Mathematical analysis of coral reef models

It is acknowledged that coral reefs are globally threatened. P.J. Mumby et al. [10] constructed a mathematical model with ordinary differential equations to investigate the dynamics of coral reefs. In this paper, we first provide a detailed global analysis of the coral reef ODE model in [10]. Next we incorporate the inherent time delay to obtain a mathematical model with delay differential equations. We consider the grazing intensity and the time delay as focused parameters and perform local stability analysis for the coral reef DDE model. If the time delay is sufficiently small, the stability results remain the same. However, if the time delay is large enough, macroalgae only state and coral only state are both unstable, while they are both stable in the ODE model. Meanwhile, if the grazing intensity and the time delay are endowed some suitable values, the DDE model possesses a nontrivial periodic solution, whereas the ODE model has no nontrivial periodic solutions for any grazing rate. We study the existence and property of the Hopf bifurcation points and the corresponding stability switching directions.     

Coexistence of periods in a bifurcation

A particular type of order-to-chaos transition mediated by an infinite set of coexisting neutrally stable limit cycles of different periods is studied in the Varley–Gradwell–Hassell population model. We prove by an algebraic method that this kind of transition can only happen for a particular bifurcation parameter value. Previous results on the structure of the attractor at the transition point are here simplified and extended.     

松弛模型中的液气共存平衡态

对密闭的一维有限长管道里的等温相变．研究了松弛模型中液气共存平衡态的稳定性．使用匹配渐近展开形式上推出了一阶扰动满足的线性系统．理论分析发现．初始小扰动通常会被耗散掉,然而在一些特殊情况下,它们会维持在一定的水平上．数值计算也表明了松弛机制对相变演化具有稳定作用．     

Coexistence and asymptotic periodicity in a competitor-competitor-mutualist model

In this paper, the competitor-competitor-mutualist three-species Lotka-Volterra model is discussed. Firstly, by Schauder fixed point theory, the coexistence state of the strongly coupled system is given. Applying the method of upper and lower solutions and its associated monotone iterations, the true solutions are constructed. Our results show that this system possesses at least one coexistence state if cross-diffusions and cross-reactions are weak. Secondly, the existence and asymptotic behavior of T-periodic solutions for the periodic reaction-diffusion system under homogeneous Dirichlet boundary conditions are investigated. Sufficient conditions which guarantee the existence of T-periodic solution are also obtained.     

Coexistence in a discrete competition model with dispersal

We propose a discrete-time competition model between two populations to study the effects of dispersal upon population interactions. It is assumed that dispersal occurs after reproduction and in synchrony. We first analyse a two-patch single species population model with no interspecific competition. Based on these results, we derive sufficient conditions for population coexistence. It is proved that the system is uniformly persistent and possesses a unique coexisting equilibrium.     

Coexistence for species sharing a predator

A class of equations describing the dynamics of two prey sharing a common predator are considered. Even though the boundary and internal dynamics can exhibit oscillatory behavior, it is shown these equations are permanent if only if they admit a positive equilibrium. Going beyond permanence, a subclass of equations are constructed that are almost surely permanent but not permanent; there exists an attractor in the positive orthant that attracts Lebesgue almost every (but not every) initial condition.     

Coexistence in the design of a series of two chemostats

We revisit the design problem of series of two chemostats, when more than one species are present for a single resource. We give precise conditions under which coexistence of two species is possible for such configurations. Furthermore, we show that for a broad class of growth functions, the optimal design cannot sustain coexistence of more than one species (either a new species is rejected or it invades the whole system).     

Coexistence of two species in a strongly coupled cooperative model

In this paper, the cooperative two-species Lotka–Volterra model is discussed. We study the existence of solutions to a elliptic system with homogeneous Dirichlet boundary conditions. Our results show that this problem possesses at least one coexistence state if the birth rates are big and self-diffusions and the intra-specific competitions are strong.     

Coexistence states of a Holling type-II predator-prey system

This paper characterize the existence of coexistence states to a reaction-diffusion predator-prey model with Holling type-II functional response subject to Dirichlet boundary conditions. We find the necessary and sufficient conditions for existence of coexistence states by fixed point index theory and bifurcation theory.     

Coexistence in a strongly coupled system describing a two-species cooperative model

This paper is concerned with a cooperative two-species Lotka–Volterra model. Using the fixed point theorem, the existence results of solutions to a strongly coupled elliptic system with homogeneous Dirichlet boundary conditions are obtained. Our results show that this model possesses at least one coexistence state if the birth rates are big and cross-diffusions are suitably weak.     

Approximations of some hazard rate estimators in a competing risks model

A general model involving k competing risks is studied and the hazard rates of these risks are simultaneously estimated. The estimators are strongly approximated by Gaussian processes and the limiting distribution of certain statistics are obtained.     

