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Empirical Support (empirical + support)
Kinds of Empirical Support Selected AbstractsEmpirical support for a multi-dimensional model of sensations experienced by youth during their initial smoking episodesADDICTION, Issue 10 2010Chris G. Richardson ABSTRACT Aims To examine the dimensionality of sensations experienced during initial tobacco smoking. Design Cross-sectional survey. Setting Thirteen secondary schools located in British Columbia, Canada. Participants Data from 1187 adolescents who responded ,yes' to the question: ,Have you ever tried cigarette smoking, even one or two puffs?'. Measurements Participants answered questions about their demographic characteristics, tobacco smoking history and sensations experienced during their initial smoking episodes. Findings The sensations appear to represent the following three separate but modestly correlated dimensions: a pleasant dimension defined by feeling good and relaxed; an unpleasant dimension defined by coughing, feeling sick and nervous; and a ,buzz' dimension defined by feeling high and dizzy. The three factors made statistically significant contributions to the prediction of transition to regular smoking (defined as having smoked at least 100 cigarettes in one's life-time) after adjusting for age, sex and age at first puff. Conclusions The results suggest that three relatively distinct physiological systems appear to explain the relationship between initial smoking sensations and probability of becoming a regular smoker. Researchers examining sensations experienced during initial tobacco smoking episodes should consider using a three-dimensional profile of symptoms composed of pleasant, unpleasant and buzz dimensions. [source] Signaling, Free Cash Flow and "Nonmonotonic" DividendsFINANCIAL REVIEW, Issue 1 2010Kathleen Fuller G35 Abstract Many argue that dividends signal future earnings or dispose of excess cash. Empirical support is inconclusive, potentially because no model combines both rationales. This paper does. Higher quality firms pay dividends to eliminate the free cash-flow problem, while firms that outsiders perceive as lower quality pay dividends to signal future earnings and reduce the free cash-flow problem. In equilibrium, dividends are nonmonotonic with respect to the signal observed by outsiders; the highest quality firms pay smaller dividends than lower perceived quality firms. The model reconciles the existing literature and generates new empirical predictions that are tested and supported. [source] Second Language Vocabulary Acquisition: A Lexical Input Processing ApproachFOREIGN LANGUAGE ANNALS, Issue 2 2004Article first published online: 31 DEC 200, Joe Barcroft PhD These principles emphasize presentation of new words as input, allocation of limited processing resources during vocabulary acquisition, distinct components of vocabulary knowledge (e.g., form, meaning, mapping), and appropriate types of instruction for different stages of development. Empirical support is included. [source] The effect of a transaction tax on exchange rate volatilityINTERNATIONAL JOURNAL OF FINANCE & ECONOMICS, Issue 2 2010Markku Lanne Abstract We argue that a transaction tax is likely to amplify, not dampen, volatility in foreign exchange markets. Our argument stems from the decentralized trading practice and the presumable discrepancy between ,informed' and ,uninformed' traders' valuations. Given that the informed valuations are likely to be less dispersed, a transaction tax penalizes informed trades disproportionately, leading to increased volatility. Empirical support for this prediction is found by investigating the effect of transaction costs on the volatility of DEM/USD and JPY/USD returns. High-frequency data are used and an increase in transaction costs is found to have a significant positive effect on volatility. Copyright © 2009 John Wiley & Sons, Ltd. [source] Task-Based Assessment Centers: Empirical support for a systems modelINTERNATIONAL JOURNAL OF SELECTION AND ASSESSMENT, Issue 2 2010Duncan J. R. Jackson Task-based assessment centers (TBACs) have been suggested to hold promise for practitioners and users of real-world ACs. However, a theoretical understanding of this approach is lacking in the literature, which leads to misunderstandings. The present study tested aspects of a systems model empirically, to help elucidate TBACs and explore their inner workings. When applied to data from an AC completed by 214 managers, canonical correlation analysis revealed that extraversion, abstract reasoning, and verbal reasoning, conceptualized as inputs into a system, explained around 21% of variance in manifest assessment center behavior. Behavior, in this regard, was found to consist of both general and situationally specific elements. Results are discussed in terms of their support for a systems model and as they pertain to the literature on TBACs. [source] Where Does Personality