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Factors Shaping (factor + shaping)
Selected AbstractsThe significance of a facultative bacterium to natural populations of the pea aphid Acyrthosiphon pisumECOLOGICAL ENTOMOLOGY, Issue 2 2003A. C. Darby Abstract. 1., Laboratory studies have implicated various accessory bacteria of aphids as important determinants of aphid performance, especially on certain plant species and under certain thermal regimes. One of these accessory bacteria is PABS (also known as T-type), which is distributed widely but is not universal in natural populations of the pea aphid Acyrthosiphon pisum in the U.K. 2., To explore the impact of PABS on the performance of A. pisum , the nymphal development time and fecundity of aphids collected directly from natural populations and caged on the host plant Vicia faba in the field were quantified. Over 4 consecutive months June,September 1999, the performance of PABS-positive and PABS-negative aphids did not differ significantly. 3., Deterministic modelling of the performance data showed that the variation in simulated population increase of PABS-positive and PABS-negative aphids would overlap substantially. 4., Analysis of aphids colonising five host plants ( Lathyrus odoratus , Medicago sativa , Pisum sativum , Trifolium pratense , Vicia faba ) between April and September 2000 and 2001, identified no robust differences between the distribution of PABS-positive and PABS-negative aphids on different plants and with season or temperature. 5., It is concluded that PABS is not an important factor shaping the performance or plant range of A. pisum under the field conditions tested. Reasons for the discrepancies between this study and laboratory-based studies are considered. [source] Does Entrepreneurship Capital Matter?ENTREPRENEURSHIP THEORY AND PRACTICE, Issue 5 2004David B. Audretsch Economics has identified three types of capital as the drivers of economic growth,physical capital, human capital, and knowledge capital. This article introduces the concept of entrepreneurship capital and suggests that it is also an important factor shaping the economic performance of an economy. We define entrepreneurship capital as those factors influencing and shaping an economy's milieu of agents in such a way as to be conducive to the creation of new firms. The hypothesis that entrepreneurship capital is positively linked to economic growth is then tested by examining the relationship between several different measures of entrepreneurship capital and regional economic performance, measured as per-capita income for Germany. The empirical evidence suggests that there is indeed a positive link between entrepreneurship capital and regional economic performance. These results suggest a new direction for public policy that focuses on instruments to enhance entrepreneurship capital. [source] Sex differences in grey seal diet reflect seasonal variation in foraging behaviour and reproductive expenditure: evidence from quantitative fatty acid signature analysisJOURNAL OF ANIMAL ECOLOGY, Issue 3 2007CARRIE A. BECK Summary 1Intraspecific variation in diet can be an important component of a species niche breadth. We tested the hypothesis that sex differences in seasonal foraging behaviour and energy storage of sexually size dimorphic grey seals Halichoerus grypus (Fabrisius 1971) are reflected in differences in the diet and niche breadth. Diet composition was estimated for 496 adult (226 males, 270 females) and 91 juvenile (46 males/45 females; all 6 months old) grey seals sampled between 1993 and 2000 using quantitative fatty acid signature analysis. Niche breadth and overlap were estimated using the Shannon,Weaver diversity index (H,) and the Morisita,Horn index (CH), respectively. 2Sand lance Ammodytes dubius (Reinhardt 1837) and redfish Sebastes sp. (Cuvier 1829) accounted for a high proportion of the diet in both sexes and age groups. However, the diets of adult males were significantly more diverse across all seasons (H,: males 0·36 ± 0·007 vs. females 0·28 ± 0·007) and less energy dense in spring (male 5·3 ± 0·07 kJ g,1 vs. females 5·6 ± 0·09 kJ g,1) than those of adult females. 3Season and sex explained most of the observed variation in adult diets, but there were significant sex,season interactions. These differences were most evident during the post-breeding (spring) foraging period when energy acquisition is important to female recovery of nutrient stores needed to support pregnancy. Females selected fewer and higher quality prey species in spring than males. 