Eduardo Liz

A note on the global stability of generalized difference equations

In this note, we prove a discrete analogue of the continuous Halanay inequality and apply it to derive sufficient conditions for the global asymptotic stability of the equilibrium of certain generalized difference equations. The relation with some numerical schemes for functional delay differential equations is discussed.

A Contribution to the Study of Functional Differential Equations with Impulses

A periodic boundary value problem for a special type of functional differential equa- tions with impulses at fixed moments is studied. A comparison result is presented that allows to construct a sequence of approximate solutions and to give an existence result. Several particular cases are considered.

Global behaviour of a second-order nonlinear difference equation

We describe the asymptotic behaviour and the stability properties of the solutions to the nonlinear second-order difference equation for all values of the real parameters a, b, and any initial condition .

A global stability criterion for a family of delayed population models

For a family of single-species delayed population models, a new global stability condition is found. This condition is sharp and can be applied in both monotone and nonmonotone cases. Moreover, the consideration of variable or distributed delays is allowed. We illustrate our approach on the Mackey-Glass equations and the Lasota-Wazewska model.

Sufficient conditions for the global stability of nonautonomous higher order difference equations

We present some explicit sufficient conditions for the global stability of the zero solution in nonautonomous higher order difference equations. The linear case is discussed in detail. We illustrate our main results with some examples. In particular, the stability properties of the equilibrium in a nonlinear model in macroeconomics is addressed.

Global dynamics in a stage-structured discrete-time population model with harvesting

The purpose of this paper is to analyze the effect of constant effort harvesting upon global dynamics of a discrete-time population model with juvenile and adult stages. We consider different scenarios, including adult-only mortality, juvenile-only mortality, and equal mortality of juveniles and adults. In addition to analytical study of equilibria of the system, we analyze global dynamics by means of an automated set-oriented rigorous numerical method. We obtain a comprehensive overview of the dynamics as the harvest rate and survival probability change. In particular, we determine the range of parameters for which the population abundance gets larger in spite of an increase in the harvest rate (so-called hydra effect), and for which subsequent increases in harvesting effort can magnify fluctuations in population abundance (destabilize it) and then stabilize it again (so-called bubble effect).

Convergence to equilibria in discrete population models

For a family of difference equations where and is continuous and decreasing, we find sufficient conditions for the convergence of all solutions to the unique positive equilibrium. In particular, we improve, up to our knowledge, all previous results on the global asymptotic stability of the equilibrium in the particular cases of the discrete Mackey–Glass and Lasota–Wazewska models in blood-cells production.

The hydra effect, bubbles, and chaos in a simple discrete population model with constant effort harvesting

We analyze the effects of a strategy of constant effort harvesting in the global dynamics of a one-dimensional discrete population model that includes density-independent survivorship of adults and overcompensating density dependence. We discuss the phenomenon of bubbling (which indicates that harvesting can magnify fluctuations in population abundance) and the hydra effect, which means that the stock size gets larger as harvesting rate increases. Moreover, we show that the system displays chaotic behaviour under the combination of high per capita recruitment and small survivorship rates.

Complex dynamics of survival and extinction in simple population models with harvesting

We study the effects of constant harvesting in a discrete population model that includes density-independent survivorship of adults in a population with overcompensating density dependence. The interaction between the survival parameter and other parameters of the model (harvesting rate, natural growth rate) reveal new phenomena of survival and extinction. The main differences with the dynamics of survival and extinction reported for semelparous populations with overcompensatory density dependence are that there can be multiple windows of extinction and conditional persistence as harvesting increases or the intrinsic growth rate is increased, and that, in case of bistability, the basin of attraction of the nontrivial attractor may consist of an arbitrary number of disjoint connected components.

Stability of non-autonomous difference equations: simple ideas leading to useful results

We address the stability properties in a non-autonomous difference equation where f is continuous, and the zero solution is assumed to be the unique equilibrium. We focus our discussion on two techniques motivated by stability results for functional differential equations (FDEs) that proved recently to be useful in the frame of difference equations too. The first one involves the use of discrete inequalities and monotonicity arguments, and it is inspired by the so-called Halanay inequality; the second one is based on the well-known 3/2 stability results for FDEs. We give further insight into the simple ideas that are behind these methods, prove some new results and show applications and open problems.