Have Its Influence?JOURNAL OF PERSONALITY, Issue 6 2008A Supermatrix of Consistency Concepts ABSTRACT An understanding of the nature of personality depends on clear conceptions of consistency. Researchers have applied the term consistency in ambiguous and inconsistent ways over the last half century, which has led to a great deal of confusion and debate over the existence of personality. This article seeks to reframe and extend conceptions of consistency and thus proposes three important ways consistency concepts differ from each other. The first way consistency concepts differ from each other is in the competing determinant of behavior that the consistency is across: time, situation content, or behavior content. The second way consistency concepts differ from each other is in the definition of behavior enactment: single enactment, aggregate enactment, contingent enactment, or patterned enactment. When these two dimensions are crossed with a third dimension,definition of similarity (absolute, relative-position, or ipsative),they create a supermatrix of 36 consistency concepts. Empirical support for each of these 36 consistency concepts, or its failure, has uniquely different implications for the fundamental nature of personality. This supermatrix can serve as a guide for future research aimed at discovering the nature of personality. [source] The determinants of corporate political strategy in Chinese transitionJOURNAL OF PUBLIC AFFAIRS, Issue 4 2007Zhilong Tian Corporate political strategy (CPS) formulation in Chinese transition is an area with little empirical work. We fill this gap validly and the primary focus of this study is to examine the firm- and industry-level factors influencing Chinese firms' political strategy choice. Empirical support is found for the taxonomy of corporate political strategies in Chinese transition,that is direct participation strategy, financial incentive strategy, prolocutor strategy, institution innovation strategy, government association strategy and government involvement strategy. The results indicate that there is no consistently significant firm- and industry-level predictor of all six political strategies and we explore what determinants are related to each specific decision independently. We also verify the random effects of industry-level variables and our hypotheses are tested through using general evaluation equations (GEEs). Our study aims to be helpful to point managers toward both industrial environments and internal resources to consider when making appropriate political strategy choices and thus improve Chinese firms' strategy management level. Some implications of findings are also discussed finally. Copyright © 2007 John Wiley & Sons, Ltd. [source] The Determinants of Successful Micro-IPOs: An Analysis of Issues Made under the Small Corporate Offering Registration (SCOR) ProcedureJOURNAL OF SMALL BUSINESS MANAGEMENT, Issue 3 2001James C. Brau In this article we extend the existing IPO literature to the case of micro-IPOs by analyzing a sample of Small Corporate Offering Registration (SCOR) documents from the U.S. state of Washington. Through theory, we identified variables that should impact the probability of success or failure in a SCOR offering and then empirically tested them. Empirical support was found for the relevance of (1) marketing mechanisms and expenses; (2) ownership and governance factors; (3) business life cycle stages; and (4) signaling factors consistent with our theoretical predictions. [source] Site-specific genetic divergence in parallel hybrid zones suggests nonallopatric evolution of reproductive barriersMOLECULAR ECOLOGY, Issue 13 2006M. PANOVA Abstract The evolution of reproductive isolation in the presence of gene flow is supported by theoretical models but rarely by data. Empirical support might be gained from studies of parallel hybrid zones between interbreeding taxa. We analysed gene flow over two hybrid zones separating ecotypes of Littorina saxatilis to test the expectation that neutral genetic markers will show site-specific differences if barriers have evolved in situ. Distinct ecotypes found in contrasting shore habitats are separated by divergent selection and poor dispersal, but hybrid zones appear between them. Swedish islands formed by postglacial uplift 5000 years ago provide opportunities to assess genetic structure in a recently evolved system. Each island houses a discrete population containing subpopulations of different ecotypes. Hybrid zones between ecotypes may be a product of ecological divergence occurring on each island or a consequence of secondary overlap of ecotypes of allopatric origin that have spread among the islands. We used six microsatellite loci to assess gene flow and genetic profiles of hybrid zones on two islands. We found reduced gene flow over both hybrid zones, indicating the presence of local reproductive barriers between ecotypes. Nevertheless, subpopulations of different