
Citation: Alexis M. Chambers, Jessica D. Payne. The Influence of Sleep on the Consolidation of Positive Emotional Memories: Preliminary Evidence[J]. AIMS Neuroscience, 2014, 1(1): 39-51. doi: 10.3934/Neuroscience.2014.1.39
[1] | Ceyu Lei, Xiaoling Han, Weiming Wang . Bifurcation analysis and chaos control of a discrete-time prey-predator model with fear factor. Mathematical Biosciences and Engineering, 2022, 19(7): 6659-6679. doi: 10.3934/mbe.2022313 |
[2] | Yajie Sun, Ming Zhao, Yunfei Du . Multiple bifurcations of a discrete modified Leslie-Gower predator-prey model. Mathematical Biosciences and Engineering, 2023, 20(12): 20437-20467. doi: 10.3934/mbe.2023904 |
[3] | Xiaoling Han, Xiongxiong Du . Dynamics study of nonlinear discrete predator-prey system with Michaelis-Menten type harvesting. Mathematical Biosciences and Engineering, 2023, 20(9): 16939-16961. doi: 10.3934/mbe.2023755 |
[4] | Shuo Yao, Jingen Yang, Sanling Yuan . Bifurcation analysis in a modified Leslie-Gower predator-prey model with fear effect and multiple delays. Mathematical Biosciences and Engineering, 2024, 21(4): 5658-5685. doi: 10.3934/mbe.2024249 |
[5] | Mengyun Xing, Mengxin He, Zhong Li . Dynamics of a modified Leslie-Gower predator-prey model with double Allee effects. Mathematical Biosciences and Engineering, 2024, 21(1): 792-831. doi: 10.3934/mbe.2024034 |
[6] | Xiaoyuan Chang, Junjie Wei . Stability and Hopf bifurcation in a diffusivepredator-prey system incorporating a prey refuge. Mathematical Biosciences and Engineering, 2013, 10(4): 979-996. doi: 10.3934/mbe.2013.10.979 |
[7] | Saheb Pal, Nikhil Pal, Sudip Samanta, Joydev Chattopadhyay . Fear effect in prey and hunting cooperation among predators in a Leslie-Gower model. Mathematical Biosciences and Engineering, 2019, 16(5): 5146-5179. doi: 10.3934/mbe.2019258 |
[8] | Hongqiuxue Wu, Zhong Li, Mengxin He . Dynamic analysis of a Leslie-Gower predator-prey model with the fear effect and nonlinear harvesting. Mathematical Biosciences and Engineering, 2023, 20(10): 18592-18629. doi: 10.3934/mbe.2023825 |
[9] | Christian Cortés García . Bifurcations in a discontinuous Leslie-Gower model with harvesting and alternative food for predators and constant prey refuge at low density. Mathematical Biosciences and Engineering, 2022, 19(12): 14029-14055. doi: 10.3934/mbe.2022653 |
[10] | A. Q. Khan, I. Ahmad, H. S. Alayachi, M. S. M. Noorani, A. Khaliq . Discrete-time predator-prey model with flip bifurcation and chaos control. Mathematical Biosciences and Engineering, 2020, 17(5): 5944-5960. doi: 10.3934/mbe.2020317 |
In biological systems, the continuous predator-prey model has been successfully investigated and many interesting results have been obtained (cf. [1,2,3,4,5,6,7,8,9] and the references therein). Moreover, based on the continuous predator-prey model, many human factors, such as time delay [10,11,12], impulsive effect [13,14,15,16,17,18,19,20], Markov Switching [21], are considered. The existing researches mainly focus on stability, periodic solution, persistence, extinction and boundedness [22,23,24,25,26,27,28].
In 2011, the authors [28] considered the system incorporating a modified version of Leslie-Gower functional response as well as that of the Holling-type Ⅲ:
$ {˙x(t)=x(a1−bx−c1y2x2+k1),˙y(t)=y(a2−c2yx+k2). $
|
(1) |
With the diffusion of the species being also taken into account, the authors [28] studied a reaction-diffusion predator-prey model, and gave the stability of this model.
In model (1) $ x $ represents a prey population, $ y $ represents a predator with population, $ a_{1} $ and $ a_{2} $ represent the growth rate of prey $ x $ and predator $ y $ respectively, constant $ b $ represents the strength of competition among individuals of prey $ x $, $ c_{1} $ measures the maximum value of the per capita reduction rate of prey $ x $ due to predator $ y $, $ k_{1} $ and $ k_{2} $ represent the extent to which environment provides protection to $ x $ and to $ y $ respectively, $ c_{2} $ admits a same meaning as $ c_{1}. $ All the constants $ a_{1}, a_{2}, b, c_{1}, c_{2}, k_{1}, k_{2} $ are positive parameters.
However, provided with experimental and numerical researches, it has been obtained that bifurcation is a widespread phenomenon in biological systems, from simple enzyme reactions to complex ecosystems. In general, the bifurcation may put a population at a risk of extinction and thus hinder reproduction, so the bifurcation has always been regarded as a unfavorable phenomenon in biology [29]. This bifurcation phenomenon has attracted the attention of many mathematicians, so the research on bifurcation problem is more and more abundant [30,31,32,33,34,35,36,37,38,39,40].
