 Research Article
 Open Access
Numerical Solutions of a Fractional PredatorPrey System
 Yanqin Liu^{1}Email author and
 Baogui Xin^{2, 3}
https://doi.org/10.1155/2011/190475
© Yanqin Liu and Baogui Xin. 2011
 Received: 10 December 2010
 Accepted: 22 February 2011
 Published: 13 March 2011
Abstract
We implement relatively new analytical technique, the Homotopy perturbation method, for solving nonlinear fractional partial differential equations arising in predatorprey biological population dynamics system. Numerical solutions are given, and some properties exhibit biologically reasonable dependence on the parameter values. And the fractional derivatives are described in the Caputo sense.
Keywords
 Fractional Derivative
 Fractional Calculus
 Fractional Differential Equation
 Prey Population
 Predator Population
1. Introduction
Recently, it has turned out that many phenomena in engineering, physics, chemistry, other sciences [1–3] can be described very successfully by models using mathematical tools form fractional calculus, such as anomalous transport in disordered systems, some percolations in porous media, and the diffusion of biological populations. But most fractional differential equations [4, 5] do not have exact analytic solutions [6, 7]. An effective method for solving such equations is needed. So approximate and numerical techniques must be used. The Homotopy Perturbation Method (HPM) is relatively new approach to provide an analytical approximation to nonlinear problem. This method was first presented by He [8, 9] and applied to various nonlinear problems [10–12]. Recently, the application of the method is extended for fractional differential equations [13–15].
Biological population problems are widely investigated in many papers [16–19]. Dunbar [20] establishes the existence of traveling wave solutions for two reaction diffusion systems based on the LotkaVolterra model for predator and prey interactions, and discusses some possible biological implications of the existence of these waves. Gourley and Britton [21] investigate stability of coexistence steadystate and bifurcations of a predatorprey system in the form of a coupled reactiondiffusion equations. Petrovskii et al. [22] obtained an exact solution of the spatiotemporal dynamics of a predatorprey community by using an appropriate change of variables, and the properties of the solution exhibit biologically reasonable dependence on the parameter values. Kadem and Baleanu[23] studied the coupled fractional LotkaVolterra equations using the Homotopy perturbation method.
where , and denotes the prey population density and represents the predator population density, denote initial conditions of population system; the nonlinear equation of this type has wide applications in the fields of population growth. The derivatives in (1.1) is the Caputo derivative.
In this paper, we consider the fractional nonlinear predatorprey population model. and the paper is organized as follows: in Section 2, a brief review of the theory of fractional calculus will be given to fix notation and provide a convenient reference. In Section 3, we extend the application of the homotopy perturbation method to construct approximate solutions for the nonlinear fractional predatorprey system. In Section 4, we present three examples with different initial conditions to the predatorprey system and show some properties of this fractional nonlinear predatorprey system. Conclusions will be presented in Section 5.
2. Fractional Calculus
There are several approaches to define the fractional calculus, for example, RiemannLiouville, GruünwaldLetnikow, Caputo, and Generalized Functions approach. RiemannLiouville fractional derivative is mostly used by mathematicians but this approach is not suitable for real world physical problems since it requires the definition of fractional order initial conditions, which have no physically meaningful explanation yet. Caputo introduced an alternative definition, which has the advantage of defining integer order initial conditions for fractional order differential equations.
Definition 2.1.
Definition 2.2.
We have chosen the Caputo fractional derivative because it allows traditional initial and boundary conditions to be included in the formulation of the problem. And some other properties of fractional derivative can be found in [1, 3].
3. Homotopy Perturbation Method
institute (3.2) into (3.1) and compare coefficients of terms with identical powers of , then you can get the numerical solutions of the equation. Because of the knowledge of various perturbation methods that loworder approximate solution leads to high accuracy, there requires no infinite series. Then after a series of recurrent calculation by using Mathematica software, we will get approximate solutions of fractional biological population model. In Section 4, we show some examples that the Homotopy perturbation method gives a very good approximation of the exact solution.
4. Fractional PredatorPrey Equation
In order to assess the advantages and the accuracy of the Homotopy perturbation method presented in this paper for nonlinear fractional Fisher's equation, we have applied it to the following several problems.
Case 1.
In this case, we consider the fractional predatorprey equation and subject to the constant initial condition
Comparison of the numerical values with Homotopy perturbation method and Variational iteration method when for (1.1), and (4.1).

 Numerical value ( ) by HPM  Numerical value ( ) by VIM 

0.02  1  (99.4831,10.6146)  (99.4834,10.6323) 
0.9  (99.1865,10.9633)  (99.3065,10.8375)  
0.2  1  (93.0910,17.8514)  (93.3908,17.7382) 
0.9  (90.5735,20.5567)  (92.4584,18.8198)  
0.3  1  (87.9348,23.4430)  (88.9466,22.7237) 
0.9  (83.7933,27.7785)  (87.8005,24.0532) 
Case 2.
In this case, the initial conditions of systems (1.1) are given by
Case 3.
We will consider the initial conditions of fractional predatorprey equation (1.1)
Because of the knowledge of various perturbation methods that loworder approximate solution leads to high accuracy, there requires no infinite series (mostly 2–4 terms are enough). The corresponding solutions are obtained according to the recurrence relation using Mathematica.
5. Conclusion
In this letter, we implement relatively new analytical techniques, the Homotopy perturbation method, for solving nonlinear fractional partial differential equations arising in preypredator biological population dynamics system. Comparing the methodology HPM to ADM, VIM and HAM have the advantages. Unlike the ADM, the HPM is free from the need to use Adomian polynomials. In this method we do not need the Lagrange multiplier, correction functional, stationary conditions, or calculating integrals, which eliminate the complications that exist in the VIM. In contrast to the HAM, this method is not required to solve the functional equations in each iteration the efficiency of HAM is very much depended on choosing auxiliary parameter. We can easily conclude that the Homotopy perturbation method is an efficient tool to solve approximate solution of nonlinear fractional partial differential equations.
Declarations
Acknowledgments
The authors thank to the referees for their fruitful advices and comments. This work was supported partly by the National Science Foundation of Shandong Province (Grant nos. Y2007A06 & ZR2010Al019) and the China Postdoctoral Science Foundation (Grant no. 20100470783).
Authors’ Affiliations
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