4There were no sex differences in the diets of juvenile grey seals. Although many of the species overlapped with those eaten by adults, juvenile niche breadth (H,: 0·41 ± 0·014, n = 91) was significantly broader than that of adults (H,: 0·30 ± 0·011, n = 115). Juvenile diets were also of lower energy density (5·3 ± 0·04 kJ g,1) than those of adults (5·6 ± 0·09 kJ g,1), suggesting less selectivity in these young and relatively naïve predators. 5Sex-specific seasonal changes in diet correspond to seasonal changes in diving behaviour and rate of body energy accumulation of adult males and females. Sex-specific reproductive requirements appear to be a primary factor generating the intraspecific variation in the seasonal foraging ecology of this large marine carnivore. However, sex differences in the breadth and energy content of diets also suggest the influence of body-size dimorphism as a factor shaping the diet of this species. [source] Biogeography of the Amazon molly, Poecilia formosaJOURNAL OF BIOGEOGRAPHY, Issue 1 2002Ingo Schlupp Aim The unisexual Amazon molly (Poecilia formosa) is a clonal, all-female fish but depends on sperm of heterospecific males to trigger embryogenesis. Thus, one very important factor shaping its geographical range is the presence of suitable host males. Several species of the genus Poecilia from Central America, Mexico and the USA can provide sperm in the laboratory, but are not utilized as hosts in nature. Consequently the potential geographic range of the Amazon molly is much larger than the actual range. This raises the question of what is responsible for the biogeographical range of the Amazon molly? Location Southern USA, Mexico and Central America. Methods We review the current data available for the distribution of the Amazon molly. We further tested whether salinity might hinder the dispersal of the species. Results Amazon mollies tolerate marine conditions. We review the available data on recent and human influenced introductions of Amazon mollies. Main conclusions We argue that male preferences are not responsible for the current range. We propose that prevailing near-shore marine currents act as an effective barrier against further dispersal. Furthermore, we discuss recent changes in the biogeography of the Amazon molly. [source] Global factors shaping the future of food aid: the implications for WFPDISASTERS, Issue 2007Daniel Maxwell Food aid is a key component of a humanitarian response but its use in other programming contexts is subject to numerous criticisms. Even in humanitarian emergencies food aid is often late, unreliable and out of proportion to other elements of the response. Three major factors will shape the future of food aid. First, mechanisms of food aid governance are being reviewed and may undergo major changes,particularly the Food Aid Convention now that hopes have diminished for an Agreement on Agriculture at the World Trade Organisation. The second significant factor is donor agency trends. Overall levels of food aid have dropped fairly steadily in recent decades and there are several discernible trends in resource allocation, procurement and the use of food aid. The third factor is an emerging body of best practice that will define acceptable standards of food aid programming in the future. [source] Testing the intermediate disturbance hypothesis: when will there be two peaks of diversity?DIVERSITY AND DISTRIBUTIONS, Issue 1 2005Karin Johst ABSTRACT Succession after disturbances generates a mosaic of patches in different successional stages. The intermediate disturbance hypothesis predicts that intermediate disturbances lead to the highest diversity of these stages on a regional scale resulting in a hump-shaped diversity,disturbance curve. We tested this prediction using field data of forest succession and hypothetical succession scenarios in combination with analytical and simulation models. According to our study the main factors shaping the diversity,disturbance curve and the position of the diversity maximum were the transition times between the successional stages, the transition type, neighbourhood effects and the choice of diversity measure. Although many scenarios confirmed the intermediate disturbance hypothesis we found that deviations in the form of two diversity maximums were possible. Such bimodal diversity,disturbance curves occurred when early and late successional stages were separated by one or more long-lived (compared to the early stages) intermediate successional stages. Although the field data which met these conditions among all those tested were rare (one of six), the consequences of detecting two peaks are fundamental. The impact of disturbances on biodiversity can be complex and deviate from a hump-shaped curve. [source] Patterns of bacterial diversity across a range of Antarctic terrestrial habitatsENVIRONMENTAL MICROBIOLOGY, Issue 11 2007Etienne Yergeau