Although the continuous predator-prey model has been successfully applied in many ways, its disadvantages are also obvious. It requires that the species studied should have continuous and overlapping generations. In fact, we have noticed that many species do not have these characteristics, such as salmon, which have an annual spawning season and are born at the same time each year. For the population with non-overlapping generation characteristics, the discrete time model is more practical than the continuous model [38], and discrete models can generate richer and more complex dynamic properties than continuous time models [39]. In addition, since many continuous models cannot be solved by symbolic calculation, people usually use difference equations for approximation and then use numerical methods to solve the continuous model.
In view of the above discussion, the study of discrete system is paid more and more attention by mathematicians. Many latest research works have focused on flip bifurcation for different models, such as, discrete predator-prey model [41,42]; discrete reduced Lorenz system [43]; coupled thermoacoustic systems [44]; mathematical cardiac system [45]; chemostat model [46], etc.
For the above reasons, we will study from different perspectives in this paper, focusing on the discrete scheme of Eq (1).
In order to get a discrete form of Eq (1), we first let
$ u = \frac{b}{a_{1}}x, v = \frac{c_{1}}{a_{1}}y, \tau = a_{1}t, $ |
and rewrite $ u, v, \tau $ as $ x, y, t, $ then (1) changes into:
$ {˙x(t)=x(1−x−β1y2x2+h1),˙y(t)=αy(1−β2yx+h2), $
|
(2) |
where $ \beta_{1} = \frac{b^{2}}{c_{1}a_{1}}, h_{1} = \frac{b^{2}k_{1}}{a_{1}^{2}}, \alpha = \frac{a_{2}}{c_{1}}, \beta_{2} = \frac{c_{2}b}{c_{1}a_{2}}, h_{2} = \frac{bk_{2}}{a_{1}}. $
Next, we use Euler approximation method, i.e., let
$ \frac{dx}{dt}\approx \frac{x_{n+1}-x_{n}}{\bigtriangleup t}, \; \; \; \; \; \; \frac{dy}{dt}\approx \frac{y_{n+1}-y_{n}}{\bigtriangleup t}, $ |
where $ \bigtriangleup t $ denotes a time step, $ x_{n}, y_{n} $ and $ x_{n+1}, y_{n+1} $ represent consecutive points. Provided with Euler approximation method with the time step $ \bigtriangleup t = 1 $, (2) changes into a two-dimensional discrete dynamical system:
$ {xn+1=xn+xn(1−xn−β1y2nx2n+h1),yn+1=yn+αyn(1−β2ynxn+h2). $
|
(3) |
For the sake of analysis, we rewrite (3) in the following map form:
$ (xy)↦(x+x(1−x−β1y2x2+h1)y+αy(1−β2yx+h2)). $
|
(4) |
In this paper, we will consider the effect of the coefficients of map (4) on the dynamic behavior of the map (4). Our goal is to show how a flipped bifurcation of map (4) can appear under some certain conditions.
The remainder of the present paper is organized as follows. In section 2, we discuss the fixed points of map (4) including existence and stability. In section 3, we investigate the flip bifurcation at equilibria $ E_{2} $ and $ E^{\ast}. $ It has been proved that map (4) can undergo the flip bifurcation provided with that some values of parameters be given certain. In section 4, we give an example to support the theoretical results of the present paper. As the conclusion, we make a brief discussion in section 5.
Obviously, $ E_{1}(1, 0) $ and $ E_{2}(0, \frac{h_{2}}{\beta_{2}}) $ are fixed points of map (4). Given the biological significance of the system, we focus on the existence of an interior fixed point $ E^{\ast}(x^{\ast}, y^{\ast}), $ where $ x^{\ast} > 0, y^{\ast} > 0 $ and satisfy
$ 1-x^{\ast} = \frac{\beta_{1}(y^{\ast})^{2}}{(x^{\ast})^{2}+h_{1}}, x^{\ast}+h_{2} = \beta_{2}y^{\ast}, $ |
i.e., $ x^{\ast} $ is the positive root of the following cubic equation:
$ β22x3+(β1−β22)x2+(β22h1+2β1h2)x+β1h22−β22h1=0. $
|
(5) |
Based on the relationship between the roots and the coefficients of Eq (5), we have
Lemma 2.1 Assume that $ \beta_{1}h_{2}^{2}-\beta_{2}^{2}h_{1} < 0, $ then Eq (5) has least one positive root, and in particular
(ⅰ) a unique positive root, if $ \beta_{1}\geq \beta_{2}^{2}; $
(ⅱ) three positive roots, if $ \beta_{1} < \beta_{2}^{2}. $
The proof of Lemma 2.1 is easy, and so it is omitted.
In order to study the stability of equilibria, we first give the Jacobian matrix $ J(E) $ of map (4) at any a fixed point $ E(x, y), $ which can be written as
$ J(E)=(2−2x−β1y2(h1−x2)(x2+h1)2−2β1xyx2+h1αβ2y2(x+h2)21+α−2αβ2yx+h2). $
|
For equilibria $ E_{1}, $ we have
$ J(E1)=(0001+α). $
|
The eigenvalues of $ J(E_{1}) $ are $ \lambda_{1} = 0, \lambda_{2} = 1+\alpha $ with $ \lambda_{2} > 1 $ due to the constant $ \alpha > 0, $ so $ E_{1}(1, 0) $ is a saddle.
