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Complex dynamic behavior of a discretetime predatorprey system of HollingIII type
Advances in Difference Equations volume 2014, Article number: 180 (2014)
Abstract
In this paper, we investigate the dynamics of a discretetime predatorprey system of HollingIII type in the closed first quadrant {\mathbb{R}}_{+}^{2}. Firstly, the existence and stability of fixed points of the system is discussed. Secondly, it is shown that the system undergoes a flip bifurcation and a NeimarkSacker bifurcation in the interior of {\mathbb{R}}_{+}^{2} by using bifurcation theory. Finally, numerical simulations including bifurcation diagrams, phase portraits, and maximum Lyapunov exponents are presented not only to explain our results with the theoretical analysis, but also to exhibit the complex dynamical behaviors, such as the period6, 7, 9, 15, 16, 22, 23, 32, 35 orbits, a cascade of perioddoubling bifurcations in period2, 4, 8, 16 orbits, quasiperiodic orbits, and chaotic sets.
MSC: 37G05, 37G35, 39A28, 39A33.
1 Introduction
The LotkaVolterra preypredator model has become one of the fundamental population models since the theoretical works going back to Lotka (1925) [1] and Volterra (1926) [2] in the last century. Holling (1965) [3] introduced three kinds of functional responses for different species to model the phenomena of predation. Qualitative analyses of more realistic preypredator models can be found in [4–11]. Recently, there is a growing evidence showing that the dynamics of the discretetime preypredator models can present a much richer set of patterns than those observed in continuoustime models [12–23].
In this paper, we consider the predatorprey system of HollingIII type that is given in [24] as follows:
where {x}_{1} and {x}_{2} denote prey and predator densities, respectively; r, K, α, β, d, γ are positive constants that stand for prey intrinsic growth rate, carrying capacity, conversion rate, half capturing saturation, the death rate of the predator, the harvesting rate of the predator, respectively. The predatorprey system (1) assumes that the prey grows logistically with intrinsic growth rate r and carrying capacity K in the absence of predation. The predator consumes the prey according to the Holling typeIII functional response {x}_{1}^{2}/({x}_{1}^{2}+\beta ) and contributes to its growth with rate \alpha {x}_{1}^{2}/({x}_{1}^{2}+\beta ). In [24], Wang et al. presented a bifurcation analysis by choosing the death rate and the harvesting rate of the predator as the bifurcation parameters and proved that system (1) can undergo the BogdanovTakens bifurcation.
Applying the forward Euler scheme to system (1), we obtain the discretetime predatorprey system of HollingIII type as follows:
where δ is the step size. In this paper, we investigate this version as a discretetime dynamical system in the interior of the first quadrant {\mathbb{R}}_{+}^{2} by using the normal form theory of the discrete system (see Section 4 in [25]; see also [26–28]), and we prove that this discrete model possesses the flip bifurcation and the NeimarkSacker bifurcation.
This paper is organized as follows. In Section 2, we discuss the existence and stability of fixed points for system (2) in the closed first quadrant {\mathbb{R}}_{+}^{2}. In Section 3, we show that there exist some values of the parameters such that (2) undergoes the flip bifurcation and the NeimarkSacker bifurcation in the interior of {\mathbb{R}}_{+}^{2}. In Section 4, we present the numerical simulations, which not only illustrate our results with the theoretical analysis, but which also exhibit the complex dynamical behaviors such as the period6, 7, 9, 15, 16, 22, 23, 32, 35 orbits, a cascade of perioddoubling bifurcations in period2, 4, 8, 16 orbits, quasiperiodic orbits, and chaotic sets. The Lyapunov exponents are computed numerically to further confirm the dynamical behaviors. A brief discussion is given in Section 5.