Epidemics in two competing species

An SIS epidemic model in two competing species with the mass action incidence is formulated and analysed. Thresholds for the existence of boundary equilibria are identified and conditions for their local asymptotic stability or instability are found. By persistence theory, conditions for the persistence of either hosts or pathogens are proved. Using Hopf bifurcation theory and numerical simulations, some aspects of the complicated dynamic behaviours of the model are shown: the system may have zero up to three internal equilibria, may have a stable limit cycle, may have three stable attractors. Through the results on persistence and stability of the boundary equilibria, some important interactions between infection and competition are revealed: (1) a species that would become extinct without the infection, may persist in presence of the infection; (2) a species that would coexist with its competitor without the infection, is driven to extinction by the infection; (3) an infection that would die out in either species without the interinfection of disease, may persist in both species in presence of this factor.     

Strategies in competing subset selection

We address an optimization problem in which two agents, each with a set of weighted items, compete in order to minimize the total weight of their solution sets. The latter are built according to a sequential procedure consisting in a fixed number of rounds. In every round each agent submits one item that may be included in its solution set. We study two natural rules to decide which item between the two will be included. We address the problem from a strategic point of view, that is finding the best moves for one agent against the opponent, in two distinct scenarios. We consider preventive or minimax strategies, optimizing the objective of the agent in the worst case, and best-response strategies, where the items submitted by the opponent are known in advance in each round.     

Analysis of a semiparametric mixture model for competing risks

Semiparametric mixture regression models have recently been proposed to model competing risks data in survival analysis. In particular, Ng and McLachlan (Stat Med 22:1097–1111, 2003) and Escarela and Bowater (Commun Stat Theory Methods 37:277–293, 2008) have investigated the computational issues associated with the nonparametric maximum likelihood estimation method in a multinomial logistic/proportional hazards mixture model. In this work, we rigorously establish the existence, consistency, and asymptotic normality of the resulting nonparametric maximum likelihood estimators. We also propose consistent variance estimators for both the finite and infinite dimensional parameters in this model.     

Coordinating a three-stage supply chain with competing manufacturers

It is common for multiple manufacturers to compete in one common market. This paper considers a three-stage supply chain consisting of two competing manufacturers, one distributor, and one retailer. The two manufacturers’ products are substitutable with each other, and both manufacturers sell their products through the common distributor and the common retailer. In this supply chain, three contract mechanisms are discussed. The first one is wholesale-price (WP) contracts. The second one is pairwise revenue-sharing (PRS) contracts indicating that the revenues are shared by all pairs of adjacent entities. The third one is spanning revenue-sharing (SRS) contract indicating that the retailer simultaneously shares his revenues with all supply chain members. First, we discuss the effects of competition between manufacturers on both decentralized and centralized supply chains under the WP contracts. Second, we discuss the coordination mechanisms. The PRS and SRS contracts are used to coordinate the entire supply chain. We present the drawbacks of the PRS contracts in coordinating this competing supply chain and suggest using the SRS contract instead. After an SRS contract is adopted, it is evaluated using the WP contracts as a benchmark. The conditions necessary for an SRS contract to achieve a win–win outcome are then presented. Finally, some numerical examples are provided.     

Coexistence and Asymptotic Periodicity in a Competition Model of Plankton Allelopathy

In this paper, the two species Lotka-Volterra competition model of plankton allelopathy from aquatic ecology is discussed. The authors study the existence of solutions to a strongly coupled elliptic system with homogeneous Dirichlet boundary conditions and consider the existence, stability and global attractivity of time-periodic solutions for a coupled parabolic equations in a bounded domain. Their results show that this model possesses at least one coexistence state if cross-diffusions and self-diffusions are weak. The existence of the positive T-periodic solutions and the global stability as well as the global attractivity for the parabolic system are also given.     

Dynamics of species in a model with two predators and one prey

In this paper, we study a predator-prey model which has one prey and two predators with Beddington-DeAngelis functional responses. Firstly, we establish a set of sufficient conditions for the permanence and extinction of species. Secondly, the periodicity of positive solutions is studied. Thirdly, by using Liapunov functions and the continuation theorem in coincidence degree theory, we show the global asymptotic stability of such solutions. Finally, we give some numerical examples to illustrate the behavior of the model.     

Coexistence states of a three-species cooperating model with diffusion

In this article, a Lotka--Volterra three-species time-periodic mutualism model with diffusion is investigated. Some sufficient conditions for the existence and estimates of coexistence states are established. Meanwhile, with the assistance of functional analysis methods, some sufficient or necessary results for the existence of positive steady state of the model are presented. Our approach to the discussion is mainly based on the skill of sub- and super-solutions for a general reaction--diffusion system.