For equilibria $ E_{2}, $ note that
$ J(E2)=(2−β1h22β22h10αβ21−α), $
|
then the eigenvalues of $ J(E_{2}) $ are $ \lambda_{1} = 2-\frac{\beta_{1}h_{2}^{2}}{\beta_{2}^{2}h_{1}}, \lambda_{2} = 1-\alpha, $ and so we get
Lemma 2.2 The fixed point $ E_{2}(0, \frac{h_{2}}{\beta_{2}}) $ is
(ⅰ) a sink if $ 1 < \frac{\beta_{1}h_{2}^{2}}{\beta_{2}^{2}h_{1}} < 3 $ and $ 0 < \alpha < 2; $
(ⅱ) a source if $ \frac{\beta_{1}h_{2}^{2}}{\beta_{2}^{2}h_{1}} < 1 $ or $ \frac{\beta_{1}h_{2}^{2}}{\beta_{2}^{2}h_{1}} > 3 $ and $ \alpha > 2; $
(ⅲ) a a saddle if $ 1 < \frac{\beta_{1}h_{2}^{2}}{\beta_{2}^{2}h_{1}} < 3 $ and $ \alpha > 2, $ or, $ \frac{\beta_{1}h_{2}^{2}}{\beta_{2}^{2}h_{1}} < 1 $ or $ \frac{\beta_{1}h_{2}^{2}}{\beta_{2}^{2}h_{1}} > 3 $ and $ 0 < \alpha < 2; $
(ⅳ) non-hyperbolic if $ \frac{\beta_{1}h_{2}^{2}}{\beta_{2}^{2}h_{1}} = 1 $ or $ \frac{\beta_{1}h_{2}^{2}}{\beta_{2}^{2}h_{1}} = 3 $ or $ \alpha = 2. $
In this section, we will use the relevant results of literature [38,39,40] to study the flip bifurcation at equilibria $ E_{2} $ and $ E^{\ast}. $
Based on (ⅲ) in Lemma 2.2, it is known that if $ \alpha = 2 $, the eigenvalues of $ J(E_{2}) $ are: $ \lambda_{1} = 2-\frac{\beta_{1}h_{2}^{2}}{\beta_{2}^{2}h_{1}}, \lambda_{2} = -1. $ Define
$ Fl = \{(\beta_{1}, \beta_{2}, h_{1}, h_{2}, \alpha):\alpha = 2, \beta_{1}, \beta_{2}, h_{1}, h_{2} \gt 0 \}. $ |
We conclude that a flip bifurcation at $ E_{2}(0, \frac{h_{2}}{\beta_{2}}) $ of map (4) can appear if the parameters vary in a small neighborhood of the set $ Fl. $
To study the flip bifurcation, we take constant $ \alpha $ as the bifurcation parameter, and transform $ E_{2}(0, \frac{h_{2}}{\beta_{2}}) $ into the origin. Let $ e = 2-\frac{\beta_{1}h_{2}^{2}}{\beta_{2}^{2}h_{1}}, \alpha_{1} = \alpha-2, $ and
$ u(n) = x(n), v(n) = y(n)-\frac{h_{2}}{\beta_{2}}, $ |
then map (4) can be turned into
$ (uv)↦(eu−u2−2β1h2β2h1uv+O((|u|+|v|+|α1|)3)2β2u−v−2β2h2u2−2β2h2v2+4h2uv+α1β2u−α1v−α1β2h2u2−α1β2h2v2+2α1h2uv+O((|u|+|v|+|α1|)3)). $
|
(6) |
Let
$ T_{1} = \left( 1+e02β21 \right), $
|
then by the following invertible transformation:
$ \left( uv \right) = T_{1} \left( sw \right), $
|
map (6) turns into
$ (sw)↦(es−(1+e)s2−2β1h2β2h1s(2sβ2+w)+O(|s|+|w|+|α1|)3−w+F2(s,w,α1)), $
|
(7) |
where
$ F_{2} = \frac{2}{\beta_{2}}[(1+e)s^{2} + \frac{2\beta_{1}h_{2}}{\beta_{2}h_{1}}s(\frac{2s}{\beta_{2}}+w)]-\frac{2}{\beta_{2}h_{2}}(1+e)^{2}s^{2}-\frac{2\beta_{2}}{h_{2}}(\frac{2s}{\beta_{2}}+w)^{2}+\frac{4(1+e)}{h_{2}}s(\frac{2s}{\beta_{2}}+w) $ |
$ +\frac{(1+e)\alpha_{1}}{\beta_{2}}s-\alpha_{1}(\frac{2s}{\beta_{2}}+w)-\frac{(1+e)^{2}\alpha_{1}}{\beta_{2}h_{2}}s^{2}-\frac{\alpha_{1}\beta_{2}}{h_{2}}(\frac{2s}{\beta_{2}}+w)^{2} $ |
$ +\frac{2(1+e)\alpha_{1}}{h_{2}}s(\frac{2s}{\beta_{2}}+w)+O(|s|+|w|+|\alpha_{1}|)^{3}.\; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; $ |
Provided with the center manifold theorem (Theorem 7 in [40]), it can be obtained that there will exist a center manifold $ W^{c}(0, 0) $ for map (7), and the center manifold $ W^{c}(0, 0) $ can be approximated as:
$ W^{c}(0, 0) = \{(w, s, \alpha_{1})\in R^{3}:s = aw^{2}+bw\alpha_{1}+c(\alpha_{1})^{2}+O(|w|+|\alpha_{1}| )^{3} \}. $ |
As the center manifold satisfies:
$ s=a(−w+F2)2+b(−w+F2)α1+c(α1)2=e(aw2+bwα1+c(α1)2)−(1+e)(aw2+bwα1+c(α1)2)2−2β1h2β2h1(aw2+bwα1+c(α1)2)(2β2(aw2+bwα1+c(α1)2)+w)+O(|s|+|w|+|α1|)3, $
|
it can be obtained by comparing the coefficients of the above equality that $ a = 0, b = 0, c = 0, $ so the center manifold of map (7) at $ E_{2}(0, \frac{h_{2}}{\beta_{2}}) $ is $ s = 0. $ Then map (7) restricted to the center manifold turns into
$ w(n+1) = -w(n)-\alpha_{1}w(n)-\frac{2\beta_{2}}{h_{2}}w^{2}(n)-\frac{\alpha_{1}\beta_{2}}{h_{2}}w^{2}(n)+O(|w(n)|+|\alpha_{1}|)^{3} $ |
$ \triangleq f(w, \alpha_{1}).\; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; $ |
Obviously,
$ f_{w}(0, 0) = -1, \; \; \; \; \; f_{ww}(0, 0) = -\frac{4\beta_{2}}{h_{2}}, $ |
so
$ \frac{(f_{ww}(0, 0))^{2}}{2}+\frac{f_{www}(0, 0)}{3}\neq 0, \; \; \; \; \; f_{w\alpha_{1}}(0, 0) = -1\neq 0. $ |
Therefore, Theorem 4.3 in [38] guarantees that map (3) undergoes a flip bifurcation at $ E_{2}(0, \frac{h_{2}}{\beta_{2}})$.
Note that
$ J(E∗)=(2−2x∗−β1(y∗)2(h1−(x∗)2)((x∗)2+h1)2−2β1x∗y∗(x∗)2+h1αβ21−α), $
|
then the characteristic equation of Jacobian matrix $ J(E^{\ast}) $ of map (3) at $ E^{\ast}(x^{\ast}, y^{\ast}) $ is:
$ λ2−(1+α0−α)λ+(1−α)α0−ηα=0, $
|
(8) |
where
$ \alpha_{0} = 2-2x^{\ast}-\frac{\beta_{1}(y^{\ast})^{2}(h_{1}-(x^{\ast})^{2})}{((x^{\ast})^{2}+h_{1})^{2}} , \eta = - \frac{2\beta_{1}x^{\ast}y^{\ast}}{\beta_{2}((x^{\ast})^{2}+h_{1})}. $ |
Firstly, we discuss the stability of the fixed point $ E^{\ast}(x^{\ast}, y^{\ast}). $ The stability results can be described as the the following Lemma, which can be easily proved by the relations between roots and coefficients of the characteristic Eq (8), so the proof has been omitted.
Lemma 3.1 The fixed point $ E^{\ast}(x^{\ast}, y^{\ast}) $ is
(ⅰ) a sink if one of the following conditions holds.
(ⅰ.1) $ 0 < \alpha_{0}+\eta < 1, $ and $ \frac{\alpha_{0}-1}{\alpha_{0}+\eta} < \alpha < \frac{2(1+\alpha_{0})}{1+\alpha_{0}+\eta}; $
(ⅰ.2) $ -1 < \alpha_{0}+\eta < 0, $ and $ \alpha < \min \{\frac{\alpha_{0}-1}{\alpha_{0}+\eta}, \frac{2(1+\alpha_{0})}{1+\alpha_{0}+\eta} \}; $
(ⅰ.3) $ \alpha_{0}+\eta < -1, $ and $ \frac{\alpha_{0}-1}{\alpha_{0}+\eta} > \alpha > \frac{2(1+\alpha_{0})}{1+\alpha_{0}+\eta}; $
(ⅱ) a source if one of the following conditions holds.
(ⅱ.1) $ 0 < \alpha_{0}+\eta < 1, $ and $ \alpha < \min \{\frac{\alpha_{0}-1}{\alpha_{0}+\eta}, \frac{2(1+\alpha_{0})}{1+\alpha_{0}+\eta} \}; $
(ⅱ.2) $ -1 < \alpha_{0}+\eta < 0, $ and $ \frac{\alpha_{0}-1}{\alpha_{0}+\eta} < \alpha < \frac{2(1+\alpha_{0})}{1+\alpha_{0}+\eta}; $
(ⅱ.3) $ \alpha_{0}+\eta < -1, $ and $ \alpha > \max \{\frac{\alpha_{0}-1}{\alpha_{0}+\eta}, \frac{2(1+\alpha_{0})}{1+\alpha_{0}+\eta} \}; $
(ⅲ) a saddle if one of the following conditions holds.
(ⅲ.1) $ -1 < \alpha_{0}+\eta < 1, $ and $ \alpha > \frac{2(1+\alpha_{0})}{1+\alpha_{0}+\eta}; $
(ⅲ.2) $ \alpha_{0}+\eta < -1, $ and $ \alpha < \frac{2(1+\alpha_{0})}{1+\alpha_{0}+\eta}; $
(ⅳ) non-hyperbolic if one of the following conditions holds.
