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Global behavior and the periodic character of some biological models
Advances in Difference Equations volume 2020, Article number: 410 (2020)
Abstract
Biological models are usually described using difference equations. As a result, we are  in this work  interested in studying a general difference model which includes two biological models as special cases. In detail, we study the qualitative behaviors (local and global stability, boundedness and periodicity character) of a general difference model. Furthermore, we apply our general results to the population model with two age classes and the flour beetle model.
Introduction
It should be emphasized that the majority of the mathematical models of realworld processes refer to evolutionary differential equations such as linear/nonlinear ODEs (ordinary differential equations) and PDEs (partial differential equations). On the other hand, owing to the difficulties the occurred while analyzing nonlinear PDEs and finding their solutions, various reduction procedures are employed to reduce problems of infinite dimensions (PDEs) to that of finite dimensions (ODEs). In particular, in mechanical engineering, the problems of reduction procedures are based on FEM (finite element method), FDM (finite difference method), the Bubnov–Galerkin methods of higherorder approximation, etc. (see, for example, [4, 5]).
The so far mentioned approaches allow one to reduce nonlinear PDEs to a finite set of nonlinear ODEs or sometimes to ODEs and AEs (algebraic equations). Thus, the problem is finally reduced to study nonlinear ODEs or ODEs/AEs which cannot be solved, in general, analytically. Therefore, a wide palette of numerical algorithms have been developed including implicit and explicit iterative methods that are based on the temporal discretization. They include, for instance, the classic Runge–Kutta method (RKM), secondorder Runge–Kutta methods with two stages, adaptive Runge–Kutta methods with estimations of the local truncation error, implicit Runge–Kutta methods, Euler methods, Dormand–Prince methods, seventh, sixth and fifthorder Runge–Kutta–Nyström algorithms modified by Fehlberg, and many other [8]. However, all of them are based on the introduced stepsize and hence in fact the problem is discretely governed by difference equations.
Difference equations are known as a description of the observed evolution of a phenomenon, where the majority of measurements of a timeevolving variable are discrete. Thus, these equations gain their importance in arithmetical models. Nonlinear difference equations of order greater than one are of paramount importance in applications. Such equations also appear naturally as discrete analogs and as numerical solutions of differential and delay differential equations which model various diverse phenomena in biology, ecology, physiology, physics, engineering and economics.
For varied reasons, rational difference equations have interest in the debate of many researchers. First, they afford many examples of nonlinear equations which are treatable, in many cases. But whose dynamics offer some strong features with regard to the linear case. In fact, the importance of studying difference equations comes from their appearance in many biological models which have many applications. One of the interesting models is describe by the Riccati difference equation
where a, b, c, d and \(\omega _{0}\) are real numbers. The richness of the dynamics of Riccati equations is very well known [11], and a specific case of these equations provides the classical Beverton–Holt model on the dynamics of exploited fish populations [6]. Another example refers to Kuruklis et al. [23] who investigated the behavior of the Pielou’s discrete logistic model
where \(\alpha \leq 1\). This equation was proposed by Pielou in [31] as a discrete analog of the delay logistic differential equation. The case \(\alpha >1\) in Pielou’s equation was considered in [19]. As an example of a map generated by a simple model for frequencydependent natural selection, May [25] introduced the difference equation
where \(\mu \in ( 0,\infty ) \). May studied the local stability of the positive equilibrium point \(\omega ^{\ast }=1/2\). Moreover, Kocic et al. [19] investigated the oscillation and the global asymptotic stability of Eq. (1.2). Cooke et al. [10] studied the stability of the discrete epidemic models
where \(A\in ( 0,\infty ) \). Also, Kuang et al. [20] established the global stability of a model of flour beetle population growth
where \(a\in ( 0,1 ) \), \(b,c,d\in [ 0,\infty ) \), \(b \neq 0\) and \(c+d>0\). As a model that describes the dynamics of baleen whales, the equation
where \(\delta \in ( 0,1 ) \) and \(M, \eta , \gamma \in ( 0,\infty ) \), has been proposed. For the global stability of Eq. (1.4), see [19].
