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Competing Hypotheses (competing + hypothesis)
Selected AbstractsElevational patterns of frog species richness and endemic richness in the Hengduan Mountains, China: geometric constraints, area and climate effectsECOGRAPHY, Issue 6 2006Cuizhang Fu We studied frog biodiversity along an elevational gradient in the Hengduan Mountains, China. Endemic and non-endemic elevational diversity patterns were examined individually. Competing hypotheses were also tested for these patterns. Species richness of total frogs, endemics and non-endemics peaked at mid-elevations. The peak in endemic species richness was at higher elevations than the maxima of total species richness. Endemic species richness followed the mid-domain model predictions, and showed a nonlinear relationship with temperature. Water and energy were the most important variables in explaining elevational patterns of non-endemic species richness. A suite of interacting climatic and geometric factors best explained total species richness patterns along the elevational gradient. We suggest that the mid-domain effect was an important factor to explain elevational richness patterns, especially in regions with high endemism. [source] Representing genetic variation as continuous surfaces: an approach for identifying spatial dependency in landscape genetic studiesECOGRAPHY, Issue 6 2008Melanie A. Murphy Landscape genetics, an emerging field integrating landscape ecology and population genetics, has great potential to influence our understanding of habitat connectivity and distribution of organisms. Whereas typical population genetics studies summarize gene flow as pairwise measures between sampling localities, landscape characteristics that influence population genetic connectivity are often continuously distributed in space. Thus, there are currently gaps in both the ability to analyze genotypic data in a continuous spatial context and our knowledge of expected of landscape genetic structure under varying conditions. We present a framework for generating continuous "genetic surfaces", evaluate their statistical properties, and quantify statistical behavior of landscape genetic structure in a simple landscape. We simulated microsatellite genotypes under varying parameters (time since vicariance, migration, effective population size) and used ancestry (q) values from STRUCTURE to interpolate a genetic surface. Using a spatially adjusted Pearson's correlation coefficient to test the significance of landscape variable(s) on genetic structure we were able to detect landscape genetic structure on a contemporary time scale (,5 generations post vicariance, migration probability ,0.10) even when population differentiation was minimal (FST,0.00015). We show that genetic variation can be significantly correlated with geographic distance even when genetic structure is due to landscape variable(s), demonstrating the importance of testing landscape influence on genetic structure. Finally, we apply genetic surfacing to analyze an empirical dataset of black bears from northern Idaho USA. We find black bear genetic variation is a function of distance (autocorrelation) and habitat patch (spatial dependency), consistent with previous results indicating genetic variation was influenced by landscape by resistance. These results suggest genetic surfaces can be used to test competing hypotheses of the influence of landscape characteristics on genetic structure without delineation of categorical groups. [source] Analysis of determinants of mammalian species richness in South America using spatial autoregressive modelsECOGRAPHY, Issue 4 2004Marcelo F. Tognelli Classically, hypotheses concerning the distribution of species have been explored by evaluating the relationship between species richness and environmental variables using ordinary least squares (OLS) regression. However, environmental and ecological data generally show spatial autocorrelation, thus violating the assumption of independently distributed errors. When spatial autocorrelation exists, an alternative is to use autoregressive models that assume spatially autocorrelated errors. We examined the relationship between mammalian species richness in South America and environmental variables, thereby evaluating the relative importance of four competing hypotheses to explain mammalian species richness. Additionally, we compared the results of ordinary least squares (OLS) regression and spatial autoregressive models using Conditional and Simultaneous Autoregressive (CAR and SAR, respectively) models. Variables associated with productivity were the most important at determining mammalian species richness at the scale analyzed. Whereas OLS residuals between species richness and environmental variables were strongly autocorrelated, those from autoregressive models showed less spatial autocorrelation, particularly the SAR model, indicating its suitability for these data. Autoregressive models also fit the data better than the OLS model (increasing R2 by 5,14%), and the relative importance of the explanatory variables shifted under CAR and SAR models. These analyses underscore the importance of controlling for spatial autocorrelation in biogeographical studies. [source] United we win, divided we fail?EUROPEAN JOURNAL OF SOCIAL PSYCHOLOGY, Issue 3 2008Effects of cognitive merger representations, performance feedback on merging groups Research has shown that cognitive representations of mergers influence intergroup evaluations. This paper extends this research by studying how cognitive representations of mergers (one group, dual identity, and two groups) interact with performance feedback (success and failure) to affect intergroup evaluations. Two competing hypotheses were tested, which made different predictions in case of superordinate group salience combined with subgroup salience after merger failure: The subgroup-salience-hypothesis predicts that subgroup salience during a merger generally results in pre-merger ingroup bias toward the pre-merger outgroup (i.e., two groups and dual identity). The superordinate- salience-hypothesis predicts that subgroup salience only results in pre-merger ingroup bias if superordinate group salience is low (i.e., two groups). Both hypotheses predict low levels of ingroup bias after merger success. Study 1 confirmed the second hypothesis using a 3 (merger representation: one group, dual identity, and two groups),×,2 (merger feedback: failure and success) design with interacting groups. Study 2 replicated the results in an adapted minimal group paradigm. Copyright © 2007 John Wiley & Sons, Ltd. [source] Early evolution of a homeobox gene: the parahox gene Gsx in the Cnidaria and the BilateriaEVOLUTION AND DEVELOPMENT, Issue 4 2003John R. Finnerty Summary Homeobox transcription factors are commonly involved in developmental regulation in diverse eukaryotes, including plants, animals, and fungi. The origin of novel homeobox genes is thought to have contributed to many evolutionary innovations in animals. We perform a molecular phylogenetic analysis of cnox2, the best studied homeobox gene from the phylum Cnidaria, a very ancient lineage of animals. Among three competing hypotheses, our analysis decisively favors the hypothesis that cnox2 is orthologous to the gsx gene of Bilateria, thereby establishing the existence of this specific homeobox gene in the eumetazoan stem lineage, some 650,900 million years ago. We assayed the expression of gsx in the planula larva and polyp of the sea anemone Nematostella vectensis using in situ hybridization and reverse transcriptase polymerase chain reaction. The gsx ortholog of Nematostella, known as anthox2, is expressed at high levels in the posterior planula and the corresponding "head" region of the polyp. It cannot be detected in the anterior planula or the corresponding "foot" region of the polyp. We have attempted to reconstruct the evolution of gsx spatiotemporal expression in cnidarians and bilaterians using a phylogenetic framework. Because of the surprisingly high degree of variability in gsx expression within the Cnidaria, it is currently not possible to infer unambiguously the ancestral cnidarian condition or the ancestral eumetazoan condition for gsx expression. [source] Modelling the basin-scale demography of Calanus finmarchicus in the north-east AtlanticFISHERIES OCEANOGRAPHY, Issue 5 2005DOUGLAS C. SPEIRS Abstract In this paper, we report on a coupled physical,biological model describing the spatio-temporal distribution of Calanus finmarchicus over an area of the North Atlantic and Norwegian Sea from 56°N, 30°W to 72°N, 20°E. The model, which explicitly represents all the life-history stages, is implemented in a highly efficient discrete space,time format which permits wide-ranging dynamic exploration and parameter optimization. The underlying hydrodynamic driving functions come from the Hamburg Shelf-Ocean Model (HAMSOM). The spatio-temporal distribution of resources powering development and reproduction is inferred from SeaWiFS sea-surface colour observations. We confront the model with distributional data inferred from continuous plankton recorder observations, overwintering distribution data from a variety of EU, UK national and Canadian programmes which were collated as part of the Trans-Atlantic Study of Calanus (TASC) programme, and high-frequency stage-resolved point time-series obtained as part of the TASC programme. We test two competing hypotheses concerning the control of awakening from diapause and conclude that only a mechanism with characteristics similar to photoperiodic control can explain the test data. [source] Control of tiller recruitment in bunchgrasses: uniting physiology and ecologyFUNCTIONAL ECOLOGY, Issue 4 2004K. W. TOMLINSON Summary 1Bunchgrasses are clonal plants whose dominance of moist grasslands worldwide is maintained largely through tiller recruitment. Tiller recruitment in clonal plants is a subset of the problem of lateral bud outgrowth in higher plants. This paper proposes that three currently competing hypotheses of lateral bud outgrowth , apical dominance; the nutrition hypothesis; and photosensitivity to the red : far-red light ratio , all operate in a manner dependent on environment and plant form. 2The evidence for each hypothesis is reviewed, following which an integrated model is provided that links the three hypotheses into a cohesive strategy. Consequently we assess tiller recruitment by bunchgrasses in terms of the constraints of their functional growth form and their environment. Of the mineral nutrients, only nitrogen is considered because it is the only nutrient whose relationship with tiller recruitment is well established. 