The Scientific World Journal

Volume 2014 (2014), Article ID 637026, 8 pages

http://dx.doi.org/10.1155/2014/637026

## Dynamic Behavior of Positive Solutions for a Leslie Predator-Prey System with Mutual Interference and Feedback Controls

Department of Mathematics, Sichuan University, Chengdu, Sichuan 610064, China

Received 14 August 2013; Accepted 7 November 2013; Published 20 January 2014

Academic Editors: A. Bellouquid, Y. Cheng, and X. Song

Copyright © 2014 Cong Zhang 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

We consider a Leslie predator-prey system with mutual interference and feedback controls. For general nonautonomous case, by using differential inequality theory and constructing a suitable Lyapunov functional, we obtain some sufficient conditions which guarantee the permanence and the global attractivity of the system. For the periodic case, we obtain some sufficient conditions which guarantee the existence, uniqueness, and stability of a positive periodic solution.

#### 1. Introduction

Leslie [1] introduced the famous Leslie predator-prey system where and stand for the population (the density) of the prey and the predator at time , respectively, and is the so-called predator functional response to prey.

In system (1), it has been assumed that the prey grows logistically with growth rate and carries capacity in the absence of predation. The predator consumes the prey according to the functional response and grows logistically with growth rate and carrying capacity proportional to the population size of the prey (or prey abundance). The parameter is a measure of the food quality that the prey provides and converted to predator birth. Leslie introduced a predator-prey model, where the carrying capacity of the predator’s environment is proportional to the number of prey, and still stressed the fact that there are upper limits to the rates of increasing of both prey and predator , which are not recognized in the Lotka-Volterra model. These upper limits can be approached under favorable conditions: for the predators, when the number of prey per predator is large; for the prey, when the number of predators (and perhaps the number of prey also) is small [2].

In population dynamics, the functional response refers to the numbers eaten per predator per unit time as a function of prey density. Kooij and Zegeling [3] and Sugie et al. [4] considered the following functional response: In fact, the functional response with has been suggested in [4].

It is easy to see that system (1) can be written as the following system: When or in system (3), the Leslie system (3) can be written as the following system: or which were considered in [5].

The mutual interference between predators and prey was introduced by Hassell in 1971 [6]. During his research of the capturing behavior between hosts and parasites, he found that the hosts or parasites had the tendency to leave from each other when they met, which interfered with the hosts capturing effects. It is obvious that the mutual interference will be stronger while the size of the parasite becomes larger. Thus, Pan [7] studied a Leslie predator-prey system with mutual interference constant : where are bounded and periodic functions and is a constant. Some sufficient conditions are obtained for the permanence, attractivity, and existence of the positive periodic solution of the system (6).

On the other hand, ecosystems in the real world are continuously distributed by unpredictable forces which can result in changes in the biological parameters such as survival rates. Of practical interest in ecology is the question of whether or not an ecosystem can withstand those unpredictable disturbances which persist for a finite period of time. In the language of control variables, we call the disturbance functions as control variables, whereas, the control variables discussed in most literatures are constants or time dependent [8–10]. In recent, there are many works on the feedback controls (see, e.g., [11–19] and the references therein). Furthermore, in recent research on species, dynamics of the Leslie system has important significance; see [20–29] and the references therein for details.

Therefore, Chen and Cao [5] have investigated the following Leslie system with feedback controls: where and denote the density of prey and predator at time , respectively, are control variables, are almost periodic functions of , () are all nonnegative almost periodic functions of , and is a positive constant denoting the constant of capturing half-saturation.

By using a comparison theorem and constructing a suitable Lyapunov function, they obtained some sufficient conditions for the existence of a unique almost periodic solution and the global attractivity of the solutions of the system (7). By using the comparison and continuation theorems, and based on the coincidence degree and by constructing a suitable Lyapunov function, Wang et al. [30] further obtained some sufficient and necessary conditions for the existence and global attractivity of periodic solutions of the system (7) with the periodic coefficients.

However, to the best of our knowledge, up to now, still no scholar has considered the general nonautonomous Leslie predator-prey system with mutual interference and feedback controls. In this paper, we will consider following the Leslie predator-prey system: where and denote the density of prey and predator at time , respectively, () are control variables, , , and are positive constants.

For the general nonautonomous case, by using differential inequality theory and constructing a suitable Lyapunov functional, we obtain some sufficient conditions which guarantee the permanence and the global attractivity of the system (8). For the periodic case, we obtain some sufficient conditions which guarantee the existence, uniqueness, and stability of a positive periodic solution of the system (8). We would like to mention that the conditions are related to the interference constant .

#### 2. Preliminaries

In this section, we state several definitions and lemmas which will be useful in proving the main results of this paper.

Let and , respectively, denote the set of all real numbers and the -dimensional real Euclidean space, and denote the nonnegative cone of . Let be a continuous bounded function on and we set and .

Throughout this paper, we assume that the coefficients of the system (8) satisfy the following conditions:

*Definition 1. *If is a positive solution of the system (8) and is any positive solution of system (8) satisfying
then we say that is globally attractive.