For, general equations, Stevo [32] investigated the periodic character of solutions of the equation
where A, \(\omega _{1}\) and \(\omega _{0}\) are positive real numbers and \(g: ( 0,\infty ) ^{2}\rightarrow ( 0,\infty ) \) is continuous and satisfies
for some continuous function \(h: ( 0,\infty ) ^{3}\rightarrow ( 0,\infty ) \) such that
The boundedness, global attractivity, oscillatory and asymptotic periodicity of the nonnegative solutions of the equation
is investigated in [17], where α is a nonnegative real number and f is a continuous function, nondecreasing in each variable and increasing in at least one. In [38], Sun and Xi studied the global behavior of the nonlinear equation
where s and t nonnegative integers, \(s< t \) and f is decreasing in u and increasing in v.
Abdelrahman et al. [2] studied the asymptotic behavior of the solutions of a general class of difference equations,
where a and b are nonnegative real numbers and \(f: ( 0,\infty ) ^{2}\rightarrow ( 0,\infty ) \) is continuous real function and homogeneous with degree zero.
Moaaz et al. [27–29] investigated the qualitative behavior of solutions of the equations
and
where l and k are positive integers, a is a positive real number, f is a continuous real function and homogeneous with degree zero.
For many results, applications and open problems on higherorder equations and difference systems, see [1–38].
This paper is concerned with the investigation of the asymptotic behavior of the solutions of the general difference model
where k is a nonnegative integer, a and b are nonnegative real numbers, the function \(f ( u,v ) : [ 0,\infty ) ^{2}\rightarrow [ 0,\infty ) \) is a continuous real function and homogeneous with degree κ and the initial conditions \(\omega _{k},\omega _{k+1},\ldots,\omega _{0}\) are positive real numbers.
Our aim in this paper is to give a complete picture regarding the stability of the equilibrium point of Eq. (E). Furthermore, we get sufficient conditions which ensure that the solutions of the studied equation are bounded, also sufficient conditions for global stability of equilibrium point. Moreover, we study the existence of periodic solutions of a prime period two. Finally, we apply our general results to the population model with two age classes and the flour beetle model.
In addition to the theoretical importance of studying the qualitative behavior of solutions to a general model of difference equations, this work is characterized by:

1.
Study of some qualitative properties of biological models which have been previously partially verified or not verified.

2.
The studied equation includes many special cases that were studied previously. It’s easy to note that Eqs. (1.3), (1.5) and (1.6) are special cases of Eq. (E). So, our results extend and complement the results in [20, 27–29].

3.
This work can be extended. Some other properties of the general model, such as bifurcations, can also be studied.
Dynamics of Eq. (E)
Stability of Eq. (E)
In the following, we state a necessary and sufficient condition for locally asymptotically stable of the equilibrium point of Eq. (E). For our next considerations, we define the function \(\varPhi : [ 0,\infty ) ^{2}\rightarrow [ 0,\infty ) \) by
An equilibrium point of Eq. (2.1) is a point \(\omega ^{\ast }\) such that \(\omega ^{\ast }=\varPhi ( \omega ^{\ast },\omega ^{\ast } ) \) (that is, \(\omega ^{\ast }\) is a fixed point of the function \(\varPhi ( u,v ) \)). Then, equilibrium point of Eq. (E) is given by \(\omega ^{\ast }=a\omega ^{\ast }+b\omega ^{\ast }\mathbf{e}^{f ( \omega ^{\ast },\omega ^{\ast } ) }\), and hence
Thus, we have
and the positive equilibrium point
The linearized equation of (E) of \(\omega ^{\ast }\) is
where \(\mu _{s}=\varPhi _{s} ( \omega ^{\ast },\omega ^{\ast } ) \), \(s=u,v\). A linear equation will be called stable, asymptotically stable, or unstable provided that the zero equilibrium has that property. From (2.1), we get
and
In the next theorems, we study the asymptotic stability for (E).
