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Global dynamics of a delayed diffusive virus infection model with cell-mediated immunity and cell-to-cell transmission

  • In this paper, we propose and analyze a delayed diffusive viral dynamic model incorporating cell-mediated immunity and both cell-free and cell-to-cell transmission. After discussing the well-posedness, we provide some preliminary results on solutions. Then we study the existence and uniqueness of homogeneous steady states, which turned out to be completely determined by the basic reproduction number of infection R0 and the basic reproduction number of immunity R1. Note that when R1 is defined, it is necessary that R0 > 1. The main result is a threefold dynamics. Roughly speaking, when R0 < 1 the infection-free steady state is globally asymptotically stable; when R1 ≤ 1 < R0 the immunity-free infected steady state is globally asymptotically stable; when R1 > 1 the infected-immune steady state is globally asymptotically stable. The approaches are linearization technique and the Lyapunov functional method. The theoretical results are also illustrated with numerical simulations.

    Citation: Chunyang Qin, Yuming Chen, Xia Wang. Global dynamics of a delayed diffusive virus infection model with cell-mediated immunity and cell-to-cell transmission[J]. Mathematical Biosciences and Engineering, 2020, 17(5): 4678-4705. doi: 10.3934/mbe.2020257

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  • In this paper, we propose and analyze a delayed diffusive viral dynamic model incorporating cell-mediated immunity and both cell-free and cell-to-cell transmission. After discussing the well-posedness, we provide some preliminary results on solutions. Then we study the existence and uniqueness of homogeneous steady states, which turned out to be completely determined by the basic reproduction number of infection R0 and the basic reproduction number of immunity R1. Note that when R1 is defined, it is necessary that R0 > 1. The main result is a threefold dynamics. Roughly speaking, when R0 < 1 the infection-free steady state is globally asymptotically stable; when R1 ≤ 1 < R0 the immunity-free infected steady state is globally asymptotically stable; when R1 > 1 the infected-immune steady state is globally asymptotically stable. The approaches are linearization technique and the Lyapunov functional method. The theoretical results are also illustrated with numerical simulations.


    In 1987, Karevia and Odell [1] first proposed the following one-predator and one-prey model with prey-taxis in order to explain that an area-restricted search creates the following predator aggregation phenomenon

    {ut=(d(w)u)(uχ(w)w)+G1(u,w),wt=DΔw+G2(u,w), (1.1)

    where D>0 is the diffusivity coefficient of preys, d(w) denotes the motility function of predators, χ(w) represents the prey-taxis sensitivity coefficient, and the term (uχ(w)w) stands for the tendency of the predator moving towards the increasing direction of the prey gradient, and it is viewed as the prey-taxis term. The functions G1(u,w) and G2(u,w) describe the predator-prey interactions, which include both intra-specific and inter-specific interactions. Generally the predator-prey interaction functions G1(u,w) and G2(u,w) possess the following prototypical forms.

    G1(u,w)=γuF(w)uh(u),G2(u,w)=uF(w)+f(w), (1.2)

    where γ>0 denotes the intrinsic predation rate, uF(w) represents the inter-specific interaction and uh(u) and f(w) stand for the intra-specific interaction. Specifically, F(w) is the functional response function accounting for the intake rate of predators as a function of prey density; it is often used in the following form in the literature [2,3,4]

    F(w)=w(Holling type I),F(w)=wλ+w(Holling type II),F(w)=wmλm+wm(Holling type III),F(w)=1eλw(Ivlev type) (1.3)

    with constants λ>0 and m>1; other types of functional response functions (e.g., Beddington-DeAngelis type in [5], Crowley-Martin type in [6]) and more predator-prey interactions can be found in [7,8,9,10]. The predator mortality rate function h(u) is typically of the form

    h(u)=θ+αu, (1.4)

    where θ>0 accounts for the natural death rate and α0 denotes the rate of death resulting from the intra-specific competition, which is also called the density-dependent death [11]. The prey growth function f(w) is usually assumed to be negative for large w due to the limitation of resources (or crowding effect), and its typical forms are

    f(w)=μw(1wK)(Logistic type),orf(w)=μw(1wK)(wk1)(Bistable or Allee effect type), (1.5)

    where μ>0 is the intrinsic growth rate of prey, K>0 is called the carrying capacity and 0<k<K. Now there exist many interesting results about global existence, uniform boundedness, asymptotic behavior, traveling waves and pattern formation of solutions to System (1.1) or its variants in [11,12,13,14,15]. When d(w)=d>0 and χ(w)=χ>0, G1(u,v) and G2(u,v) have the forms of (1.2), Wu et al. [15] obtained the global existence and uniform persistence of solutions to (1.1) in any dimension provided that χ is suitably small. Then, Jin and Wang[13] derived the global boundedness and asymptotic stability of solutions for System (1.1) without the smallness assumption on χ in a two-dimensional bounded domain. Moreover, Wang et al. [16] studied the nonconstant positive steady states and pattern formation of (1.1) in a one-dimensional bounded domain. Under the conditions that d(w) and χ(w) are not constants and h(u) is given by (1.4), Jin and Wang[14] established the global boundedness, asymptotic behavior and spatio-temporal patterns of solutions for (1.1) under some conditions on the parameters in a two-dimensional smooth bounded domain. For more related results in predator-prey models, we refer the readers to [17,18,19,20,21,22,23,24,25,26,27,28,29] and the references therein.

    However, all the aforementioned works are devoted to studying prey-taxis models with one-predator and one prey. Now let us mention some predator-prey models with two-predator and one-prey. Recently, the following general two-predator and one-prey model with prey-taxis has attracted a lot of attention.

    {ut=(d1(w)u)(uχ1(w)w)+γ1uF1(w)uh1(u)β1uv,vt=(d2(w)v)(vχ2(w)w)+γ2vF2(w)vh2(v)β2uv,wt=DΔwuF1(w)vF2(w)+f(w), (1.6)

    as applied in a smooth bounded domain ΩRn, n1. Given d1(w)=d2(w)=1 and β1=β2=0, Wang et al. [30] derived the global boundedness, nonconstant positive steady states and time-periodic patterns of solutions for System (1.6). Wang and Wang [31] studied the uniform boundedness and asymptotic stability of nonnegative spatially homogeneous equilibria for (1.6) in any dimension. Given d1(w)=d2(w)=1, χi(w)=χi>0(i=1,2) and β1=β2=β>0, Mi et al. [32] obtained the global boundedness and stability of classical solutions in any dimension under suitable conditions of parameters. Under the conditions that d1(w) and d2(w) are non-constants and β1=β2=0, Qiu et al.[33] rigorously proved the global existence, uniform boundedness and stabilization of classical solutions in any dimension with suitable conditions on motility functions and the coefficients of the logistic source. However, when β1,β20, the global existence and stabilization of solutions for (1.6) are still open. Given χi(w)=di(w)0 if di(w)0(i=1,2), the diffusion-advection terms in (1.6) can respectively become the forms Δ(d1(w)u) and Δ(d2(w)v), which could be interpreted as "density-suppressed motility" in [34,35]. This means that the predator will reduce its motility when encountering the prey, which is a rather reasonable assumption that has very sound applications in the predator-prey systems. Since the possible degeneracy caused by the density-suppressed motility brings considerable challenges for mathematical analysis, many works have showed various interesting results, which can be found in [36,37,38,39,40,41,42,43,44]. Given χi(w)=di(w)0(i=1,2), F1(w)=F2(w)=w, h1(u)=u,h2(v)=v and f(w)=μw(m(x)w), System (1.6) can be simplified as

    {ut=Δ(d1(w)u)+u(γ1wuβ1v),vt=Δ(d2(w)v)+v(γ2wvβ2u),wt=DΔw(u+v)w+μw(m(x)w), (1.7)

    where the parameters D,μ,γi,βi(i=1,2) are positive, the dispersal rate functions di(w)(i=1,2) satisfy following the hypothesis: di(w)C2([0,)),di(w)0 on [0,) and di(w)>0. Wang and Xu [45] have found some interesting results for System (1.7) in a two-dimensional smooth bounded domain. More specifically, when D=1 and m(x)=1, System (1.7) has a unique globally bounded classical solution. By constructing appropriate Lyapunov functionals and using LaSalle's invariant principle, the authors proved that the global bounded solution of (1.7) converges to the co-existence steady state exponentially or competitive exclusion steady state algebraically as time tends to infinity in different parameter regimes. For a prey's resource that is spatially heterogeneous (i.e., m(x) is non-constant), the authors used numerical simulations to demonstrate that the striking phenomenon "slower diffuser always prevails" given in [46,47] fails to appear if the non-random dispersal strategy is employed by competing species (i.e., either d1(w) or d2(w) is non-constant) while it still holds if both d1(w) and d2(w) are constants. However, there are few results about global boundedness and large time behavior of solutions for (1.7) in the general form.

