Kochia (Bassia Scoparia) Growth and Fecundity As Influenced By Crop Competition and Weed Density

Kochia [Bassia scoparia (L.) A. J. Scott] represents one the most troublesome weeds in crop production systems in the North American Great Plains. The development of herbicide-resistant B. scoparia populations further exacerbated this problem. More ecologically driven approaches to its control are necessary. This study examined the competitive effects of four crops (sugar beet, soybean, barley, and corn) in combination with B. scoparia densities (3, 13, 24, 47, 94, and 188 plants m-2) on B. scoparia development and seed production across 2 years. Corn and barley had the greatest impact on B. scoparia growth and fecundity. B. scoparia biomass was 87 and 82% lower and seed production was 98 and 96% lower (p<0.001) in corn and barley, respectively, relative to fallow. Corn had greatest effect in reducing B. scoparia biomass and seed production. Barley had greatest effect in delaying B. scoparia flowering which occurred 113 days after B. scoparia emergence (p<0.001). Soybean and sugar beet had the least effect reducing B. scoparia biomass by 70 and 65% and seed production by 84 and 80% (p<0.001), respectively, relative to fallow. Increasing B. scoparia densities resulted in reductions in B. scoparia width, number of primary branches, biomass plant-1, and seeds plant-1 but increased B. scoparia height, biomass m-2, and seeds m-2 (p<0.001) under all cropping treatments except corn. Barley represents the greatest opportunity to impact B. scoparia through reduced fecundity and delayed flowering, with the latter providing a window of opportunity for post-harvest control. The effects observed here were isolated from differences in herbicide practices that are associated with each of these crops, differences that have a dramatic effect on B. scoparia in their own right.

PRICE DISCRIMINATION IN A FORM OF DISCOUNTS: CATEGORIZATION AND IMPACT ON COMPETITION

This paper is aimed to clarify the definition and categorization of discounts as well as pro- and anticompetitive effects of discounts. The author applied qualitative methods to the research. The modern literature review unfolds the gap of proper discounts definition, which is proposed to be covered by five-dimensions approach to discounts categorization. Based on such aspects of discount scheme as time, product, threshold, distribution level and customer, the approach provides comprehensive and uniform characteristics of discount. It allows assessing effects of competition, which are classified in two groups. Pro-competitive effects include stimulation of demand, decreasing cost due to economy of scale, solving coordination problems within a supply chain. Anti-competitive effects encompass predation scheme, raising rival’s cost, exclusive dealing, leverage and exclusionary bundling. The importance of correct assessment of the discounts by antitrust authorities is high as an overenforcement in this sphere may lead to adverse effect on total welfare.

An Extension of Two Species Lotka-Volterra Competition Model

Limiting resource is a angular stone of the interactions between species in ecosystems such as competition, prey-predators and food chain systems. In this paper, we propose a planar system as an extension of Lotka-Voterra competition model. This describes? two competitive species for a single resource? which are affected by intra and inter-specific interference. We give its complete analysis for the existence and local stability of all equlibria and some conditions of global stability. The model exhibits a rich set of behaviors with a multiplicity of coexistence equilibria, bi-stability, tri-stability and occurrence of global stability of the exclusion of one species and the coexistence? equilibrium. The asymptotic behavior and the number of coexistence equilibria are shown by a saddle-node bifurcation of the level of resource under conditions on competitive effects relatively to associated growth rate per unit of resource.Moreover, we determine the competition outcome in the situations of Balanced and Unbalanced intra-inter species competition effects. Finally, we illustrate results by numerical simulations.

Sorption of Monothioarsenate to the Natural Sediments and Its Competition with Arsenite and Arsenate