Theorem 2.1
For local stability of the equilibrium point\(\omega ^{\ast }=0\)of Eq. (E), we have the following cases:

(1)
If\(a+b<1\), then\(\omega ^{\ast }\)is locally asymptotically stable and sink.

(2)
If\(b1>a\), then\(\omega ^{\ast }\)is unstable and repeller.

(3)
If\(\vert b1 \vert < a\), then\(\omega ^{\ast }\)is an unstable saddle point.

(4)
If\(\vert b1 \vert =a\), then\(\omega ^{\ast }\)is a nonhyperbolic point.
Proof
If we put \(\omega ^{\ast }=0\) in (2.4) and (2.5), then we have \(\mu _{u}=a\) and \(\mu _{v}=b\). The rest of the ς is immediate (from [21, Theorem 1.1.1]) and hence is omitted. □
Theorem 2.2
Assume that\(a\neq 0\), \(\kappa \neq 0\), and\(b>1a>0\). For local stability of the equilibrium point (2.2) of Eq. (E), we have the following cases:

(1)
Equilibrium point\(\omega ^{\ast }\)is locally asymptotically stable and sink if and only if\(\kappa >0\)and
$$ \alpha 2\sigma \gamma < \beta < ( 2/a1 ) \sigma \gamma . $$(2.6) 
(2)
Equilibrium point\(\omega ^{\ast }\)is unstable and repeller if and only if
$$\begin{aligned}& \beta < \min \{ \sigma \gamma , \alpha 2\sigma \gamma \} \quad \textit{for }\kappa < 0, \end{aligned}$$(2.7)$$\begin{aligned}& \beta >\max \bigl\{ \alpha 2\sigma \gamma , ( 2/a1 ) \sigma \gamma \bigr\} \quad \textit{for }\kappa >0. \end{aligned}$$(2.8) 
(3)
Equilibrium point\(\omega ^{\ast }\)is an unstable saddle point if and only if
$$ \bigl( ( 2/a1 ) \sigma \gamma +\alpha \bigr) ^{2}> \frac{4}{a}\sigma \kappa \gamma ^{2}, $$(2.9)and
$$ \begin{gathered} \sigma \gamma < \beta < ( \alpha 2\sigma \gamma ) \quad \textbf{or}\quad \beta < \sigma \gamma \quad \textit{for }\kappa >0, \\ \sigma \gamma >\beta > ( \alpha 2\sigma \gamma ) \quad \textbf{or}\quad \beta >\sigma \gamma \quad \textit{for }\kappa < 0.\end{gathered} $$(2.10) 
(4)
Equilibrium point\(\omega ^{\ast }\)is a nonhyperbolic point if and only if one of the following condition hold:
$$\begin{aligned}& \beta =\alpha 2\sigma \gamma ,\quad \textbf{or} \end{aligned}$$(2.11)$$\begin{aligned}& \beta = ( 2/a1 ) \sigma \gamma \quad \textit{and}\quad  ( 2/a1 ) \sigma \gamma \leq \alpha \leq ( 2/a+1 ) \sigma \gamma , \end{aligned}$$(2.12)where\(\alpha =f_{u} ( 1,1 ) \), \(\beta =f_{v} ( 1,1 ) \), \(\gamma =f ( 1,1 ) \)and\(\sigma = \frac{a}{ ( 1a ) \ln ( b/ ( 1a ) ) }\).