(ⅳ.1) $ \alpha_{0}+\eta = 1; $
(ⅳ.2) $ \alpha_{0}+\eta\neq -1; $ and $ \alpha = \frac{2(1+\alpha_{0})}{1+\alpha_{0}+\eta}; $
(ⅳ.3) $ \alpha_{0}+\eta\neq 0, \alpha = \frac{\alpha_{0}-1}{\alpha_{0}+\eta} $ and $ (1+\alpha_{0}-\alpha)^{2} < 4((1-\alpha)\alpha_{0}-\eta\alpha). $
Then based on (ⅳ.2) of Lemma 3.1 and $ \alpha\neq 1+\alpha_{0}, 3+\alpha_{0}, $ we get that one of the eigenvalues at $ E^{\ast}(x^{\ast}, y^{\ast}) $ is $ -1 $ and the other satisfies $ |\lambda|\neq 1. $ For $ \alpha, \beta_{1}, \beta_{2}, h_{1}, h_{2} > 0, $ let us define a set:
$ Fl = \{(\beta_{1}, \beta_{2}, h_{1}, h_{2}, \alpha):\alpha = \frac{2(1+\alpha_{0})}{1+\alpha_{0}+\eta}, \alpha_{0}+\eta\neq -1, \alpha\neq 1+\alpha_{0}, 3+\alpha_{0} \}. $ |
We assert that a flip bifurcation at $ E^{\ast}(x^{\ast}, y^{\ast}) $ of map (3) can appear if the parameters vary in a small neighborhood of the set $ Fl. $
To discuss flip bifurcation at $ E^{\ast}(x^{\ast}, y^{\ast}) $ of map (3), we choose constant $ \alpha $ as the bifurcation parameter and adopt the central manifold and bifurcation theory [38,39,40].
Let parameters $ (\alpha_{1}, \beta_{1}, \beta_{2}, h_{1}, h_{2})\in Fl, $ and consider map (3) with $ (\alpha_{1}, \beta_{1}, \beta_{2}, h_{1}, h_{2}), $ then map (3) can be described as
$ {xn+1=xn+xn(1−xn−β1y2nx2n+h1),yn+1=yn+α1yn(1−β2ynxn+h2). $
|
(9) |
Obviously, map (9) has only a unique positive fixed point $ E^{\ast}(x^{\ast}, y^{\ast}), $ and the eigenvalues are $ \lambda_{1} = \; -\; 1, \lambda_{2} = 2+\alpha_{0}-\alpha, $ where $ |\lambda_{2}|\neq1. $
Note that $ (\alpha_{1}, \beta_{1}, \beta_{2}, h_{1}, h_{2})\in Fl, $ then $ \alpha_{1} = \frac{2(1+\alpha_{0})}{1+\alpha_{0}+\eta}. $ Let $ |\alpha^{\ast}| $ small enough, and consider the following perturbation of map (9) described by
$ {xn+1=xn+xn(1−xn−β1y2nx2n+h1),yn+1=yn+(α1+α∗)yn(1−β2ynxn+h2), $
|
(10) |
with $ \alpha^{\ast} $ be a perturbation parameter.
To transform $ E^{\ast}(x^{\ast}, y^{\ast}) $ into the origin, we let $ u = x-x^{\ast}, v = y- y^{\ast}, $ then map (10) changes into
$ (uv)↦(a1u+a2v+a3u2+a4uv+a5v2+a6u3+a7u2v+a8uv2+a9v3+O((|u|+|v|)4)b1u+b2v+b3u2+b4uv+b5v2+c1uα∗+c2vα∗+c3u2α∗+c4uvα∗+c5v2α∗+b6u3+b7u2v+b8uv2+b9v3+O((|u|+|v|+|α∗|)4)), $
|
(11) |
where
$ a_{1} = 2-2x^{\ast}-\beta_{1}(y^{\ast})^{2}f(0)-\beta_{1}x^{\ast}(y^{\ast})^{2}f'(0); $ $ a_{2} = -2\beta_{1}x^{\ast}y^{\ast}f(0); $
$ a_{3} = -1-\beta_{1}(y^{\ast})^{2}f'(0)-\frac{1}{2}\beta_{1}x^{\ast}(y^{\ast})^{2}f''(0); $ $ a_{4} = -2\beta_{1}y^{\ast}f(0)-2\beta_{1}x^{\ast}y^{\ast}f'(0); $
$ a_{5} = -\beta_{1}x^{\ast}f(0); $ $ a_{6} = -\frac{1}{2}\beta_{1}(y^{\ast})^{2}f''(0)-\frac{1}{6}\beta_{1}x^{\ast}(y^{\ast})^{2}f'''(0); $
$ a_{7} = -\beta_{1}x^{\ast}y^{\ast}f''(0)-2\beta_{1}y^{\ast}f'(0); $ $ a_{8} = -\beta_{1}f(0)-\beta_{1}x^{\ast}f'(0), \; \; \; a_{9} = 0; $
$ f(0) = \frac{1}{(x^{\ast})^{2}+h_{1}}, f'(0) = \frac{-2x^{\ast}}{[(x^{\ast})^{2}+h_{1}]^{2}}, f''(0) = \frac{6(x^{\ast})^{2}-2h_{1}}{[(x^{\ast})^{2}+h_{1}]^{3}}, f'''(0) = \frac{ 24x^{\ast} (h_{1}-(x^{\ast})^{2})}{[(x^{\ast})^{2}+h_{1}]^{4}}. $
$ b_{1} = \frac{\alpha_{1}\beta_{2}(y^{\ast})^{2} }{(x^{\ast}+h_{2})^{2} }; $ $ b_{2} = 1+\alpha_{1}-\frac{\alpha_{1}\beta_{2}y^{\ast} }{x^{\ast}+h_{2}}; $ $ b_{3} = -\frac{\alpha_{1}\beta_{2}(y^{\ast})^{2} }{(x^{\ast}+h_{2})^{3} }; $ $ b_{4} = \frac{2\alpha_{1}\beta_{2}y^{\ast} }{ (x^{\ast}+h_{2})^{2} }; $