    Inspired by the above works, this paper is concerned with the following two-species competitive predator-prey system with the following density-dependent diffusion

    {ut=Δ(d1(w)u)+γ1uF1(w)uh1(u)β1uv,(x,t)Ω×(0,),vt=Δ(d2(w)v)+γ2vF2(w)vh2(v)β2uv,(x,t)Ω×(0,),wt=DΔwuF1(w)vF2(w)+f(w),(x,t)Ω×(0,),uν=vν=wν=0,(x,t)Ω×(0,),(u,v,w)(x,0)=(u0,v0,w0)(x),xΩ, (1.8)

    where ΩR2 is a bounded domain with a smooth boundary Ω, ν denotes the derivative with respect to the outward normal vector ν of Ω, and the parameters D and γi, βi (i=1,2) are positive. The unknown functions u=u(x,t) and v=v(x,t) denote the densities of two-competing species (e.g., predators), and w=w(x,t) represents the density of predators' resources (e.g., the prey) at a position x and time t>0. When d1(w)=d1>0 and d2(w)=d2>0, System (1.8) becomes the well-known diffusive predator-prey system, which has been widely studied in [48,49,50,51]. However, to the best of our knowledge, the results of the two-predator and one-prey system given by (1.8) with density-suppressed motility (i.e., d1(w) and d2(w) are non-constants) indicate that the competition and general predator mortality rate hi(u) are almost vacant. The main aim of this paper is to explore the influence of the predation interaction, competition and general predator mortality on the dynamical behavior of System (1.8). Throughout this paper, we assume that the functions di(s),Fi(s),hi(s),(i=1,2),f(s) and initial data (u0,v0,w0) mentioned in (1.8) satisfy the following hypotheses:

    (H1) di(s)C2([0,)) with di(s)>0 and di(s)0, i=1,2 on [0,). The typical example is di(s)=1(1+s)κi or di(s)=exp(κis) with κi>0, i=1,2.

    (H2) Fi(s)C1([0,)), Fi(0)=0, Fi(s)>0 and Fi(s)>0, i=1,2 in (0,).

    (H3) hi(s)C2([0,)) and there exist constants θi>0 and αi0 such that hi(s)θi and hi(s)αi, i=1,2 for all s>0.

    (H4) f(s)C1([0,)) with f(0)=0, and there exist positive constants μ and K such that f(s)μs for all s0, f(K)=0 and f(s)<0 for s>K.

    (H5) (u0,v0,w0)(W1,p(Ω))3 with p>2 and u0,v0,w00.

    Here, we note that there are many candidates for the above functions Fi(s), hi(s) and f(s) as in (1.3)–(1.5). Due to the presence of the prey's density dependent diffusion coefficient, Model (1.8) is a cross-diffusion system and the parabolic comparison principle is no longer applicable. Moreover, when α1=α2=0, the key L2-spatiotemporal estimates of u and v cannot be directly derived; thus, the uniform boundedness of solutions is not an obvious result and needs to be justified. Based on the above hypotheses, the first main result of this paper asserts the global existence and boundedness of solutions for System (1.8) as follows.

    Theorem 1.1. Let D,γi,βi>0(i=1,2), ΩR2 be a smooth bounded domain and the hypotheses (H1)–(H5) hold. Then System (1.8) has a unique global nonnegative classical solution (u,v,w)(C(¯Ω×[0,))C2,1(¯Ω×(0,)))3, which is uniformly bounded in time, i.e., there exists a constant C>0 independent of t such that

    u(,t)L(Ω)+v(,t)L(Ω)+w(,t)W1,(Ω)Cforallt>0. (1.9)

    In particular, one has 0w(x,t)K0 for all (x,t)Ω×(0,), where

    K0:=max{||w0||L(Ω),K}. (1.10)

    Remark 1.1. For the special case F1(w)=F2(w)=w, h1(u)=u,h2(v)=v and f(w)=μw(1w), the results of Theorem 1.1 have been obtained in [45]. However, since α1 and α2 may be equal to zero in the hypotheses of this paper, the L2-spatiotemporal estimates of u and v cannot be directly obtained by using the method in [45]. By means of the mechanism "density-suppressed motility", we invoke some ideas used in [14] and apply the self-adjoint realization of Δ+δ with some δ>0 in L2(Ω) to establish the key L2-spatiotemporal estimates of u and v.

    The second main aim of this paper is to study the role of non-random dispersal and competition between two predators in the asymptotic properties of the nonnegative spatial homogeneous equilibria of System (1.8). For simplicity, we let F1(w)=F2(w)=w, h1(u)=θ1+α1u, h2(v)=θ2+α2v and f(w)=μw(1w), where θ1=θ2=θ>0 and α1,α2,μ>0; then, System system (1.8) can be simplified as

    {ut=Δ(d1(w)u)+γ1uwu(θ+α1u)β1uv,(x,t)Ω×(0,),vt=Δ(d2(w)v)+γ2vwv(θ+α2v)β2uv,(x,t)Ω×(0,),wt=DΔw(u+v)w+μw(1w),(x,t)Ω×(0,),uν=vν=wν=0,(x,t)Ω×(0,),(u,v,w)(x,0)=(u0,v0,w0)(x),xΩ. (1.11)

    Theorem 1.1 ensures that System (1.11) possesses a unique global bounded nonnegative classical solution (u,v,w) such that 0w(x,t)K0:=max{||w0||L(Ω),1} for all (x,t)Ω×(0,). Now we find some sufficient conditions of parameters so that (1.11) admits a positive constant solution (u,v,w) satisfying

    {γ1wθα1uβ1v=0,γ2wθα2vβ2u=0,uv+μμw=0, (1.12)

    i.e.,

    AX=B, (1.13)

    where

    A=[α1β1γ1β2α2γ211μ],X=[uvw],B=[θθμ].

    If the determinant Φ of the coefficient matrix A in (1.13) does not equal zero, it follows from Cramer's rule that

    u=ΦuΦ,v=ΦvΦ,w=ΦwΦ, (1.14)

    where

    {Φ=(γ1+β1μ)(α2β2)+(γ2+α2μ)(α1β1),Φu=α2μ(γ1θ)β1μ(γ2θ)+θ(γ1γ2),Φv=α1μ(γ2θ)β2μ(γ1θ)+θ(γ2γ1),Φw=(θ+β1μ)(α2β2)+(θ+α2μ)(α1β1). (1.15)

    When β1<α1 and β2<α2, it follows that Φ>0 and Φw>0, and thus we know w>0. Next, we shall discuss the sign of Φu and Φv. For convenience, we let

    β1:=l1μ(γ2θ) (1.16)

    and

    β2:=l2μ(γ1θ), (1.17)

    where

    l1:=α2μ(γ1θ)+θ(γ1γ2) (1.18)

    and

    l2:=α1μ(γ2θ)+θ(γ2γ1). (1.19)

    It is not difficult to see that u=ΦuΦ, v=ΦvΦ and w=ΦwΦ are positive, if γi>θ, i=1,2 and one of the following conditions holds:

    (H6) γ1<γ2, l1>0, β1<min{α1,β1} and β2<min{α2,β2};

    (H7) γ1>γ2, l2>0, β1<min{α1,β1} and β2<min{α2,β2};

    (H8) γ1=γ2 and max{β1,β2}<min{α1,α2}.

    Now, we give our main results on the asymptotic stability properties of the nonnegative spatial homogeneous equilibria of System (1.11) as follows.

    Theorem 1.2. Let ΩR2 be a smooth bounded domain and the parameters γi,αi,βi, (i=1,2), θ, μ and D be positive. Assume that d1(w) and d2(w) satisfy (H1), and that (u,v,w) is a global bounded classical solution of System (1.11). Suppose that γi>θ,i=1,2,

    (β1γ2+β2γ1)2<4γ1γ2α1α2 (1.20)

    and

    D>maxw[0,K0]w24w[u|d1(w)|2γ1d1(w)+v|d2(w)|2γ2d2(w)] (1.21)

    as well as one of the conditions (H6)–(H8) holds. Then for all initial data (u0,v0,w0) satisfying (H5), there exist positive constants C and λ such that

    ||u(,t)u||L(Ω)+||v(,t)v||L(Ω)+||w(,t)w||L(Ω)Ceλt (1.22)

    for all t>0, where (u,v,w) is given by (1.14).

    Remark 1.2. From a biological point of view, it is well known that the change of the predators comes from predation, competition and mortality in System (1.11). The parameters γi, βi, αi(i=1,2) and θ respectively stand for the predation rate, competition strength, density-dependent death and natural death rate of the predators, which play a collective role in studying the dynamical behavior of (1.11). More specifically, when γi>θ, it is called strong predation; otherwise, it is weak predation. Hence the results of Theorem 1.2 can tell us that if the predations of two predators are strong and the prey diffusion coefficient D is suitably large, all species can reach a coexistence state.