Lemma 2 (see [31]). *If , , and , when and , one has
*

*Lemma 3 (see [31]). If , , and , when and , one has
*

*Lemma 4 (see [32]). If function is nonnegative, integral, and uniformly continuous on , then
One assumes the following hypothesis holds: ();
();
() − ;();
();
()for ,
() for ,
where and () are positive constants.*

*For any given the initial conditions of the system (8), , (), it is not difficult to see that the corresponding solution satisfies , (), for .*

*3. General Nonautonomous Case*

*3. General Nonautonomous Case**In this section, we will explore the dynamics of the system (8) and present some results including the permanence and the global attractivity of the system.*

*Theorem 5. Suppose that system (8) satisfies the assumptions and . Then system (8) is permanent; that is, any positive solution of the system (8) satisfies
where
with
*

*Proof. *From the first equation of the system (8), it follows that
Applying Lemma 3 to (19), for a small enough positive constant , there exists a enough large such that
From the second equation of the system (8) and (20), it follows that, for ,
Setting in inequality (21), we get
For any , it follows from (22) and Lemma 3 that there exists a such that, for ant ,
By the third equation of system (8) and (20), we obtain
Letting in inequality (24), we get
For any , it follows from (25) and Lemma 2 that there exists a such that, for any ,
By the forth equation of system (8) and (23), we have
Setting in inequality (27), we obtain
For any , it follows from (28) and Lemma 2 that there exists a such that, for any ,
By the first equation of system (8), (20), (23), and (26), we obtain
Taking in inequality (30), we have
In view of condition () and Lemma 3, for any , it follows from (28) that there exists a such that, for any ,
From the second equation of the system (8), (29), and (32), we have
Setting in inequality (33), we have
In view of condition () and Lemma 3, for any , (34) shows that there exists a such that, for any ,
By the third equation of system (8) and (32), we obtain
Letting in inequality (36), we get
For any , it follows from (37) and Lemma 2 that there exists a such that, for any ,
By the forth equation of system (8) and (35), we have
Taking in inequality (39), we get
For any , by Lemma 2 and (40), there exists a such that, for any ,
Under the conditions and , it follows from (20), (23), (26), (29), (32), (35), (38), and (41) that the system (8) is permanent. This completes the proof.

*In the following, by constructing a suitable Lyapunov functional, we get the sufficient conditions for the globally attractive solution for the system (8).*

*Theorem 6. Suppose that system (8) satisfies the assumptions – or – and . Then for any positive solution and of the system (8), one has
*

*Proof. *Let and be any positive solutions of the system (8). It follows from Theorem 5 that there exists such that
Consider the following functional:
Calculating the upper right derivative of along the solution of the system (8), it follows that
By the mean value theorem and Theorem 5, in view of , for , we have
Note that
When , according to (45), (46), (47), and (49), it follows that, for ,
When , according to (45), (46), (48), and (49), for , we have
When , it follows from (50) and assumptions – that there exist four positive constants () such that
which shows that is nonincreasing on . Integrating both sides of (52) on , we get
This implies that
By Lemma 4, we have
for , and so
When , by similar way, from (51) and assumptions ()–() and (), we can show that
This completes the proof.

*4. Periodic Case*

*4. Periodic Case**To this end, in order to get the existence and uniqueness of a positive periodic solution of the system (8), we further assume that system (8) satisfies the following condition.(), () are all continuous, real-valued positive -periodic functions; is a constant.*

*Let , , , . Let . for be the uniqueness solution of the system (8) with the initial condition . By Theorem 5, there exists a such that , for .*

*Since is continuous on , there exist two positive constants and such that for . Let and . Then , for . Similarly, we can find positive constants and such that and positive constants and such that () for . Let , , , . Therefore, we have , for . Define the Poincare mapping as follows:
where is defined in assumption .*

*It is easy to see that the existence of periodic solution in (8) with assumptions is equal to prove that the mapping has at least one fixed point.*

*Theorem 7. If the assumptions , , and hold, system (8) has at least one positive -periodic solution.*

*Proof. *According to discussion above, we obtain . And we can get that the mapping is continuous by the theory of ordinary differential equation. It is obvious that is a closed and convex set. Therefore, has at least one fixed point by Brouwer fixed point theorem. That is to say, if system (8) satisfies , , and , system (8) has at least one positive -periodic solution. This completes the proof.

*Finally, some sufficient conditions are obtained for the uniqueness of the positive -periodic solution for the system (8).*

*Theorem 8. If system (8) satisfies – and or –, and , system (8) has only one positive -periodic solution which is globally attractive.*

*Proof. *If system (8) satisfies – and , (8) has at least one -periodic solution by Theorem 7. For any two positive -periodic solutions and of the system (8). We claim that , for all . Otherwise, there must be at least such that ; that is, . It follows that
which contracts with (42). Thus , for all , hods. Similarly, we can prove that
Therefore, the uniqueness of the periodic solution of the system (8) is obtained. By Theorem 6, if system (8) satisfies ()–() and , (8) has only one positive -periodic solution which is globally attractive. Similarly, we can prove that system (8) satisfying ()–(), , and has a unique positive -periodic solution which is globally attractive. This completes the proof.

*Conflict of Interests*

*Conflict of Interests*

*The authors declare that there is no conflict of interests regarding the publication of this paper.*

*Acknowledgment*

*Acknowledgment*

*This work was supported by the Key Program of NSFC (Grant no. 70831005) and the National Natural Science Foundation of China (111171237).*

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