2 The existence and stability of fixed points
It is clear that the fixed points of (2) satisfy the following equations:
Next, we consider the existence of the positive fixed points of system (2). Suppose that {E}^{\ast}({x}_{1}^{\ast},{x}_{2}^{\ast}) is a positive fixed point of map (2). Then {x}_{1}^{\ast} and {x}_{2}^{\ast} are positive solutions of the following equations:
From Eq. (4), we can see that {x}_{1}^{\ast} is the root in the interval (0,K) of the following equation:
Let
Using the Cardano formula (see [[29], p.106]), we have the following results.
Lemma 2.1

(i)
If \tilde{\mathrm{\Delta}}>0, then system (2) has one unique positive fixed point {E}_{11}({x}_{1}^{11},{x}_{2}^{11}), where {x}_{1}^{11}={(\frac{\tilde{q}}{2}+{\tilde{\mathrm{\Delta}}}^{\frac{1}{2}})}^{\frac{1}{3}}+{(\frac{\tilde{q}}{2}{\tilde{\mathrm{\Delta}}}^{\frac{1}{2}})}^{\frac{1}{3}}+\frac{K}{3}.

(ii)
If \tilde{\mathrm{\Delta}}=0 and \tilde{p}<0, then system (2) has two different fixed points, {E}_{0}({x}_{1}^{0},{x}_{2}^{0}) and {E}_{1}({x}_{1}^{1},{x}_{2}^{1}), where {x}_{1}^{0} is a real root of double multiplicity and {x}_{1}^{1} is another real root of (5), respectively. Here {x}_{1}^{0}={(\frac{\tilde{q}}{2})}^{\frac{1}{3}}+\frac{K}{3} and {x}_{1}^{1}=2{(\frac{\tilde{q}}{2})}^{\frac{1}{3}}+\frac{K}{3}.

(iii)
If \tilde{\mathrm{\Delta}}<0, then system (2) has three different fixed points, {E}_{21}({x}_{1}^{21},{x}_{2}^{21}), {E}_{22}({x}_{1}^{22},{x}_{2}^{22}) and {E}_{23}({x}_{1}^{23},{x}_{2}^{23}), where {x}_{1}^{2i}=2{(\frac{\tilde{p}}{3})}^{\frac{1}{2}}cos(\frac{\mathrm{\Psi}}{3}+\frac{2(i1)\pi}{3})+\frac{K}{3} (i=1,2,3), and \mathrm{\Psi}=arccos[\frac{\tilde{q}}{2}{(\frac{\tilde{p}}{3})}^{\frac{3}{2}}].
Now we study the stability of the fixed points for (2). The Jacobian matrix J of system (2) evaluated at the fixed point ({x}_{1}^{\ast},{x}_{2}^{\ast}) is given by
where
and the characteristic equation of the Jacobian matrix J can be written as
where
Using the SchurCohn criterion [30], we can show the stability of the fixed points as follows.
Lemma 2.2 The positive fixed point ({x}_{1}^{\ast},{x}_{2}^{\ast}) of system (2) is stable if one of the following conditions holds:

(1)
\mathrm{\Delta}<0 and 0<\delta <\frac{{a}_{1}+{b}_{2}}{{a}_{1}{b}_{2}+{a}_{2}{b}_{1}};

(2)
\mathrm{\Delta}>0 and 0<\delta <\frac{({a}_{1}+{b}_{2})\sqrt{\mathrm{\Delta}}}{{a}_{1}{b}_{2}+{a}_{2}{b}_{1}},
where
3 Flip bifurcation and NeimarkSacker bifurcation
In this section, we choose the parameter δ as a bifurcation parameter to study the flip bifurcation and the NeimarkSacker bifurcation of ({x}_{1}^{\ast},{x}_{2}^{\ast}) by using bifurcation theory in (see Section 4 in [25]; see also [26–28]).
We first discuss the flip bifurcation of (2) at ({x}_{1}^{\ast},{x}_{2}^{\ast}). Suppose that \mathrm{\Delta}>0, i.e.,
If
or
then the eigenvalues of the positive fixed point ({x}_{1}^{\ast},{x}_{2}^{\ast}) are {\lambda}_{1}=1, {\lambda}_{2}=3+{\delta}_{1}({a}_{1}+{b}_{2}).