    Theorem 1.3. Let ΩR2 be a smooth bounded domain and the parameters γi,αi,βi, (i=1,2), θ, μ and D be positive. Assume that d1(w) and d2(w) satisfy (H1), and the (u,v,w) is a global bounded classical solution of System (1.11). Suppose that we have (1.20) and

    D>maxw[0,K0]¯uw2|d1(w)|24γ1¯wd1(w) (1.23)

    as well as one of the following conditions holds:

    (i) γ1>γ2>θ, l20, β1<min{α1,β1} and β2<α2;

    (ii) γ1>γ2>θ, l2>0, β1<min{α1,β1} and β2[β2,α2);

    (iii) γ1>θγ2,

    where

    ¯u=μ(γ1θ)α1μ+γ1and¯w=α1μ+θα1μ+γ1. (1.24)

    Then for all initial data (u0,v0,w0) satisfying (H5), one has

    ||u(,t)¯u||L(Ω)+||v(,t)||L(Ω)+||w(,t)¯w||L(Ω)0ast, (1.25)

    exponentially if θ>γ2¯wβ2¯u or algebraically if θ=γ2¯wβ2¯u.

    Theorem 1.4. Let ΩR2 be a smooth bounded domain and the parameters γi,αi,βi, (i=1,2), θ, μ and D be positive. Assume that d1(w) and d2(w) satisfy (H1), and the (u,v,w) is a global bounded solution of System (1.11). Suppose that we have (1.20) and

    D>maxw[0,K0]˜vw2|d2(w)|24γ2˜wd2(w) (1.26)

    as well as one of the following conditions holds:

    (i) γ2>γ1>θ, l10, β2<min{α2,β2} and β1<α1;

    (ii) γ2>γ1>θ, l1>0, β2<min{α2,β2} and β1[β1,α1);

    (iii) γ2>θγ1,

    where

    ˜v=μ(γ2θ)α2μ+γ2and˜w=α2μ+θα2μ+γ2. (1.27)

    Then for all initial data (u0,v0,w0) satisfying (H5), one has

    ||u(,t)||L(Ω)+||v(,t)˜v||L(Ω)+||w(,t)˜w||L(Ω)0ast, (1.28)

    exponentially if θ>γ1˜wβ1˜v or algebraically if θ=γ1˜wβ1˜v.

    Remark 1.3. It follows from Theorem 1.3 that if the predator u is superior over v in the competition and the prey diffusion coefficient D is suitably large, the semi-trivial equilibrium (¯u,0,¯w) is globally asymptotically stable. Similarly, we can obtain Theorem 1.4. Hence, we only give the conclusion of Theorem 1.4, without showing the details of the proof for brevity.

    Theorem 1.5. Let ΩR2 be a smooth bounded domain and the parameters γi,αi,βi, (i=1,2), θ, μ and D be positive. Assume that d1(w) and d2(w) satisfy (H1), and the (u,v,w) is a global bounded solution of System (1.11). Suppose that

    γiθ,i=1,2.

    Then for all initial data (u0,v0,w0) satisfying (H5), one has

    ||u(,t)||L(Ω)+||v(,t)||L(Ω)+||w(,t)1||L(Ω)0ast, (1.29)

    exponentially if γi<θ, i=1,2 or algebraically if γi=θ, i=1,2.

    Remark 1.4. It follows from Theorem 1.5 that if the capture rates of the two predators are low (i.e. γiθ, i=1,2), the prey-only steady state (0,0,1) is globally asymptotically stable regardless of the size of the prey diffusion coefficient D.

    Remark 1.5. Compared with the previous results of [33] without competitive terms, the results of Theorems 1.2–1.5 indicate that the competition terms play a crucial role in the global stability of the constant steady states in (1.11). Moreover, under the condition of density-suppressed motility, our global stability results of Theorems 1.2–1.5 can also generalize the ranges of parameters αi and βi(i=1,2) for two dimensional cases in [32]. However, since the heat-semigroup estimates of u and v are no longer applicable due to the appearance of density-suppressed motility, the global stability in L-norm is still open in the higher-dimensional problem.

    The rest of this paper is organized as follows. In Section 2, we first state the local existence of the classical solution to (1.8) and collect preliminary lemmas. In Section 3, we derive the global existence and boundedness of classical solutions for (1.8) and prove Theorem 1.1. Finally, we shall study the asymptotic stability of global bounded solutions for (1.11) and prove Theorems 1.2–1.5.

    In this section, we shall give the local existence and some preliminary lemmas. Firstly, we state the local existence of the classical solution to (1.8), as obtained by means of the abstract theory of quasilinear parabolic systems in [52].

    Lemma 2.1. Let D,γi,βi>0(i=1,2), ΩR2 be a smooth bounded domain and the hypotheses (H1)–(H5) hold. Then, there exists a Tmax(0,] such that System (1.8) possesses a unique classical solution (u,v,w)(C(¯Ω×[0,Tmax))C2,1(¯Ω×(0,Tmax)))3 satisfying

    u,v0and0wK0:=max{||w0||L(Ω),K}. (2.1)

    In addition, the following extensibility criterion holds, i.e. if Tmax<, then

    lim suptTmax(u(,t)L(Ω)+v(,t)L(Ω)+w(,t)W1,(Ω))=. (2.2)

    Proof. Let z=(u,v,w)T; then, System (1.8) can be rewritten as

    {zt=(P(z)z)+Q(z),(x,t)Ω×(0,),zν=0,(x,t)Ω×(0,),z(,0)=z0=(u0,v0,w0),xΩ, (2.3)

    where

    P(z)=(d1(w)0ud1(w)0d2(w)vd2(w)00D)andQ(z)=(γ1uF1(w)uh1(u)β1uvγ2vF2(w)vh2(v)β2uvuF1(w)vF2(w)+f(w)). (2.4)

    According to the conditions that D>0 and di(w)>0(i=1,2), the matrix P(z) is positively definite for the given initial data z0, which asserts that System (1.8) is normally parabolic. Thus it follows from Theorem 7.3 of [53] that there exists a Tmax(0,] such that System (1.8) admits a unique classical solution (u,v,w)(C0(¯Ω×[0,Tmax))C2,1(¯Ω×(0,Tmax)))3. The nonnegativity of (u,v,w) directly comes from the maximum principle [14,45]. It similarly follows from Lemma 2.2 of [13] that wK0:=max{||w0||L(Ω),K}. Since P(z) is an upper triangular matrix, we can deduce from Theorem 5.2 of [54] that the extensibility criterion given by (2.2) holds. The proof of Lemma 2.1 is complete.

    Lemma 2.2. Let ΩRn(n1) be a smooth bounded domain, D>0 and T(0,]. Assume that φ(x,t)C(¯Ω×[0,T))C2,1(¯Ω×(0,T)) satisfies

    {φt=DΔφφ+ψ,(x,t)Ω×(0,T),φν=0,(x,t)Ω×(0,T), (2.5)

    where ψL((0,T);Lp(Ω)) with p1. Then there exists a positive constant C such that

    ||φ(,t)||W1,q(Ω)Cforallt(0,T), (2.6)

    where

    q{[1,npnp),ifp<n,[1,),ifp=n,[1,],ifp>n. (2.7)

    Proof. This lemma directly comes from Lemma 1 of [55].

    Now, we give the following lemma ([56], Lemma 3.4) to derive some a priori estimates for w.

    Lemma 2.3. Let T>0,τ(0,T) and a,d>0, and assume that y:[0,T)[0,) is absolutely continuous. If there exists a nonnegative function hL1loc([0,T)) satisfying

    t+τth(s)dsdforallt[0,Tτ) (2.8)

    and

    y(t)+ay(t)h(t), (2.9)

    one has

    y(t)max{y(0)+d,daτ+2d}forallt[0,T). (2.10)

    Next, we give a basic property of the solution components u and v for System (1.8).

    Lemma 2.4. Let the assumptions of Lemma 2.1 hold. Then there exists a constant C>0 such that

    Ωu+vdxCforallt(0,Tmax) (2.11)

    and

    t+τtΩu2+v2dxdsCforallt(0,Tmaxτ), (2.12)

    where τ=min{1,12Tmax}.