3The integrated model maintains the accepted paradigm that actual bud release is hormonally controlled by the auxin : cytokinin ratio, although local nutrient concentrations may also be inhibitory. Importantly, each hormone is controlled by local signals in the shoots and roots, respectively, facilitating appropriate responses to environmental conditions. Auxin production and export from the shoots is moderated by phytochrome responses to red : far-red light ratios. Cytokinin production is mediated by root N concentration which, in turn, is a function of N absorption from the soil and seasonal reallocation of tissue N. 4The growth form of bunchgrasses and the environment in which they are found emphasize that N has a strong mediatory role over tiller production which allows the grass plant to respond appropriately to shifts in this limiting resource. This suggests that control of lateral bud outgrowth may have an evolutionary basis in resource competition for N. [source] A Bayesian approach to the transmission/disequilibrium test for binary traitsGENETIC EPIDEMIOLOGY, Issue 1 2002Varghese George Abstract The transmission/disequilibrium test (TDT) for binary traits is a powerful method for detecting linkage between a marker locus and a trait locus in the presence of allelic association. The TDT uses information on the parent-to-offspring transmission status of the associated allele at the marker locus to assess linkage or association in the presence of the other, using one affected offspring from each set of parents. For testing for linkage in the presence of association, more than one offspring per family can be used. However, without incorporating the correlation structure among offspring, it is not possible to correctly assess the association in the presence of linkage. In this presentation, we propose a Bayesian TDT method as a complementary alternative to the classical approach. In the hypothesis testing setup, given two competing hypotheses, the Bayes factor can be used to weigh the evidence in favor of one of them, thus allowing us to decide between the two hypotheses using established criteria. We compare the proposed Bayesian TDT with a competing frequentist-testing method with respect to power and type I error validity. If we know the mode of inheritance of the disease, then the joint and marginal posterior distributions for the recombination fraction (,) and disequilibrium coefficient (,) can be obtained via standard MCMC methods, which lead naturally to Bayesian credible intervals for both parameters. Genet. Epidemiol. 22:41,51, 2002. © 2002 Wiley-Liss, Inc. [source] Private placements of convertible securities: stock returns, operating performance and abnormal accrualsACCOUNTING & FINANCE, Issue 4 2009Jan L. Williams G14; G32 Abstract This study examines long-run stock returns, operating performance and abnormal accruals of private placements of convertible securities. We investigate the effects surrounding private placements to test and differentiate the implications of several competing hypotheses. While the monitoring and certification hypotheses suggest positive effects, the managerial entrenchment, overvaluation and windows-of-opportunity hypotheses suggest the opposite. We find that placing firms generally experience positive effects in the pre-periods and negative effects in the post-periods. Our overall findings are more consistent with the predictions of the overvaluation and windows-of-opportunity hypotheses while our post-placement evidence is also consistent with the predictions of the managerial entrenchment hypothesis. [source] There's more to macroecology than meets the eyeGLOBAL ECOLOGY, Issue 6 2006Tim M. Blackburn ABSTRACT Macroecology sits at the junction of, and can contribute to, the fields of ecology, biogeography, palaeontology and macroevolution, using a broad range of approaches to tackle a diverse set of questions. Here, we argue that there is more to macroecology than mapping, and that while they are potentially useful, maps are insufficient to assess macroecological pattern and process. The true nature of pattern can only be assessed, and competing hypotheses about process can only be disentangled, by adopting a statistical approach, and it is this that has been key to the development of macroecology as a respected and rigorous scientific discipline. [source] An exploratory analysis of the effect of the "buy it now" option on sellers' revenues in silent auctionsINTERNATIONAL JOURNAL OF NONPROFIT & VOLUNTARY SECTOR MARKETING, Issue 3 2009Karen Page This paper tests three competing hypotheses regarding the effect of a "buy it now" option in silent auctions: that the option has a positive, negative, or neutral effect on the seller's revenues. These hypotheses were tested on 4 years of data from a university art museum's silent auctions. The results indicate that the "buy it now" option has a significant negative effect on the seller's revenues. Possible explanation, implications, and limitations are discussed. Copyright © 2009 John Wiley & Sons, Ltd. [source] In the Nick of Time: Conflict Management, Mediation Timing, and the Duration of Interstate DisputesINTERNATIONAL STUDIES QUARTERLY, Issue 2 2000Patrick M. Regan This paper develops a theoretical argument linking time and the timing of conflict management efforts to dispute duration. We test competing hypotheses on conflict data drawn from disputes in the post-1945 period. Our analysis demonstrates that the effects of mediation vary substantially over the course of a dispute. Specifically, we note that mediation has a curvilinear relationship with time and the ending of disputes. Mediation efforts that occur soon after disputes begin have the best chance of reducing expected future dispute duration. Following this initial period, subsequent mediation efforts lead to longer rather than shorter disputes. After a long period, mediation again leads to shorter rather than longer disputes. We also find that there should be consistency in the mediators used to manage a conflict rather than shifting personnel to interject new ideas. [source] Linking resources with demography to understand resource limitation for bearsJOURNAL OF APPLIED ECOLOGY, Issue 6 2007MELISSA J. REYNOLDS-HOGLAND Summary 1,Identifying the resources that limit growth of animal populations is essential for effective conservation; however, resource limitation is difficult to quantify. Recent advances in geographical information systems (GIS) and resource modelling can be combined with demographic modelling to yield insights into resource limitation. 