Simple Competition Research Articles

Note sur la biogéographie de la biodiversité du genre Artemia dans la région ouest de l’Afrique du Nord (Algérie, Maroc et Tunisie)

The crustacean Artemia (Branchiopoda, Anostraca) is one of the most common inhabitants of aquatic hypersaline, coastal and/ or continental lakes, lagoons and saltworks. With the indispensable use of its nauplii in marine aquaculture, the cysts of Artemia have become a natural resource of great commercial importance, which has led to the need to study its biodiversity and to know its biogeography, in order to provide and establish its commercial exploitation as a resource. Although the biogeography of species and populations of Artemia is known in the Mediterranean area, its distribution in the countries of North Africa is not yet well established. During the last decades great efforts have been made in this regard, especially in countries such as Algeria, Morocco and Tunisia, where we have verified the existence of a pattern of biodiversity similar to that described in the European Western Mediterranean, represented mainly by three common forms : the sexual species Artemia salina (Leach 1758) and the two parthenogenetic strains (A. parthenogenetica Barigozzi, 1980) : diploid and tetraploid. Furthermore, the exclusive use of cysts of the species from America A. franciscana (Kellogg 1906) in marine aquaculture and its commercial generalization, has conducted to the introduction of this exotic species in the Mediterranean basin, taking the profile of an invasive species, and leading to the elimination of native strains by a simple competition phenomenon. This potential threat on the diversity of the genus can also affect the North African countries today, where we have verified the presence of some populations of the American species in Morocco, and in Tunisia.

Synthesis and Biochemical Evaluation of Δ2-Isoxazoline Derivatives as DNA Methyltransferase 1 Inhibitors

A series of Δ(2)-isoxazoline constrained analogues of procaine/procainamide (7a-k and 8a-k) were prepared and their inhibitory activity against DNA methyltransferase 1 (DNMT1) was tested. Among them, derivative 7b is far more potent in vitro (IC(50) = 150 μM) than other non-nucleoside inhibitors and also exhibits a strong and dose-dependent antiproliferative effect against HCT116 human colon carcinoma cells. The binding mode of 7b with the enzyme was also investigated by means of a simple competition assay as well as of docking simulations conducted using the recently published crystallographic structure of human DNMT1. On the basis of the findings, we assessed that the mode of inhibition of 7b is consistent with a competition with the cofactor and propose it as a novel lead compound for the development of non-nucleoside DNMT inhibitors.

The development of a simple basal area increment model

AbstractIn most cases forest practice in Austria use yield tables to predict the growth of their forests. Common yield tables show the increment of pure even-aged stands which are treated in a way the table developer recommends. The usage of these tables in stands which are either uneven-aged, mixed or treated in another way, may lead to inaccurate predictions. To avoid these problems, forest growth models have been developed. Until now they are not widely used in Austria. One reason may be, that most of the models need some input parameters which are usually not gathered by companies. In this work a basal area increment per hectare model has been developed which is based on the input parameters: diameter at breast height, height to diameter ratio, top height at age 100 years and a selection out of several simple competition indices (growing space, basal area of larger trees, competing basal area, crown cross sectional area, crown competition factor, d/dg, d-dg, basal area and stand density index) which are distance independent. The model parametrization was done with seven different statistical methods (linear regression, linear mixed effect model, resistant linear regression, local polynomial regression, lazy learning model, random forest model and neural network model). By using only few input-parameters it should be possible to parametrize this model for many local areas by using inventory data sets of the specific region. The model works in pure and mixed stands of spruce and beech at the Rosaliengebirge. The observed average diameter increment per 5 years is 18.1 mm for spruce and 21.1 mm for beech. The average difference of the predicted and observed diameter-increment on a validation data-set is 0.3 mm for spruce and -0.3 mm for beech within 5 years and the estimated additional spread caused by the model is +-4.5 mm/5 years for spruce and +-4.0 mm/5 years for beech.

Possible implications of insulin resistance and glucose metabolism in Alzheimer's disease pathogenesis.