    Proof. It follows from a direct computation for System (1.8) that

    ddtΩ(1γ1u+1γ2v+w)dx=Ωf(w)dx1γ1Ωuh1(u)dxβ1γ1Ωuvdx1γ2Ωvh2(v)dxβ2γ2ΩuvdxμΩwdx1γ1Ωu(θ1+α1u)dx1γ2Ωv(θ2+α2v)dx=μΩwdxθ1Ω1γ1udxθ2Ω1γ2vdxα1γ1Ωu2dxα2γ2Ωv2dx, (2.13)

    for all t\in (0, T_{\max}) , where we have applied ( H_{3} ), ( H_{4} ), \beta_{1}, \beta_{2} > 0 and (2.1).

    Let \theta: = \min\{\theta_{1}, \theta_{2}\} , it follows from (2.1) that

    \begin{equation} \begin{split} &\frac{\text{d}}{\text{dt}}\int_{\Omega}\left(\frac{1}{\gamma_{1}}u+\frac{1}{\gamma_{2}}v+w\right)dx +\frac{\alpha_{1}}{\gamma_{1}}\int_{\Omega}u^{2}dx+\frac{\alpha_{2}}{\gamma_{2}}\int_{\Omega}v^{2}dx\\ &\leq-\theta\int_{\Omega}\left(\frac{1}{\gamma_{1}}u+\frac{1}{\gamma_{2}}v+w\right)dx+(\mu K_{0}+\theta)|\Omega|, \end{split} \end{equation} (2.14)

    which leads to (2.11) by Gronwall's inequality. If \alpha_{i} > 0 , i = 1, 2 , then integrating (2.14) over (t, t+\tau) , we have (2.12) directly. If \alpha_{i} = 0 , i = 1, 2 , we can also prove (2.12) by means of the idea used in [14]. For the readers' convenience, we give the sketch of the proof.

    Let \mathcal{A} denote the self-adjoint realization of -\Delta+\delta under homogeneous Neumann boundary conditions in L^{2}(\Omega) , where \delta\in\left(0, \min\{\frac{\theta_{1}}{d_{1}(0)}, \frac{\theta_{2}}{d_{2}(0)}\}\right) . It follows from \delta > 0 that \mathcal{A} has an order-preserving bounded inverse \mathcal{A}^{-1} on L^{2}(\Omega) . Thus this allows us to obtain a positive constant c_{1} such that

    \begin{equation} ||\mathcal{A}^{-1}\Psi||_{L^{2}(\Omega)}\leq c_{1}||\Psi||_{L^{2}(\Omega)}\quad\text{for all}\;\;\Psi\in L^{2}(\Omega) \end{equation} (2.15)

    and

    \begin{equation} ||\mathcal{A}^{-\frac{1}{2}}\Psi||_{L^{2}(\Omega)}^{2} = \int_{\Omega}\Psi\cdot\mathcal{A}^{-1}\Psi dx\leq c_{1}||\Psi||_{L^{2}(\Omega)}^{2}\quad\text{for all}\;\;\Psi\in L^{2}(\Omega). \end{equation} (2.16)

    By a simple calculation in (1.8), we have

    \begin{equation} \begin{split} \left(\frac{1}{\gamma_{1}}u+\frac{1}{\gamma_{2}}v+w\right)_{t} & = \Delta\left(\frac{1}{\gamma_{1}}d_{1}(w)u+\frac{1}{\gamma_{2}}d_{2}(w)v+Dw\right)-\frac{1}{\gamma_{1}}uh_{1}(u)-\frac{\beta_{1}}{\gamma_{1}}uv\\ &\quad-\frac{1}{\gamma_{2}}vh_{2}(v)-\frac{\beta_{2}}{\gamma_{2}}uv+f(w), \end{split} \end{equation} (2.17)

    which can be written as

    \begin{equation} \begin{split} &\left(\frac{1}{\gamma_{1}}u+\frac{1}{\gamma_{2}}v+w\right)_{t}+\mathcal{A}\left(\frac{1}{\gamma_{1}}d_{1}(w)u+\frac{1}{\gamma_{2}}d_{2}(w)v+Dw\right)\\ & = \delta\left(\frac{1}{\gamma_{1}}d_{1}(w)u+\frac{1}{\gamma_{2}}d_{2}(w)v+Dw\right)-\frac{1}{\gamma_{1}}uh_{1}(u)-\frac{\beta_{1}}{\gamma_{1}}uv\\ &\quad-\frac{1}{\gamma_{2}}vh_{2}(v)-\frac{\beta_{2}}{\gamma_{2}}uv+f(w)\\ & = \frac{1}{\gamma_{1}}u\left(\delta d_{1}(w)-h_{1}(u)\right)+\frac{1}{\gamma_{2}}v\left(\delta d_{2}(w)-h_{2}(v)\right)+\delta Dw+f(w)-\frac{\beta_{1}}{\gamma_{1}}uv-\frac{\beta_{2}}{\gamma_{2}}uv\\ &\leq\frac{1}{\gamma_{1}}u\left(\delta d_{1}(0)-\theta_{1}\right)+\frac{1}{\gamma_{2}}v\left(\delta d_{2}(0)-\theta_{2}\right)+(\delta D+\mu)K_{0}\\ &\leq (\delta D+\mu)K_{0}\\ &: = c_{2}, \end{split} \end{equation} (2.18)

    where we have applied ( H_{1} ), ( H_{3} ), ( H_{4} ), (2.1) and \delta\in\left(0, \min\{\frac{\theta_{1}}{d_{1}(0)}, \frac{\theta_{2}}{d_{2}(0)}\}\right) . Hence, by multiplying (2.18) by \mathcal{A}^{-1}\left(\frac{1}{\gamma_{1}}u+\frac{1}{\gamma_{2}}v+w\right)\geq0 and integrating it over \Omega , we derive

    \begin{equation} \begin{split} &\frac{1}{2}\frac{\text{d}}{\text{dt}}\int_{\Omega}\left|\mathcal{A}^{-\frac{1}{2}}\left(\frac{1}{\gamma_{1}}u+\frac{1}{\gamma_{2}}v+w\right)\right|^{2}dx\\&\qquad +\int_{\Omega}\left(\frac{1}{\gamma_{1}}d_{1}(w)u+\frac{1}{\gamma_{2}}d_{2}(w)v+Dw\right)\left(\frac{1}{\gamma_{1}}u+\frac{1}{\gamma_{2}}v+w\right)dx\\ &\leq c_{2}\int_{\Omega}\mathcal{A}^{-1}\left(\frac{1}{\gamma_{1}}u+\frac{1}{\gamma_{2}}v+w\right)dx. \end{split} \end{equation} (2.19)

    According to the fact that 0 < d_{i}(K_{0})\leq d_{i}(w) , i = 1, 2 , due to ( H_{1} ) and (2.1), and by letting c_{3}: = \min\{d_{1}(K_{0}), d_{2}(K_{0}), D\} > 0 , we deduce

    \begin{equation} \begin{split} &\frac{\text{d}}{\text{dt}}\int_{\Omega}\left|\mathcal{A}^{-\frac{1}{2}}\left(\frac{1}{\gamma_{1}}u+\frac{1}{\gamma_{2}}v+w\right)\right|^{2}dx +2c_{3}\int_{\Omega}\left(\frac{1}{\gamma_{1}}u+\frac{1}{\gamma_{2}}v+w\right)^{2}dx\\ &\leq 2c_{2}\int_{\Omega}\mathcal{A}^{-1}\left(\frac{1}{\gamma_{1}}u+\frac{1}{\gamma_{2}}v+w\right)dx. \end{split} \end{equation} (2.20)

    It follows from Hölder's and Young's inequality as well as (2.15) that

    \begin{equation} \begin{split} 2c_{2}\int_{\Omega}\mathcal{A}^{-1}\left(\frac{1}{\gamma_{1}}u+\frac{1}{\gamma_{2}}v+w\right)dx&\leq 2c_{2}|\Omega|^{\frac{1}{2}}\left(\int_{\Omega}\left|\mathcal{A}^{-1}\left(\frac{1}{\gamma_{1}}u+\frac{1}{\gamma_{2}}v+w\right)\right|^{2}dx\right)^{\frac{1}{2}} \\&\leq 2c_{1}c_{2}|\Omega|^{\frac{1}{2}}\left(\int_{\Omega}\left(\frac{1}{\gamma_{1}}u+\frac{1}{\gamma_{2}}v+w\right)^{2}dx\right)^{\frac{1}{2}}\\ &\leq \frac{c_{3}}{2}\int_{\Omega}\left(\frac{1}{\gamma_{1}}u+\frac{1}{\gamma_{2}}v+w\right)^{2}dx+\frac{2c_{1}^{2}c_{2}^{2}|\Omega|}{c_{3}}. \end{split} \end{equation} (2.21)