Proof
First, since f homogeneous with degree κ, we have from [7] that \(f_{u}\) and \(f_{v}\) homogeneous with degree \(\kappa 1\) and hence
where \(A=\ln ( \frac{b}{1a} ) \), and
Thus, the characteristic equation of (2.3) is
For Case (1). From Euler’s homogeneous function theorem, we have \(uf_{u}+vf_{v}=\kappa f\), and hence \(\alpha +\beta =\kappa \gamma \) (at \(( u,v ) = ( 1,1 ) \)). Thus and from (2.6), we get
where \(\kappa \gamma >0\). Then, we obtain (by adding \(( \alpha \beta ) \))
Next, we get (by multiplying \(\times ( \frac{1a}{\gamma }A ) \))
By adding a to the last inequality, we find
and hence
Also, from (2.6), we have
and hence
so
From (2.16) and (2.17), we obtain
Hence, and from [21, Theorem 1.1.1(c)], we see that \(\omega ^{\ast }\) is a locally asymptotically stable and sink.
For Case (2). First, we let (2.7) hold. Thus,
and so
Then we find
Also, from (2.7), we have
where \(\kappa <0\). As in Case (1), we can prove that
Similarly, if we consider the condition (2.8), we can prove that
Therefore, and from [21, Theorem 1.1.1(d)], we see that \(\omega ^{\ast }\) is an unstable and repeller.
For Case (3). If we have (2.9) hold, then we get
and so,
Since \(\sigma =a/ ( 1a ) A\), we have
so
This is equivalent (after performing some simple algebraic operations) to
This implies
Next, let (2.10) hold. Proceeding as in the proof of Case (1), we can prove that
Therefore, and from [21, Theorem 1.1.1(e)], we see that \(\omega ^{\ast }\) is an unstable saddle point.
For Case (4), if \(\beta =\alpha 2\sigma \gamma \), then we find \(\mu _{u}=\mu _{v}1\). Finally, let (2.12) hold. Then, we have \(\beta = ( 2/a1 ) \sigma \gamma \), and hence \(\mu _{v}=1\). Also, from (2.12), we have
which is equivalent to
so,
Then, from [21, Theorem 1.1.1(f)], we see that \(\omega ^{\ast }\) is a nonhyperbolic point. The proof is complete. □
Theorem 2.3
Assume that\(a=0\), \(\kappa \neq 0\)and\(b>1\). For local stability of the equilibrium point (2.2) of Eq. (E), we have the following cases:

(1)
Equilibrium point\(\omega ^{\ast }\)is locally asymptotically stable and sink if and only if
$$ \vert \alpha \vert < \beta < \frac{2}{\ln b}\gamma . $$(2.22) 
(2)
Equilibrium point\(\omega ^{\ast }\)is unstable and repeller if and only if
$$ \beta <  \vert \alpha \vert ,\quad \textbf{or}\quad \beta >\max \bigl\{ \vert \alpha \vert , 2\gamma /\ln b \bigr\} . $$(2.23) 
(3)
Equilibrium point\(\omega ^{\ast }\)is an unstable saddle point if and only if
$$ \biggl( \frac{\alpha }{\gamma }\ln b+2 \biggr) ^{2}>4\kappa \ln b, $$(2.24)and
$$ \vert \alpha \vert >\beta >0,\quad \textbf{or} \quad 2\gamma /\ln b< \beta < \vert \alpha \vert . $$(2.25) 
(4)
Equilibrium point\(\omega ^{\ast }\)is a nonhyperbolic point if and only if
$$ \vert \alpha \vert = \vert \beta \vert \quad \textbf{or}\quad \vert \alpha \vert \leq \beta =2 \gamma /\ln b, $$(2.26)whereα, βandγare defined as in Theorem 2.2.
Proof
The proof is similar to the proof of Theorem 2.2 and hence is omitted. □
Boundedness of Eq. (E)
In the following theorems, we study the boundedness of the solutions of Eq. (E).
Theorem 2.4
Assume that\(a=0\)and\(b\in ( 0,1 ] \). Then every solution of Eq. (E) is bounded and
for all\(n>0\).
