Competition Coefficients Research Articles

An experimental extreme drought reduces the likelihood of species to coexist despite increasing intransitivity in competitive networks

Abstract Very little is known about how variation in environmental conditions alters the strength and the structure of competitive networks and what are the consequences of this for species coexistence. We performed a competition experiment with 10 annual plant species to parameterise a population model describing species’ dynamics according to their vital rates and pairwise competitive coefficients. Seeds from all species were sown under two different climatic scenarios: (1) right before the first major storm of the growing season and (2) after an imposed fall drought of 2 months simulating an extreme climatic event of intense aridity. Species’ demography and competitive responses were used to estimate pairwise stabilising niche differences and average fitness differences. In addition, we used tools from network theory to characterise the structure of multispecies competition from the determinants of species coexistence. Specifically, we evaluated changes in competitive dominance between species pairs, and the prevalence of intransitive competitive relationships for 120 triplets between these two climatic events. The experimental extreme event significantly reduced fitness differences between species pairs. Such an equalising mechanism promotes coexistence. However, niche differences were also reduced in such a way that the number of species pairs whose niche differences overcame their fitness differences was reduced from six to two. Contrary to our expectations, the extreme event did not increase the hierarchy of competitive dominance. Instead, and depending on the technique used, the prevalence of intransitivity remained marginally similar (17% to 22%) or significantly increased from 19.4% to 29.8%. This pattern was likely a consequence of the significant changes in competitive dominance between species pairs (26 changes out of 45; 58%). Although fitness differences were equalised and intransitive competition promoted, our model predicted a lower likelihood of coexistence under the extreme event for both species pairs and triplets, mainly because competitive interactions did not promote enough niche differences to balance the observed fitness asymmetries in our competitive networks. Synthesis. We empirically proved that an extreme climate results in communities with reduced niche and fitness differences in which species are less likely to coexist despite the increasing prevalence of intransitive competition.

Invasion waves in the biochemical warfare between living organisms.

Microorganisms and plants very commonly release toxic secondary chemical compounds (allelochemicals) that inhibit or kill sensitive strains or individuals from their own or other species. In this work we study a model that describes two species interacting through allelopathic suppression and competing for resources. Employing linear stability analysis, the conditions for coexistence or extinction of species in spatially homogeneous systems were determined. We found that the borders between the regimes of bistability, coexistence, and the extinction of the weaker by the stronger competitor, are altered by allelopathic interactions. In addition, traveling wave solutions for one species invasion were obtained considering the spatially explicit nature of the model. Our findings indicate that the minimum speed of the invasion wavefronts depends primarily on the competition coefficients and the parameters characterizing the species' functional responses to their allelochemicals. As a general rule, the species provided with the most effective chemical weapons dominates the population dynamics. Finally, we found a tristability at the coexistence region due to the combination of allelopathy and patchy population distributions in space. So, our model provides a distinct mechanism, independent of social behaviors, that produces such unexpected tristability impossible in classical competition models involving one-to-one individual interactions.

Improving imprinted shape cavities of molecularly imprinted sol–gel host matrix with minimal relaxation for sensing of creatinine

Molecularly imprinted polymer (MIP) is of great attention in biomimetic recognition systems due to its selective molecular recognition towards any guest of interest. In this study, creatinine (Cre) was eluted from MIP via physical means to create the best molecular fitting to Cre. Among the polar eluents, methanol could overcome the intermolecular attractions between Cre and aluminium ion (Al3+) while conserving the Cre-shape memory to optimum with the minimal relaxation of the sol–gel host matrix simultaneously. With regard to the optimised shape complementarity of MIP, the solvation effect was scrutinised to reveal the interactions with Cre and MIP/NIP, respectively. Again, the Cre-adsorption in methanol compromised both the binding magnitude and imprinting factor reasonably the best at 19.48 ± 0.64 mg g−1 and 2.00 ± 0.09, respectively. Nevertheless, MIP was capable of selective uptake of Cre even in the presence of interfering analogues, i.e., creatine (Cr), N-hydroxysuccinimide (N-hyd), and 2-pyrrolidinone (2-pyr), by competitive selectivity coefficients of 3.01 ± 1.11, 3.75 ± 0.57, and 5.24 ± 4.59, respectively. In overall, MIP has proven its feasibility as a selective sorbent in capturing the molecule of interest with good recognition ability.