ecotypes from the same island were genetically more similar to each other than were subpopulations of the same ecotype from different islands. Moreover, neutral genetic traits separating the two ecotypes across hybrid zones were site-specific. This supports a scenario of in situ origin of ecotypes by ecological divergence and nonallopatric evolution of reproductive barriers. [source] Family mediation research: Is there empirical support for the field?CONFLICT RESOLUTION QUARTERLY, Issue 1-2 2004Joan B. Kelly First page of article [source] Corporate Governance and International Location Decisions of Multinational EnterprisesCORPORATE GOVERNANCE, Issue 6 2007Lammertjan Dam This paper analyses international location decisions of corporations based on corporate governance considerations. Using firm level data on 540 Multinational Enterprises (MNEs) with 44,149 subsidiaries in 188 countries, we test whether firms with relatively good governance standards are more often located in countries with a weak governance system. We find empirical support for this hypothesis, especially for those corporations present in low-income countries. [source] The effect of discordance among violence and general recidivism risk estimates on predictive accuracyCRIMINAL BEHAVIOUR AND MENTAL HEALTH, Issue 3 2006Jeremy F. Mills Introduction,Previous research has shown that the prediction of short-term inpatient violence is negatively affected when clinicians' inter-rater agreement is low and when confidence in the estimate of risk is low. This study examined the effect of discordance between risk assessment instruments used to predict long-term general and violence risk in offenders. Methods,The Psychopathy Checklist , Revised (PCL,R), Level of Service Inventory , Revised (LSI,R), Violence Risk Appraisal Guide (VRAG), and the General Statistical Information on Recidivism (GSIR) were the four risk-prediction instruments used to predict post-release general and violent recidivism within a sample of 209 offenders. Results,The findings lend empirical support to the assumption that predictive accuracy is threatened where there is discordance between risk estimates. Discordance between instruments had the impact of reducing predictive accuracy for all instruments except the GSIR. Further, the influence of discordance was shown to be greater on certain instruments over others. Discordance had a moderating effect on both the PCL,R and LSI,R but not on the VRAG and GSIR. Conclusions,There is a distinct advantage when attempting to predict recidivism to employing measures such as the LSI-R, which includes dynamic variables and intervention-related criminogenic domains, over a measure purely of fixed characteristics, such as the GSIR; however, if there is discordance between the risk estimates, caution should be exercised and more reliance on the more static historically based instrument may be indicated. Copyright © 2006 John Wiley & Sons, Ltd. [source] BETTER GUN ENFORCEMENT, LESS CRIME,CRIMINOLOGY AND PUBLIC POLICY, Issue 4 2005JENS LUDWIG Research Summary: Project Safe Neighborhoods (PSN), which for the past several years has been the major federal initiative to combat gun violence, includes several elements (such as gun locks and other efforts to reduce gun availability) that research suggests are likely to have at best modest effects on gun crime. In general, enforcement activities targeted at the "demand side" of the underground gun market currently enjoy stronger empirical support. However much of PSN's budget has been devoted to increasing the severity of punishment, such as by federaliz-ing gun cases, which seems to be less effective than targeted street-level enforcement designed to increase the probability of punishment for gun carrying or use in crime. Policy Implications: PSN and other enforcement activities could be made more effective by redirecting resources toward activities such as targeted patrols against illegal gun carrying. Given the substantial social costs of gun violence, an efficiency argument can also be made for increasing funding beyond previous levels. [source] The Decision of the Supply Chain Executive to Support or Impede Supply Chain Integration: A Multidisciplinary Behavioral Agency Perspective,DECISION SCIENCES, Issue 4 2009Verónica H. Villena ABSTRACT Applying the behavioral agency model developed by Wiseman and Gomez-Mejia (1998), this article analyzes human resource factors that induce supply chain executives (SCEs) to make decisions that foster or hinder supply chain integration. We examine two internal sources (compensation and employment risk) and one external source (environmental volatility) of risk bearing that can make SCEs more reluctant to make the decision to promote supply chain integration. We argue and empirically confirm the notion that an employment and compensation system that increases SCE risk bearing reduces the SCE's willingness to make risky decisions and thus discourages