具常数投放率功能反应为／x的食饵-捕食系统的定性分析

本文研究一类具有常数投放率的食饵-捕食系统的定性行为,得到了正平衡点全局渐近稳定以及在正平衡点周围存在唯一极限环的充分条件．利用数值模拟检验了结论．     

具常数投放率功能反应为x~(1/2)的食饵-捕食系统的定性分析

本文研究一类具有常数投放率的食饵-捕食系统的定性行为,得到了正平衡点全局渐近稳定以及在正平衡点周围存在唯一极限环的充分条件.利用数值模拟检验了结论.     

具有状态反馈收获项的第Ⅲ类功能性反应模型的分支与极限环

研究了带有功能性反应捕食项的捕食与食饵模型在线性状态反馈收获的作用下所呈现的复杂性质,其中包括正平衡点的存在与唯一性、平衡点的渐近稳定性、产生分支的原因与极限坏的存在性等,研究结果表明：通过调整反馈项的系数,可以改变该系统正平衡点的稳定性,从而使系统或是稳定在正平衡点处,或是在正平衡点处产生周期运动,本文的结果为研究再生性资源管理中的复杂性问题奠定了理论基础。     

一类食饵具有常数收获率和Holling Ⅲ型功能性反应的捕食者-食饵模型的定性分析

本文对捕食者种群、食饵种群均在线性密度制约的条件下,食饵种群具有常数收获率的HollingⅢ型功能性反应模型进行定性分析,通过运用定性分析的方法和利用Dulac函数方法,分别讨论了模型正平衡点稳定性、极限环的存在性以及无穷远奇点的稳定性,得到了正平衡点存在的条件和在其周围不存在极限环的条件,以及无穷远点的性态,并给出了模型轨线的全局结构图.最后,对该模型作了数值的仿真模拟验证.     

食饵种群具有收获(存放)率的第Ⅱ类功能性反应模型的定性分析

本文研究了非密度制约的捕食与被捕食系统中被捕食者(食饵)种群具有常数收获(存放)率的第Ⅱ类功能性反应模型的定性性质:当该系统具有存放率时,证明了该系统在一定的条件下极限环的存在性、不存在性及唯一性;当该系统具有收获率时,证明了该系统若存在正平衡点,则它是全局不稳定性.     

食饵种群具有收获（存放）率的第II类功能性反应模型的定性分析

本文研究了非密度制约的捕食与捕食系统中被捕食者（食饵）种群具有常数收获（存放）率的第Ⅱ类功能性反应模型的定性性质：当该系统具有存放率时,证明了该系统在一定的条件下极限环的存在性、不存在性及唯一性;当该系统具有收获率时,证明了该系统若存在正平衡点,则它是全局不稳定性。     

一类两种群均有收获率捕食系统的细焦点与极限环

研究一类具有HollingⅡ类功能反应且两种群均为非常数收获率的捕食系统,其中食饵种群具有非线性密度制约.利用微分方程定性与稳定性理论及分支理论,得到系统平衡点的性态及极限环存在与否的充分条件,利用Hopf分支理论得到存到多个极限环的充分条件.     

食饵具有Smith增长且基于比率依赖捕食系统模型的定性分析

研究一类食饵为Smith增长且基于比率依赖的HollingⅢ型功能反应捕食系统模型,运用示性方程讨论参数变化时奇点(0,0)邻域内轨线的走向,给出系统平衡点为全局吸引子或吸引子的充分条件,得到系统正周期解的不存在性、正平衡点的全局渐近稳定性及系统存在极限环的充分条件.     

一个食饵种群具有常数收获率和具有第Ⅲ类功能性反应的捕-食系统的定性分析

本文对一个食饵种群具有常数收获率的和具有第Ⅲ类功能性反应的捕食系统作了较完整的定性分析,讨论了分界线的相对位置和分界线环的存在性、稳定性,得到了极限环存在性和唯一性的条件．     

一类具有时滞的微生物连续培养数学模型研究

研究了具有强核函数时滞的微生物连续培养数学模型,利用泛函微分方程理论和数值解法得到系统在一定操作条件下存在Hopf分叉以及分叉值随操作参数变化的规律,并研究了Hopf分叉产生的方向及周期解的稳定性,绘制了周期解的图形和相图.该模型定性地描述了实验中的振荡和过渡现象.最后与弱核函数时滞模型、离散时滞模型进行比较,分析了它们对多态、振荡等动态行为的影响。     

Global behaviour of a predator–prey like model with piecewise constant arguments

The present study deals with the analysis of a predator–prey like model consisting of system of differential equations with piecewise constant arguments. A solution of the system with piecewise constant arguments leads to a system of difference equations which is examined to study boundedness, local and global asymptotic behaviour of the positive solutions. Using Schur–Cohn criterion and a Lyapunov function, we derive sufficient conditions under which the positive equilibrium point is local and global asymptotically stable. Moreover, we show numerically that periodic solutions arise as a consequence of Neimark-Sacker bifurcation of a limit cycle.     

The Beverton–Holt model with periodic and conditional harvesting

In this theoretical study, we investigate the effect of different harvesting strategies on the discrete Beverton–Holt model in a deterministic environment. In particular, we make a comparison between the constant, periodic and conditional harvesting strategies. We find that for large initial populations, constant harvest is more beneficial to both the population and the maximum sustainable yield. However, periodic harvest has a short-term advantage when the initial population is low, and conditional harvest has the advantage of lowering the risk of depletion or extinction. Also, we investigate the periodic character under each strategy and show that periodic harvesting drives population cycles to be multiples (period-wise) of the harvesting period.     

