Abstract and Applied Analysis

Volume 2014 (2014), Article ID 867313, 19 pages

http://dx.doi.org/10.1155/2014/867313

## Dynamic Behaviors of a Discrete Lotka-Volterra Competition System with Infinite Delays and Single Feedback Control

^{1}College of Mathematics and Computer Science, Fuzhou University, Fuzhou, Fujian 350116, China^{2}Department of Mathematics, Ningde Normal University, Fujian 352100, China

Received 21 May 2014; Revised 28 July 2014; Accepted 28 July 2014; Published 14 October 2014

Academic Editor: Ming Mei

Copyright © 2014 Liang Zhao et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

A nonautonomous discrete two-species Lotka-Volterra competition system with infinite delays and single feedback control is considered in this paper. By applying the discrete comparison theorem, a set of sufficient conditions which guarantee the permanence of the system is obtained. Also, by constructing some suitable discrete Lyapunov functionals, some sufficient conditions for the global attractivity and extinction of the system are obtained. It is shown that if the the discrete Lotka-Volterra competitive system with infinite delays and without feedback control is permanent, then, by choosing some suitable feedback control variable, the permanent species will be driven to extinction. That is, the feedback control variable, which represents the biological control or some harvesting procedure, is the unstable factor of the system. Such a finding overturns the previous scholars’ recognition on feedback control variables.

#### 1. Introduction

During the last decade, the study of the dynamic behaviors of discrete time models governed by difference equation has become one of the most important topics in mathematics biology; many interesting results concerned with permanence, extinction, and existence of positive periodic solution (almost periodic solution) and so forth have been extensively studied by many scholars; see [1–30] and the references cited therein.

As far as two-species discrete competition model is concerned, Chen and Zhou [1] proposed and studied the following discrete two-species Lotka-Volterra system: where , represent the environmental carrying capacity of species and , respectively; , are the intrinsic growth rate of two species; and , represent the density of species and at the th generation, respectively. The authors obtained a set of sufficient conditions which ensure the persistence of system (1). Also, for the periodic case, they gave a set of sufficient conditions which guarantee the existence of a globally stable periodic solution of the system. Chen [2] argued that it is more realistic to incorporate delays into system (1), and he proposed and investigated the following model: Concerned with the persistent property of system (2), the author obtained the following result.

Throughout this paper, given a bounded nonnegative sequence defined on , let and denote and , respectively.

Theorem A. *Assume that
**
hold; then system (2) is permanent.*

However, the author did not investigate the stability and extinction property of the system (2), which are two of the most important topics on the study of population dynamics.

On the other hand, it is well known that, in the real world, ecosystems are continuously disturbed by unpredictable forces which can result in some changes of the biological parameters such as survival rates ([3]). For having a more accurate description of such a system, scholars introduced feedback controls into ecosystems and studied a variety of systems with feedback controls. Based on the work of Chen and Zhou [1], X. X. Chen and F. D. Chen [4] proposed and studied the following nonautonomous two-species discrete competitive system with feedback controls:
Some sufficient conditions for the persistence and global stability of system (3) were obtained. Xu et al. [5] further considered the following two-species nonautonomous Lotka-Volterra competitive system with delays and feedback controls:
By using the comparison theorem of discrete differential equation and constructing a suitable discrete type Lyapunov functional, they obtained new sufficient conditions on the permanence of species and global attractivity for system (4). Their results show that feedback controls are harmless to the permanence of system (4);* that is, feedback controls have no influence on the permanence of system (4).* X. Chen and F. Chen [29] and Liao et al. [30] also proposed a discrete time periodic -species Lotka-Volterra competition system with feedback controls and deviating arguments; some sufficient conditions which ensure the existence of unique globally asymptotically stable periodic solution were obtained. Recently, Wu and Zhang [19] proposed a discrete autonomous Lotka-Volterra competition system with infinite delays and feedback controls; by using the iterative method, sufficient conditions which ensure the global attractivity of the system were obtained.

As we can see, those models considered in [4, 5, 19, 29, 30] contain two or more feedback control variables, which means that, for the different species, different control strategy is adopted. But, in the real world, the strategy adopted for one species may also affect the other species; in other words, such a strategy has influence on both species. For instance, in the agricultural system, spraying pesticide can reduce the number of weeds, but pesticide can also have a negative impact on the growth of crops or beneficial animals [6, 7]. In the medical system, when doctor takes chemotherapeutic drugs as tools to cure the cancer patients, cancer cells will decrease rapidly, but at the same time, drugs also do harm to normal cells and body's regulatory immune function. Yao et al. [8] studied the effect of chemotherapeutic drugs on cellular immunity in patients with lung cancer; they found that cell immunity is inhibited in patients with lung cancer; moreover, it is impaired considerably by chemotherapy. So how to keep the negative effect caused by the single strategy adopted for the weeds or cancer cells to a minimum?

The above phenomenons motivated us to propose and study the discrete Lotka-Volterra competition system with infinite delays and single feedback control variable as follows:

In system (5), () is the density of species at the th generation and is the single feedback control variable.