supply chain integration. We also reveal that this negative relationship becomes stronger under conditions of high environmental volatility. In addressing the "so what?" question, we found empirical support for the hypothesis that supply chain integration positively influences operational performance. Even though this decision has a positive value for the firm, we showed that SCEs discourage supply chain integration when they face higher risk bearing. Hypotheses are tested using a combination of primary survey data and archival measures in a sample of 133 Spanish firms. [source] Impaired selection of relevant positive information in depressionDEPRESSION AND ANXIETY, Issue 5 2009Sara M. Levens Ph.D. Abstract Background: A hallmark characteristic of depression is the inability to regulate the effect of emotional material on cognition. Previous research has demonstrated that depressed individuals are less able than are nondepressed persons to expel irrelevant negative information from working memory (WM), thereby exacerbating the effects of negative content on cognition. The primary goal of this study was to examine whether depressed individuals are also impaired at selecting relevant positive content in the context of representations competing for resources in WM; such an impairment would limit depressed persons' ability to use positive material to ameliorate the cognitive effects of negative information. Methods: We administered a Recency-probes task with neutral, positive, and negative words to 20 currently depressed and 22 never-depressed participants. This task assesses the selection of relevant content in WM by inducing interference between current and prior representations of a stimulus in WM. Reaction times to interference and noninterference trials were compared across valence and group to assess how effectively depressed individuals select task-relevant emotional content to resolve interference. Results: Compared to never-depressed controls, depressed individuals were impaired in selecting task-relevant positive stimuli; the performance of the two groups was comparable for selecting task-relevant neutral and negative stimuli. Conclusions: Findings indicate that a valence-specific deficit in WM may contribute to the inability of depressed individuals to regulate emotion, and provide empirical support for formulations that implicate positive insensitivity in the maintenance of depression. Depression and Anxiety, 2009. Published 2009 Wiley-Liss, Inc. [source] The dynamics of development and evolution: Insights from behavioral embryologyDEVELOPMENTAL PSYCHOBIOLOGY, Issue 8 2007Robert Lickliter Abstract The perspective that features of species-typical behavior could be traced to experience that occurred prenatally was raised by Zing-Yang Kuo [1921 Journal of Philosophy 18: 645,664] early in the last century and Gilbert Gottlieb subsequently elaborated on and provided empirical support for this idea over the course of more than four decades of innovative psychobiological research. Although we are still a long way from fully understanding the specific pathways and processes by which prenatal experience can influence postnatal development, Gottlieb's research with precocial birds provided significant insights into the conditions and experiences of prenatal development involved in the achievement of species-typical perception and behavior. In particular, his elegant series of studies on the development of species identification in ducklings documented how the features and patterns of recurring prenatal sensory experience (including self-stimulation) guide and constrain the young individual's selective attention, perception, learning, and memory during both prenatal and postnatal periods. I review how this body of research supports the view that the structure and functions of the developing organism and its developmental ecology together form a relationship of mutual influence on the emergence, maintenance, and transformation of species-typical behavior. I also explore how Gottlieb's empirical demonstrations of the prenatal roots of so-called "instinctive" behavior provided a foundation for his conceptual efforts to define the links between developmental and evolutionary change. © 2007 Wiley Periodicals, Inc. Dev Psychobiol 49: 749,757, 2007. [source] Allee effects in biological invasionsECOLOGY LETTERS, Issue 8 2005Caz M. Taylor Abstract Understanding the dynamics of small populations is obviously important for declining or rare species but is also particularly important for invading species. The Allee effect, where fitness is reduced when conspecific density is low, can dramatically affect the dynamics of biological invasions. Here, we summarize the literature of Allee effects in biological invasions, revealing an extensive theory of the consequences of the Allee effect in invading species and some empirical support for the theory. Allee effects cause longer lag times, slower spread and