Proof
Assume that \(\{ \omega _{n} \} _{n=k}^{\infty }\) is a solution of Eq. (E). From (E) and \(f ( u,v ) \geq 0\), we note that
Since \(b\leq 1\), we get \(\omega _{n+1}\leq \omega _{nk}\). Thus, we can divide the sequence \(\{ \omega _{n} \} _{n=k}^{\infty }\) into \(k+1\) subsequences bounded above by the initial conditions
Hence, we see that \(\omega _{n}\leq \max \{ \omega _{k},\omega _{k+1},\ldots, \omega _{0} \} \) for all \(n>0\). The proof is complete. □
Theorem 2.5
Assume that\(a\in [ 0,1 ) \)and there exists a constantλsuch that\(f ( u,v ) \geq \lambda v\). Then every solution of Eq. (E) is bounded and
Proof
Assume that \(\{ \omega _{n} \} _{n=k}^{\infty }\) is a solution of Eq. (E). Since \(f ( u,v ) \geq \lambda v\), we obtain
Now, we define the function \(Q ( u ) =\lambda u \mathbf{e}^{1\lambda u}\). Then, we have \(Q^{\prime } ( u ) =\lambda \mathbf{e}^{1\lambda u} ( 1\lambda u ) \). Hence, the critical point \(u^{\ast }\) of the function \(Q ( u ) \) is \(u^{\ast }=1/\lambda \), and \(Q ( 1/\lambda ) =1\) is the maximum value of \(Q ( u ) \). Thus, we obtain \(\lambda u \mathbf{e}^{1\lambda u}<1\) and so
Consequently, and from (2.29), we see that
Next, we let
Thus, the solution of (2.31) is
Since \(a\in ( 0,1 ) \), we get
Then every solution of Eq. (E) is bounded and the proof is complete. □
Global stability of equilibrium point
In the next theorem, we study the globally asymptotically stable of zero equilibrium point of Eq. (E) when \(k=1\).
Theorem 2.6
If\(a\in ( 0,1 ) \), \(b\in [ 0,1 ) \), \(a+b<1\)andfhas positive partial derivatives, then the zero equilibrium of (E) is globally asymptotically stable.
Proof
From Eq. (E), we have
Now, we let \(f_{0} ( u,v ) =a\) and \(f_{1} ( u,v ) =b \mathbf{e}^{f ( u,v ) }\). Firstly, we have
Then we have
Secondly, we note that
Finally, since \(f ( u,v ) \geq 0\), we obtain
for all \(u,v\in ( 0,\infty ) \). Therefore, from [21, Theorem 1.3.1] and (2.32)–(2.34), the zero equilibrium of (E) is globally asymptotically stable. □
Theorem 2.7
Assume that\(\kappa >0\), \(a\in ( 0,1 ) \), \(b/ ( 1a ) \in ( 1,\mathbf{e} ) \), there exists a constantλsuch that\(f ( u,v ) \geq \lambda v\), \(0< f_{u}\leq \lambda a \mathbf{e}/b\)and\(0< f_{v}\leq \lambda \). Then every positive solution of Eq. (E) converges to\(\omega ^{\ast }\).
Proof
Consider the function \(\varPhi : ( 0,\infty ) ^{2}\rightarrow ( 0,\infty ) \) defined as (2.1). Since \(f ( u,v ) \geq \lambda v\) and \(f_{u}\leq \lambda a \mathbf{e}/b\), we find
Next, since \(a\in ( 0,1 ) \) and \(f ( u,v ) \geq \lambda v\), we see that the equation \(\omega _{n+1}=\varPhi ( \omega _{n},\omega _{nk} ) \) is bounded [from Theorem 2.5] and
Thus, for some integer \(N>k\), we see that
where \(b ( 1a ) <\mathbf{e}\). Hence, we obtain
Now, we define the function
We note that \(\varPsi ( \omega ) =0\) if and only if \(\omega =\omega ^{\ast }\). Next, let \(\omega <\omega ^{\ast }\), then
and so
Thus, \(\varPsi ( \omega ) <0\). Similarly, if \(\omega >\omega ^{\ast } \), then we have \(\varPsi ( \omega ) >0\). Consequently, we see that the function Φ satisfies the negative feedback condition
Hence, from [21, Theorem 1.4.1] and (2.35)–(2.37), every positive solution of Eq. (E) converges to \(\omega ^{\ast }\). □
Theorem 2.8
Assume that\(\kappa >0\), \(a=0\), there exists a constantλsuch that\(f ( u,v ) \geq \lambda v\), \(f_{u}>0\), \(0< f_{v}\leq \lambda \mathbf{e}/b\)and
Then every positive solution of Eq. (E) converges to\(\omega ^{\ast }\).