Summary Although soil-borne bacteria represent the world's greatest source of biological diversity, it is not well understood whether extreme environmental conditions, such as those found in Antarctic habitats, result in reduced soil-borne microbial diversity. To address this issue, patterns of bacterial diversity were studied in soils sampled along a > 3200 km southern polar transect spanning a gradient of increased climate severity over 27° of latitude. Vegetated and fell-field plots were sampled at the Falkland (51°S), South Georgia (54°S), Signy (60°S) and Anchorage Islands (67°S), while bare frost-sorted soil polygons were examined at Fossil Bluff (71°S), Mars Oasis (72°S), Coal Nunatak (72°S) and the Ellsworth Mountains (78°S). Bacterial 16S rRNA gene sequences were recovered subsequent to direct DNA extraction from soil, polymerase chain reaction amplification and cloning. Although bacterial diversity was observed to decline with increased latitude, habitat-specific patterns appeared to also be important. Namely, a negative relationship was found between bacterial diversity and latitude for fell-field soils, but no such pattern was observed for vegetated sites. The Mars Oasis site, previously identified as a biodiversity hotspot within this region, proved exceptional within the study transect, with unusually high bacterial diversity. In independent analyses, geographical distance and vegetation cover were found to significantly influence bacterial community composition. These results provide insight into the factors shaping the composition of bacterial communities in Antarctic terrestrial habitats and support the notion that bacterial diversity declines with increased climatic severity. [source] Environmental factors shaping the ecological niches of ammonia-oxidizing archaeaFEMS MICROBIOLOGY REVIEWS, Issue 5 2009Tuba H. Erguder Abstract For more than 100 years it was believed that bacteria were the only group responsible for the oxidation of ammonia. However, recently, a new strain of archaea bearing a putative ammonia monooxygenase subunit A (amoA) gene and able to oxidize ammonia was isolated from a marine aquarium tank. Ammonia-oxidizing archaea (AOA) were subsequently discovered in many ecosystems of varied characteristics and even found as the predominant causal organisms in some environments. Here, we summarize the current knowledge on the environmental conditions related to the presence of AOA and discuss the possible site-related properties. Considering these data, we deduct the possible niches of AOA based on pH, sulfide and phosphate levels. It is proposed that the AOA might be important actors within the nitrogen cycle in low-nutrient, low-pH, and sulfide-containing environments. [source] The role of oceanographic conditions and plankton availability in larval fish assemblages off the Catalan coast (NW Mediterranean)FISHERIES OCEANOGRAPHY, Issue 3 2010M. PILAR OLIVAR Abstract In the northwestern Mediterranean, most fish species reproduce in early summer and fewer in the autumn mixing period. This study analyses and compares larval fish assemblages (LFA) in both seasons, and is the first attempt to characterize LFA structure for the autumn period. We analyze horizontal and vertical distribution of fish larvae and the micro- and mesozooplankton biomass and abundance of the main zooplankton groups. The oceanographic situation was analyzed through the study of data from CTD, N,-Shuttle and ADCP surveys. LFA were determined by ordination analyses based on larval abundance, and the relationships between larval assemblages and environmental variables were investigated through canonical correspondence analysis. The importance of some hydrographic variables (temperature, salinity and stability of the water column), current fields (along-shelf and across-shelf transport) and the abundance of zooplankton are discussed as important factors shaping the structure of larval assemblages. In early summer, LFA were mainly structured by a combination of bathymetry and trophic components, although sea surface temperature also played a role in shaping the horizontal larval distributions. In autumn, trophic variables were the main factors influencing the shelf-dwelling species assemblage. Larvae of oceanic species, on the other hand, were not related to trophic variables but were more affected by current fields. [source] Assessing factors that influence spatial variations in duff moistureHYDROLOGICAL PROCESSES, Issue 15 2008L. D. Raaflaub Abstract Patterns and spatial variations in the moisture of the decomposing organic matter on the forest floor (the duff) of a montane forest were analysed in an effort to determine the primary factors shaping these patterns. Above and below