    According to (2.16), we have

    \begin{equation} \begin{split} \frac{c_{3}}{2c_{1}}\int_{\Omega}\left|\mathcal{A}^{-\frac{1}{2}}\left(\frac{1}{\gamma_{1}}u+\frac{1}{\gamma_{2}}v+w\right)\right|^{2}\leq \frac{c_{3}}{2}\int_{\Omega}\left(\frac{1}{\gamma_{1}}u+\frac{1}{\gamma_{2}}v+w\right)^{2}dx. \end{split} \end{equation} (2.22)

    By combining (2.20)–(2.22), we derive

    \begin{equation} \begin{split} &\frac{\text{d}}{\text{dt}}\int_{\Omega}\left|\mathcal{A}^{-\frac{1}{2}}\left(\frac{1}{\gamma_{1}}u+\frac{1}{\gamma_{2}}v+w\right)\right|^{2}dx +\frac{c_{3}}{2c_{1}}\int_{\Omega}\left|\mathcal{A}^{-\frac{1}{2}}\left(\frac{1}{\gamma_{1}}u+\frac{1}{\gamma_{2}}v+w\right)\right|^{2}\\&\qquad +c_{3}\int_{\Omega}\left(\frac{1}{\gamma_{1}}u+\frac{1}{\gamma_{2}}v+w\right)^{2}dx\leq \frac{2c_{1}^{2}c_{2}^{2}|\Omega|}{c_{3}}. \end{split} \end{equation} (2.23)

    By the ordinary differential equations (ODE) argument, there exists a c_{4} > 0 such that

    \begin{equation} \begin{split} \int_{\Omega}\left|\mathcal{A}^{-\frac{1}{2}}\left(\frac{1}{\gamma_{1}}u+\frac{1}{\gamma_{2}}v+w\right)\right|^{2}dx\leq c_{4}, \end{split} \end{equation} (2.24)

    which implies that

    \begin{equation} \begin{split} \int_{t}^{t+\tau}\int_{\Omega}\frac{1}{\gamma_{1}^{2}}u^{2}+\frac{1}{\gamma_{2}^{2}}v^{2}dxds&\leq \int_{t}^{t+\tau}\int_{\Omega}\left(\frac{1}{\gamma_{1}}u+\frac{1}{\gamma_{2}}v\right)^{2}dxds \\&\leq\int_{t}^{t+\tau}\int_{\Omega}\left(\frac{1}{\gamma_{1}}u+\frac{1}{\gamma_{2}}v+w\right)^{2}dxds \\ &\leq\frac{c_{4}}{c_{3}}+\frac{2c_{1}^{2}c_{2}^{2}|\Omega|}{c_{3}^{2}}. \end{split} \end{equation} (2.25)

    The proof of Lemma 2.4 is complete.

    Finally, we shall give the following key estimate of w , which plays a crucial role in the proof of Theorem 1.1.

    Lemma 2.5. Let the assumptions of Lemma 2.1 hold. Then there exists a constant C > 0 such that

    \begin{equation} \int_{\Omega}|\nabla w|^{2}dx\leq C \quad{for\;all}\quad t\in(0,T_{\max}) \end{equation} (2.26)

    and

    \begin{equation} \int_{t}^{t+\tau}\int_{\Omega}|\Delta w|^{2}dxds\leq C \quad{for \;all}\quad t\in(0,T_{\max}-\tau), \end{equation} (2.27)

    where \tau = \min\{1, \frac{1}{2}T_{\max}\} .

    Proof. Multiplying the third equation of System (1.8) with -2\Delta w and integrating it by parts, we deduce from Young's inequality and (2.1) that

    \begin{equation} \begin{split} &\frac{\text{d}}{\text{dt}}\int_{\Omega}|\nabla w|^{2}dx\\& = -2D\int_{\Omega}|\Delta w|^{2}dx+2\int_{\Omega}(uF_{1}(w)+vF_{2}(w))\Delta wdx-2\int_{\Omega}f(w)\Delta wdx\\ &\leq-D\int_{\Omega}|\Delta w|^{2}dx+\frac{2}{D}\int_{\Omega}(uF_{1}(w)+vF_{2}(w))^{2}dx+\frac{2}{D}\int_{\Omega}f^{2}(w)dx\\ &\leq-D\int_{\Omega}|\Delta w|^{2}dx+\frac{4F_{1}^{2}(K_{0})}{D}\int_{\Omega}u^{2}dx+\frac{4F_{2}^{2}(K_{0})}{D}\int_{\Omega}v^{2}dx+\frac{2(\mu K_{0})^{2}}{D}|\Omega|, \end{split} \end{equation} (2.28)

    where we have used the hypotheses ( H_{2} ) and ( H_{4} ).

    It follows from \frac{\partial w}{\partial\nu} = 0 , Young's inequality and (2.1) that

    \begin{equation} \begin{split} \int_{\Omega}|\nabla w|^{2}dx = -\int_{\Omega}w\Delta wdx&\leq\frac{D}{2}\int_{\Omega}|\Delta w|^{2}dx+\frac{1}{2D}\int_{\Omega}w^{2}dx\\ &\leq\frac{D}{2}\int_{\Omega}|\Delta w|^{2}dx+\frac{K_{0}^{2}}{2D}|\Omega|. \end{split} \end{equation} (2.29)

    Let c_{5}: = \max\left\{\frac{4F_{1}^{2}(K_{0})}{D}, \frac{4F_{2}^{2}(K_{0})}{D}\right\} ; we infer from (2.28) and (2.29) that

    \begin{equation} \begin{split} &\frac{\text{d}}{\text{dt}}\int_{\Omega}|\nabla w|^{2}dx+\int_{\Omega}|\nabla w|^{2}dx+\frac{D}{2}\int_{\Omega}|\Delta w|^{2}dx \\&\leq c_{5}\int_{\Omega}u^{2}+v^{2}dx+c_{6}, \end{split} \end{equation} (2.30)

    where c_{6}: = \frac{2(\mu K_{0})^{2}}{D}|\Omega|+\frac{K_{0}^{2}}{2D}|\Omega| . It follows from Lemma 2.3 and Lemma 2.4 that (2.26) holds. Then integrating (2.30) over (t, t+\tau) , we can deduce from (2.12) and (2.26) that (2.27) holds.

    In this section, we shall study the global existence and uniform boundedness of solutions for system (1.8) when n = 2 . To do this, we need the following lemmas.

    Lemma 3.1. Let the conditions of Theorem 1.1 hold. Then the solution (u, v, w) of system (1.8) satisfies

    \begin{equation} \begin{split} \int_{\Omega}u^{2}dx+\int_{\Omega}v^{2}dx\leq C \end{split} \end{equation} (3.1)

    and

    \begin{equation} \begin{split} ||w(\cdot,t)||_{W^{1,q}(\Omega)}\leq C \end{split} \end{equation} (3.2)

    for all q\in[1, \infty) and t\in(0, T_{\max}) , where C > 0 is a constant independent of t .

    Proof. Multiplying the first equation of System (1.8) by 2u and integrating by parts, we deduce from Young's and Hölder's inequalities that

    \begin{equation} \begin{split} \frac{\text{d}}{\text{dt}}\int_{\Omega}u^{2}dx& = -2\int_{\Omega}d_{1}(w)|\nabla u|^{2}dx-2\int_{\Omega}d'_{1}(w)u\nabla u\cdot\nabla wdx\\ &\quad+2\gamma_{1}\int_{\Omega}u^{2}F_{1}(w)dx-2\int_{\Omega}u^{2}h_{1}(u)dx-2\beta_{1}\int_{\Omega}u^{2}vdx\\ &\leq-\int_{\Omega}d_{1}(w)|\nabla u|^{2}dx+\int_{\Omega}\frac{|d'_{1}(w)|^{2}}{d_{1}(w)}u^{2}|\nabla w|^{2}dx+2\gamma_{1}F_{1}(K_{0})\int_{\Omega}u^{2}dx\\ &\leq -d_{1}(K_{0})\int_{\Omega}|\nabla u|^{2}dx+\mathcal{K}_{1}\int_{\Omega}u^{2}|\nabla w|^{2}dx+2\gamma_{1}F_{1}(K_{0})\int_{\Omega}u^{2}dx\\ &\leq -d_{1}(K_{0})\int_{\Omega}|\nabla u|^{2}dx+\mathcal{K}_{1}\left(\int_{\Omega}u^{4}dx\right)^{\frac{1}{2}}\left(\int_{\Omega}|\nabla w|^{4}dx\right)^{\frac{1}{2}}\\&\quad+2\gamma_{1}F_{1}(K_{0})\int_{\Omega}u^{2}dx, \end{split} \end{equation} (3.3)

    where \mathcal{K}_{1}: = \max_{w\in[0, K_{0}]}\frac{|d'_{1}(w)|^{2}}{d_{1}(w)} and we have applied ( H_{1} )–( H_{3} ) and (2.1).

