As far as we know, rate-dependent predator-prey system models have become the focus of mathematical ecology and have been extensively studied in recent years (see e.g.,    ). The dynamic relationship between predator and prey is ubiquitous in ecology and mathematical ecology . The relationship between two species is usually thought of as competition, predation and cooperation. Here is the Lotka-Volterra model of a predator-predator with intra-species competition:
where and represent the population density of prey species and predators species at time t, parameters , , and are all positive constants describing the interaction of two species. The positive constants , represent the effect of one species on the other. It is well known that the solution of system (1.1) is asymptotically stable.
In the study of biological phenomena, there are many factors affecting the dynamic properties of biological and mathematical models, and functional reaction is one of the common nonlinear factors . System (1.1) assumes the prey biomass is enough and a individual predator consume the prey with functional response of type . When predators face an increase in the density of their local prey, they usually change their consumption rate. The concept of functional response was first proposed by Solomon and later discussed in detail by Holling. Holling  proposed three types of functional responses, i.e., Hollings type
I of , Hollings type II of and Hollings type III of . Proportional-dependent functional responses are a better description of how predators
must find food and therefore must share or compete for it. Based on Holling type II function, Arditi and Ginzburg  first proposed a rate-dependent functional response model:
where parameters are all positive constants, representing capturing rate, conversion rate and half capturing saturation constant, respectively.
These papers are all deterministic models, which do not consider the impact of environmental fluctuations, nor the impact of population randomness. Population dynamics in nature will inevitably be affected by environmental noise in the ecosystem. More recently, a number of authors have looked at stochastic predator-prey models with white noise and revealed how white noise affects population systems, such as    . Considering that the environmental fluctuation is mainly manifested as the fluctuation of the internal growth rate of the predator population and the mortality rate of the predator population , they supposed parameters and were perturbed with
where is a standard Brownian process defined on a complete probability space with a filtration satisfying the usual conditions, and represent the intensities of the white noise.
Nguyen and Ta  introduced intra-specific competition into the stochastic rate-dependent model to obtain the model (4), and considered the corresponding non-autonomous stochastic system, and estimated the high population growth rate and exponential mortality rate. The stochastic predator-prey system with rate-dependent functional response can be expressed as follows:
Furthermore, from a biological point of view, population dynamics may encounter sudden environmental disturbances that cannot be described by white noise, such as earthquakes, epidemics, floods and hurricanes. In this case, there are many references to stochastic differential equations with jumps (see e.g.,      ), and Lévy jumping into a potential population system may be a reasonable method to describe these phenomena. Therefore, this paper considers the random ratio-dependent model with jumps:
where and represent the left limit of and , respectively: the parameters , , , and are all positive constant, N is a poisson counting measure with compensator and characteristic measure on a measurable subset of with , and , the function is bounded and continuous with respect to and is -measurable, .
Now let’s go one step further and add another environmental noise that is Telegraph noise. Telegraph noise can be described as a random switch between two or more environmental states that differ in factors such as nutrition or rainfall  . The stochastic differential equations driven by a continuous-time Markov chain have been used to model the population system     with this type of noise. Suppose the Markov chain on the state space controls the switching between the environmental regimes. Then the prey-predator model with two types of noise can be described by the following stochastic differential equation
with initial data
where is a right-continuous Markov chain, taking values in . System (1.6) will switch from one mode to another according to the law of Markov chain. If , then system (1.6) obeys
with until time when Markov chain jumps to from ; the system will then obey (8) with from to when the Markov chain jumps to from . The system will continue to switch as long as the Markov chain jumps. In other words, system (8) can be regarded as system (6) switching from one to another according to the law of the Markov chain. If the switching between environmental regimes disappears, then system (6) degenerates into system (8).