canopy meteorological conditions were monitored to determine the influence of canopy cover on duff moisture. The spatial and temporal distributions of duff moisture were assessed through daily duff moisture measurements collected at regular intervals in ten 10 × 10 m plots representing a variety of canopy types and densities. Meteorological conditions ranged from very wet to very dry and resulted in duff moisture variations that were more pronounced during wet periods than in extended periods of drying. Investigations on the influence of canopy type, tree density, and tree proximity on duff moisture patterns indicated that canopy type and tree proximity are the most important factors affecting duff moisture. Interception seems to be the primary controller of duff moisture patterns with an influence at the centimetre scale. Copyright © 2008 John Wiley & Sons, Ltd. [source] An Activation-Based Model of Sentence Processing as Skilled Memory RetrievalCOGNITIVE SCIENCE - A MULTIDISCIPLINARY JOURNAL, Issue 3 2005Richard L. Lewis Abstract We present a detailed process theory of the moment-by-moment working-memory retrievals and associated control structure that subserve sentence comprehension. The theory is derived from the application of independently motivated principles of memory and cognitive skill to the specialized task of sentence parsing. The resulting theory construes sentence processing as a series of skilled associative memory retrievals modulated by similarity-based interference and fluctuating activation. The cognitive principles are formalized in computational form in the Adaptive Control of Thought,Rational (ACT,R) architecture, and our process model is realized in ACT,R. We present the results of 6 sets of simulations: 5 simulation sets provide quantitative accounts of the effects of length and structural interference on both unambiguous and garden-path structures. A final simulation set provides a graded taxonomy of double center embeddings ranging from relatively easy to extremely difficult. The explanation of center-embedding difficulty is a novel one that derives from the model' complete reliance on discriminating retrieval cues in the absence of an explicit representation of serial order information. All fits were obtained with only 1 free scaling parameter fixed across the simulations; all other parameters were ACT,R defaults. The modeling results support the hypothesis that fluctuating activation and similarity-based interference are the key factors shaping working memory in sentence processing. We contrast the theory and empirical predictions with several related accounts of sentence-processing complexity. [source] Applying Andersen's behavioural model to oral health: what are the contextual factors shaping perceived oral health outcomes?COMMUNITY DENTISTRY AND ORAL EPIDEMIOLOGY, Issue 6 2009S. R. Baker Abstract,,, Objectives:, Andersen's revised behavioural model provides a framework for understanding the factors which influence utilization of health services and key health outcomes. To date, there have been few studies that have explicitly tested the model in relation to oral health. The aim of this study was to test the model and to examine the direct and mediated pathways between social, attitudinal and behavioural factors and perceived oral health outcomes. Methods:, The model was tested in a general population sample with data from the UK adult dental health survey (N = 3815) using the two-stage process of structural equation modelling. Results:, Structural equation modelling indicated support in line with the hypotheses within the model; enabling resources (oral health education advice, type of dental service, finding NHS treatment expensive, dental anxiety) predicted need (number of decayed or unsound teeth and perceived treatment need); enabling resources and need predicted personal health practices and use of services (frequency of toothbrushing, recent dental attendance, attendance orientation) which, in turn, predicted perceived oral health outcomes (oral health quality of life). Both enabling resources and need also predicted perceived oral health outcomes. The impact of predisposing factors (social class, qualifications, income) on need, personal health practices and use of services, and oral health outcomes was indirect; that is, mediated by intervening factors. In the final model, 26%, 37%, 49% and 21% of the variance was accounted for in enabling resources, treatment need, personal health practices and use of services and perceived oral health outcomes respectively. Conclusion:, The results provide support for Andersen's behavioural model as applied to perceived oral health. Further conceptual development of the model is discussed. [source] |