions to their occurrence in the habitat. There was a statistically significant preference for sand, although its magnitude was not strong. These results indicate that curlews select habitat most strongly at a between-flat rather than within-flat scale. [source]
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