    By using the Gagliardo-Nirenberg inequality in two dimensions, there exists a C_{1} > 0 such that

    \begin{equation} \begin{split} \left(\int_{\Omega}u^{4}dx\right)^{\frac{1}{2}} = ||u||_{L^{4}(\Omega)}^{2}\leq C_{1}(||\nabla u||_{L^{2}(\Omega)}||u||_{L^{2}(\Omega)}+||u||_{L^{2}(\Omega)}^{2}). \end{split} \end{equation} (3.4)

    According to Lemma 2.5 of [19] when n = 2 , it follows from Lemma 2.5 that

    \begin{equation} \begin{split} \left(\int_{\Omega}|\nabla w|^{4}dx\right)^{\frac{1}{2}}&\leq C_{2}(||\Delta w||_{L^{2}(\Omega)}||\nabla w||_{L^{2}(\Omega)}+||\nabla w||_{L^{2}(\Omega)}^{2})\\ &\leq C_{3}(||\Delta w||_{L^{2}(\Omega)}+1), \end{split} \end{equation} (3.5)

    for all t\in(0, T_{\max}) , where C_{2}, C_{3} > 0 . Thus, by combining (3.4) with (3.5), we infer from Young's inequality that

    \begin{equation} \begin{split} \mathcal{K}_{1}\left(\int_{\Omega}u^{4}dx\right)^{\frac{1}{2}}\left(\int_{\Omega}|\nabla w|^{4}dx\right)^{\frac{1}{2}}&\leq d_{1}(K_{0})\int_{\Omega}|\nabla u|^{2}dx +C_{4}||u||_{L^{2}(\Omega)}^{2}||\Delta w||_{L^{2}(\Omega)}^{2}\\&\quad+C_{5}||u||_{L^{2}(\Omega)}^{2}, \end{split} \end{equation} (3.6)

    where C_{4}, C_{5} are positive constants. Thus it follows from (3.3) and (3.6) that

    \begin{equation} \begin{split} \frac{\text{d}}{\text{dt}}\int_{\Omega}u^{2}dx\leq C_{6}\int_{\Omega}u^{2}dx\left(\int_{\Omega}|\Delta w|^{2}dx+1\right), \end{split} \end{equation} (3.7)

    where C_{6}: = \max\{C_{4}, C_{5}+2\gamma_{1}F_{1}(K_{0})\} .

    By Lemma 2.4, we can find t_{0} = t_{0}(t)\in((t-\tau)_{+}, t) for any t\in(0, T_{\max}) such that there exists a C_{7} > 0 satisfying

    \begin{equation} \begin{split} \int_{\Omega}u^{2}(x,t_{0})dx\leq C_{7}, \end{split} \end{equation} (3.8)

    where \tau is defined in Lemma 2.4. It follows from Lemma 2.5 that there exists a C_{8} > 0 such that

    \begin{equation} \begin{split} \int_{t_{0}}^{t_{0}+\tau}\int_{\Omega}|\Delta w(x,t)|^{2}dxdt\leq C_{8}. \end{split} \end{equation} (3.9)

    Therefore, integrating (3.7) over (t_{0}, t) , we deduce from t_{0} < t < t_{0}+\tau\leq t_{0}+1 , (3.8) and (3.9) that

    \begin{equation} \begin{split} \int_{\Omega}u^{2}dx\leq \int_{\Omega}u^{2}(x,t_{0})dx e^{C_{6}\int_{t_{0}}^{t}\left(\int_{\Omega}|\Delta w|^{2}dx+1\right)ds}\leq C_{7}e^{C_{6}(C_{8}+1)} \end{split} \end{equation} (3.10)

    for all t\in(0, T_{\max}) .

    Similarly, we obtain

    \begin{equation} \begin{split} \int_{\Omega}v^{2}dx \leq C_{9} \quad\text{for all}\;\;t\in(0,T_{\max}). \end{split} \end{equation} (3.11)

    It follows from the third equation of System (1.8), we know that w solves the following problem

    \begin{eqnarray} \left\{ \begin{split}{} &w_t = D\Delta w-w+g(u,v,w),&(x,t)\in \Omega\times (0,T_{\max}),\\ &\frac{\partial w}{\partial\nu} = 0,&(x,t)\in \partial\Omega\times (0,T_{\max}), \end{split} \right. \end{eqnarray} (3.12)

    where g(u, v, w) = w-uF_{1}(w)-vF_{2}(w)+f(w) . According to ( H_{2} ), ( H_{3} ) and (2.1), we infer from (3.10) and (3.11) that

    \begin{equation} \begin{split} ||g(u,v,w)||_{L^{2}(\Omega)}\leq C_{10}(||u||_{L^{2}(\Omega)}+||v||_{L^{2}(\Omega)}+1)\leq C_{11} \end{split} \end{equation} (3.13)

    for all t\in(0, T_{\max}) . Hence, it follows from Lemma 2.2 in two dimensions that (3.2) holds. The proof of Lemma 3.1 is complete.

    Next, we shall prove the boundedness of w in W^{1\infty}(\Omega) .

    Lemma 3.2. Let the conditions of Theorem 1.1 hold. Then the solution component w of system (1.8) satisfies

    \begin{equation} \begin{split} ||w(\cdot,t)||_{W^{1,\infty}(\Omega)}\leq C \end{split} \end{equation} (3.14)

    for all t\in(0, T_{\max}) , where C > 0 is a constant independent of t .

    Proof. Multiplying the first equation of System (1.8) by u^{2} and integrating by parts, we deduce from Young's and Hölder's inequalities that

    \begin{equation} \begin{split} \frac{1}{3}\frac{\text{d}}{\text{dt}}\int_{\Omega}u^{3}dx& = -2\int_{\Omega}d_{1}(w)u|\nabla u|^{2}dx-2\int_{\Omega}d'_{1}(w)u^{2}\nabla u\cdot\nabla wdx\\ &\quad+\gamma_{1}\int_{\Omega}u^{3}F_{1}(w)dx-\int_{\Omega}u^{3}h_{1}(u)dx-\beta_{1}\int_{\Omega}u^{3}vdx\\ &\leq-\int_{\Omega}d_{1}(w)u|\nabla u|^{2}dx+\int_{\Omega}\frac{|d'_{1}(w)|^{2}}{d_{1}(w)}u^{3}|\nabla w|^{2}dx\\&\quad+\gamma_{1}F_{1}(K_{0})\int_{\Omega}u^{3}dx-\theta_{1}\int_{\Omega}u^{3}dx\\ &\leq -\frac{4d_{1}(K_{0})}{9}\int_{\Omega}|\nabla u^{\frac{3}{2}}|^{2}dx+\mathcal{K}_{1}\int_{\Omega}u^{3}|\nabla w|^{2}dx\\&\quad+\gamma_{1}F_{1}(K_{0})\int_{\Omega}u^{3}dx-\theta_{1}\int_{\Omega}u^{3}dx\\ &\leq -\frac{4d_{1}(K_{0})}{9}\int_{\Omega}|\nabla u^{\frac{3}{2}}|^{2}dx+\mathcal{K}_{1}\left(\int_{\Omega}u^{6}dx\right)^{\frac{1}{2}}\left(\int_{\Omega}|\nabla w|^{4}dx\right)^{\frac{1}{2}}\\&\quad+\gamma_{1}F_{1}(K_{0})\int_{\Omega}u^{3}dx-\theta_{1}\int_{\Omega}u^{3}dx, \end{split} \end{equation} (3.15)

    for all t\in(0, T_{\max}) , where \mathcal{K}_{1} is defined in the proof of Lemma 3.1 and we have applied ( H_{1} )–( H_{3} ) and (2.1).