decreased establishment likelihood of invasive species. Expected spatial ranges, distributions and patterns of species may be altered when an Allee effect is present. We examine how the theory can and has been used to detect Allee effects in invasive species and we discuss how the presence of an Allee effect and its successful or unsuccessful detection may affect management of invasives. The Allee effect has been shown to change optimal control decisions, costs of control and the estimation of the risk posed by potentially invasive species. Numerous ways in which the Allee effect can influence the efficacy of biological control are discussed. [source] Trait variability and stress: canalization, developmental stability and the need for a broad approachECOLOGY LETTERS, Issue 2 2001Hoffmann Trait variability (particularly fluctuating asymmetry) may provide a general measure of environmental stress applicable across taxa but consistent empirical support is lacking. Historically, stress effects were considered to act independently on trait canalization, developmental noise and trait size. However, in trait comparisons these processes are often assumed to be associated. Here we reconsider this issue and implications for detecting stress effects using trait variability. Published studies that consider multiple environments report little association between the effects of environmental variation on trait canalization and on developmental noise measured as fluctuating asymmetry, sug-gesting that environmental effects often act independently on these processes. To further test the usefulness of trait variability as an indicator of stress, comparisons across environ-ments should take a broad approach and report on several measures of trait variability, rather than focusing on only one index of fluctuating asymmetry as is commonly done. [source] THE OPTIMAL PUBLIC EXPENDITURE FINANCING POLICY: DOES THE LEVEL OF ECONOMIC DEVELOPMENT MATTER?ECONOMIC INQUIRY, Issue 3 2007NILOY BOSE This paper explores how the optimal mode of public finance depends on the level of economic development. The theoretical analysis suggests that in the presence of capital market imperfection and liquidity shocks, the detrimental effect of inflation on growth is stronger (weaker) at lower (higher) levels of economic development. Consequently, income taxation (seigniorage) is a relatively less distortionary way of financing public expenditure for low-income (high-income) countries. We provide empirical support for our model's predictions using a panel of 21 Organization for Economic Cooperation and Development countries and 40 developing countries observed over the period 1972,1999. (JEL E44, E6, H6, O42) [source] Enter at your own risk: HMO participation and enrollment in the Medicare risk marketECONOMIC INQUIRY, Issue 3 2000J Abraham We examine HMO participation and enrollment in the Medicare risk market for the years 1990 to 1995. We develop a profit-maximization model of HMO behavior, which explicitly considers potential linkages between an HMO's production decision in the commercial enrollee market and its participation and production decisions in the Medicare risk market. Our results suggest that the payment rate is a primary determinant of HMO participation, while the price of a supplemental Medicare insurance policy positively affects HMO Medicare enrollment. We also find empirical support for the existence of complementarities in the joint production of an HMO's commercial and Medicare products. [source] Empirically evaluated treatments for body image disturbance: a reviewEUROPEAN EATING DISORDERS REVIEW, Issue 5 2006Clare Farrell Abstract Body image disturbance is both a risk factor for the development of disturbed eating and a central feature of clinical eating disorders. This review examines empirically tested interventions for people with high levels of body image disturbance. The most commonly used therapies with the most empirical support are cognitive-behavioural. The specificity of the body image interventions and the importance of individual components have not yet been established. Prevention programmes to address body image disturbance appear promising, although further research evidence is required. It is concluded that treatments for addressing body image disturbance are hindered by the lack of a clearly specified theoretical model of the maintenance of body image disturbance and that such an analysis is needed to increase the effectiveness of current interventions. Copyright © 2006 John Wiley & Sons, Ltd and Eating Disorders Association. [source] Theories of drug craving, ancient and modernADDICTION, Issue 1 2001D. Colin Drummond This paper reviews the principal theoretical models of drug craving and provides some directions for future research. The main models are classified broadly into three categories: (1) phenomenological models; based on clinical observation and description; these have been influential