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Productivity Levels (productivity + level)
Selected AbstractsSize traits and site conditions determine changes in seed bank structure caused by grazing exclusion in semiarid annual plant communitiesECOGRAPHY, Issue 1 2006Yagil Osem 1. Contrasting patterns of change in the seed bank of natural grasslands are frequently found in response to grazing by domestic herbivores. Here, we studied the hypotheses that a) patterns of change in seed bank density and composition in response to grazing depend on spatial variation in resource availability and productivity, and b) that variation among species in patterns of seed bank response to grazing is linked to differences in species size traits (i.e. size of plant, dispersal unit and seed). 2. Effects of sheep grazing exclusion on the seed bank were followed during five years in a semiarid Mediterranean annual plant community in Israel. Seed bank density and composition were measured in autumn, before the rainy season, inside and outside fenced exclosures in four neighboring topographic sites differing in vegetation characteristics, soil resources and primary productivity: Wadi (dry stream terraces, high productive site), Hilltop, South- and North-facing slopes (less productive sites). 3. Topographic sites differed in seed density (range ca 2500,18000 seed m,2) and in seed bank response to grazing exclusion. Fencing increased seed density by 78, 51 and 18% in the Wadi, South- and North-facing slopes, respectively, but had no effect in the Hilltop. At the species level, grazing exclusion interacted with site conditions in determining species seed bank density, with larger or opposite changes in the high productive Wadi compared to the other less productive sites. 4. Changes in seed bank structure after grazing exclusion were strongly related to species size traits. Grazing exclusion favored species with large size traits in all sites, while seed density of tiny species decreased strongly in the high productive Wadi. Species with medium and small size traits showed lesser or no responses. 5. The size of plants, dispersal units and seeds were strongly correlated to each other, thus confounding the evaluation of the relative importance of each trait in the response of species to grazing and site conditions. We propose that the relative importance of plant size vs seed size in the response to grazing changes with productivity level. [source] EFFECTS OF TECHNOLOGY ADOPTION ON PRODUCTIVITY AND INDUSTRY GROWTH: A STUDY OF STEEL REFINING FURNACES,THE JOURNAL OF INDUSTRIAL ECONOMICS, Issue 3 2008TSUYOSHI NAKAMURA This paper examines the impact of new technology on plant-level productivity in the Japanese steel industry during the 1950's and 1960's. We estimate the production function, considering the differences in technology between the refining furnaces owned by a plant. We find that a more productive plant was likely to adopt the new technology and that the adoption would be expected to occur immediately following the peak of the productivity level achieved with the old technology. The adoption of the new technology primarily accounted not only for the industry's productivity slowdown but also for the industry's remarkable growth. [source] Dispersal limitation may result in the unimodal productivity-diversity relationship: a new explanation for a general patternJOURNAL OF ECOLOGY, Issue 1 2007MEELIS PÄRTEL Summary 1Variation in diversity with habitat productivity has long been a central ecological topic. Plant diversity is mostly highest at intermediate productivity, exhibiting the unimodal (so-called ,hump-back') relationship. This relationship has been explained by both evolutionary and ecological processes, but the potential role of dispersal limitation has not been considered. 2We used European flora data to show that dispersal limitation may contribute to the unimodal productivity-diversity relationship. Species were characterized by their habitat productivity preference and dispersal probability (determined by the number of seeds and the presence of a dispersal syndrome). We calculated average relative dispersal probabilities for species assemblages occurring preferentially in different habitat productivity levels. 3At low productivity levels, species without dispersal syndromes predominate (R2 = 0.89), but at high productivity levels, species with a low number of seeds are common (R2 = 0.89). The total relative dispersal probability, combining both the dispersal probabilities attributable to the number of seeds and to the presence of dispersal syndrome, had a unimodal relationship with habitat productivity (R2 = 0.86). Thus, the unimodal productivity-diversity relationship may arise due to the minimal dispersal limitation of local richness in conditions of moderately low productivity. At very low productivity, the lack of dispersal syndromes may limit dispersal. At high productivity, the low number of seeds may limit dispersal. 