The condition {\lambda}_{2}\ne 1 leads to
Let {\tilde{x}}_{1}={x}_{1}{x}_{1}^{\ast}, {\tilde{x}}_{2}={x}_{2}{x}_{2}^{\ast}, A(\delta )=J({x}_{1}^{\ast},{x}_{2}^{\ast}), we transform the fixed point ({x}_{1}^{\ast},{x}_{2}^{\ast}) of system (2) into the origin, then system (2) becomes
where
and \tilde{x}={({\tilde{x}}_{1},{\tilde{x}}_{2})}^{T}. It follows that
and \delta ={\delta}_{2}.
We know that A has the simple eigenvalue {\lambda}_{1}({\delta}_{1})=1, and the corresponding eigenspace {E}^{c} is onedimensional and spanned by an eigenvector q\in {\mathbb{R}}^{2} such that Aq=q. Let p\in {\mathbb{R}}^{2} be the adjoint eigenvector, that is, {A}^{T}p=p. By direct calculation we obtain
In order to normalize p with respect to q, we denote
where
It is easy to see \u3008p,q\u3009=1, where \u3008\cdot ,\cdot \u3009 means the standard scalar product in {\mathbb{R}}^{2}: \u3008p,q\u3009={p}_{1}{q}_{1}+{p}_{2}{q}_{2}.
Following the algorithms given in [25], the sign of the critical normal form coefficient c({\delta}_{1}), which determines the direction of the flip bifurcation, is given by the following formula:
From the above analysis and the theorem in [25–28], we have the following result.
Theorem 3.1 Suppose that ({x}_{1}^{\ast},{x}_{2}^{\ast}) is the positive fixed point. If the conditions (9), (10) hold and c({\delta}_{1})\ne 0, then system (2) undergoes a flip bifurcation at the fixed point ({x}_{1}^{\ast},{x}_{2}^{\ast}) when the parameter δ varies in a small neighborhood of {\delta}_{1}. Moreover, if c({\delta}_{1})>0 (respectively, c({\delta}_{1})<0), then the period2 orbits that bifurcate from ({x}_{1}^{\ast},{x}_{2}^{\ast}) are stable (respectively, unstable).
In Section 4 we will give some values of the parameters such that c({\delta}_{1})\ne 0, thus the flip bifurcation occurs as δ varies (see Figure 1).
We next discuss the existence of a NeimarkSacker bifurcation by using the NeimarkSacker theorem in [25–28].
The eigenvalues of the characteristic (8) are
where
The eigenvalues {\lambda}_{1,2} are complex conjugate for {(trJ)}^{2}4detJ<0, which leads to \mathrm{\Delta}<0, i.e.,
Let
we have detJ({\delta}_{2})=1.
For \delta ={\delta}_{2}, the eigenvalues of the matrix associated with the linearization of the map (11) at ({\tilde{x}}_{1},{\tilde{x}}_{2})=(0,0) are conjugate with modulus 1, and they are written as
and \lambda ({\delta}_{2})=1, \frac{d\lambda (\delta )}{d\delta}{}_{\delta ={\delta}_{2}}=\frac{{a}_{1}+{b}_{2}}{2}\ne 0.
In addition, if trJ({\delta}_{2})\ne 0,1, which leads to
then we have {\lambda}^{k}({\delta}_{2})\ne 1 for k\in \{1,2,3,4\}.
Let q\in {\mathbb{C}}^{2} be an eigenvector of A({\delta}_{2}) corresponding to the eigenvalue \lambda ({\delta}_{2}) such that
Also let p\in {\mathbb{C}}^{2} be an eigenvector of the transposed matrix {A}^{T}({\delta}_{2}) corresponding to its eigenvalue, that is, \overline{\lambda ({\delta}_{2})},
By direct calculation we obtain
In order to normalize p with respect to q, we denote
where
It is easy to see that \u3008p,q\u3009=1, where \u3008\cdot ,\cdot \u3009 means the standard scalar product in {\mathbb{C}}^{2}: \u3008p,q\u3009={\overline{p}}_{1}{q}_{1}+{\overline{p}}_{2}{q}_{2}.
