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Suitable Mechanisms (suitable + mechanism)
Selected AbstractsReproductive interference in two ground-hopper species: testing hypotheses of coexistence in the fieldOIKOS, Issue 9 2007Julia Gröning Similar to resource competition, reproductive interference may hamper the coexistence of closely related species. Species that utilize similar signal channels during mate finding may face substantial fitness costs when they come into contact and demographic displacement of the inferior species (sexual exclusion) is a likely outcome of such interactions. The two ground-hopper species Tetrix ceperoi and Tetrix subulata broadly overlap in their ranges and general habitat requirements, but rarely co-occur on a local scale. Results from laboratory and field experiments suggest that this mosaic pattern of sympatry might be influenced by reproductive interference. Here, we examine the significance of sexual interactions for these species in the field and test hypotheses on mechanisms of coexistence. Our results show that heterospecific sexual interactions also occur under field conditions, but in contrast to the experiments T. ceperoi was not the inferior species. The number of male mating attempts of both species was strongly correlated with encounter frequencies. Males discriminated between the sexes but not between the species, suggesting an incomplete mate recognition system in both species. The analysis of microhabitat preferences and spatial distribution revealed that habitat partitioning is not a suitable mechanism of coexistence in this system. Instead, the costs of reproductive interference are substantially mitigated by different niche breadths leading to different degrees of aggregation. Despite a considerable niche overlap T. ceperoi displayed a stronger preference for bare ground and occurred more aggregated than T. subulata, which had a broader niche. These differences may reduce the frequencies of heterospecific encounters and interactions in the field. Our results demonstrate that coexistence in the presence of reproductive interference is comparable to resource competition, being strongly influenced by ecological traits of the involved species, such as niche breadth and dispersion pattern. [source] Modification of polystyrene properties through grafting with N -vinylcarboxamido-2-methylpropane sulfonic acid monomerPOLYMER INTERNATIONAL, Issue 12 2004A Aggour Abstract Polystyrene (PS) possesses good mechanical properties, but its surface is relatively inert and hydrophobic. Grafting of N -vinylcarboxamido-2-methylpropane sulfonic acid (VCMP) is useful to hydrophilize the PS surface. Grafting was performed using benzoyl peroxide (BPO) as an initiator in toluene:methanol solvent mixture (3:1 volume ratio). The influence of the main factors on grafting, such as temperature, time, concentrations of initiator, PS and VCMP, has been studied. The results show that the initial rate of polymerization and percentage of grafting are enhanced by increased temperature. Furthermore, the specific rate constants of the first order reaction/are determined, and the activation energy of the grafting reaction is estimated. The grafting parameters are established and a suitable mechanism of the reaction is proposed. The grafted PS is to characterized through infrared spectra, intrinsic viscosity, thermogravimetric analysis (TGA) and differential gravimetric analysis (DTG). The kinetics of thermal degradation and the order of the thermal stabilities are given. Also the decomposition activation energies of the thermal degradation are determined, and confirm the thermal stabilities of the polymers used. © 2004 Society of Chemical Industry [source] The evolution of senescence from a comparative perspectiveFUNCTIONAL ECOLOGY, Issue 3 2008R. E. Ricklefs Summary 1Comparative studies of ageing address the evolutionary lability of the rate of ageing as an indication of potential for, and constraints on, the extension of life span. 2Experimental studies on ageing have focused on damage induced by reactive oxygen species (ROS) and other stresses, and on the mechanisms to prevent or repair this damage. Research on animal models has revealed genes with large effects on life span. However, the relevance of some animal models to human ageing is unclear and it is not known whether evolved differences in ageing involve such major gene effects. 3Studies on the demography of populations of vertebrates in the wild show that animals suffer from senescence in nature. Variation in the rate of ageing is consistent with evolutionary theory in that senescence is delayed in populations that suffer relatively low extrinsic mortality. 4Populations of longer-lived individuals suffer a higher proportion of ageing-related mortality, and thus stronger selection against early ageing. The presence of ageing-related deaths in these populations suggests a lack of suitable mechanisms that would further extend life span. 5Similar patterns of ageing-related mortality in wild and captive or domesticated populations indicate that most ageing-related death is caused by intrinsic factors, such as tumours and cardiovascular failure, rather than increasing vulnerability to extrinsic causes of mortality. 6Studies of several wild populations of long-lived birds suggest that ageing-related mortality is often catastrophic, with individuals maintaining high levels of condition until shortly before their demise. 7Comparative studies of many species suggest connections between early development and the pattern of ageing later in life, consistent with laboratory studies on variation within individual species. The physiological connections across the life span are not well understood. 8Comparative studies have provided important insights into the ageing process. However, we still lack information on important issues, including the causes of death in natural populations, the relationship of within- and between-population variation in the rate of ageing, the genetic basis of variation in rate of ageing in natural populations, and detailed longitudinal studies of individual health and reproductive success in relation to age at death. [source] New directions: a South Asian perspectiveINTERNATIONAL SOCIAL SCIENCE JOURNAL, Issue 167 2001Gamini Lakshman Peiris The central challenge facing countries of the developing world such as Sri Lanka is how to reconcile ethnic and cultural diversity with the concept of mature and cohesive nationhood. This is especially so where a federation is created not by the traditional pattern of independent entities coming together, but by devolution from a unitary state to one involving power sharing. In such situations there arealways fears that federalism is a precursor of dismemberment or disintegration. What is needed is to reconcile competing objectives for a strong and effective centre and for recognition of cultural and ethnic diversity. This may require hybrid or quasi-federal structures that do not fit neatly into unitary or federal categories. In attempting to achieve this reconciliation practicalities may require asymmetrical devolution, but this in turn may provoke emotional resistance to special or disparate treatment of particular minorities. Nor is devolution by itself sufficient. To be viable there must be suitable mechanisms to resolve intergovernmental disputes. Particularly important if confrontation and polarisation are to be minimised isemphasis upon compromise and proportionality and a public respect for pluralism, secularism, and representative democracy. [source] Exploring the suitability of the European Foundation for Quality Management (EFQM) Excellence Model as a framework for delivering clinical governance in the UK National Health ServiceQUALITY ASSURANCE JOURNAL, Issue 1 2001Sue Jackson Abstract In December 1997 the United Kingdom (UK) government publicized its vision for the National Health Service (NHS) to become the best health care system in the world. In line with this vision a number of consultative and directive documents were circulated, one of which was Clinical Governance: in the new NHS. This particular document provided insight into the principles and proposed framework for delivering clinical governance. However, the document suggested that health care organizations create mechanisms for delivering clinical governance which implied that the government had failed to recognize that suitable mechanisms were already available. The author suggests that one such suitable mechanism/framework is the EFQM Excellence Model. The article therefore examines the similarities of the principles behind clinical governance and the EFQM Excellence Model and recommends the latter as a suitable tool for ensuring that the country's people have the best health care system in the world. Copyright © 2001 John Wiley & Sons, Ltd. [source] | ||||||||||