Competitive adsorption analyses of a pure magadiite and a new silylated magadiite on methylene blue and phenol from related aqueous solution

Organic contaminants have a destructive influence on the environment. Industrial emissions are the main source of such contaminants and simultaneously contain numerous and diverse types. These contaminants interact and influence each other when eliminated by sorbents. The aim of this research study was to explore the competitive adsorption of methylene blue and phenol on magadiite. In this research work, competitive adsorption properties of a new silylated magadiite--which is Na-magadiiite–cetyltrimethylammonium-3-Aminopropyltriethoxysilane (Na-MAG-CTAB-KH550) -- on methylene blue and phenol, were investigated. The prepared pure Na-magadiite (Na-MAG) and Na-MAG-CTAB-KH550 adsorbents were systematically characterized by a Nitrogen adsorption-desorption processes, X-ray diffraction and by use of a scanning electron microscope. Sorbents possessed a mesoporous characteristic. Based on the molding data obtained from the part of the adsorption experiment using the Langmuir and Freundlich models, the results indicated that the Na-MAG-CTAB-KH550 possessed a distinct advantage for adsorbing methylene blue and phenol. The results further showed that when the concentration of methylene blue was higher, the phenol more significantly influenced the adsorption of methylene blue. Moreover, compared with Na-MAG-CTAB-KH550, the presence of methylene blue exhibited a more striking influence on the Na-MAG and absorbing phenol. Incidental to this research the authors have proposed an innovative competitive elastic coefficient as a basis for in depth competitive discussion and analyses of the interaction between methylene blue and phenol.

Global stability and pattern formation in a nonlocal diffusive Lotka–Volterra competition model

A diffusive Lotka–Volterra competition model with nonlocal intraspecific and interspecific competition between species is formulated and analyzed. The nonlocal competition strength is assumed to be determined by a diffusion kernel function to model the movement pattern of the biological species. It is shown that when there is no nonlocal intraspecific competition, the dynamics properties of nonlocal diffusive competition problem are similar to those of classical diffusive Lotka–Volterra competition model regardless of the strength of nonlocal interspecific competition. Global stability of nonnegative constant equilibria are proved using Lyapunov or upper–lower solution methods. On the other hand, strong nonlocal intraspecific competition increases the system spatiotemporal dynamic complexity. For the weak competition case, the nonlocal diffusive competition model may possess nonconstant positive equilibria for some suitably large nonlocal intraspecific competition coefficients.

Functional and numerical responses of shrews to competition vary with mouse density.

For decades, ecologists have debated the importance of biotic interactions (e.g., competition) and abiotic factors in regulating populations. Competition can influence patterns of distribution, abundance, and resource use in many systems but remains difficult to measure. We quantified competition between two sympatric small mammals, Keen’s mice (Peromyscus keeni) and dusky shrews (Sorex monticolus), in four habitat types on Prince of Wales Island in Southeast Alaska. We related shrew density to that of mice using standardized regression models while accounting for habitat variables in each year from 2010–2012, during which mice populations peaked (2011) and then crashed (2012). Additionally, we measured dietary overlap and segregation using stable isotope analysis and kernel utilization densities and estimated the change in whole community energy consumption among years. We observed an increase in densities of dusky shrews after mice populations crashed in 2012 as expected under competitive release. In addition, competition coefficients revealed that the influence of Keen’s mice was dependent on their density. Also in 2012, shrew diets shifted, indicating that they were able to exploit resources previously used by mice. Nonetheless, increases in shrew numbers only partially compensated for the community energy consumption because, as insectivores, they are unlikely to utilize all food types consumed by their competitors. In pre-commercially thinned stands, which exhibit higher diversity of resources compared to other habitat types, shrew populations were less affected by changes in mice densities. These spatially and temporally variable interactions between unlikely competitors, observed in a relatively simple, high-latitude island ecosystem, highlight the difficulty in assessing the role of biotic factors in structuring communities.

Price effect and competition coefficients of agricultural exports - the case for Vietnamese export rice

In order to support a previous analysis of the increase in export value in Vietnamese rice market, the paper aims to identify whether or not the increase was caused by quantity or price effects. Along with the monthly data between 02/2009 and 08/2015, this paper uses the double logarit and error correction model (ECM) to estimate the price competition coefficients from Thai and Pakistani rice. Regression results confirmed the price effects of Thai and Pakistani rice price on Vietnamese price in the long run but not vice versa. The Vietnamese price was also altered which was followed by a change of exchange rate and yearly seasons. To reduce the risk of fluctuation in price, the Vietnamese Government and producers need to concern about momentous solutions such as increasing the quality of rice in proportion to consumer safety, establishing crop monitoring systems effectively to warn weather risks. Rice producers should apply information technology to correctly get an accurate reflection of the current market, manage the production process as well as take care of macroeconomic variables such as the exchange rate.