Any vector x\in {\mathbb{R}}^{2} can be represented for δ near {\delta}_{2} as
for some complex z. Obviously, z=\u3008p,x\u3009. Thus, system (11) can be transformed for δ near {\overline{\delta}}^{\ast} into the following form:
where \lambda (\delta ) can be written as \lambda (\delta )=(1+\phi (\delta )){e}^{i\theta (\delta )} (\phi (\delta ) is a smooth function with \phi ({\delta}_{2})=0) and g is a complexvalued smooth function of z, \overline{z}, and δ, whose Taylor expression with respect to (z,\overline{z}) contains quadratic and higherorder terms:
with {g}_{kj}\in \mathbb{C}, k,j=0,1,\dots . By (13) and the formulas
we can calculate the coefficient a({\delta}_{2}) via
where {e}^{i\theta ({\delta}_{2})}=\lambda ({\delta}_{2}).
For the above argument and the theorem in [25–28], we have the following result.
Theorem 3.2 Suppose that ({x}_{1}^{\ast},{x}_{2}^{\ast}) is the positive fixed point. If a({\delta}_{2})<0 (respectively, >0) the NeimarkSacker bifurcation of system (2) at \delta ={\delta}_{2} is supercritical (respectively, subcritical) and there exists a unique closed invariant curve bifurcation from ({x}_{1}^{\ast},{x}_{2}^{\ast}) for \delta ={\delta}_{2}, which is asymptotically stable (respectively, unstable).
In Section 4 we will choose some values of the parameters so as to show the process of a NeimarkSacker bifurcation for system (2) in Figure 2 by numerical simulation.
4 Numerical simulations
In this section, we present the bifurcation diagrams, phase portraits, and maximum Lyapunov exponents for system (2) to explain the above theoretical analysis and show the new interesting complex dynamical behaviors by using numerical simulations. The bifurcation parameters are considered in the following three cases:

(1)
Varying δ in the range 0.8\le \delta <2.3, and fixing d=0.05, r=1.5, K=1.2, \alpha =0.8, \beta =2.5, \gamma =0.1.

(2)
Varying δ in the range 0.8\le \delta <1.7, and fixing d=2, r=2, K=\frac{8}{5}, \alpha =3, \beta =\frac{1}{3}, \gamma =\frac{1}{4}.

(3)
Varying r in the range 1.6<r<3.6, and fixing d=2, \delta =1, K=\frac{8}{5}, \alpha =3, \beta =\frac{1}{3}, \gamma =\frac{1}{4}.
Case (1). The bifurcation diagrams of system (2) in the (\delta ,{x}_{1}) and (\delta ,{x}_{2}) plane for d=0.05, r=1.5, K=1.2, \alpha =0.8, \beta =2.5, \gamma =0.1 are given in Figure 1(a) and (b), respectively. From Figure 1(a) and (b), we can see that the flip bifurcation emerges from the fixed point (0.4903,4.9591) at {\delta}_{1}=1.5929 with c({\delta}_{1})=57.3688. We also observe that there is a cascade of perioddoubling bifurcations in period2, 4, 8, 16 orbits. The maximum Lyapunov exponents corresponding to Figure 1(a) and (b) are calculated and plotted in Figure 1(c), confirming the existence of the chaotic regions and period orbits in the parametric space.