2,Using long-term data on a population of black bears Ursus americanus, we evaluated competing hypotheses about whether availability of hard mast (acorns and nuts) or soft mast (fleshy fruits) limited bears in the southern Appalachians, USA, during 1981,2002. The effects of clearcutting on habitat quality were also evaluated. Annual survival, recruitment and population growth rate were estimated using capture,recapture data from 101 females. The availability of hard mast, soft mast and clearcuts was estimated with a GIS, as each changed through time as a result of harvest and succession, and then availabilities were incorporated as covariates for each demographic parameter. 3,The model with the additive availability of hard mast and soft mast across the landscape predicted survival and population growth rate. Availability of young clearcuts predicted recruitment, but not population growth or survival. 4,Availability of hard mast stands across the landscape and availability of soft mast across the landscape were more important than hard mast production and availability of soft mast in young clearcuts, respectively. 5,Synthesis and applications. Our results indicate that older stands, which support high levels of hard mast and moderate levels of soft mast, should be maintained to sustain population growth of bears in the southern Appalachians. Simultaneously, the acreage of intermediate aged stands (10,25 years), which support very low levels of both hard mast and soft mast, should be minimized. The approach used in this study has broad application for wildlife management and conservation. State and federal wildlife agencies often possess long-term data on both resource availability and capture,recapture for wild populations. Combined, these two data types can be used to estimate survival, recruitment, population growth, elasticities of vital rates and the effects of resource availability on demographic parameters. Hence data that are traditionally used to understand population trends can be used to evaluate how and why demography changes over time. [source] Diet reconstruction and historic population dynamics in a threatened seabirdJOURNAL OF APPLIED ECOLOGY, Issue 4 2007D. RYAN NORRIS Summary 1For the overwhelming majority of species, we lack long-term information on the dynamics of populations. As a consequence, we face considerable uncertainty about how to discriminate among competing hypotheses of population decline and design conservation plans. 2The marbled murrelet Brachyramphus marmoratus is a small seabird that nests in coastal old-growth forest but feeds year-round in near-shore waters of the north-eastern Pacific. Although a decline in nesting habitat is the primary reason why marbled murrelets are listed as threatened in Canada, nest predation and food availability may also influence population abundance. To examine the hypothesis that murrelet populations are influenced by variation in diet quality, we analysed stable-carbon and -nitrogen isotopes in feathers of museum specimens collected in the Georgia Basin, British Columbia. 3Between 1889 and 1996, we found a decline in stable isotopic signatures that was approximately equal to a 62% drop in trophic feeding level. We also found that the estimated proportion of fish in murrelet diet was related closely to murrelet abundance over the past 40 years, as estimated from volunteer surveys. Using these isotopic data, we modelled population size as a function of variation in reproductive rate due to changes in diet quality and found that our model matched closely the 40-year field estimates. We then applied our 107-year isotopic record to the model to back-cast estimates of population growth rate to 1889. 4Our results suggest that, up to the 1950s, murrelet populations in the Georgia Basin were capable of growing and were probably limited by factors other than diet quality. After this period, however, our results imply that murrelets were often, but not solely, limited by diet quality. 5Synthesis and applications. Protecting nesting habitat may not be sufficient to rebuild populations of this highly secretive and threatened seabird and recovery might also require the restoration of marine habitat quality, as well as a better understanding of how ocean climate affects prey abundance and reproductive rate. Combined with contemporary demographic data, stable isotope analysis of historic samples provides a unique opportunity to reconstruct population histories for species where we lack long-term information. [source] Vicariance or dispersal: the use of natural historical data to test competing hypotheses of disjunction on the Tyrrhenian coastJOURNAL OF BIOGEOGRAPHY, Issue 1 2001George F. Estabrook Aim To illustrate the use of natural historical data to evaluate vicariance and dispersal as hypotheses competing to explain disjunct populations. Location Nine disjunct areas on the margin of the Tyrrhenian basin of the Mediterranean Sea. Methods First describe how each hypothesized mechanism might explain the observed morphological variation in the model species complex, Genista ephedroides (Fabaceae); then confront the hypotheses with natural historical data including geology, oxygen isotopes, palynology, macro-, micro- and nano-fossils, and sea level changes, and with the ecological tolerances of the model species complex. Results Dispersal seems the more credible explanation. Main conclusion Patterns of morphological (or other) variation among related disjunct taxa can fit both vicariance and dispersal hypotheses. However they can possibly be distinguished by considering natural historical data. [source] Vanishing Trials: The Bankruptcy ExperienceJOURNAL OF EMPIRICAL LEGAL STUDIES, Issue 3 2004Elizabeth Warren The federal bankruptcy system provides two critical points of comparison with data about the overall trends of federal lawsuits and trials. The first is the rising number of bankruptcy filings, which indicates that a growing number of collection actions and debtor-creditor disputes are funneled into the bankruptcy system for relatively quick, cheap resolution. The second point of comparison focuses on adversary proceedings, the lawsuit-like subset of disputes that sometimes are resolved within a bankruptcy. The trend lines here suggest that the number of adversary proceedings filed is climbing, while the number of such disputes that are actually resolved by trial is declining. Like the data about the federal court system generally, these data suggest that the trial is quietly vanishing from the bankruptcy system. Data about the number of judges and about business and nonbusiness bankruptcy cases make it possible to explore two competing hypotheses,a Judicial Workload Hypothesis and a Cost Hypothesis,to explain the overall findings. The data are not conclusive, but they are consistent with the view that judicial workloads explain less of the decline in the number of trials than an increase in litigants' costs of resolving disputes in bankruptcy. The data are also consistent with a vision of bankruptcy as an evolving process that is increasingly standardized (and cheaper) for nonbusiness debtors, while it is highly individualized (and more costly) for business cases. If that vision is right, it has implications both for understanding the changing role of the trial and for considering various statutory proposals to differentiate further the treatment of large business, small business, and nonbusiness cases. [source] Are German, Japanese and Anglo-Saxon Strategic Decision Styles Still Divergent in the Context of Globalization?*JOURNAL OF MANAGEMENT STUDIES, Issue 6 2005Chris Carr abstract Issues of globalization and divergence in terms of national systems and cultures are equally contentious, yet equally important, in the context of increasing cross-continental co-operation. This article investigates comparative strategic decision styles in Britain, the USA, Germany and Japan. An industry at an advanced stage in terms of globalization, vehicle components manufacture, was selected in order to explore the extent of convergence and whether this has changed. Between 1989 and 1998, field case studies were made of 100 strategic investment decisions (SIDs) by manufacturers in these four countries. Longitudinal judgements were supplemented by earlier comparative strategy field research carried out in 60 suppliers between 1980 and 1983, and two longitudinal case studies, one from the UK and one from Japan, interviewed throughout both these periods and again in 2002. Two competing hypotheses, derived from rich research literatures, are investigated. The first (H1) suggests that national institutional and cultural factors exert profound differences, and should therefore be afforded more significance as globalization proceeds further. The second (H2) is apparently contradictory and emphasizes that institutions and organizations are likely to respond to convergence pressures, spurred by global capital markets and competition on the one hand, and a diffusion of ,professional management' practices on the other. Japanese firms generally, and German family firms in particular, were still found to exhibit deep-rooted differences from the Anglo-Saxon model, which appears to confirm H1. However study of German public companies reveals that their strategic approaches are far less divergent from what is now an increasingly consistent Anglo-Saxon model than they were a decade ago, which appears to confirm the competing hypothesis H2. [source] Schumpeterian Dynamics Versus Williamsonian Considerations: A Test of Export Intermediary PerformanceJOURNAL OF MANAGEMENT STUDIES, Issue 2 2000Mike W. Peng Using a sample of export intermediaries connecting domestic producers and foreign buyers, the study tests competing hypotheses on firm performance derived from the Austrian and transaction cost perspectives. Specifically, the Austrian perspective suggests that the more distant the export market and the more complex the product that the intermediary specializes in, the better its performance. Transaction cost theory, on the other hand, offers conflicting predictions. Our results indicate that these two theories are complementary to each other, and a contingency framework is proposed and discussed. [source] Effects of Spouse Support and Hostility on Trajectories of Czech Couples' Marital Satisfaction and InstabilityJOURNAL OF MARRIAGE AND FAMILY, Issue 4 2001Frederick O. Lorenz This article examines differences in the role of spouses' hostile and supportive behaviors in predicting level and change in marital satisfaction and marital instability. We propose 2 competing hypotheses. The first hypothesis proposes that hostility is relatively volatile and support is relatively stable, and that change in hostility affects change in marital outcomes over the course of the study, whereas the overall level of support functions to maintain the level of marital outcomes. The second hypothesis argues that change in marital satisfaction is a function of change in support, whereas change in marital instability is a function of change in hostility. We tested the hypotheses