Approximate Solutions of the One-Dimensional Fisher–Kolmogorov–Petrovskii– Piskunov Equation with Quasilocal Competitive Losses

The modified Fisher–Kolmogorov–Petrovskii–Piskunov equation with quasilocal quadratic competitive losses and variable coefficients in the small nonlocality parameter approximation is reduced to an equation with a nonlinear diffusion coefficient. Within the framework of a perturbation method, equations are obtained for the first terms of an asymptotic expansion of an approximate solution of the reduced equation. Particular solutions in separating variables are considered for the equations determining the first terms of the asymptotic series. The problem is reduced to an elliptic integral and one linear, homogeneous ordinary differential equation.

Price effect and competition coefficients of agricultural exports - the case for Vietnamese export rice

Price effect and competition coefficients of agricultural exports - the case for Vietnamese export rice

Statistical Assessment of the Banks’ Competitiveness at the Financial Market: Theoretical and Methodological Aspect

The article is devoted to the vital problem of substantiating theoretical and methodological aspects of statistical assessment of the banks’ competitiveness at the financial market. The growing market competition makes the bankers chose competition methods by relating their business success to the business performance of their competitors, investors, corporate and private clients. The bank product competitiveness is assessed by comparing the economic parameters of an analyzed service with the benchmarking parameters, by group of parameters. A method based on the theory of effective competition is proposed for use as an option of the assessment of the competitiveness of a commercial bank. It enables for applying a universal method that allows for computing the integral coefficient of the competitiveness of a commercial bank by estimating the most important criteria of its operation.
 The assessment of the bank competitiveness has to include an analysis of the internal environment, covering quantitative and qualitative characteristics of its operation, and an analysis of external environment. The assessment involves differential and complex methods of assessment. The assessment of the internal environment includes a quantitative analysis of its financial position and a qualitative analysis of its image and competitiveness of its services. The method enables to produce the integral coefficient of competitiveness; it is based on the assessment of the internal and external environment of the banks that are main competitors, by computing a number of criteria. An analysis of the financial position of a bank is the central one, as it aims to produce a quantitative measure of the capacities promoting the development of a bank in future. The main advantage of the proposed method for the assessment of the competitiveness of a commercial bank is its feasibility, because it is based on data from published reports and results of market analyses. The comparative assessment of the operation of banks that are main competitors allows for quick and robust computation of each bank’s position at the financial market, whereas the results of the analysis give good idea of their business conditions and allow for the dynamic assessment of the effectiveness of the national bank system.

Application of competitive models in predicting the simultaneous growth of Staphylococcus aureus and lactic acid bacteria in milk

The simultaneous growth of Staphylococcus aureus and lactic acid bacteria (LAB) starter culture was studied in milk at different temperatures and LAB inoculums (ranging from 12 °C to 30 °C and 103–107 CFU ml−1, respectively). The modelling and predictive ability of three competition models were evaluated. Competition coefficients representing mutual population influence were incorporated into two of the models. This enabled the use of model parameters from individual S. aureus and LAB growth curves as well as those from co-culture growth in milk. Both the results and their statistical indices showed that incorporation of averaged competition coefficients resulting from individual co-culture trials improved the prediction of S. aureus behaviour in co-culture with LAB.

Quantitative predictions from competition theory with an incomplete knowledge of model parameters tested against experiments across diverse taxa

The capacity of community ecology for making quantitative predictions is often limited by incomplete empirical information which precludes obtaining reasonable estimates of model parameters. This is particularly the case for communities with large species richness S since it is practically impossible to perform the S monoculture experiments (to obtain the species carrying capacities) plus the S×(S−1)/2 pairwise experiments (required to estimate the entire set of interspecific interaction coefficients of the interaction or community matrix). However quantitative predictive tools are vital for understanding the fate of ecological communities.Here we derive an analytical approximation for predicting the relative yield total (or equivalently the mean relative yield) as a function of the mean intensity of the interspecific competition and the species richness. The rationale is that with incomplete information on model parameters it seems more reasonable to attempt to predict “macroscopic” or mean quantities, defined for the whole community of competing species, rather than making detailed “microscopic” predictions, like species abundances.This method, with only a fraction of the model parameters (carrying capacities and competition coefficients), is able to predict accurately empirical measurements covering a wide variety of taxa −algae, plants, protozoa, etc.Our aim with this approach is to contribute in making community ecology a more quantitative and predictive science. We argue that such parsimonious modeling is preferable than more realistic/complex theories involving additional parameters which can be very difficult to measure.