    It follows from Lemma 3.1 that there exist positive constants C_{1} and C_{2} such that ||\nabla w||_{L^{4}(\Omega)}\leq C_{1} and ||u||_{L^{2}(\Omega)}\leq C_{2} for all t\in(0, T_{\max}) . Then by using the Gagliardo-Nirenberg inequality and Young's inequality, we can find positive constants C_{i} , i = 3, \cdot\cdot\cdot, 6 such that

    \begin{equation} \begin{split} \mathcal{K}_{1}\left(\int_{\Omega}u^{6}dx\right)^{\frac{1}{2}}\left(\int_{\Omega}|\nabla w|^{4}dx\right)^{\frac{1}{2}}&\leq\mathcal{K}_{1}C_{1}^{2}||u^{\frac{3}{2}}||_{L^{4}(\Omega)}^{2}\\ &\leq C_{3}\left(||\nabla u^{\frac{3}{2}}||_{L^{2}(\Omega)}^{\frac{4}{3}}\cdot||u^{\frac{3}{2}}||_{L^{\frac{4}{3}}(\Omega)}^{\frac{2}{3}}+||u^{\frac{3}{2}}||_{L^{\frac{4}{3}}(\Omega)}^{2}\right)\\ &\leq\frac{2d_{1}(K_{0})}{9}\int_{\Omega}|\nabla u^{\frac{3}{2}}|^{2}dx+C_{4} \end{split} \end{equation} (3.16)

    and

    \begin{equation} \begin{split} \gamma_{1}F_{1}(K_{0})\int_{\Omega}u^{3}dx&\leq\gamma_{1}F_{1}(K_{0})||u^{\frac{3}{2}}||_{L^{2}(\Omega)}^{2}\\ &\leq C_{5}\left(||\nabla u^{\frac{3}{2}}||_{L^{2}(\Omega)}^{\frac{2}{3}}\cdot||u^{\frac{3}{2}}||_{L^{\frac{4}{3}}(\Omega)}^{\frac{4}{3}}+||u^{\frac{3}{2}}||_{L^{\frac{4}{3}}(\Omega)}^{2}\right)\\ &\leq\frac{2d_{1}(K_{0})}{9}\int_{\Omega}|\nabla u^{\frac{3}{2}}|^{2}dx+C_{6} \end{split} \end{equation} (3.17)

    for all t\in(0, T_{\max}) .

    Combining (3.15)–(3.17), we have

    \begin{equation} \begin{split} \frac{\text{d}}{\text{dt}}\int_{\Omega}u^{3}dx+3\theta_{1}\int_{\Omega}u^{3}dx\leq C_{7}: = 3(C_{4}+C_{6}) \end{split} \end{equation} (3.18)

    for all t\in(0, T_{\max}) . By the ODE argument, we can derive

    \begin{equation} \begin{split} \int_{\Omega}u^{3}dx\leq \max\left\{\int_{\Omega}u_{0}^{3}dx,\frac{C_{7}}{3\theta_{1}}\right\} \quad \text{for all}\;\;t\in (0,T_{\max}). \end{split} \end{equation} (3.19)

    Similarly, we also derive the boundedness of ||v||_{L^{3}(\Omega)} . Then it follows from Lemma 2.2 in two dimensions that (3.14) holds.

    By means of the boundedness of ||w(\cdot, t)||_{W^{1, \infty}(\Omega)} , it follows from the Moser iteration of [45] that we can obtain the boundedness of ||u(\cdot, t)||_{L^{\infty}(\Omega)} and ||v(\cdot, t)||_{L^{\infty}(\Omega)} for all t\in(0, T_{\max}) .

    Lemma 3.3. Let the conditions of Theorem 1.1 hold. Then the solution component (u, v) of system (1.8) satisfies

    \begin{equation} \begin{split} ||u(\cdot,t)||_{L^{\infty}(\Omega)}+||v(\cdot,t)||_{L^{\infty}(\Omega)}\leq C \end{split} \end{equation} (3.20)

    for all t\in(0, T_{\max}) , where C > 0 is a constant independent of t .

    Proof. Multiplying the first equation of System (1.8) by u^{p-1} with p\geq2 and integrating by parts, we deduce from Young's inequality that

    \begin{equation} \begin{split} \frac{1}{p}\frac{\text{d}}{\text{dt}}\int_{\Omega}u^{p}dx& = -(p-1)\int_{\Omega}d_{1}(w)u^{p-2}|\nabla u|^{2}dx-(p-1)\int_{\Omega}d'_{1}(w)u^{p-1}\nabla u\cdot\nabla wdx\\ &\quad+\gamma_{1}\int_{\Omega}u^{p}F_{1}(w)dx-\int_{\Omega}u^{p}h_{1}(u)dx-\beta_{1}\int_{\Omega}u^{p}vdx\\ &\leq-\frac{p-1}{2}\int_{\Omega}d_{1}(w)u^{p-2}|\nabla u|^{2}dx+\frac{p-1}{2}\int_{\Omega}\frac{|d'_{1}(w)|^{2}}{d_{1}(w)}u^{p}|\nabla w|^{2}dx\\&\quad+\gamma_{1}F_{1}(K_{0})\int_{\Omega}u^{p}dx\\ &\leq -\frac{p-1}{2}d_{1}(K_{0})\int_{\Omega}u^{p-2}|\nabla u|^{2}dx+\frac{p-1}{2}\mathcal{K}_{1}\int_{\Omega}u^{p}|\nabla w|^{2}dx\\&\quad+\gamma_{1}F_{1}(K_{0})\int_{\Omega}u^{p}dx \end{split} \end{equation} (3.21)

    for all t\in(0, T_{\max}) , where \mathcal{K}_{1} is defined in the proof of Lemma 3.1 and we have applied ( H_{1} )–( H_{3} ) and (2.1).

    It follows from Lemma 3.2 that there exists a C_{1} > 0 such that ||\nabla w(\cdot, t)||_{L^{\infty}(\Omega)}\leq C_{1} for all t\in (0, T_{\max}) . Hence, we deduce from (3.21) that

    \begin{equation} \begin{split} &\frac{\text{d}}{\text{dt}}\int_{\Omega}u^{p}dx+\frac{p(p-1)d_{1}(K_{0})}{2}\int_{\Omega}u^{p-2}|\nabla u|^{2}dx+p(p-1)\int_{\Omega}u^{p}dx\\ &\qquad\leq C_{2}p(p-1)\int_{\Omega}u^{p}dx, \end{split} \end{equation} (3.22)

    for all t\in(0, T_{\max}) , where C_{2}: = \frac{\mathcal{K}_{1}C_{1}^{2}}{2}+\gamma_{1}F_{1}(K_{0})+1 is independent of p . The rest can be handled exactly as the Moser iteration in Lemma 2.7 of [45] to derive the boundedness of ||u(\cdot, t)||_{L^{\infty}(\Omega)} for all t\in(0, T_{\max}) . Similarly, we can obtain the boundedness of ||v(\cdot, t)||_{L^{\infty}(\Omega)} for all t\in(0, T_{\max}) . The proof of Lemma 3.3 is complete.

    Proof of Theorem 1.1. Theorem 1.1 is a direct consequence of Lemma 2.1, Lemma 3.2 and Lemma 3.3.

    In this section, we shall study the asymptotic stability of global bounded solutions for System (1.11) by constructing energy functionals used in [13,57]. To do this, we first give some regularity results of the solution (u, v, w) for System (1.11).

    Lemma 4.1. Let (u, v, w) be a global bounded classical solution for (1.11) ensured in Theorem 1.1. Then there exist \sigma\in(0, 1) and C > 0 such that

    \begin{equation} \begin{split} ||u||_{C^{\sigma,\frac{\sigma}{2}}(\overline{\Omega}\times [t,t+1])}+||v||_{C^{\sigma,\frac{\sigma}{2}}(\overline{\Omega}\times [t,t+1])}+||w||_{C^{2+\sigma,1+\frac{\sigma}{2}}(\overline{\Omega}\times [t,t+1])}\leq C\quad{for \;all}\;\;t > 1. \end{split} \end{equation} (4.1)

    Proof. This lemma can be verified by a similar argument in Lemma 4.1 of [14], so we omit the details here for brevity.

    Lemma 4.2. Let (u, v, w) be a global bounded classical solution for (1.11) ensured in Theorem 1.1. Then there exists a C > 0 such that

    \begin{equation} \begin{split} ||u(\cdot,t)||_{W^{1,4}(\Omega)}+||v(\cdot,t)||_{W^{1,4}(\Omega)}\leq C\quad{for \;all}\;\;t > 0. \end{split} \end{equation} (4.2)

    Proof. This lemma can be verified by a similar argument in Lemma 3.6 of [45], so we omit the details here for brevity.

    In order to prove the asymptotic stabilization of global bounded solutions for system (1.11), we provide the following lemma, which is proved in [57].

    Lemma 4.3. Let \phi:(1, \infty)\rightarrow [0, \infty) be uniformly continuous such that \int_{1}^{\infty}\phi(t)dt < \infty . Then

    \begin{equation} \phi(t)\rightarrow 0\;\;{as}\;\;t\rightarrow \infty. \end{equation} (4.3)

    In this subsection, we are devoted to studying the stabilization of the coexistence steady state (u^{*}, v^{*}, w^{*}) for some parameters cases. Let us introduce the following functionals

    \begin{aligned} \mathcal{E}_{1}(t) = &\frac{1}{\gamma_{1}}\int_{\Omega}\left(u-u^{*}-u^{*} \ln \frac{u }{u^{*}}\right)dx+\frac{1}{\gamma_{2}}\int_{\Omega}\left(v-v^{*}-v^{*} \ln \frac{v }{v^{*}}\right)dx \\ &+\int_{\Omega}\left(w-w^{*}-w^{*} \ln \frac{w }{w^{*}}\right)dx,\\ \end{aligned}

    and

    \begin{aligned} \mathcal{F}_{1}(t) = &\int_{\Omega}\left(u -u^{*}\right)^{2}dx+\int_{\Omega}\left(v -v^{*}\right)^{2}dx+ \int_{\Omega}\left(w-w^{*}\right)^{2}dx\\ &+\int_\Omega {{{\left| {\frac{{\nabla u}}{u}} \right|}^2}}dx+\int_\Omega{{{\left| {\frac{{\nabla v}}{v}} \right|}^2}}dx+\int_\Omega {{{\left| {\nabla w} \right|}^2}}dx, \end{aligned}

    where (u^{*}, v^{*}, w^{*}) is given by (1.14).