in classification systems of addictive disorders and in the development of pharmacological therapies; (2) conditioning models: based on conditioning theory; these have been influential in the development of cue exposure treatments; (3) cognitive theories; based on cognitive social learning theory: these have been influential in the development of cognitive therapies of addiction. It is concluded that no one specific theory provides a complete explanation of the phenomenon of craving. However, theories of craving grounded in general theories of human behaviour offer greatest promise, and generate more specific and testable research hypotheses. Theories that do not require craving to be present for relapse to occur have more empirical support than those that provide simplistic causal explanations. The cue-reactivity model shows promise in the exploration of the relationship between craving and relapse. However, further attention to the phenomenology of craving could help to advise the future measurement and study of drug craving, particularly in the context of research in which drugs are available to human subjects, with adequate ethical safeguards. There is a need for further study of the temporal dynamics of craving and consensus in the field on the most appropriate methods of measurement. Finally, new psychotherapies such as cue exposure and pharmacotherapies that aim to attenuate drinking behaviour, such as naltrexone and acamprosate, provide opportunities to improve understanding of the nature and significance of craving. However, the relatively uncritical assumption that craving is the underlying basis of addiction and represents the most appropriate target for treatment is challenged. [source] The effects of adolescent cannabis use on educational attainment: a reviewADDICTION, Issue 11 2000Michael Lynskey This paper reviews research examining the link between cannabis use and educational attainment among youth. Cross-sectional studies have revealed significant associations between cannabis use and a range of measures of educational performance including lower grade point average, less satisfaction with school, negative attitudes to school, increased rates of school absenteeism and poor school performance. However, results of cross-sectional studies cannot be used to determine whether cannabis use causes poor educational performance, poor educational performance is a cause of cannabis use or whether both outcomes are a reflection of common risk factors. Nonetheless, a number of prospective longitudinal studies have indicated that early cannabis use may significantly increase risks of subsequent poor school performance and, in particular, early school leaving. This association has remained after control for a wide range of prospectively assessed covariates. Possible mechanisms underlying an association between early cannabis use and educational attainment include the possibility that cannabis use induces an 'amotivational syndrome' or that cannabis use causes cognitive impairment. However, there appears to be relatively little empirical support for these hypotheses. It is proposed that the link between early cannabis use and educational attainment arises because of the social context within which cannabis is used. In particular, early cannabis use appears to be associated with the adoption of an anti-conventional lifestyle characterized by affiliations with delinquent and substance using peers, and the precocious adoption of adult roles including early school leaving, leaving the parental home and early parenthood. [source] Minority influence: the role of ambivalence toward the sourceEUROPEAN JOURNAL OF SOCIAL PSYCHOLOGY, Issue 4 2008Angelica Mucchi-Faina According to literature on social influence, a minority source may indirectly influence group members by fostering ambivalent reactions. Two studies were carried out in order to provide empirical support for this theoretical assumption. In Study 1 participants (n,=,133), were exposed to a counter-attitudinal minority message and ambivalence was manipulated by facilitating the accessibility of either ambivalent (positive and negative) or univalent (positive or negative) thoughts toward the source. We predicted and found more indirect influence in ambivalent condition than in univalent conditions. No effect of ambivalence on direct influence was found. In Study 2 (n,=,127), ambivalence was measured and two possible antecedents of ambivalence, consistency of the minority and personal relevance of the topic for participants, were taken into account. Findings suggest that ambivalence mediates the effects of the two factors on indirect influence. In sum, these studies provide evidence of the importance of ambivalence in minority influence context, an early assumption that was still lacking in strong empirical support. Copyright © 2007 John Wiley & Sons, Ltd. [source] In-group reassurance in a pain setting produces lower levels of physiological