The Port Service Ecosystem Research Based on the Lotka-Volterra Model

Abstract Under the new normal of China’s economy, the competition among the port enterprises is not only the competition of the core competence of the port, the port industry chain or the port supply chain, but also the competition of the port service ecosystem. In this paper, the concept and characteristics of the port service ecosystem is discussed, a hierarchical model of the port service ecosystem is constructed. As an extended logistic model, Lotka-Volterra model is applied to study the competitive co-evolution and mutually beneficial co-evolution of enterprises in the port service ecosystem. This paper simulates the co-evolution of enterprises in the port service ecosystem by using MATLAB programming. The simulation results show that the breadth of the niche of the enterprises is changing with the change of the competition coefficient and the coefficient of mutual benefit in the port service ecosystem. Based on that, some proposals are put forward to ensure the healthy and orderly development of the port service ecosystem.

Maximization of viability time in a mathematical model of cancer therapy

In this paper, we study a dynamic optimization problem for a general nonlinear mathematical model for therapy of a lethal form of cancer. The model describes how the populations of cancer and normal cells evolve under the influence of the concentrations of nutrients (oxygen, glucose, etc.) and the applied therapeutic agent (drug). Regulated intensity of the therapy is interpreted as a time-dependent control strategy. The therapy (control) goal is to maximize the viability time, i. e., the duration of staying in a so-called safety region (which specifies safe living conditions of a patient in terms of constraints on the amounts of cancer and normal cells), subject to limited resources of the therapeutic agent. In a specific benchmark case, a novel optimality principle for admissible therapy strategies is established. It states that the optimal trajectories should finally reach a certain corner of the safety region or at least the upper constraint on the quantity of cancer cells. The results of numerical simulations appear to be in good agreement with the proposed principle. Typical qualitative structures of optimal treatment strategies are also obtained. Furthermore, important characteristics of the model are the competition coefficient (describing the negative influence of cancer cells on normal cells), the upper bound in the drug integral constraint, and the ratio between the therapy and damage coefficients (i. e., the ratio between the positive primary and negative side effects of the therapy).

Lead-Free Piezoelectric Ceramic Coatings Fabricated by Thermal Spray Process.

This paper starts from a review on the progress in fabrication of piezoelectric ceramic coatings by thermal spray method. For our experimental work, two types of lead-free piezoelectric ceramic coatings, including potassium-sodium niobate-based and bismuth sodium titanate-based, are fabricated by thermal spray process, and their structure, morphology, and piezoelectric properties are characterized. Our obtained lead-free ceramic coatings exhibit single phase of perovskite structure, relatively dense morphology, and competitive piezoelectric coefficients. The mechanism of forming the piezoelectric perovskite crystalline phase by thermal spray involving melting-recrystallization process is analyzed in comparison to that of ceramic synthesis through solid-state reaction. Suppression of volatile loss and decomposition at high temperature due to the extremely high melting and cooling rate in the thermal spray process, and the impact on the resulting structure are discussed. Significant advantages of the thermal spray method over alternative processing methods for forming piezoelectric ceramic coatings are summarized. The combination of environmentally friendly lead-free compositions and the scalable thermal spray processing method will promote more applications of piezoelectric ceramic coatings for producing distributive sensors and transducers, and forming advanced smart structures and systems.

A measure of marketing price transmission in the Red Onion Market of Sri Lanka

In the past there were several protectionist trade policies to safeguard the local onion production. This study examines their impact by means of nominal and effective protection rates and competiveness in resource utilization by competitiveness coefficient. There is a long-run co-integration relationship between the farm and the retail prices marketing margin resulting from this long-run relationship cause asymmetric short-run dynamic adjustments between the farm and the retail prices Welfare distribution among stakeholders is measured by classical welfare analysis. The analysis indicates that both big and red onion producers are noticeably protected by the trade policies and receive returns greater than they would get under a free market condition. Trade policies benefit consumers over producers. Gains to the nation are substantial.

Agronomic viability of New Zealand spinach and kale intercropping.

The intercropping is a production system that aims to provide increased yield with less environmental impact, due to greater efficiency in the use of natural resources and inputs involved in the production process. An experiment was carried out to evaluate the agronomic viability of kale and New Zealand spinach intercropping as a function of the spinach transplanting time. (0, 14, 28, 42, 56, 70, 84 and 98 days after transplanting of the kale). The total yield (TY) and yield per harvest (YH) of the kale in intercropping did not differ from those obtained in monoculture. The spinach TY was influenced by the transplanting time, the earlier the transplanting, the higher the TY. The spinach YH was not influenced by the transplanting time, but rather by the cultivation system. In intercropping, the spinach YH was 13.5% lower than in monoculture. The intercropping was agronomically feasible, since the land use efficiency index, which was not influenced by the transplanting time, had an average value of 1.71, indicating that the intercropping produced 71% more kale and spinach than the same area in monoculture. Competitiveness coefficient, aggressiveness and yield loss values showed that kale is the dominating species and spinach is the dominated.