Type 2 diabetes mellitus (DM) appears to be a significant risk factor for Alzheimer disease (AD). Insulin and insulin-like growth factor-1 (IGF-1) also have intense effects in the central nervous system (CNS), regulating key processes such as neuronal survival and longevity, as well as learning and memory. Hyperglycaemia induces increased peripheral utilization of insulin, resulting in reduced insulin transport into the brain. Whereas the density of brain insulin receptor decreases during age, IGF-1 receptor increases, suggesting that specific insulin-mediated signals is involved in aging and possibly in cognitive decline. Molecular mechanisms that protect CNS neurons against β-amyloid-derived-diffusible ligands (ADDL), responsible for synaptic deterioration underlying AD memory failure, have been identified. The protection mechanism does not involve simple competition between ADDLs and insulin, but rather it is signalling dependent down-regulation of ADDL-binding sites. Defective insulin signalling make neurons energy deficient and vulnerable to oxidizing or other metabolic insults and impairs synaptic plasticity. In fact, destruction of mitochondria, by oxidation of a dynamic-like transporter protein, may cause synapse loss in AD. Moreover, interaction between Aβ and τ proteins could be cause of neuronal loss. Hyperinsulinaemia as well as complete lack of insulin result in increased τ phosphorylation, leading to an imbalance of insulin-regulated τ kinases and phosphatates. However, amyloid peptides accumulation is currently seen as a key step in the pathogenesis of AD. Inflammation interacts with processing and deposit of β-amyloid. Chronic hyperinsulinemia may exacerbate inflammatory responses and increase markers of oxidative stress. In addition, insulin appears to act as ‘neuromodulator’, influencing release and reuptake of neurotransmitters, and improving learning and memory. Thus, experimental and clinical evidence show that insulin action influences cerebral functions. In this paper, we reviewed several mechanisms by which insulin may affect pathophysiology in AD.

Reply to Ferrarini: Strengths and weaknesses of simple competition models

In our work (1), we showed how a largely overlooked mechanism of coexistence based on intransitive competitive relations could be widespread in nature and improve our understanding of biodiversity maintenance. We outlined the basic mechanism, providing a simplified model that can be expanded in several directions. In his comment, Ferrarini (2) raises four points that he believes weaken our approach. Here, we show that these arise from a misunderstanding of our framework, and it is not clear that any of these points would change our fundamental results.

The Clark plot: a semi-historical case study.

A study has been made of the origins of the quantitative theory of simple competitive antagonism as manifest in the papers of Gaddum and of Clark. The classical data of Clark on the antagonism of acetylcholine by atropine were reanalysed by recently developed computer-based methods. It was seen how close Clark came to initiating a method having the following significant advantages over the Schild plot: (i) symmetrical treatment with respect to the control (zero antagonist) data; (ii) absence of difficulty with the cases where an estimated dose-ratio is less than unity; (iii) straightforward calculation of approximate standard errors for departure from overall simple competitivity at each antagonist level including control.

Target-Mediated Protection of Endogenous MicroRNAs in C. elegans

MicroRNAs (miRNAs) are tightly regulated through transcriptional and posttranscriptional mechanisms, including degradation by nucleases. Here, we report that in C. elegans, target mRNAs can protect their cognate miRNAs from degradation invivo. We show that the let-7(n2853) mutation destabilizes the mature let-7 miRNA by impairing this protection. Moreover, presence of a cognate target or depletion of the xrn-1 (XRN1) or xrn-2 (XRN2/Rat1p) exoribonucleases enforces accumulation of certain miRNA passenger (miR(∗)) strands. Thus, following biased miRNA strand loading into Argonaute, elimination of nonfunctional RNAs can further refine miRNA strand selection. Conversely, by aligning the levels of miRNAs with those of their targets, the opposing activities of mature miRNA degradation and target-mediated miRNA protection (TMMP) may enable dynamic expression of either mature strand ofa pre-miRNA, and evolution of miRNAs. Thus, it seems that mRNAs are more than inert targets and function with miRNAs in a network of mutual regulation.

Partnering with Competitors - An Empirical Analysis of Airline Alliances and Multimarket Competition

Competition has become an important theme in the operations management literature and, according to recent theoretical and empirical work, the key finding is that firms tend to overstock or overproduce under competition. Following this prediction, one would expect that, after airlines start a multifaceted collaboration by forming an alliance, their networks would be consolidated and capacity redundancies would be eliminated, as intensity of competition decreases among alliance partners. Surprisingly, we find exactly the opposite: in the post-alliance era, alliance partners seek to overlap their networks more and they increase capacities on the markets in which two partners are already present. At the same time, average prices in those markets increase by about $11 per one-way segment coupon. We explain these results using predictions based on the theory of multimarket competition: as firms seek out opportunities to establish multimarket contact to strengthen mutual forbearance, they have incentives to increase overlap even though this decision may not seem optimal or efficient locally or in the short term. We examine other plausible competing mechanisms built on theories of capacity and service competition and commonly cited benefits of airline alliances but ultimately we conclude that our findings are most likely driven by the multimarket competition. This paper therefore underscores the importance of going beyond simple bilateral competition models whose predictions may not hold when firms compete operationally in multiple markets, a phenomenon which is widespread in many operations-intensive industries.