Proof
Consider the function \(\varPhi : ( 0,\infty ) ^{2}\rightarrow ( 0,\infty ) \) defined as (2.1). Since \(f_{u}>0\), we find
From Theorem 2.5, we obtain, for some integer \(N>k\),
Hence, we see that
Since \(f_{v}\leq \lambda \mathbf{e}/b\), we have \(\varPhi _{v} ( u,v ) >0\). Now, we will prove that Eq. (E) has no solutions of prime period two. Suppose otherwise, we assume that Eq. (E) has prime period two \(\ldots,\rho ,\sigma ,\rho ,\sigma ,\ldots \) . Thus, we get
Thus, we have \(f ( \rho ,\sigma ) =f ( \sigma ,\rho ) =\ln b\) and hence \(\rho =\sigma \) [from (2.38)], and this is a contradiction. Therefore, from [21, Theorem 1.4.6], every positive solution of Eq. (E) converges to \(\omega ^{\ast }\). □
Theorem 2.9
Assume that\(k=1\), \(\kappa >0\), \(a\in ( 0,1 ) \), \(b\in [ 0,1 ) \), \(a+b<1\)andfhas positive partial derivatives. If the solution\(\{ \omega _{n} \} _{n=1}^{\infty }\)of (E) is a nonzero eventually, then
where
Proof
The linearized equation of (E) at \(\omega ^{\ast }=0\) is
The solutions of characteristic equation of (2.40) are \(\rho _{\pm }\). Next, we can formulate (E) as
where
From Theorem 2.6, we have \(\lim_{n\rightarrow \infty }\omega _{n}=0 \), and so \(\lim_{n\rightarrow \infty }f ( \omega _{n},\omega _{nk} ) =\lim_{n\rightarrow \infty }\omega _{n}^{\kappa } F ( \frac{\omega _{nk}}{\omega _{n}} ) =0\). Hence,
Therefore, the limiting equation of (2.41) is exactly (2.40). From Poincaré’s theorem, we see that (2.39) holds, and this completes the proof of the theorem. □
The existence of periodic solutions
Here, we give the periodicity character of the solution for Eq. (E).
Theorem 2.10
Suppose thatkis even and\(\kappa \neq 0\). Then Eq. (E) has a periodic solution of prime period two\(\{ \ldots,\tau \sigma ,\sigma ,\tau \sigma ,\sigma ,\ldots \} \), \(\tau \neq 1\), if and only if
Proof
Assume that Eq. (E) has a periodic solution of prime period two \(\ldots, \rho , \sigma , \rho , \sigma ,\ldots \) . Thus, and from (E), we get
this implies that
Let \(\tau =\rho /\sigma \) and \(\tau \neq 1\), we find
Also, from Eq. (E), we obtain
and hence
Since \(\rho ^{\kappa }=\tau ^{\kappa }\sigma ^{\kappa }\), we have
it follows that
On the other hand, if (2.42) holds, then we choose
and
for \(r=1,2,\ldots,k/2\), \(t\in ( 0,\infty ) \) and \(t\neq 1\). Thus, we see that
From (2.42), we see that (2.45) holds. By using (2.45), we obtain
Similarly, we can prove that \(\omega _{2}=\omega _{0}\). Therefore, it follows by induction that
Hence, Eq. (E) has a prime period two solution and the proof is complete. □
Theorem 2.11
Suppose thatkis odd\(a\neq 0\)and\(\kappa \neq 0\). Then, Eq. (E) has a periodic solution of prime period two\(\{ \ldots,\tau \sigma ,\sigma ,\tau \sigma ,\sigma ,\ldots \} \), \(\tau \neq 1\), if and only if
where\(\eta _{1}=f ( \tau ,1 ) \)and\(\eta _{2}=f ( 1,\tau ) \).