arousal: direct support for a self-categorization analysis of social influence,EUROPEAN JOURNAL OF SOCIAL PSYCHOLOGY, Issue 4 2007Michael J. Platow A large body of research demonstrates a strong social component to people's pain experiences and pain-related behaviours. We investigate this by examining the impact of social-influence processes on laboratory-induced pain responses by manipulating the social-categorical relationship between the person experiencing pain and another who offers reassurance. We show that physiological arousal associated with laboratory-induced pain is significantly lower in normal, healthy participants following reassurance about the pain-inducing activity when that reassurance comes from an in-group member in contrast to reassurance from an out-group member and a no reassurance control. These data are consistent with predictions derived from self-categorization theory, providing convincing empirical support of its analysis of social influence using a non-reactive measure. These data also represent a clear advance within the pain literature by identifying a possible common process to the social-psychological component of pain responses. Copyright © 2006 John Wiley & Sons, Ltd. [source] Stereotypes as justifications for prior intergroup discrimination: Studies of Scottish national stereotypingEUROPEAN JOURNAL OF SOCIAL PSYCHOLOGY, Issue 2 2001Adam Rutland Two studies provide support for the group-justification approach to stereotyping (Tajfel, 1981; Huici, 1984). This approach contends that stereotypes not only serve cognitive functions for individuals but also provide a means of justifying prior intergroup discrimination. Study 1 investigated whether the content of the Scottish ingroup stereotype changes due to the prior expression of intergroup discrimination. Scottish students were primed with either a ,differentiation' or a ,fairness' ingroup norm and completed two intergroup judgement tasks. Other Scottish students were primed only with a ,differentiation' ingroup norm, while a control group received no prime or judgement tasks. Only participants who experienced the ,differentiation' ingroup norm prime and the intergroup judgement tasks changed the content of their ingroup stereotype as an attempt to justify their discriminatory behaviour. Study 2 examined whether Scottish students would use both positive ingroup and negative outgroup stereotypes to rationalize intergroup discrimination. Students who experienced a ,differentiation' ingroup norm prime and intergroup judgement tasks showed the highest level of superior recall for positive ingroup and negative outgroup stereotype-consistent words compared to stereotype-neutral words. This finding suggests that the expression of intergroup discrimination activates the use of both positive ingroup and negative outgroup stereotypes. Together the findings of these two studies provide empirical support for the notion that stereotypes serve social as well as cognitive functions. Copyright © 2001 John Wiley & Sons, Ltd. [source] THE LOCI OF EVOLUTION: HOW PREDICTABLE IS GENETIC EVOLUTION?EVOLUTION, Issue 9 2008David L. Stern Is genetic evolution predictable? Evolutionary developmental biologists have argued that, at least for morphological traits, the answer is a resounding yes. Most mutations causing morphological variation are expected to reside in the cis -regulatory, rather than the coding, regions of developmental genes. This "cis -regulatory hypothesis" has recently come under attack. In this review, we first describe and critique the arguments that have been proposed in support of the cis -regulatory hypothesis. We then test the empirical support for the cis -regulatory hypothesis with a comprehensive survey of mutations responsible for phenotypic evolution in multicellular organisms. Cis -regulatory mutations currently represent approximately 22% of 331 identified genetic changes although the number of cis -regulatory changes published annually is rapidly increasing. Above the species level, cis -regulatory mutations altering morphology are more common than coding changes. Also, above the species level cis -regulatory mutations predominate for genes not involved in terminal differentiation. These patterns imply that the simple question "Do coding or cis -regulatory mutations cause more phenotypic evolution?" hides more interesting phenomena. Evolution in different kinds of populations and over different durations may result in selection of different kinds of mutations. Predicting the genetic basis of evolution requires a comprehensive synthesis of molecular developmental biology and population genetics. [source] CAN INTRASPECIFIC COMPETITION DRIVE DISRUPTIVE SELECTION?EVOLUTION, Issue 3 2004AN EXPERIMENTAL TEST IN NATURAL POPULATIONS OF STICKLEBACKS Abstract Theory suggests that frequency-dependent resource competition will disproportionately impact the most common phenotypes in a population. The resulting disruptive