Characteristics of Cd uptake, translocation and accumulation in a novel Cd-accumulating tree, star fruit ( Averrhoa carambola L., Oxalidaceae)

Cadmium (Cd) accumulation by terrestrial higher plants is an intriguing phenomenon that may be exploited for phytoextraction of Cd-contaminated soils. Characterizing the physiological processes responsible for elevated concentrations of Cd in shoots is a first step towards a comprehensive understanding of the mechanisms underlying Cd accumulation in plants and may eventually improve the efficiency of phytoextraction. Woody species that can accumulate Cd have been recently recommended as good candidates for phytoextraction of Cd-contaminated soils. However, little is known about the mechanisms of Cd accumulation by woody species. In an attempt to understand the physiological processes contributing to Cd accumulation in woody species, Cd uptake and translocation by a novel tropical Cd-accumulating tree, star fruit ( Averrhoa carambola) were characterized and compared with those of a non-Cd-accumulating tree ( Clausena lansium). Our results showed that A. carambola had higher Cd uptake and root-to-shoot translocation efficiencies than C. lansium, which might account for its greater Cd-accumulating capacity. Furthermore, Cd accumulation by A. carambola was not significantly affected by zinc (Zn), whereas Zn accumulation was greatly lowered by Cd. This phenomenon could not be fully explained by a simple competition between Cd 2+ and Zn 2+, implying the existence of a transport system with a preference for Cd over Zn. Collectively, our results indicate that A. carambola has noteworthy physiological traits associated with accumulation of Cd to high levels.

Dynamics of stochastic and nearly stochastic two-party competitions

We introduce a stochastic model to study the problem of time evolution and outcome of simple two-party competitions or battles on a lattice where each party randomly deploys its constituents or elements to the lattice. The elements have assigned strength levels that determine how competitive or effective they are against the opponent. In our models, the elements neutralize one another when they are at the same site with a combination of strength levels and numbers determining which one gains control of the site. The competitions last until complete dominance has been established by one side by eliminating the opponents or a draw is achieved (unless the time evolution is terminated via some ad hoc condition). A Markov chain approach is used to describe the time-dependent dynamics of such competitions. The advantage of the approach is that it allows us to develop a theoretical framework for describing competitive systems where a combination of random and correlated events decide the outcome. We use the approach here for studies of highly contentious stochastic battles and for that of a battle with correlated events along with stochastic events. We present the method, a simple illustrative example on how the method works and close by considering two non-trivial cases including one with a combination of stochasticity and correlations.

Quantifying distance-independent tree competition for predicting Norway spruce mortality in unmanaged forests

Abstract The competition environments of trees in pristine forests and managed single-cohort systems differ substantially. Unconventional forest management or conservation planning for Norway spruce ( Picea abies (L.) Karst) forests is currently impaired due to a lack of quantitative data on what factors drive its mortality. We collected data from 57 unmanaged Norway spruce stands in Finland to estimate factors influencing the competition-induced mortality of spruce. We investigated how a simple competition index ( CI) should be formulated in order to predict spruce mortality in these forests. According to our measurements and the competition index, competition among spruce was clearly one-sided, meaning that smaller trees did not affect the mortality probabilities of larger trees. In the best performing CI, which was based on competitor d b h , competitors were approximately 4 cm larger in dbh than the subject trees before they began to affect subject tree mortality. A nearly size-invariant threshold suggests that smaller spruces tolerate their larger competitors relatively better, when competitor effect is proportional to their d b h . In contrast, the CI based on competitor basal areas (∝ dbh 2) predicted tree mortality poorly, and the threshold was size-dependent. Our study suggests that a simple competition index based on a constant dbh-threshold and a sum of the square roots of competitors’ dbh is used to predict spruce mortality in unmanaged spruce forests. This index seems to capture both the competition asymmetry and the slow mortality of suppressed trees frequently observed in forests. A simple competition index for predicting spruce mortality in unmanaged forests can easily be integrated to many forest growth models to support modeling of mortality and conservation value of Norway spruce stands.