Proof
We proceed as in proof of Theorem 2.10. Thus, we get
and
Since \(\rho ^{\kappa }=\tau ^{\kappa }\sigma ^{\kappa }\) and \(\tau ^{\kappa }f ( 1,1/\tau ) =f ( \tau ,1 ) \), we have
Thus, we see that (2.47) holds. The rest of the proof proceeds as the proof of Theorem 2.10, and hence the proof is complete. □
Theorem 2.12
Suppose thatkis odd\(a=0\)and\(\kappa \neq 0\). Then, Eq. (E) has a periodic solution of prime period two\(\{ \ldots,\tau \sigma ,\sigma ,\tau \sigma ,\sigma ,\ldots \} \), \(\tau \neq 1\), if and only if
Proof
The proof is similar to the proof of Theorem 2.11, so it is omitted. □
Applications on biological models
The great importance of difference equations comes from their ability to describe natural phenomena, in particular its ability to describe and study biological models. In this section, by using our general results in the previous section, we study the qualitative behavior of two biological models, and we answer some of the problems that have been raised previously.
Population model with two age classes
The discrete model with two age classes, adults and juveniles
where \(r,\delta \in ( 0,\infty ) \). The term \(\exp ( r ( \delta \omega _{n}+y_{n} ) ) \) represents the reproduction rate and is a decreasing exponential which captures the over crowding phenomenon as the population grows. To apply our results, we set system (3.1) as follows:
Note that \(k=1\), \(a=0\), \(b=\mathbf{e}^{r}>1\) and \(f ( u,v ) =\delta u+v\). Equilibrium points of Eq. (3.2) are \(\omega ^{\ast }=0\) and positive equilibrium point \(r/ ( \delta +1 ) \) [for system (3.1) is \(( r/ ( \delta +1 ) ,r/ ( \delta +1 ) ) \)]. For stability of the equilibrium points, we introduce the following corollaries.
Corollary 3.1
Zero equilibrium point of (3.2) is unstable and repeller.
Corollary 3.2
The positive equilibrium point\(\omega ^{\ast }=r/ ( \delta +1 ) \)of (3.2) has one of the following cases; see Fig. 1:

(1)
\(\omega ^{\ast }\)is a locally asymptotically stable and sink if and only if\(\delta <1<\frac{2}{r} ( \delta +1 ) \);

(2)
\(\omega ^{\ast }\)is an unstable and repeller if and only if\(\max \{ \delta , \frac{2}{r} ( \delta +1 ) \} <1\);

(3)
\(\omega ^{\ast }\)is an unstable saddle point if and only if\(\delta >1\);

(4)
\(\omega ^{\ast }\)is a nonhyperbolic point if and only if\(\delta =1\)or\(\delta = ( \frac{1}{2}r1 ) \leq 1\).
Corollary 3.3
Every solution of (3.2) is bounded and\(\lim \sup_{n\rightarrow \infty }\omega _{n}\leq \mathbf{e}^{r1}\).
Corollary 3.4
Assume that\(0< r\leq 1\)and\(0<\delta <1\). Then every positive solution of (3.2) converges to\(\omega ^{\ast }\).
Corollary 3.5
Let\(\delta =1\). Then the model (3.2) has a periodic solution of prime period two\(\{ \ldots,r\sigma ,\sigma ,r\sigma ,\sigma ,\ldots \} \).