Monothioarsenate (MTAsV) is one of the major arsenic species in sulfur- or iron-rich groundwater, and the sediment adsorption of MTAsV plays an important role in arsenic cycling in the subsurface environment. In this study, batch experiments and characterization are conducted to investigate the sorption characteristic and mechanism of MTAsV on natural sediments and the influences of arsenite and arsenate. Results show that MTAsV adsorption on natural sediments is similar to arsenate and arsenite, manifested by a rapid early increasing stage, a slowly increasing stage at an intermediate time until 8 h, before finally approaching an asymptote. The sediment sorption for MTAsV mainly occurs on localized sites with high contents of Fe and Al, where MTAsV forms a monolayer on the surface of natural sediments via a chemisorption mechanism and meanwhile the adsorbed MTAsV mainly transforms into other As species, such as AlAs, Al-As-O, and Fe-As-O compounds. At low concentration, MTAsV sorption isotherm by natural sediments becomes the Freundlich isotherm model, while at high concentration of MTAsV, its sorption isotherm becomes the Langmuir isotherm model. The best-fitted maximum adsorption capacity for MTAsV adsorption is about 362.22 μg/g. Furthermore, there is a competitive effect between MTAsV and arsenate adsorption, and MTAsV and arsenite adsorption on natural sediments. More specifically, the presence of arsenite greatly decreases MTAsV sorption, while the presence of MTAsV causes a certain degree of reduction of arsenite adsorption on the sediments before 4 h, and this effect becomes weaker when approaching the equilibrium state. The presence of arsenate greatly decreases MTAsV sorption and the presence of MTAsV also greatly decreases arsenate sorption. These competitive effects may greatly affect MTAsV transport in groundwater systems and need more attention in the future.

Competitive asymmetry confers polyploid advantage under environmental stress

Competitive asymmetry across heterogeneous environments is crucial for the success of polyploid plants, however, little is known about it. As the major force in plant evolution, polyploids are predicted to maintain the competitive dominance relative to diploids under increased stress conditions. To evaluate the hypothesis of competitive asymmetry, we competed tetraploid and diploid plants of perennial herbaceous Chrysanthemum indicum L. (Asteraceae) at different relative frequencies under low and high water stress. We quantified the interaction intensity between competing plants of the same (intraploidy) and different ploidy levels (interploidy), and measured functional traits related to gas exchange and plant water use to understand the underlying mechanisms. Stronger competitive effects of the tetraploid on diploid provided evidence for the competitive asymmetry between polyploid and diploid plants in C. indicum. Such competitive asymmetry was not only maintained under drought (increased water stress), but also translated into higher fitness of the tetraploid consistently across water stress conditions. Functional traits associated with fast growth and efficient water use likely explained the competitive dominance of the tetraploid. These results will advance our understanding of species interactions between polyploid and diploid plants, and provide insights into population dynamics and species distribution under environmental change.

Condition-Specific Competitive Effects of the Invasive Mosquito Aedes albopictus on the Resident Culex pipiens among Different Urban Container Habitats May Explain Their Coexistence in the Field

Condition-specific competition, when environmental conditions alter the outcome of competition, can foster the persistence of resident species after the invasion of a competitively superior invader. We test whether condition-specific competition can facilitate the areawide persistence of the resident and principal West Nile virus vector mosquito Culex pipiens with the competitively superior invasive Aedes albopictus in water from different urban container habitats. (2) Methods: We tested the effects of manipulated numbers of A. albopictus on C. pipiens’ survival and development in water collected from common functional and discarded containers in Baltimore, MD, USA. The experiment was conducted with typical numbers of larvae found in field surveys of C. pipiens and A. albopictus and container water quality. (3) Results: We found increased densities of A. albopictus negatively affected the survivorship and development of C. pipiens in water from discarded containers but had little effect in water from functional containers. This finding was driven by water from trash cans, which allowed consistently higher C. pipiens’ survival and development and had greater mean ammonia and nitrate concentrations that can promote microbial food than other container types. (4) Conclusions: These results suggest that the contents of different urban containers alter the effects of invasive A. albopictus competition on resident C. pipiens, that trash cans, in particular, facilitate the persistence of C. pipiens, and that there could be implications for West Nile virus risk as a result.

Investigating and Prioritizing Factors Affecting Technology Selection Using Multi Criteria Decision Making Methods in the National Iranian Petrochemical Company

Technology can be considered as the most important factor in changing human experiences. Much of the success of most top companies in the field of competition rests on innovative activities that often rely on technology. On the other hand, defining valid and reliable as well as measurable indicators is necessary in order to make the most accurate decision. This refers to the famous saying that anything that can be measured can be managed. Therefore, using various scientific sources, the present study seeks to identify indicators of appropriate technology selection and then, prioritize them using multi-criteria decision making methods in the National Iranian Petrochemical Company. For this purpose, first important factors have been identified by studying the research literature and utilizing experts’ opinion gathered and aggregated by Delphi method. Then, by these factors have been ranked by screening and final identification through a hybrid approach of TOPSIS and Shannon entropy. According to the obtained results, technology efficiency has the highest priority among the factors which shows that in technology with the highest level of efficiency must be transferred and used in petrochemical industry. The competitive effects of technology have the lowest priority which shows that it is the least impact for technology transfer in this industry, and it need less attention from the industry practitioners