by fitting growth curves to 3 waves of panel data collected from 436 Czech couples between 1994 and 1996. The results offer some support for the first hypothesis. However, the dominant pattern was for level and change in spouses' reports of their hostility to affect both wives' and husbands' level and change in marital instability, respectively, and for the level and change in husbands' reports of their support to predict level and change in wives' marital satisfaction. Other variables suggested by previous research in the United States and by the Czech transition to a market economy are examined. [source] Competition from Large, Multimarket Firms and the Performance of Small, Single-Market Firms: Evidence from the Banking IndustryJOURNAL OF MONEY, CREDIT AND BANKING, Issue 2-3 2007ALLEN N. BERGER banks; community banking; bank size; multimarket banks; technological progress We offer and test two competing hypotheses for the consolidation trend in banking using U.S. banking industry data over the period 1982,2000. Under the efficiency hypothesis, technological progress improved the performance of large, multimarket firms relative to small, single-market firms, whereas under the hubris hypothesis, consolidation was largely driven by corporate hubris. Our results are consistent with an empirical dominance of the efficiency hypothesis over the hubris hypothesis,on net, technological progress allowed large, multimarket banks to compete more effectively against small, single-market banks in the 1990s than in the 1980s. We also isolate the extent to which technological progress occurred through scale versus geographic effects and how they affected the performance of small, single-market banks through revenues versus costs. The results may shed light as well on some of the research and policy issues related to community banking. [source] Dropping out of medical school in the UK: explaining the changes over ten yearsMEDICAL EDUCATION, Issue 4 2007Wiji Arulampalam Context, In the context of changing admissions criteria and an expanding medical school intake in the UK, we analysed the determinants of the medical school dropout probability. Objectives, We aimed to analyse the determinants of the probability that a student will drop out of medical school during Year 1 and to compare the results of this analysis over time. Methods, We carried out logistic regression analysis for the 6 intake cohorts of 1990,92 and 1998,2000. Results, Between 1990,92 and 1998,2000, there were substantial increases in both the size of the entry cohort and the proportion of students dropping out of medical school. A logit model for the 1990,92 and 1998,2000 cohorts reveals that the probability of dropping out depended on both the medical school attended and the personal characteristics of the student, including academic preparedness. Almost none of the increase in the dropout rate between the 2 cohort groups can be explained by changes in observable characteristics of the students over this period. Instead, most of the increase in the dropout rate is associated with changes at the level of the institution and in unobserved student characteristics. Conclusions, University effects, rather than changes in observed student characteristics, explain most of the increased dropout rate over the time period considered. Candidate explanations behind these effects include: less effective admissions policies; changing curricula; greater costs of attending medical school, and a growing mismatch between student and school characteristics. Testing between these competing hypotheses is left for future work. [source] Detecting Technological Catch-Up in Economic ConvergenceMETROECONOMICA, Issue 2-3 2003Francesco Pigliaru We address the problem of measuring, in the absence of reliable indices of technology levels, how much of the convergence we observe is due to convergence in technology or in capital,labour ratios. We first develop a growth model where technology accumulation in lagging economies depends on their propensity to innovate and on technological spillovers, with convergence due both to capital-deepening and to technological diffusion. Then we study the transitional dynamics of the model to show how to discriminate empirically between the following three hypotheses: (i) convergence is due to capital-deepening with technology levels uniform across economies, as in Mankiw, Romer and Weil; (ii) convergence is due to capital-deepening with stationary differences in individual technologies, as in Islam; (iii) convergence is due to both technological catch-up and capital-deepening. Our main findings are as follows. First, we show that it may be difficult to distinguish between hypotheses (ii) and (iii) in cross-section or panel data. This problem has often been overlooked in the empirical literature on convergence. Second, we suggest how the problem can be overcome by noting that hypothesis (iii) does (and hypothesis (ii) does not) imply that the initial differences in technology levels may tend to decrease over time. A careful analysis of the fixed-effects estimates obtained by means of panel data methodology proposed in Islam should allow researchers to discriminate between the two competing hypotheses. [source] Working at the interface of phylogenetics and population genetics: a biogeographical analysis of Triaenops spp. (Chiroptera: Hipposideridae)MOLECULAR ECOLOGY, Issue 4 2007A. L. RUSSELL Abstract New applications of genetic data to questions of historical biogeography have revolutionized our understanding of how organisms have come to occupy their present distributions. Phylogenetic methods in combination with divergence time estimation can reveal