Effectively tuning plant growth models with different spatial complexity: A statistical perspective

Forest gap models (non-spatial, patch- and individual-based models) and size structure models (non-spatial stand models) rely on two assumptions: the mean field assumption (A-I) and the assumption that plants in one patch do not compete with plants in other patches (A-II). These assumptions lead to differences in plant size dynamics between these models and spatially explicit models (or observations of real forests). Therefore, to more accurately replicate dynamics, these models require model tuning by (1) adjusting model parameter values or (2) introducing a correction term into models. However, these model tuning methods have not been systematically and statistically investigated in models using different patch sizes.We used a simple spatially explicit model that simulated growth and competition processes, and rewrote it as patch models. The patch sizes of the patch models were set between 4 and 1500m2. First, we estimated the parameter values (the intrinsic growth rate, metabolic loss, competition coefficient, and competitive asymmetry) of these models that best reproduce plant size growth under competition using field data from a Sakhalin fir stand, and compared the parameter values among the models. Second, we introduced correction terms into the patch models and estimated the optimal correction term for reproducing plant size growth under competition using the field data.The estimated parameter values of the patch models for all patch sizes differed greatly from those of the spatially explicit models. Therefore, parameter values should not be shared between spatially explicit models and patch models. In addition, the parameter value sets for the models with small patches differed from those with large patches. This is because parameter values for small patches mainly improve biases of A-II, while those for large patches mainly improve biases of A-I. Therefore, parameter values should not be shared between patch models with small patches and with large patches.The estimated correction term in the patch models with large patches excluded the competitive effects of small and medium-sized plants on their neighbors, even though these effects exist in real stands. This exclusion can be ascribed to the discrepancy between their competition in real plant populations and A-I. Therefore, the competitive effects of small and medium-sized plants should not be included in patch models with large patches. Finally, the reproducibility of the models tuned with correction terms was higher than those with adjusted parameters.

On the validity of Zeeman's classification for three dimensional competitive differential equations with linearly determined nullclines

We study three dimensional competitive differential equations with linearly determined nullclines and prove that they always have 33 stable nullcline classes in total. Each class is given in terms of inequalities on the intrinsic growth rates and competitive coefficients and is independent of generating functions. The common characteristics are that every trajectory converges to an equilibrium in classes 1–25, that Hopf bifurcations do not occur within class 32, and that there is always a heteroclinic cycle in class 27. Nontrivial dynamical behaviors, such as the existence and multiplicity of limit cycles, only may occur in classes 26–33, but these nontrivial dynamical behaviors depend on generating functions. We show that Hopf bifurcation can occur within each of classes 26–31 for continuous-time Leslie/Gower system and Ricker system, the same as Lotka–Volterra system; but it only occurs in classes 26 and 27 for continuous-time Atkinson/Allen system and Gompertz system. There is an apparent distinction between Lotka–Volterra system and Leslie/Gower system, Ricker system, Atkinson/Allen system, and Gompertz system with the identical growth rate. Lotka–Volterra system with the identical growth rate has no limit cycle, but admits a center on the carrying simplex in classes 26 and 27. But Leslie/Gower system, Ricker system, Atkinson/Allen system, and Gompertz system with the identical growth rate do possess limit cycles. At last, we provide examples to show that Leslie/Gower system and Ricker system can also admit two limit cycles. This general classification greatly widens applications of Zeeman's method and makes it possible to investigate the existence and multiplicity of limit cycles, centers and stability of heteroclinic cycles for three dimensional competitive systems with linearly determined nullclines, as done in planar systems.

Numerical modeling of dynamics of a population system with time delay

Mathematical models of interacting populations are often constructed as systems of differential equations, which describe how populations change with time. Below we study such a model connected to the nonlinear dynamics of a system of populations in presence of time delay. The consequence of the presence of the time delay is that the nonlinear dynamics of the studied system become more rich, eg, new orbits in the phase space of the system arise, which are dependent on the time‐delay parameters. In more detail, we introduce a time delay and generalize the model system of differential equations for the interaction of 3 populations based on generalized Volterra equations in which the growth rates and competition coefficients of populations depend on the number of members of all populations. Then we solve numerically the system with and without time delay. We use a modification of the method of Adams for the numerical solution of the system of model equations with time delay. By appropriate selection of the parameters and initial conditions, we show the impact of the delay time on the dynamics of the studied population system.