selection forms the driving force behind evolutionary models of niche diversification, character release, ecological sexual dimorphism, resource polymorphism, and sympatric speciation. However, there is little empirical support for the idea that intraspecific competition generates disruptive selection. This paper presents a test of this theory, using natural populations of the three-spine stickleback, Gasterosteus aculeatus. Sticklebacks exhibit substantial individual specialization associated with phenotypic variation and so are likely to experience frequency-dependent competition and hence disruptive selection. Using body size and relative gonad mass as indirect measures of potential fecundity and hence fitness, I show that an important aspect of trophic morphology, gill raker length, is subject to disruptive selection in one of two natural lake populations. To test whether this apparent disruptive selection could have been caused by competition, I manipulated population densities in pairs of large enclosures in each of five lakes. In each lake I removed fish from one enclosure and added them to the other to create paired low- and high-population-density treatments with natural phenotype distributions. Again using indirect measures of fitness, disruptive selection was consistently stronger in high-density than low-density enclosures. These results support long-standing theoretical arguments that intraspecific competition drives disruptive selection and thus may be an important causal agent in the evolution of ecological variation. [source] Increased growth and recruitment of piscivorous perch, Perca fluviatilis, during a transient phase of expanding submerged vegetation in a shallow lakeFRESHWATER BIOLOGY, Issue 12 2005ANDERS HARGEBY Summary 1. In this study, we examine how a 7-year period of expanding submerged stonewort (Chara spp.) vegetation during a shift from turbid to clear water in a shallow lake influenced individual growth and population size structure of perch (Perca fluviatilis). We expected that a shift from phytoplankton to macrophyte dominance and clear water would improve feeding conditions for perch during a critical benthivorous ontogenetic stage, and enhance the recruitment of piscivorous perch. 2. Growth analysis based on opercula showed that growth during the second year of life was significantly higher in years with abundant vegetation than in years with turbid water and sparse vegetation. Growth was not affected during the first, third and fourth year of life. Stable isotope analyses on opercula from 2-year-old perch showed that the increase in growth coincided with a change in carbon source in the diet. Stable nitrogen ratio did not change, indicating that the increased growth was not an effect of any change in trophic position. 3. Following the expansion of submerged vegetation, perch size range and abundance of piscivorous perch increased in central, unvegetated areas of the lake. In stands of stoneworts, however, mainly benthivorous perch were caught, and size range did not change with time. 4. Our findings provide empirical support for the notion that establishment of submerged vegetation may lead to increased recruitment of piscivorous perch, because of improved competitive conditions for perch during the benthivorous stage. This is likely to constitute a benthic-pelagic feedback coupling, in which submerged vegetation and clear water promote the recruitment of piscivorous perch, which, in turn, may increase water clarity through top-down effects in the pelagic. [source] The reproductive role hypothesis explains trophic morphology dimorphism in the northern map turtleFUNCTIONAL ECOLOGY, Issue 5 2008G. Bulté Summary 1Sexually dimorphic traits often reflect factors limiting the reproductive success of animals. Thus, most sexually dimorphic traits can be directly linked to the reproductive role of each sex. Sexual dimorphism in trophic structures (e.g. beak, jaws, teeth), however, often lacks a direct link to reproduction. 2Trophic structures can be linked indirectly to reproductive allocation via energy acquisition. The reproductive role hypothesis (also known as the dimorphic niche hypothesis) posits such an indirect link, but has received heretofore little direct empirical support. We tested this hypothesis in a molluscivorous turtle exhibiting marked female-biased trophic morphology dimorphism. 3Bite force analysis showed that females have stronger jaws than males and dietary analysis revealed that females ingest snails closer to their maximum biting capacity than males. Body condition of both sexes and reproductive output of females increased with relative head width, indicating that fitness is tightly linked to head size and bite force. 4Our study provides strong evidence that reproductive role contributes to sexual dimorphism in trophic morphology. Our findings should apply to any animal in which energy intake is limited by trophic morphology. [source] |