Case (2). The bifurcation diagrams of system (2) in the (\delta ,{x}_{1}) and (\delta ,{x}_{2}) plane for d=2, r=2, K=\frac{8}{5}, \alpha =3, \beta =\frac{1}{3}, \gamma =\frac{1}{4} are given in Figure 2(a) and (b), respectively. After calculation for the positive fixed point of system (2), the NeimarkSacker bifurcation emerges from the fixed point (1,1) at {\delta}_{2}=1, and its eigenvalues are {\lambda}_{\pm}=0.6875\pm 0.7262i. For {\delta}_{2}=1, we have {\lambda}_{\pm}=1, l=\frac{d\lambda }{d\delta}{}_{\delta ={\delta}_{2}}=0.3125>0, {g}_{20}=1.40631.3798i, {g}_{11}=1.47661.8336i, {g}_{02}=2.2500+1.8881i, {g}_{21}=2.1357+3.0023i, a({\delta}_{2})=7.8212. It shows the correctness of Theorem 3.2.
From Figure 2(a) and (b), we observe that the fixed point of system (2) is stable for \delta <1, loses its stability at \delta =1, and an invariant circle appears when the parameter δ exceeds 1.
The maximum Lyapunov exponents corresponding to Figure 2(a) and (b) are calculated and plotted in Figure 2(c), confirming the existence of the chaotic regions and period orbits in the parametric space. Figure 3(a) and (b) show the local amplification corresponding to Figure 2(a) for \delta \in [1.488,1.588] and \delta \in [1.608,1.616], respectively. From Figure 3(c) and (d), we observe that some Lyapunov exponents are bigger than 0, some are smaller than 0, so there exist stable fixed points or stable period windows in the chaotic region. In general the positive Lyapunov exponent is considered to be one of the characteristics implying the existence of chaos [31, 32].
The phase portraits which are associated with Figure 2(a) and (b) are revealed in Figure 4, which clearly depicts the process of how a smooth invariant circle bifurcates from the stable fixed point (1,1). When δ exceeds 1 there appears a circle curve enclosing the fixed point (1,1), and its radius becomes larger with respect to the growth of δ. When δ increases at certain values, for example, at \delta =1.288, the circle disappears and a period7 orbit appears. From Figure 4, we observe that there are period7, 9, 15, 22 orbits, quasiperiodic orbits, and attracting chaotic sets.
Case (3). The bifurcation diagrams of system (2) in the (r,{x}_{1}) and (r,{x}_{2}) plane for d=2, \delta =1, K=\frac{8}{5}, \alpha =3, \beta =\frac{1}{3}, \gamma =\frac{1}{4} are given in Figure 5(a) and (b), respectively. After calculation for the positive fixed point of system (2), the NeimarkSacker bifurcation emerges from the fixed point (1,1) at r=2. From Figure 5(a) and (b), we observe that the fixed point of map (2) is stable for r<2, loses its stability at r=2, and an invariant circle appears when the parameter r exceeds 2.
The maximum Lyapunov exponents corresponding to Figure 5(a) and (b) are calculated and plotted in Figure 5(c). For r\in (2.9,3.6), some Lyapunov exponents are bigger than 0, some are smaller than 0, which implies that there exist stable fixed points or stable period windows in the chaotic region.
The phase portraits which are associated with Figure 5(a) and (b) are revealed in Figure 6. From Figure 6, we observe that there are period6, 16, 23, 32, 35 orbits, quasiperiodic orbits, and attracting chaotic sets.
5 Conclusion
In this paper, we investigate the complex behaviors of the discretetime predatorprey system of HollingIII type obtained by the Euler method in the closed first quadrant {\mathbb{R}}_{+}^{2}, and we show that system (2) can undergo a flip bifurcation and a NeimarkSacker bifurcation in the interior of {\mathbb{R}}_{+}^{2}. Moreover, system (2) displays very interesting dynamical behaviors, including period6, 7, 9, 15, 16, 22, 23, 32, 35 orbits, a cascade of perioddoubling bifurcations in period2, 4, 8, 16 orbits, an invariant cycle, quasiperiodic orbits, and chaotic sets. These results reveal far richer dynamics of the discretetime models compared to the continuoustime models.
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He, Z., Li, B. Complex dynamic behavior of a discretetime predatorprey system of HollingIII type. Adv Differ Equ 2014, 180 (2014). https://doi.org/10.1186/168718472014180
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DOI: https://doi.org/10.1186/168718472014180