$ b_{5} = -\frac{\alpha_{1}\beta_{2} }{x^{\ast}+h_{2}}; $ $ c_{1} = \frac{\beta_{2}(y^{\ast})^{2} }{(x^{\ast}+h_{2})^{2} }; $ $ c_{2} = 1-\frac{\beta_{2}y^{\ast} }{x^{\ast}+h_{2}}; $ $ c_{3} = -\frac{\beta_{2}(y^{\ast})^{2} }{(x^{\ast}+h_{2})^{3} }; $
$ c_{4} = \frac{2\beta_{2}y^{\ast} }{(x^{\ast}+h_{2})^{2} }; $ $ c_{5} = -\frac{\beta_{2} }{x^{\ast}+h_{2} }; $ $ b_{6} = \frac{\alpha_{1}\beta_{2}(y^{\ast})^{2} }{(x^{\ast}+h_{2})^{4} }; $ $ b_{7} = -\frac{2\alpha_{1}\beta_{2}y^{\ast} }{ (x^{\ast}+h_{2})^{3} }; $
$ b_{8} = \frac{\alpha_{1}\beta_{2} }{(x^{\ast}+h_{2})^{2} }; \; \; \; \; b_{9} = 0.\; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; $ |
Now let's construct an matrix
$ T2=(a2a2−1−a1λ2−a1). $
|
It's obvious that the matrix $ T_{2} $ is invertible due to $ \lambda_{2}\neq -1, $ and then we use the following invertible translation
$ \left( uv \right) = T_{2} \left( sw \right), $
|
map (11) can be described by
$ (sw)↦(−s+f1(s,w,α∗)λ2w+f2(s,w,α∗)), $
|
(12) |
where
$ f_{1}(s, w, \alpha^{\ast}) = \frac{(\lambda_{2}-a_{1})a_{3}-a_{2} b_{3}}{ a_{2}(\lambda_{2}+1) }u^{2} + \frac{(\lambda_{2}-a_{1})a_{4}-a_{2} b_{4}}{ a_{2}(\lambda_{2}+1) }uv +\frac{(\lambda_{2}-a_{1})a_{5}-a_{2} b_{5}}{ a_{2}(\lambda_{2}+1) }v^{2} +\frac{(\lambda_{2}-a_{1})a_{6}-a_{2} b_{6}}{ a_{2}(\lambda_{2}+1) }u^{3} \\ \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; +\frac{(\lambda_{2}-a_{1})a_{7}-a_{2} b_{7}}{ a_{2}(\lambda_{2}+1) }u^{2}v +\frac{(\lambda_{2}-1)a_{8}-a_{2} b_{8}}{ a_{2}(\lambda_{2}+1) }uv^{2} +\frac{(\lambda_{2}-a_{1})a_{9}-a_{2} b_{9}}{ a_{2}(\lambda_{2}+1) }v^{3}- \frac{a_{2}c_{1}}{a_{2}(\lambda_{2}+1)}u\alpha^{\ast} \\ \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; - \frac{a_{2}c_{2}}{a_{2}(\lambda_{2}+1)}v\alpha^{\ast}- \frac{a_{2}c_{3}}{a_{2}(\lambda_{2}+1)}u^{2}\alpha^{\ast} - \frac{a_{2}c_{4}}{a_{2}(\lambda_{2}+1)}uv\alpha^{\ast} - \frac{a_{2}c_{5}}{a_{2}(\lambda_{2}+1)}v^{2}\alpha^{\ast} \\ \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; +O((|s|+ |w|+|\alpha^{\ast}| )^{4}), \\ f_{2}(s, w, \alpha^{\ast}) = \frac{(a_{1}+1)a_{3}+a_{2} b_{3}}{ a_{2}(\lambda_{2}+1) }u^{2} + \frac{(a_{1}+1)a_{4}+a_{2} b_{4}}{ a_{2}(\lambda_{2}+1) }uv +\frac{(a_{1}+1)a_{5}+a_{2} b_{5}}{ a_{2}(\lambda_{2}+1) }v^{2} +\frac{(a_{1}+1)a_{6}+a_{2} b_{6}}{ a_{2}(\lambda_{2}+1) }u^{3} \\ \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; +\frac{(a_{1}+1)a_{7}+a_{2} b_{7}}{ a_{2}(\lambda_{2}+1) }u^{2}v +\frac{(a_{1}+1)a_{8}+a_{2} b_{8}}{ a_{2}(\lambda_{2}+1) }uv^{2}+\frac{(a_{1}+1)a_{9}+a_{2} b_{9}}{ a_{2}(\lambda_{2}+1) }v^{3}+ \frac{a_{2}c_{1}}{a_{2}(\lambda_{2}+1)}u\alpha^{\ast}\\ \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; + \frac{a_{2}c_{2}}{a_{2}(\lambda_{2}+1)}v\alpha^{\ast}+ \frac{a_{2}c_{3}}{a_{2}(\lambda_{2}+1)}u^{2}\alpha^{\ast}+ \frac{a_{2}c_{4}}{a_{2}(\lambda_{2}+1)}uv\alpha^{\ast} + \frac{a_{2}c_{5}}{a_{2}(\lambda_{2}+1)}v^{2}\alpha^{\ast}\\ \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; +O((|s|+ |w|+|\alpha^{\ast}| )^{4}), $ |
with
$ u = a_{2}(s+w), v = (\lambda_{2}-a_{1})w-(a_{1}+1)s; $