More recently, several authors have discussed the effects of environmental fluctuations on populations     . C. Ji et al.  studied a stochastic predator-prey system with white noise and concluded that the predator population and ratio-dependent functions were stable on average time. M. Ouyang, X. Li  studied stochastic predator-prey systems with Markovian switching, and obtained that the stable distribution of Markov chains was related to the parameters of subsystems, and the switching between subsystems made them neither permanent nor dissipative. L. Bai et al.  studied a stochastic predator-prey system with Lévy noise and revealed that Lévy noise and white noise can have an impact on biological systems. But previous results were insufficient to reveal the effects of Markovian switching and Lévy noise on prey and predators. Thus, these factors let do investigate the dynamics of the stochastic random predator-prey system described in system (1.8). Till now, the available tools for analyzing stochastic population models with Markovian switching are limited  . The key methods used in this paper are m-matrix analysis (e.g.,  ) and stochastic analysis of Lyapunov functions developed by Khasminskii (see e.g.,   ).
This paper is organized as follows: In Section 2, we give the global existence and positive properties of the solutions of system (1.8). In section 3 and section 4, we give sufficient conditions for the non-persistence, weak persistence and extinction and stochastic permanence respectively. In Section 5, we demonstrate that system (5.1) has a unique stationary distribution under some appropriate conditions when Lévy jumps are not present. Finally, we illustrate our main results with two examples.
Throughout this paper, let be a complete probability space with a filtration satisfying the usual conditions (i.e. it is right continuous and contains all P-null sets). Let , , be a scalar standard Brownian motion defined on this probability space. We also denote by the positive cone in , and denote by the nonnegative cone in .
Let be a right-continuous Markov chain on the probability space, taking values in a finite state space with the generator given by
where . Here represents the transition rate from i to j and , if while
We assume that the Markov chain is independent of the Brownian motion and is irreducible. Under this condition, the Markov chain has a unique stationary (probability) distribution which can be determined by solving the following linear equation
Next, let be a solution of the stochastic differential equation with regime-switching jump-diffusion processes taking the form
where , and are measurable functions. Moreover, let denote the family of all real-valued function on which are continuously twice differentiable in x. For each , we define an operator by
Then the generalized Itô’s formula with jumps is given by
For convenience and simplicity in the following discussion, define
In this paper, we impose the following assumptions:
Assumption 1. There is a constant such that .
Assumption 2. , , , are all positive constant, and there exists such that , , .
Assumption 3. For some , , , , and there exists such that , .
Assumption 4. For some , , .
Assumption 5. , , and , where
Lemma 2.1. If Assumption 1 holds, then for any given initial data , , system (6) has a unique solution on a.s..
Proof. The proof is standard (see e.g.,   ) and hence is omitted.
3. The Persistence and Extinction of Populations
Definition 3.1. Let be a solution of system (1.6). Then
1) the species is said to be extinct, if , a.s.;
2) the species is said to be weakly persistent in the mean a.s., if , a.s.;
3) the species is said to non-persistence in mean a.s., if , a.s.
Lemma 3.1. (see Lipster  ). Suppose that is a local martingale with . Then
and is Meyer’s angle bracket process.
Lemma 3.2. If Assumption 1 holds, then for any given initial value , the solutio to system (1.6) has the following property
Proof. Applying the generalized Itô’s formula to and leads to
are local martingale with the quadratic variations
In view of the exponential martingale inequality, for any positive number ,
Let , , , we can get
where and . Applying the Borel-Cantelli Lemma, we can obtain that for all , there is a random integer such that for each ,
Namely, we have shown
Substituting the above inequalities into (3.2) leads to
It is easy to find that for any and , there exists two constants and which are independent of k such that
In other words, for any , we obtain
Letting , we get
This proof is completed.
Theorem 3.1. Let Assumption 1 hold, if and , then species and of system (1.6) will tend to be extinct.
Proof. By the generalized Itô’s formula, we derive from (1.6) that
are local martingale with the quadratic variations
It follows from Lemma 3.1 that
Dividing by t on both sides of (18) and then taking the superior limit, we obtain
This proof is completed.
Theorem 3.2. Let Assumption 1 hold, if and , then species and of system (1.6) will be non-persistent in the mean.
Proof. Due to the fact that and (3.5), for any given , there is a positive constant T such that
Then for any and sufficiently large , we have
Let for , then one gets
which shows that
Integrating the above inequality from T to t results in
Taking the logarithm on both sides, we have
Then letting , and making use of the L’Hospital’s rule results in
By the arbitrariness of , we can get
which is the desired assertion for . The corresponding result of can also be proved by the same method, so it is omitted. Thus the proof of Theorem 3.2 is completed.