4Consequently, in conditions where species pool size and biotic interactions do not vary along productivity gradients, the variation in dispersal probabilities with productivity alone can produce unimodal relationships between diversity and productivity. Thus, dispersal limitation may contribute to the observed diversity pattern and ecosystem functioning to a greater extent than usually assumed. [source] Site productivity and plant size explain the response of annual species to grazing exclusion in a Mediterranean semi-arid rangelandJOURNAL OF ECOLOGY, Issue 2 2004Yagil Osem Summary 1The response of an annual plant community to protection from grazing as a function of variation in site productivity was studied in a semi-arid Mediterranean rangeland in Israel over 4 years (1996,99). The abundance of species was compared in grazed vs. ungrazed plots (exclosures) in four neighbouring topographic sites (south- and north-facing slopes, hilltop and Wadi shoulders), representing a gradient of resource availability and productivity. 2Above-ground potential productivity at peak standing crop in spring (i.e. inside exclosures) varied considerably between years and topographic sites. Productivity was similar among the hilltop, south- and north-facing slopes, and was typical of semi-arid ecosystems (10,200 g,2). Productivity in the Wadi was consistently greater (up to 700 g,2) and reached the range of subhumid grassland ecosystems. 3The effect of grazing exclusion on the composition of the annual vegetation was productivity-dependent. Lower similarity (Sorenson's quantitative similarity index) between grazed and ungrazed subplots was observed in the productive Wadi compared with the less productive sites. The small-scale variation in grazing impact on species composition, due to differences in productivity, is consistent with models predicting similar trends in perennial grasslands across larger scale gradients. 4The relationship between plant size (above-ground dry-weight), site productivity and response to fencing was analysed for the 36 most abundant annual species. Large species were more abundant in more productive sites, and small species at lower productivity, although few species were restricted to particular productivity levels. The response of individual species to protection from grazing was productivity dependent, with plant size playing a central role. Larger species tended to increase and small ones to decrease in abundance after fencing, with a mixed response in species with intermediate size. 5A conceptual model is presented relating the response to protection from grazing along gradients of productivity to species plant size. [source] Estimating the supply response of cotton and cereal crops in smallholder production systems: recent evidence from MaliAGRICULTURAL ECONOMICS, Issue 5 2009Jeffrey D. Vitale Cotton; Supply response; Rotation; Mali Abstract Cotton is one of the most important crops in West Africa and is a major catalyst of economic development in rural areas, but the sector has suffered from a decline in the world cotton price after 1999. This article exploits an unusual data set following 82 farmers over 14 years, from 1994 through 2007, to estimate a Nerlovian supply response model for cotton, maize, sorghum, and millet in long-term rotation. The resulting system of equations is estimated with two-stage least squares (2SLS), showing that this sample of Malian cotton producers have responded to prices in a relatively inelastic manner, with supply elasticities only about one-half of those estimated for producers in developed countries. Policy reforms could help producers respond more easily to prices changes, as well as to raise average productivity levels. [source] Interregional Disparities in Productivity and the Choice of Fiscal RegimeJOURNAL OF PUBLIC ECONOMIC THEORY, Issue 3 2009KIMIKO TERAI Two districts with divergent productivity levels engage in policy-making on the provision of local public goods that enhance future income and hence create a dynamic linkage across periods. The policy choices of district representatives are derived under alternative fiscal systems, and the relative merits of the systems are evaluated. It is predicted that a decentralized system is more likely to be selected in a more equal society. On the other hand, when a great deal of benefit spills over from a local public good, or when policy makers are expected to care solely about the immediate effects of their decisions on their districts, a centralized system is more likely to be selected. [source] Employment and Total Factor Productivity ConvergenceKYKLOS INTERNATIONAL REVIEW OF SOCIAL SCIENCES, Issue 4 2006David Greasley SUMMARY Using a new 16-country data set we demonstrate a robust