biogeographical centres of origin, differentiate between hypotheses of vicariance and dispersal, and reveal the directionality of dispersal events. Despite their power, however, phylogenetic methods can sometimes yield patterns that are compatible with multiple, equally well-supported biogeographical hypotheses. In such cases, additional approaches must be integrated to differentiate among conflicting dispersal hypotheses. Here, we use a synthetic approach that draws upon the analytical strengths of coalescent and population genetic methods to augment phylogenetic analyses in order to assess the biogeographical history of Madagascar's Triaenops bats (Chiroptera: Hipposideridae). Phylogenetic analyses of mitochondrial DNA sequence data for Malagasy and east African Triaenops reveal a pattern that equally supports two competing hypotheses. While the phylogeny cannot determine whether Africa or Madagascar was the centre of origin for the species investigated, it serves as the essential backbone for the application of coalescent and population genetic methods. From the application of these methods, we conclude that a hypothesis of two independent but unidirectional dispersal events from Africa to Madagascar is best supported by the data. [source] Testing models of diversification in mice in the Abrothrix olivaceus/xanthorhinus complex in Chile and ArgentinaMOLECULAR ECOLOGY, Issue 2 2001M. F. Smith Abstract Samples of the forest-dwelling mouse Abrothrix olivaceus and the steppe-dwelling A. xanthorhinus across a transect between 45 and 47° S in southern Chile were analysed using the mitochondrial cytochrome b (cyt b) sequence, substantially adding to the data presented previously for these taxa from Argentina and Chile. The level of variation in the cyt b sequence throughout the entire olivaceus/xanthorhinus complex is comparable to that seen within a single species in many South American sigmodontine rodents, consistent with a previous conclusion that both taxa are sub-species of A. olivaceus. Haplotypes of xanthorhinus have not yet achieved reciprocal monophyly relative to those of olivaceus. We evaluate competing hypotheses for the morphological divergence of xanthorhinus and olivaceus by allopatry in Pleistocene refuges versus postglacial diversification across ecological gradients. Two contrasting patterns are predicted for plots of the distribution of pairwise genetic differences, depending on whether the taxa diverged in allopatric refuges or through selection across a gradient. Examples of both modes of diversification are found in this complex. [source] Can differences in autonomous selfing ability explain differences in range size among sister-taxa pairs of Collinsia (Plantaginaceae)?NEW PHYTOLOGIST, Issue 3 2009An extension of Baker's Law Summary ,,Species with greater selfing ability are predicted to be better adapted for colonizing new habitats (Baker's Law). Here, we tested an expansion of this hypothesis: that species proficient at autonomous selfing have larger range sizes than their less proficient sister taxa. We also tested competing hypotheses regarding seed production and niche breadth on range size. ,,Floral traits affecting the proficiency of autonomous selfing were measured and seed production was calculated for six sister-taxa pairs in the clade Collinsia. We tested for the hypothesized effects of these variables on elevational distribution and range size. ,,We found that species most proficient at selfing had significantly larger range sizes than their sister-taxa that were less proficient at selfing. Species proficient at autonomous selfing occupied a higher mean elevation than their sister taxa, but they did not differ in their total elevational range. Species with greater seed production did not have larger range sizes. ,,Our results extend Baker's Law, suggesting that species proficient at autonomous selfing are better adapted to establish new populations and thus can more readily expand their range. Autonomous selfing ability may play a vital role in explaining variance in range size among other species. [source] Dispersal limitation inferred from an experimental translocation of Lomatium (Apiaceae) species outside their geographic rangesOIKOS, Issue 12 2009Travis D. Marsico Determining limitations on poleward range expansion is important for predicting how climate change will alter the distribution of species. For most species, it is not known what factors set their distributional limits and the role dispersal limitation might play if range-limiting factors were altered. We conducted a transplant study of three related and co-occurring Lomatium species at their northern range limits to test competing hypotheses of range limitation. We added seeds to experimental plots inside and outside the species' geographic range (a regional treatment) in a replicated design with vegetation intact and vegetation reduced (a disturbance treatment) and with herbivore access and herbivore exclusion (an herbivory treatment). Germination and reemergence were measured through two growing seasons, along with community-level variables. A fully-crossed linear mixed model revealed that Lomatium survivorship outside the current range was as good or better than survivorship within the range, at least when the vegetative community remained intact. This suggests that the species are dispersal limited. Germination often was improved in the presence of an intact vegetative community, but this potentially facilitative effect was absent in second-year reemergence. Plots exposed to herbivory had slightly, but significantly, reduced germination, though reemergence did not differ between herbivore treatments. Lomatium dissectum, a