The flour beetle model
Flour beetles are members of the darkling beetle genera Tribolium or Tenebrio. They are pests of cereal silos and are widely used as laboratory animals, as they are easy to keep. The flour beetles consume wheat and other grains, are adapted to survive in very dry environments, and can withstand even higher amounts of radiation than cockroaches [39]. They are a major pest in the agricultural industry and are highly resistant to insecticides. The flour beetle model obeys
where \(a,b\in ( 0,\infty ) \), \(\eta _{1},\eta _{2}\in [ 0,\infty ) \) and \(\eta _{1}+\eta _{2}>0\). The equilibrium points of (3.3) are \(\omega ^{\ast }=0\) and the positive point
By Theorem 2.1, we see the local stability behavior of the zero equilibrium point of (3.3); see Fig. 2.
By Theorem 2.2, if we put \(\kappa =1\), \(\alpha =\eta _{1}\), \(\beta =\eta _{2}\) and \(\gamma =\eta _{1}+\eta _{2}\), then we see the local stability behavior of the positive equilibrium point of (3.3).
Corollary 3.6
Assume that\(a\in ( 0,1 ) \). Then every solution of Eq. (3.3) is bounded and
Corollary 3.7
Let\(a\in ( 0,1 ) \)and\(a+b<1\). Then the zero equilibrium of (3.3) is globally asymptotically stable.
Corollary 3.8
Assume that\(a\in ( 0,1 ) \), \(b/ ( 1a ) \in ( 1,\mathbf{e} ) \)and\(b\eta _{1}\leq \mathbf{e}a\eta _{2} \). Then every positive solution of (3.3) converges to\(\omega ^{\ast }\).
Remark 3.1
Let \(\eta _{1}=\eta _{2}=1\). Figure 3 shows the regions for which conditions of Corollary 3.8 are satisfied, that is, the regions for which the positive equilibrium point of the model (3.3) is globally asymptotically stable.
Corollary 3.9
The model (3.3) has a periodic solution of prime period two\(\{\ldots, \tau \sigma ,\sigma , \tau \sigma , \sigma ,\ldots\}\), if and only if
Example 3.1
Consider the model (3.3) with \(a=1/4\), \(b=49/4\), \(\omega _{2}=\omega _{1}=1\) and \(\omega _{0}=2\). By Corollary 3.9, we see that (3.3) has a periodic solution of prime period two \(\{ \ldots,\ln 7,\ln \sqrt{7},\ln 7,\ln \sqrt{7},\ldots \} \); see Fig. 4.
Conclusion
Difference equations are widely being used as mathematical models for describing real life situations in biology.
In this work, we studied the global behavior and the periodic character of the solution of a general class of the nonlinear difference equations. In detail, we established criteria for stability (local and global), boundedness and periodicity character of the solution of (E). Moreover, by applying our general results on biological models (as special cases), we examined several qualitative behaviors of the solutions of these models.
For the discrete model with two age classes, Corollaries 3.1–3.4 set the criteria for local and global stability, and Corollary 3.5 studied the existence of periodic solutions for this model. On the other hand, Corollaries 3.6–3.8 gave the global behavior of equilibrium points of the flour beetle model (3.3). Furthermore, Corollary 3.9 gave the necessary and sufficient condition for the existence of periodic solutions.
We can use our results to study many special cases of (E). For example, if \(f ( u,v ) =\ln ( 1/h ( u,v ) ) \) and h is homogeneous with degree zero, then Eq. (E) becomes
In particular, we can use our results to study the equation
Further, in future work, we can try to get some qualitative behavior of the more general equation
where \(\varPhi ( u,v ) \) is a homothetic function, that is, there exist a strictly increasing function \(G:\mathbb{R} \rightarrow \mathbb{R} \) and a homogeneous function \(H:\mathbb{R} ^{2}\rightarrow \mathbb{R} \) with degree β, such that \(\varPhi =G\circ H\).
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Moaaz, O., Awrejcewicz, J. & Mahjoub, H. Global behavior and the periodic character of some biological models. Adv Differ Equ 2020, 410 (2020). https://doi.org/10.1186/s13662020028687
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DOI: https://doi.org/10.1186/s13662020028687
MSC
 39A10
 39A23
 39A30
Keywords
 Population model
 Equilibrium points
 Local and global stability
 Periodic solution