$ u^{2} = (a_{2}(s+w))^{2}; $
$ uv = (a_{2}(s+w))((\lambda_{2}-a_{1})w-(a_{1}+1)s); $
$ v^{2} = ((\lambda_{2}-a_{1})w-(a_{1}+1)s)^{2}; $
$ u^{3} = (a_{2}(s+w))^{3}; $
$ u^{2}v = (a_{2}(s+w))^{2}((\lambda_{2}-a_{1})w-(a_{1}+1)s); $
$ uv^{2} = (a_{2}(s+w))((\lambda_{2}-a_{1})w-(a_{1}+1)s)^{2}; $
$ v^{3} = ((\lambda_{2}-a_{1})w-(a_{1}+1)s)^{3}. $
In the following, we will study the center manifold of map (12) at fixed point (0, 0) in a small neighborhood of $ \alpha^{\ast} = 0. $ The well-known center manifold theorem guarantee that a center manifold $ W^{c}(0, 0) $ can exist, and it can be approximated as follows
$ W^{c}(0, 0) = \{(s, w, \alpha^{\ast})\in R^{3}:w = d_{1}s^{2}+d_{2}s\alpha^{\ast}+d_{3}(\alpha^{\ast})^{2}+ O(( |s|+ |\alpha^{\ast}|)^{3}) \}, $ |
which satisfies
$ w = d_{1}(-s+f_{1}(s, w, \alpha^{\ast}))^{2}+d_{2}(-s+f_{1}(s, w, \alpha^{\ast}))\alpha^{\ast}+d_{3}(\alpha^{\ast})^{2} $ |
$ = \lambda_{2}( d_{1}s^{2}+d_{2}s\alpha^{\ast}+d_{3}(\alpha^{\ast})^{2} )+f_{2}(s, w, \alpha^{\ast}).\; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; $ |
By comparing the coefficients of the above equation, we have
$ d_{1} = \frac{a_{2}((a_{1}+1)a_{3}+a_{2}b_{3})}{1-\lambda_{2}^{2}}-\frac{(a_{1}+1)((a_{1}+1)a_{4}+a_{2}b_{4})}{1-\lambda_{2}^{2}}+ \frac{(a_{1}+1)^{2}((a_{1}+1)a_{5}+a_{2}b_{5})}{1-\lambda_{2}^{2}}, \\ d_{2} = \frac{c_{2}(a_{1}+1) -a_{2}c_{1} }{(1+\lambda_{2})^{2}}, \; \; \; \; \; \; d_{3} = 0.\; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; $ |
So, restricted to the center manifold $ W^{c}(0, 0), $ map (12) turns into
$ s↦−s+e1s2+e2sα∗+e3s2α∗+e4s(α∗)2+e5s3+O((|s|+|α∗|)4)≜F2(s,α∗), $
|
(13) |
where
$ e_{1} = A_{1}a_{2}^{2}-A_{2}a_{2}(a_{1}+1)+ A_{3}(a_{1}+1)^{2}; $
$ e_{2} = -A_{8}a_{2}+ A_{9}(a_{1}+1); $
$ e_{3} = 2A_{1}d_{2}a_{2}^{2}+ A_{2}a_{2}d_{2}(\lambda_{2}-2a_{1}-1)-2A_{3}d_{2}(\lambda_{2}-a_{1})(a_{1}+1)-A_{8}a_{2}d_{1} $
$ -A_{9}(\lambda_{2}-a_{1})d_{1}-A_{10}a_{2}^{2}+A_{11}a_{2}(a_{1}+1)-A_{12}(a_{1}+1)^{2}; $
$ e_{4} = -A_{8}a_{2}d_{2}-A_{9}(\lambda_{2}-a_{1})d_{2}; $
$ e_{5} = 2A_{1}a_{2}^{2}d_{1}+A_{2}a_{2}d_{1}(\lambda_{2}-2a_{1}-1)-2A_{3}d_{1}(\lambda_{2}-a_{1})(a_{1}+1)+A_{4}a_{2}^{3} $
$ -A_{5}a_{2}^{2}(a_{1}+1)+A_{6}a_{2}(a_{1}+1)^{2}-A_{7}(a_{1}+1)^{3}; $
with
$ A_{1} = \frac{(\lambda_{2}-a_{1})a_{3}-a_{2} b_{3}}{ a_{2}(\lambda_{2}+1) }; \; \; A_{2} = \frac{(\lambda_{2}-a_{1})a_{4}-a_{2} b_{4}}{ a_{2}(\lambda_{2}+1) }; \; \; A_{3} = \frac{(\lambda_{2}-a_{1})a_{5}-a_{2} b_{5}}{ a_{2}(\lambda_{2}+1) }; \; \; A_{4} = \frac{(\lambda_{2}-a_{1})a_{6}-a_{2} b_{6}}{ a_{2}(\lambda_{2}+1) }; $
$ A_{5} = \frac{(\lambda_{2}-a_{1})a_{7}-a_{2} b_{7}}{ a_{2}(\lambda_{2}+1) }; \; \; A_{6} = \frac{(\lambda_{2}-1)a_{8}-a_{2} b_{8}}{ a_{2}(\lambda_{2}+1) }; \; \; A_{7} = \frac{(\lambda_{2}-a_{1})a_{9}-a_{2} b_{9}}{ a_{2}(\lambda_{2}+1) }; \; \; A_{8} = \frac{a_{2}c_{1}}{a_{2}(\lambda_{2}+1)}; $
$ A_{9} = \frac{a_{2}c_{2}}{a_{2}(\lambda_{2}+1)}; \; \; \; \; \; \; \; \; A_{10} = \frac{a_{2}c_{3}}{a_{2}(\lambda_{2}+1)}; \; \; \; \; \; \; \; \; A_{11} = \frac{a_{2}c_{4}}{a_{2}(\lambda_{2}+1)}; \; \; \; \; \; \; \; \; A_{12} = \frac{a_{2}c_{5}}{a_{2}(\lambda_{2}+1)}. $
To study the flip bifurcation of map (13), we define the following two discriminatory quantities