Climate and site characteristics affect juvenile trembling aspen development in conifer plantations across southern British Columbia

In southern British Columbia, juvenile trembling aspen is managed primarily as a competitor with conifers rather than for its ecological and economic value. As a result, brushing treatments have been applied on a widespread basis and this practice is likely to continue in the near future. Given the potential for climate change to affect our valuation of aspen, we require a better understanding of factors that affect its development, its competitive ability with conifers and its responses to brushing. We used data from 11 aspen management experiments to examine the influence of climate and site factors on aspen height, cover, and density in 17–24 year-old control stands and 9–16 years after manual cutting or girdling. Models explained 64% and 89% of the variation in aspen height in control and manually brushed stands, respectively, but were poor for girdling. Increasing length of the frost-free period was associated with increasing aspen height in control stands, whereas drier summer conditions on cool aspects favoured height growth of aspen suckers following manual cutting. We also examined the influence of climate and site factors on three simple competition indices that describe the height and density of aspen relative to conifer height, and then tested how well these indices predicted conifer growth. The density of aspen taller than conifers accounted for 39% of the variation in lodgepole pine diameter and the ratio of aspen/conifer height accounted for 33% of the variation in Douglas-fir height, suggesting that aspen competition was only moderately important to conifer growth. Our findings imply that aspen may become more productive with warmer summers provided it is not limited by summer moisture availability and that mixed stand management is a viable option in southern interior stands.

Species pool size and realized species richness affect productivity differently: A modeling study

Current and expected decline in biodiversity have motivated a number of experiments studying how biodiversity affects ecosystem functioning. The positive relationship is usually found in experiments where species pool is manipulated; the relationship between productivity and realized species richness does not show any single trend. We constructed a simple competition model for a plant community based on the classical Lotka–Volterra equations, with randomly generated parameters. We varied the species pool size and intensity of competition (range of competition coefficients). Then, we compared two measures of diversity used as predictors of productivity: (1) the size of the species pool and (2) the realized species richness, i.e. the number of species that remained in the system after competitive exclusion. Simulation results showed that productivity was always positively affected by the size of the species pool. With increasing species pool, both the selection effect and complementarity increase. The relationship between realized species richness and productivity was extremely weak within a set of simulations with a fixed species pool (i.e. where the diversity gradient was caused only by differences in the randomly generated parameters). The relationship between realized species richness and productivity was slightly positive for small species pool sizes and slightly negative for larger species pools. A species with high carrying capacity within the generated set of species usually decreases the chance of other species to survive but increases the productivity of the mixture, leading to negative diversity productivity relationship. On the contrary, presence of highly complementary species (i.e. species with low mutual competition coefficients) increases both, the realized species richness and productivity, leading to positive diversity productivity relationship. These two effects mostly counterbalance each other. These trends are not affected by the competition intensity.

Probing chaos and biodiversity in a simple competition model

Recent theoretical work has reported that chaos facilitates biodiversity. In this paper, we study the lowest-dimensional Lotka–Volterra competition model that exhibits chaotic trajectories, a model with four species. We observe that interaction and growth parameters leading respectively to extinction of three species, or coexistence of two, three or four species, are for the most part arranged in large regions with clear boundaries. Small islands of parameters that lead to chaos are also found. These regions where chaos occurs are, in the three cases presented here, situated at the interface between a non-chaotic four-species region and a region where extinction occurs. This implies a high sensitivity of biodiversity with respect to parameter variations in the chaotic regions. Additionally, in regions where extinction occurs which are adjacent to chaotic regions, the computation of local Lyapunov exponents reveals that a possible cause of extinction is the overly strong fluctuations in species abundances induced by local chaos at the beginning of the interval of study. For this model, we conclude that biodiversity is a necessary condition for chaos rather than a consequence of chaos, which can be seen as a signal of a high extinction risk.

Trade Policy, Fiscal Coalitions and the Structure of Taxation in Industrialized Countries, 1870-1918

Why do different countries adopt different tax policies? This paper argues that domestic tax policy outcomes may be strongly influenced by the orientations of different economic and political actors to international trade, as well as by their positions on domestic dimensions. Considering the period between 1870 and 1918 in 9 western European countries provides support to this contention. International openness does matter for tax structure. Further, the dynamics are more complex than a simple tax competition argument might predict. Greater trade is actually associated with higher levels of direct domestic taxation. I propose a theory grounded in the political coalitions underpinning tax and tariff reforms to explain this relationship. Tax as well as tariff outcomes depend on the joint distribution of interests along the potentially independent dimensions of exposure to openness, and relative income. Different distributions yield different political alliances and thus divergent tax outcomes. This theory is considered with regard to comparative case studies of the UK and France between 1890 and 1918.