negative employment-total factor productivity trade-off 1870,2004. Widely disparate cross country employment growth had a powerful long term influence on productivity dispersion. Unexceptional US productivity growth principally resulted from her exceptional employment growth rather than from her initially high productivity levels. The negative externalities associated with higher employment are shown to have dominated the diminishing of total factor productivity gaps among the 16 countries, and led to the erosion of US productivity leadership over the twentieth century. [source] The dynamics of top-down and bottom-up effects in food webs of varying prey diversity, composition, and productivityOIKOS, Issue 2 2007Jeremy W. Fox Prey diversity is thought to mediate the strength of top-down and bottom-up effects, but few experiments directly test this hypothesis. I assembled food webs of bacteria and bacterivorous protist prey in laboratory microcosms with all combinations of five productivity levels, two top predator treatments (present or absent), and three prey compositions. Depauperate food chains contained one of two edible prey species, while more diverse food webs contained both edible prey species plus two additional less-edible/inedible prey. Equilibrium theory predicts that prey diversity should weaken the top-down and bottom-up effects on trophic level biomasses, due to density compensation among prey species. Top-down effects should increase with productivity in food chains, but decrease with productivity in food webs. Results revealed highly dynamic top-down effects, the strength of which varied more over time than among treatments. Further, top-down effects did not merely vary in absolute strength over time, but also in relative strength across different prey compositions and productivity levels. It might be expected that equilibrium models would qualitatively reproduce time-averaged results. However, time-averaged data largely failed to support equilibrium predictions. This failure may reflect strong temporal variability in treatment effects combined with nonlinear density dependence of species' per-capita growth rates. Strong temporal variability in the strength of top-down effects has not previously been demonstrated, but likely is common in nature as well. [source] SCHOLARLY COLLABORATION AND PRODUCTIVITY PATTERNS IN PUBLIC ADMINISTRATION: ANALYSING RECENT TRENDSPUBLIC ADMINISTRATION, Issue 3 2010ELIZABETH A. CORLEY Previous studies have confirmed the interdisciplinary nature of the field of public administration (Mosher 1956; Ventriss 1991; Forrester 1996; Rodgers and Rodgers 2000; Schroeder et al. 2004) and encouraged the exploration of one important indicator of interdisciplinarity: research collaboration. One way that collaboration patterns are explored is through the study of co-authorship among faculty members (Smart and Bayer 1986; Forrester 1996; Katz and Martin 1997). In the field of public administration, studies on co-authorship and productivity of scholars are sparse. In this article, we use bibliometric data to explore collaboration patterns as they relate to productivity levels and quality of publications within the field of public administration. Our study finds that more productive scholars, as well as those with the highest impact, are less likely to collaborate than their colleagues. Our results also indicate that there are gender differences in collaboration patterns and productivity within the field of public administration. [source] Future of Economic Growth for South Korea,ASIAN ECONOMIC JOURNAL, Issue 4 2008Byung Woo KimArticle first published online: 11 DEC 200 O41; O53 More than 80 percent of US growth between 1950 and 1993 can be attributed to transition dynamics (increases in R&D intensity and educational attainment), with less than 20 percent of growth deriving from population growth. Similarly, growth accounting shows that 80 percent of economic growth in Korea can be attributed to transition dynamics. However, the specific factors that have moved Korea far from its steady state are significantly different from the factors that have done so for the USA. In addition to the growth rates of the two countries, we also analyzed the (steady-state) level of output per worker to determine where the Korean economy is headed relative to the USA. In 1960, Korea was characterized as poor (0.111) relative to its own steady state (0.765), and incomes were at 11.1 percent of those in the USA. Since then, however, Korea has been growing more rapidly than the USA. In our analysis, we also consider the extreme case where total factor productivity levels converge completely. Interestingly, in this case, the USA and Korea exhibit unconditional convergence similar to what is generally observed in the OECD. As the economy approaches the steady-state income level, however, the