$ \mu_{1} = \left( \frac{\partial^{2}F_{2}}{\partial s\partial\alpha^{\ast}}+\frac{1}{2}\frac{\partial F_{2}}{\partial\alpha^{\ast}} \frac{\partial^{2}F_{2}}{\partial s^{2}} \right )|_{(0, 0)}, $ |
and
$ \mu_{2} = \left(\frac{1}{6} \frac{\partial^{3}F_{2}}{\partial s^{3}}+\left(\frac{1}{2} \frac{\partial^{2}F_{2}}{\partial s^{2}}\right)^{2} \right )|_{(0, 0)} $ |
which can be showed in [38]. Then provided with Theorem 3.1 in [38], the following result can be given as
Theorem 3.1. Assume that $ \mu_{1} $ and $ \mu_{2} $ are not zero, then a flip bifurcation can occur at $ E^{\ast}(x^{\ast}, y^{\ast}) $ of map (3) if the parameter $ \alpha^{\ast} $ varies in a small neighborhood of origin. And that when $ \mu_{2} > 0 (<0), $ the period-2 orbit bifurcated from $ E^{\ast}(x^{\ast}, y^{\ast}) $ of map (3) is stable (unstable).
As application, we now give an example to support the theoretical results of this paper by using MATLAB. Let $ \beta_{1} = 1, \beta_{2} = 0.5, h_{1} = 0.05, h_{2} = 0.1, $ then we get from (5) that map (3) has only one positive point $ E^{\ast}(0.0113, 0.2226). $ And we further have $ \mu_{1} = e_{2} = 0.1134 \neq 0, \mu_{2} = e_{5}+e_{1}^{2} = -4.4869 \neq 0, $ which implies that all conditions of Theorem 3.1 hold, a flip bifurcation comes from $ E^{\ast} $ at the bifurcation parameter $ \alpha = 2.2238 $, so the flip bifurcation is supercritical, i.e., the period-2 orbit is unstable.
According to Figures 1 and 2, the positive point $ E^{\ast}(0.0113, 0.2226) $ is stable for $ 2\leq \alpha \leq 2.4 $ and loses its stability at the bifurcation parameter value $ \alpha = 2.2238. $ Which implies that map (3) has complex dynamical properties.
In this paper, a predator-prey model with modified Leslie-Gower and Holling-type Ⅲ schemes is considered from another aspect. The complex behavior of the corresponding discrete time dynamic system is investigated. we have obtained that the fixed point $ E_{1} $ of map (4) is a saddle, and the fixed points $ E_{2} $ and $ E^{\ast} $ of map (4) can undergo flip bifurcation. Moreover, Theorem 3.1 tell us that the period-2 orbit bifurcated from $ E^{\ast}(x^{\ast}, y^{\ast}) $ of map (3) is stable under some sufficient conditions, which means that the predator and prey can coexist on the stable period-2 orbit. So, compared with previous studies [28] on the continuous predator-prey model, our discrete model shows more irregular and complex dynamic characteristics. The present research can be regarded as the continuation and development of the former studies in [28].
This work is supported by the National Natural Science Foundation of China (60672085), Natural Foundation of Shandong Province (ZR2016EEB07) and the Reform of Undergraduate Education in Shandong Province Research Projects (2015M139).
The authors would like to thank the referee for his/her valuable suggestions and comments which led to improvement of the manuscript.
The authors declare that they have no competing interests.
YYL carried out the proofs of main results in the manuscript. FXZ and XLZ participated in the design of the study and drafted the manuscripts. All the authors read and approved the final manuscripts.
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