Throughout this paper, we assume the following.(H_{1}), , , , and () are bounded sequences of real numbers defined on such that
(H_{2}), , and () are nonnegative bounded sequences such that

According to the biological background of system (5), we only consider the solution of system (5) with the following initial conditions: where . It is easy to prove that the solution of system (5) which satisfies initial conditions (8) is positive.

We mention here that this is the first time such kind of model is proposed and studied, and, as far as system (5) is concerned,* whether the single feedback control variable has influence on the persistent property of the system or not* is an interesting problem. The aim of this paper is to investigate the dynamic behaviors of the system (5); in particular, we will find out the answer to the above problem.

The organization of this paper is as follows. We introduce some useful lemmas in the next section and then state and prove the main results in Sections 3, 4, and 5, respectively. Three examples together with their numeric simulations are presented to show the feasibility of the main results in Section 6. We end this paper by a brief discussion.

#### 2. Lemmas

Now, let us consider the following difference equation: where are positive constants.

Lemma 1 (see [9]). *Assume that ; for any initial value , there exists a unique solution of (9), which can be expressed as follows:
**
where . Thus, for any solution y(k) of the system (10), we have
*

*Lemma 2 (see [9]). Let , . For any fixed , is nondecreasing function with respect to , and, for , the following inequalities hold:
If , then for all .*

*Lemma 3 (see [2]). Assume that , satisfies , and
for , where a is a positive constant. Then
*

*Lemma 4 (see [2]). Assume that , satisfies , and
for , , and , where a and are positive constants such that . Then
*

*Lemma 5 (see [2]). Let be a nonnegative bounded sequence, and let be a nonnegative sequence such that ; then
*

*3. Permanence*

*3. Permanence**Concerned with the persistent property of the system (5), we have the following result.*

*Theorem 6. Assume that
holds; then, for any positive solution of the system (5), we have
where
*

*Proof. *From the first and second equations of system (5), we have
And so, from Lemma 3, we can obtain
According to Lemma 5, from the above inequality we have
For any , there exists a positive integer such that
By the third equation of system (5), we have
Hence, by applying Lemmas 1 and 2 to (25), we obtain
Setting , it follows that
Condition (18) implies that, for enough small positive constant , the following inequalities hold:
For the above , it follows from (22) and (27) that there exists a positive integer such that
Thus, for all , from (28), (29), and the first two equations of system (5), we have
where for , .

Noticing that
then
Hence, according to Lemma 4, we have
Setting , it follows that
where , .

According to Lemma 5, from (34) we have that, for any small enough (without loss of generality, assume that ), there exists an , such that
For , from (35) and the last equation of system (5), we have
Hence, by applying Lemmas 1 and 2 to (36), we obtain
Setting , it follows that
This ends the proof Theorem 6.

*4. Global Attractivity*

*4. Global Attractivity**Concerned with the stability property of the system (5), we have the following result.*

*Theorem 7. Assume that there exist positive constants , , and such that
hold; then, for any two positive solutions and of system (5), we have
where
*

*Proof. *By (39), we can choose enough small positive constants and such that
where

Let be any positive solution of system (5). For the above , from (22) and (27), there exists an enough large , such that

Now, let us define a Lyapunov functional
where , , are positive constants:
Then, from the definition of , , one could easily see that for all . Also, for any fixed ,

Also, from the first equation of system (5) and using the Mean Value Theorem, we can obtain
where lies between and .

Similarly to the analysis of (48), we can obtain
where lies between and :

From (42)–(44) and (48)–(50), for any , we have
Summating both sides of the above inequalities from to , we have
Hence
Then, we have
Therefore
which means that
Consequently
This completes the proof of Theorem 7

*5. Extinction*

*5. Extinction**Concerned with the extinction property of the system (5), when the coefficients of the third equation are all constants, we could establish the following results.*

*Theorem 8. Assume that
hold; let be any positive solution of system (5); then
*

*Theorem 9. Assume that
hold; let be any positive solution of system (5); then
*

*Proof of Theorem 8. *By conditions (58), we can choose positive constants , such that
Thus, there exists a positive constant such that
There exists a constant such that
Consider the following discrete Lyapunov functional:
From (65), we obtain
From inequalities (63) and (64), we can obtain
Therefore
From (22) and (27) we know that there exists an such that
and so
On the other hand, we also have
Combining inequalities (68), (70), and (71), we have
where
Hence we obtain that
This ends the proof of Theorem 8.

*Proof of Theorem 9. *By (60), we can choose positive constants , , and and constant such that
Define the following Lyapunov functional:
From (76), we have
Similarly to the analysis of (68)–(73), we have
This ends the proof of Theorem 9.

*From Theorems 8 and 9 we know that, under some suitable assumption, one of the species in the system may be driven to extinction; in this case, one interesting problem is to investigate the stability property of the rest of the species.*

*Consider the following discrete equations:
*

*Theorem 10. Assume that (58) holds and also
holds; then, for any positive solution of system (5) and any positive solution of system (79), we have
where is defined in Theorem 7.*

*Theorem 11. Assume that (60) holds and also
holds; then, for any positive solution of system (5) and any positive solution of system (80), we have
where is defined in Theorem 7.*

*Proof of Theorem 10. *By conditions (81), we can choose positive constants , such that
Thus, there exist enough small positive constants and such that
where is defined in(43)

Now, we define a Lyapunov functional
where