rare species, had significantly lower survivorship than its congeners, suggesting that range shifts in rare taxa may be particularly difficult. Seed additions beyond species' range limits may be a strategy for overcoming dispersal limitation and assisting species in poleward migrations. [source] Party Identification and Core Political ValuesAMERICAN JOURNAL OF POLITICAL SCIENCE, Issue 4 2005Paul Goren Party identification and core political values are central elements in the political belief systems of ordinary citizens. Are these predispositions related to one another? Does party identification influence core political values or are partisan identities grounded in such values? This article draws upon theoretical works on partisan information processing and value-based reasoning to derive competing hypotheses about whether partisanship shapes political values or political values shape partisanship. The hypotheses are tested by using structural equation modeling techniques to estimate dynamic models of attitude stability and constraint with data from the 1992,94,96 National Election Study panel survey. The analyses reveal that partisan identities are more stable than the principles of equal opportunity, limited government, traditional family values, and moral tolerance; party identification constrains equal opportunity, limited government, and moral tolerance; and these political values do not constrain party identification. [source] Age-specific functions of Stone Handling, a solitary-object play behavior, in Japanese Macaques (Macaca fuscata)AMERICAN JOURNAL OF PRIMATOLOGY, Issue 3 2007Charmalie A.D. Nahallage Abstract Stone handling (SH) in Japanese macaques, a form of solitary-object play, is newly acquired only by young individuals, and is the first example of a directly nonadaptive behavior that is maintained as a behavioral tradition within free-ranging provisioned social troops. We report here the first systematic investigation of this behavior in a stable captive social troop, the Takahama troop, which is housed in an outdoor enclosure of the Primate Research Institute (PRI), Kyoto University, Japan. This study was conducted to evaluate relevant competing hypotheses regarding the function of object play (e.g., misdirected foraging behavior and motor training) to explain the proximal causes and ultimate function(s) of SH. The "misdirected foraging behavior" hypothesis can be ruled out because of the lack of a clear temporal relationship between feeding and the occurrence of SH in any age class. Age-related differences in SH performance and behavioral patterns were observed, suggesting possible differences in the immediate cause and ultimate function between young and adults. Young individuals engaged in frequent bouts of short duration, involving locomotion and vigorous body actions throughout the day, which is typical for play by young in general. This pattern of behavior is consistent with the motor training hypothesis, which states that play occurs during the development of motor and perceptual skills and is thus potentially critical for neural and cognitive development. This practice is continued by those who acquire it at an early age, with adults engaging in significantly fewer but longer bouts that involve more stationary, complex manipulative patterns, almost exclusively in the late afternoon. We propose that for adults, at the proximate level SH is psychologically relaxing, but ultimately functions to maintain and regenerate neural pathways, and potentially helps to slow down the deterioration of cognitive function associated with advanced age in long-lived provisioned and captive macaques. Am. J. Primatol. 69:1,15, 2007.© 2006 Wiley-Liss, Inc. [source] Racism, Sexism, and Candidate Evaluations in the 2008 U.S. Presidential ElectionANALYSES OF SOCIAL ISSUES & PUBLIC POLICY, Issue 1 2009Caitlin E. Dwyer In an attempt to understand the extent to which racism and sexism influenced affect toward Barack Obama and Sarah Palin, we analyze data from a national survey conducted in October 2008. Situating our investigation in previous examinations of modern racism and modern sexism, we test competing hypotheses about the role of these attitudes in the 2008 presidential election. Our results suggest that racism had a significant impact on candidate evaluations while sexism did not. We find that respondents who hold racist attitudes expressed negative attitudes toward Obama and positive attitudes toward Palin. When interacted with party identification, racism continued to exert a strong effect, indicating findings that are robust across partisan affiliations. Sexism, on the other hand, did not significantly influence evaluations of either Palin or Obama. [source] The Price Premium of China A-Shares over Hong Kong H-Shares: A Further Visit of the Liquidity Hypothesis,ASIA-PACIFIC JOURNAL OF FINANCIAL STUDIES, Issue 5 2009Hing-Wah Lee Abstract I examine the price premium between A-shares and H-shares using a sample of Hong Kong, Shenzhen, and Shanghai stock market intraday data in 2004. Following the market-microstructure approach, I reinvestigate the liquidity hypothesis by incorporating spread and depth. The study generates two important results. First, China A-shares on average provide better market liquidity than their Hong Kong H-share counterparts do. Second, after controlling for traditional liquidity measures and variables related to competing hypotheses, the percentage differences in quoted spread and depth between A-shares and H-shares still explain significantly the price premium. Endogeneity between spread and depth does not affect the major findings. [source] | ||||||||||||||||||||||||||||||||||