growth rate of output per capita will decline. [source] Grazing and landscape controls on nitrogen availability across 330 South African savanna sitesAUSTRAL ECOLOGY, Issue 7 2009JOSEPH M. CRAINE Abstract The availability of nitrogen (N) is an important determinant of ecosystem and community dynamics for grasslands and savannas, influencing factors such as biomass productivity, plant and herbivore composition, and losses of N to waters and the atmosphere. To better understand the controls over N availability at landscape to regional scales, we quantified a range of plant and soil characteristics at each of 330 sites in three regions of South Africa: Kruger National Park (KNP), private game reserves adjacent to KNP (private protected areas , PPAs) and Hluhluwe-iMfolozi Park (HiP). In comparing regions and sites within regions, grazing appeared to have a strong influence on N availability. Sites in the PPAs adjacent to KNP as well as sodic and alluvial sites in general typically had the highest N availability. The high N availability of these sites was not generally associated with greater potential N mineralization, but instead with less grass biomass and more forb biomass that indicated greater grazing pressure. Whereas sodic sites had a long history of high N availability as evidenced by their high soil ,15N, the greater N availability in the PPAs over the two parks appeared to be relatively recent. Grazer biomass, average potential mineralization rates and grass biomass for HiP were greater than KNP, yet there were no differences in N availability as indexed by soil and foliar ,15N between sites in the two parks. Although the short-term increase in N availability in PPAs is not necessarily deleterious, it is uncertain whether current productivity levels in those ecosystems is sustainable. With differences in management causing herbivore biomass to be 150% greater in the PPAs than the adjacent KNP, changes in plant communities and nitrogen cycling might lead to long-term degradation of these ecosystems, their ability to sustain herbivore populations, and also serve as an economic resource for the region. [source] Future developments in global livestock and grains markets: the impacts of livestock productivity convergence in Asia-PacificAUSTRALIAN JOURNAL OF AGRICULTURAL & RESOURCE ECONOMICS, Issue 3 2000Allan N. Rae Increasing livestock product consumption in many Asian countries has been accompanied by growth in some countries' imports of feedgrains for their domestic livestock sectors. This contributes to debate over future levels of grain imports. Yet projections often pay little attention to developments in livestock production. The impacts of technological catch-up in livestock production on trade in livestock and grains products among countries in the Asia-Pacific region are assessed. Tests are conducted of the hypothesis that productivity levels in the Asia-Pacific region are converging. Projections of livestock productivity are made and incorporated in a modified GTAP model. The consequences for regional and global trade in livestock and grains products are explored. [source] Virus-like particle production at low multiplicities of infection with the baculovirus insect cell systemBIOTECHNOLOGY & BIOENGINEERING, Issue 2 2003Luis Maranga Abstract The baculovirus insect cell expression system (BEVS) was used for the production of self-forming Porcine parvovirus -like particles (VLPs) in serum-free medium. A low multiplicity of infection (MOI) strategy was used to overcome an extra virus amplification step, undesirable in industrial production, and to minimize the virus passage effect. It was confirmed that the time of infection (TOI) and MOI are dependent variables. Higher cell densities were obtained at low MOIs, keeping a constant TOI; however, both volumetric and specific productivities were lower. In synchronous infection, at high MOI, the specific productivity decreased when the cells were infected in the late phase of growth. Product degradation due to cell lysis strongly influenced the optimal time of harvest (TOH). Time of harvest was found to be highly dependent on the MOI, and a direct relationship with the cell yield was obtained. Analysis of the culture medium reveals that glutamine depletion occurs in the late phase of the growth. Supplementation of glutamine to uninfected cell cultures resulted in an increased cell yield. Its addition to cultures infected in the middle phase of the growth curve was also able to restore the productivity levels, but addition to cells in their stationary phase caused no observable effect on product expression. The study clearly shows that for a specific TOI it is not obvious what the correct MOI should be to obtain the best volumetric productivity. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 84: 245,253, 2003. [source] | |||||||||||||||||||||||||