Theorem 3.3. Let Assumption 1 hold, if , then species of system (1.6) will be weakly persistent in the mean.
Proof. By the generalized Itô’s formula, and dividing by t on both sides, we have
Taking the superior limit and combining with (3.1), (3.5), we conclude
The proof is completed.
Corollary 3.1. According to Theorem 3.1, the solutions of subsystems (1.8) can be obtained with the following properties:
1) If , , then both and tend to extinction a.s., i.e., and ;
2) If , , then both and will be non-persistent in the mean a.s.;
3) If , then is weakly persistent in the mean a.s.
4. Stochastic Permanence
In the study of population dynamics, stochastic permanence is one of the most important properties. We first introduce the definition of stochastic permanence , which is widely used in the field of population dynamics (see e.g.,   ). In this section, we shall discuss this property.
Definition 4.1. System (1.6) is stochastically permanent if for any , there exist and such that
Lemma 4.1. Suppose Assumption 2 hold, let be the solution to system (1.6) with initial value , then for any , there exists such that
Proof. Define . By the generalized Itô’s formula, we deduce
dropping t from and . We notice that both coefficients of the higher , are negative. From (4.4) and , we derive that there exists a positive constant such that
According to (4.5) and the generalized Itô’s formula, we obtain
Integrating from 0 to t and taking expectations of both sides, we obtain that
which implies the required assertion (4.3).
To state our main result, we give some notations. Let C be vector or matrix. By we mean all elements are positive. Let
Lemma 4.2. (see Lemma 5.3 in  ). If has all of its row sums positive, that is
for all .
Lemma 4.3. (see Lemma 5.3 in  ). If , then the following statements are equivalent:
1) C is nonsingular M-matrix.
2) All of the principal minors of are positive; that is
for every .
3) C is semi-positive; that is, there exists in such that .
The proof of the stochastic permanence is rather technical, so we prepare several useful lemmas.
Lemma 4.4. Assumptions 3 and 4 imply that there is a constant such that for , the matrix
is a nonsingular M-matrix, where
and is defined in Assumption 5.
Proof. The proof is rather standard and hence is omitted (see  ).
Lemma 4.5. If and there exists a constant such that is a nonsingular M-matrix, then the solution of system (1.6) with initial value has the property that
Applying the generalized Itô’s formula, we have
Noting that is a nonsingular M-matrix, thank to Lemma 4.3, there exists such that , namely, for every , . So there exists such that
With the help of Itô’s formula, we have
It is obvious that . Based on Jensen’s inequality, we derive
In view of (4.7), (4.8) and (4.9), there exists such that
Integrating (4.10) from 0 to t and taking expectation of both sides, we have
This means that
Base on (4.11), we obtain
From (4.6), we have
which is the required assertion.
Theorem 4.1. Under assumptions 2 and 4, if , then system (1.6) is stochastically permanent.
Proof. By Lemma 4.4 and Lemma 4.5, we know
Based on Chebyshev’s inequality, for any , there exists such that
Proof of using the same method, namely,
Finally, (4.2) is obtained by combining lemma 4.1 and Chebyshev inequality. Therefore, the system (1.6) is stochastically permanent.
In the same spirit as in the proof of Theorem 4.1, we yield the result of the subsystem (1.8) as follows.
Corollary 4.1. Under assumption 3, if , then the subsystem (8) is stochastically permanent.
Proof. Note that for some , . We can choose so small that for ,
So, is a positive constant and is also a nonsingular M-matrix. According to Lemma 4.4 and Theorem 4.1, subsystem (1.8) is stochastically permanent.
5. Stationary Distribution
As far as we know, the existence of the ergodic stationary distribution of a stochastic competition model with high order stochastic perturbations has not been obtained theoretically. Therefore, this section mainly studies the existence and uniqueness of the stationary distribution of system (1.6) without Lévy jumps, namely system (5.1).
Next, from the theorem in  we have the following lemma, we will use this lemma to prove ergodic stationary distribution.