The Beverton-Holt model with periodic and conditional harvesting

In this theoretical study, we investigate the effect of different harvesting strategies on the discrete Beverton-Holt model in a deterministic environment. In particular, we make a comparison between the constant, periodic and conditional harvesting strategies. We find that for large initial populations, constant harvest is more beneficial to both the population and the maximum sustainable yield. However, periodic harvest has a short-term advantage when the initial population is low, and conditional harvest has the advantage of lowering the risk of depletion or extinction. Also, we investigate the periodic character under each strategy and show that periodic harvesting drives population cycles to be multiples (period-wise) of the harvesting period.     

固定周期脉冲微分方程到状态依赖脉冲的转化及应用

本文研究了一类二维状态依赖脉冲微分方程的阶1周期解存在性和轨道稳定性条件．然后,将一维固定周期脉冲的微分方程转化为二维状态依赖脉冲微分方程,研究其阶一周期解的存在性和稳定性．作为应用,我们研究了固定周期常数收获的Logistic方程的动力学性质,以及两个固定周期注射药物单室扩散模型的动力学性质．     

A tale of two cycles – distinguishing quasi-cycles and limit cycles in finite predator–prey populations

Periodic predator – prey dynamics in constant environments are usually taken as indicative of deterministic limit cycles. It is known, however, that demographic stochasticity in finite populations can also give rise to regular population cycles, even when the corresponding deterministic models predict a stable equilibrium. Specifically, such quasi-cycles are expected in stochastic versions of deterministic models exhibiting equilibrium dynamics with weakly damped oscillations. The existence of quasi-cycles substantially expands the scope for natural patterns of periodic population oscillations caused by ecological interactions, thereby complicating the conclusive interpretation of such patterns. Here we show how to distinguish between quasi-cycles and noisy limit cycles based on observing changing population sizes in predator – prey populations. We start by confirming that both types of cycle can occur in the individual-based version of a widely used class of deterministic predator – prey model. We then show that it is feasible and straightforward to accurately distinguish between the two types of cycle through the combined analysis of autocorrelations and marginal distributions of population sizes. Finally, by confronting these results with real ecological time series, we demonstrate that by using our methods even short and imperfect time series allow quasi-cycles and limit cycles to be distinguished reliably.     

Dynamics of a physiologically structured population in a time-varying environment

Physiologically structured population models have become a valuable tool to model the dynamics of populations. In a stationary environment such models can exhibit equilibrium solutions as well as periodic solutions. However, for many organisms the environment is not stationary, but varies more or less regularly. In order to understand the interaction between an external environmental forcing and the internal dynamics in a population, we examine the response of a physiologically structured population model to a periodic variation in the food resource. We explore the addition of forcing in two cases: (A) where the population dynamics is in equilibrium in a stationary environment, and (B) where the population dynamics exhibits a periodic solution in a stationary environment. When forcing is applied in case A, the solutions are mainly periodic. In case B the forcing signal interacts with the oscillations of the unforced system, and both periodic and irregular (quasi-periodic or chaotic) solutions occur. In both cases the periodic solutions include one and multiple period cycles, and each cycle can have several reproduction pulses.     

Multiple limit cycles in the standard model of three species competition for three essential resources

We consider the dynamics of the standard model of 3 species competing for 3 essential (non-substitutable) resources in a chemostat using Liebig's law of the minimum functional response. A subset of these systems which possess cyclic symmetry such that its three single-population equilibria are part of a heteroclinic cycle bounding the two-dimensional carrying simplex is examined. We show that a subcritical Hopf bifurcation from the coexistence equilibrium together with a repelling heteroclinic cycle leads to the existence of at least two limit cycles enclosing the coexistence equilibrium on the carrying simplex- the ``inside' one is an unstable separatrix and the ``outside' one is at least semi-stable relative to the carrying simplex. Numerical simulations suggest that there are exactly two limit cycles and that almost every positive solution approaches either the stable limit cycle or the stable coexistence equilibrium, depending on initial conditions. Bifurcation diagrams confirm this picture and show additional features. In an alternative scenario, we show that the subcritical Hopf together with an attracting heteroclinic cycle leads to an unstable periodic orbit separatrix. This research was partially supported by NSF grant DMS 0211614. KY 40292, USA. This author's research was supported in part by NSF grant DMS 0107160     

The dynamics of a Lotka–Volterra predator–prey model with state dependent impulsive harvest for predator

According to the economic and biological aspects of renewable resources management, we propose a Lotka–Volterra predator–prey model with state dependent impulsive harvest. By using the Poincaré map, some conditions for the existence and stability of positive periodic solution are obtained. Moreover, we show that there is no periodic solution with order larger than or equal to three under some conditions. Numerical results are carried out to illustrate the feasibility of our main results. The bifurcation diagrams of periodic solutions are obtained by using the numerical simulations, and it is shown that a chaotic solution is generated via a cascade of period-doubling bifurcations, which implies that the presence of pulses makes the dynamic behavior more complex.     

Mathematical modelling of dynamics and control in metabolic networks: VI. Dynamic bifurcations in single biochemical control loops

A dynamic stability analysis of an extended form of the Goodwin equations is presented. The Goodwin equations are extended to include Michaelis-Menten kinetics for the removal of the end-product. Inclusion of saturation kinetic behavior substantially increases the likelihood of dynamic instability in this model control loop. Oscillations are found for reaction chains of low order, as low as second order, and low degrees of co-operativity, as low as v = 2, simultaneously, thus indicating that dynamic instability in this system exists for physiologically realistic parameter values. The branches of bifurcated solutions are computed numerically and unstable Hopf bifurcations are found. Further, solution branches from stable Hopf bifurcation points are found to "fold back", i.e. have periodic limit points, producing situations where multiple stable limit cycles exist.