Positive interactions and the emergence of community structure in metacommunities

The significant role of space in maintaining species coexistence and determining community structure and function is well established. However, community ecology studies have mainly focused on simple competition and predation systems, and the relative impact of positive interspecific interactions in shaping communities in a spatial context is not well understood. Here we employ a spatially explicit metacommunity model to investigate the effect of local dispersal on the structure and function of communities in which species are linked through an interaction web comprising mutualism, competition and exploitation. Our results show that function, diversity and interspecific interactions of locally linked communities undergo a phase transition with changes in the rate of species dispersal. We find that low spatial interconnectedness favors the spontaneous emergence of strongly mutualistic communities which are more stable but less productive and diverse. On the other hand, high spatial interconnectedness promotes local biodiversity at the expense of local stability and supports communities with a wide range of interspecific interactions. We argue that investigations of the relationship between spatial processes and the self-organization of complex interaction webs are critical to understanding the geographic structure of interactions in real landscapes.

High‐affinity binding of phosphatidylinositol 4‐phosphate by Legionella pneumophila DrrA

The DrrA protein of Legionella pneumophila is involved in mistargeting of endoplasmic reticulum-derived vesicles to Legionella-containing vacuoles through recruitment of the small GTPase Rab1. To this effect, DrrA binds specifically to phosphatidylinositol 4-phosphate (PtdIns(4)P) lipids on the cytosolic surface of the phagosomal membrane shortly after infection. In this study, we present the atomic structure of the PtdIns(4)P-binding domain of a protein (DrrA) from a human pathogen. A detailed kinetic investigation of its interaction with PtdIns(4)P reveals that DrrA binds to this phospholipid with, as yet unprecedented, high affinity, suggesting that DrrA can sense a very low abundance of the lipid.

THE PHYSICS OF THE FAR-INFRARED-RADIO CORRELATION. II. SYNCHROTRON EMISSION AS A STAR FORMATION TRACER IN HIGH-REDSHIFT GALAXIES

We construct one-zone steady-state models of cosmic ray (CR) injection, cooling, and escape over the entire dynamic range of the FIR-radio correlation (FRC), from normal galaxies to starbursts, over the redshift interval 0 <= z <= 10. Normal galaxies with low star-formation rates become radio-faint at high z, because Inverse Compton (IC) losses off the CMB cool CR electrons and positrons rapidly, suppressing their nonthermal radio emission. However, we find that this effect occurs at higher redshifts than previously expected, because escape, bremsstrahlung, ionization, and starlight IC losses act to counter this effect and preserve the radio luminosity of galaxies. The radio dimming of star-forming galaxies at high z is not just a simple competition between magnetic field energy density and the CMB energy density; the CMB must also compete with every other loss process. We predict relations for the critical redshift when radio emission is significantly suppressed compared to the z ~ 0 FRC as a function of star-formation rate per unit area. Additionally, we provide a quantitative explanation for the relative radio brightness of some high-z submillimeter galaxies. We show that at fixed star formation rate surface density, galaxies with larger CR scale heights are radio bright with respect to the FRC, because of weaker bremsstrahlung and ionization losses compared to compact starbursts. We predict that these "puffy starbursts" should have steeper radio spectra than compact galaxies with the same star-formation rate surface density. We find that radio bright submillimeter galaxies alone cannot explain the excess radio emission reported by ARCADE2, but they may significantly enhance the diffuse radio background with respect to a naive application of the z ~ 0 FRC.

A simple model of foreign brand penetration under monopolistic competition

The main purpose of this study is to illustrate, with a simple monopolistic competition trade model, how trade liberalization (i.e., a decline in trade costs) can affect domestic entrepreneurs’ decision between providing domestic or foreign brands, and thus the degree of foreign brand penetration. It is shown that, as trade costs decrease, more entrepreneurs choose to provide foreign brands. Furthermore, the shift to foreign brands is shown to magnify the negative impact of trade liberalization on the profits of firms selling domestic brands.

A view from the top: new ligands controlling stomatal development in Arabidopsis

A view from the top: new ligands controlling stomatal development in Arabidopsis