Lemma 5.1. If the following conditions are satisfied:
1) for any ;
2) for each , is symmetric and satisfies
with some constant for all ;
3) there exists a bounded open subset of with a regular boundary satisfying that, for each there exists a nonnegative function such that is twice continuously differential and that for some ,
then of system (5.1) is positive recurrent and ergodic. That is to say, there exsist a unique stationary distribution such that for any Borel measurable function satisfying
Theorem 5.1. Under , then for any given initial value , system (5.1) has a unique ergodic stationary distribution on .
Proof. Define a -function by
Choose a constant such that for any ,
Combining (5.2) and (5.3), we obtain
Then we have
To sum up, when or , or or , we can derive . Consequently, take sufficiently small and let , one can see that
That is to say, the condition (3) in Lemma 5.1 is satisfied. On the other hand, Assumption 3 indicates the condition (1) that satisfies Lemma 5.1, and the diffusion matrix of system (5.1) is positive definite, which implies that condition (2) in Lemma 5.1 holds. According to lemma 5.1, system (5.1) is ergodic and has a unique stationary distribution. The proof is completed.
6. Conclusions and Example
The stochastic persistence and extinction of a stochastic ratio-dependent predator-prey system with Markovian switching and Lévy noise are studied. Our main results are as follows: Theorem 3.1 gives sufficient conditions on extinction and non-persistent in mean of each population. Theorem 3.3 gives sufficient conditions for each population to be weakly persistent. Further, Corollaries 3.1 tells us that for some , if , system (1.8) is weakly persistent, and if , system (1.8) is extinct. Theorem 4.1 gives sufficient condition for the stochastic permanence of (1.6). Theorem 4.1 and Corollaries 4.1 tell us that if some subsystems are stochastically persistent and others are extinctive, then as the result of the Markovian switch, the system (1.6) is still stochastically persistent. Finally, when there is no Lévy jump, a sufficient condition for the existence of ergodic stationary distribution of system (5.1) is established under certain conditions.
Next, two examples are introduced to support our theoretical analysis results.
Example 6.1. First of all, we will discuss the effect of Markov switches on population dynamics. Consider (1.8) with the Markov chain taking value in the state space value , be deemed to have been the result of the switching between
where , the initial value and the coefficients
Case 1. Let the generator of Markov chain be
Solving (2.3) yields the unique stationary distribution
Based on (6.3), we compute
From (6.4) and Corollary 4.2, it is easy to find that the subsystem (6.1) is extinct, but subsystem (6.2) is persistent. According to Theorem 4.1, system (1.6) is stochastically permanent. This example shows that although some subsystems are impermanent, the overall behavior of system (1.6) is stochastically permanent as a result of Markovian switching. Thus, Markovian switching may contribute to permanence to some extent. The numerical result is shown in Figure 1(a), Figure 1(b) and Figure 1(c).
Case2. Let and . We obtain
According to Theorem 4.1, system (1.6) is extinctive (see Figure 1(d)).
Example 6.2. Next, we explain the impacts of Lévy jumps on population dynamics. Consider (1.6) with Markov chain taking value in state space . Let and , , and the coefficients
Case 1. Under the condition of without Lévy jumps effect, a simple computation yields
Figure 1. Time series of system (6) for , , , step size , the initial data , . (a) is with , , , , , , , . (b) is with , , , , , , , , . ((c), (d)) The parameters are the same as in (a) and (b). These two sets of figures suggest that populations may switch between extinction and persistence as a result of the Markovian switch.
Therefore, by Theoerm 4.1, system (6) is stochastically permanent (see Figure 2(a)).
Case2. When , , , , that is, there is jump noise. By calculation
Figure 2. Time series of system (1.6) for , , , , , , , , , , , , . step size , the initial data , . (a) is with . (b) is with , , , . These two sets of figures show that Lévy jumps suppression population of persistent.
By Theoerm 3.1, system (1.6) is extinctive. This example suggests that Lévy jumps may suppress the permanence (see Figure 2(b)). The results suggest that Lévy jumps may suppress for the persistence of species.
This work was supported by the National Natural Science Foundation of China (11861027).
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