    Lemma 4.4. Let the conditions of Theorem 1.2 hold. Then there exists a positive constant \varepsilon_{1} independent of t such that

    \begin{equation} \begin{aligned} \mathcal{E}_{1}(t) \geq 0 \end{aligned} \end{equation} (4.4)

    and

    \begin{equation} \begin{aligned} \frac{\text{d}}{\text{dt}} \mathcal{E}_{1}(t) \leq-\varepsilon_{1} \mathcal{F}_{1}(t) \;\;\;{for\; all\; t > 0 } . \end{aligned} \end{equation} (4.5)

    Proof. Let

    \begin{array}{l} I_{1}(t): = \frac{1}{\gamma_{1}}\int_{\Omega}\left(u-u^{*}-u^{*} \ln \frac{u}{u^{*}}\right)dx, \\ I_{2}(t): = \frac{1}{\gamma_{2}}\int_{\Omega}\left(v-v^{*}-v^{*} \ln \frac{v}{v^{*}}\right)dx, \\ I_{3}(t): = \int_{\Omega}\left(w-w^{*}-w^{*} \ln \frac{w }{w^{*}}\right)dx, \end{array}

    then \mathcal{E}_{1}(t) can be rewritten as

    \mathcal{E}_{1}(t) = I_{1}(t)+I_{2}(t)+I_{3}(t)\quad\text{for all}\;\;t > 0.

    Step 1: We shall prove the nonnegativity of \mathcal{E}_{1}(t) for all t > 0 . Let H(\xi): = \xi-u^{*}\ln \xi for \xi > 0 ; it follows from Taylor's formula for all x \in \Omega and each t > 0 that there exists a \tau = \tau(x, t) \in(0, 1) such that

    \begin{aligned} u-u^{*}-u^{*} \ln \frac{u}{u^{*}}& = H(u)-H\left(u^{*}\right) \\ & = H^{\prime}\left(u^{*}\right) \cdot\left(u-u^{*}\right)+\frac{1}{2} H^{\prime \prime}\left(\tau u+(1-\tau) u^{*}\right) \cdot\left(u-u^{*}\right)^{2} \\ & = \frac{u^{*}}{2\left(\tau u+(1-\tau) u^{*}\right)^{2}}\left(u-u^{*}\right)^{2} \geq 0. \end{aligned}

    Hence, we immediately derive that I_{1}(t) = \int_{\Omega}\left(H(u)-H\left(u^{*}\right)\right)dx \geq 0 . Similarly, we know that I_{2}(t) \geq 0 and I_{3}(t) \geq 0 for all t > 0 . Thus, we know that (4.4) holds.

    Step 2: Now, we further prove (4.5). By a series of simple calculations, we get

    \begin{equation} \begin{aligned} \frac{\text{d}}{\text{dt}} I_{1}(t)& = \frac{1}{\gamma_{1}}\int_{\Omega}\frac{u-u^{*}}{u}u_{t}dx\\ & = \frac{1}{\gamma_{1}}\int_{\Omega}\frac{u-u^{*}}{u}(\Delta (d_{1}(w)u)+\gamma_{1}uw-u(\theta+\alpha_{1} u)-\beta_{1}uv)dx\\ & = -\frac{u^{*}}{\gamma_{1}}\int_{\Omega}\frac{d_{1}(w)|\nabla u|^{2}}{u^{2}}dx-\frac{u^{*}}{\gamma_{1}}\int_{\Omega}\frac{d'_{1}(w)\nabla u\cdot\nabla w}{u}dx\\&\quad +\frac{1}{\gamma_{1}}\int_{\Omega}(u-u^{*})(\gamma_{1}w-\theta-\alpha_{1}u-\beta_{1}v)dx\\ & = -\frac{u^{*}}{\gamma_{1}}\int_{\Omega}\frac{d_{1}(w)|\nabla u|^{2}}{u^{2}}dx-\frac{u^{*}}{\gamma_{1}}\int_{\Omega}\frac{d'_{1}(w)\nabla u\cdot\nabla w}{u}dx\\&\quad +\int_{\Omega}(u-u^{*})(w-w^{*})dx-\frac{\alpha_{1}}{\gamma_{1}}\int_{\Omega}(u-u^{*})^{2}dx\\&\quad-\frac{\beta_{1}}{\gamma_{1}}\int_{\Omega}(u-u^{*})(v-v^{*})dx, \end{aligned} \end{equation} (4.6)

    where we have used the fact that \theta = \gamma_{1}w^{*}-\alpha_{1}u^{*}-\beta_{1}v^{*} .

    Similarly, it follows from the identities \theta = \gamma_{2}w^{*}-\beta_{2}u^{*}-\alpha_{2}v^{*} and \mu = u^{*}+v^{*}+\mu w^{*} that

    \begin{equation} \begin{aligned} \frac{\text{d}}{\text{dt}} I_{2}(t) & = -\frac{v^{*}}{\gamma_{2}}\int_{\Omega}\frac{d_{2}(w)|\nabla v|^{2}}{v^{2}}dx-\frac{v^{*}}{\gamma_{2}}\int_{\Omega}\frac{d'_{2}(w)\nabla v\cdot\nabla w}{v}dx\\&\quad +\int_{\Omega}(v-v^{*})(w-w^{*})dx-\frac{\alpha_{2}}{\gamma_{2}}\int_{\Omega}(v-v^{*})^{2}dx\\&\quad-\frac{\beta_{2}}{\gamma_{2}}\int_{\Omega}(v-v^{*})(u-u^{*})dx, \end{aligned} \end{equation} (4.7)

    and

    \begin{equation} \begin{aligned} \frac{\text{d}}{\text{dt}} I_{3}(t) & = -Dw^{*}\int_{\Omega}\frac{|\nabla w|^{2}}{w^{2}}dx- \int_{\Omega}(w-w^{*})(u-u^{*})dx-\int_{\Omega}(w-w^{*})(v-v^{*})dx\\&\quad-\mu\int_{\Omega}(w-w^{*})^{2}dx. \end{aligned} \end{equation} (4.8)

    Hence, by combining (4.6)–(4.8), we derive

    \begin{equation} \begin{aligned} \frac{\text{d}}{\text{dt}}\mathcal{E}_{1}(t)& = -\frac{\alpha_{1}}{\gamma_{1}}\int_{\Omega}(u-u^{*})^{2}dx -\frac{\alpha_{2}}{\gamma_{2}}\int_{\Omega}(v-v^{*})^{2}dx-\mu\int_{\Omega}(w-w^{*})^{2}dx\\&\quad -\left(\frac{\beta_{1}}{\gamma_{1}}+\frac{\beta_{2}}{\gamma_{2}}\right)\int_{\Omega}(u-u^{*})(v-v^{*})dx-\frac{u^{*}}{\gamma_{1}}\int_{\Omega}\frac{d_{1}(w)|\nabla u|^{2}}{u^{2}}dx\\&\quad-\frac{v^{*}}{\gamma_{2}}\int_{\Omega}\frac{d_{2}(w)|\nabla v|^{2}}{v^{2}}dx-Dw^{*}\int_{\Omega}\frac{|\nabla w|^{2}}{w^{2}}dx-\frac{u^{*}}{\gamma_{1}}\int_{\Omega}\frac{d'_{1}(w)\nabla u\cdot\nabla w}{u}dx\\ &\quad-\frac{v^{*}}{\gamma_{2}}\int_{\Omega}\frac{d'_{2}(w)\nabla v\cdot\nabla w}{v}dx\\ &: = -\int_{\Omega}X_{1}A_{1}X_{1}^{T}dx-\int_{\Omega}Y_{1}B_{1}Y_{1}^{T}dx, \end{aligned} \end{equation} (4.9)

    where X_{1} = (u-u^{*}, v-v^{*}, w-w^{*}) and Y_{1} = \left(\frac{\nabla u}{u}, \frac{\nabla v}{v}, \nabla w\right) , as well as

    \begin{equation} A_{1} = \left( \begin{array}{ccc} \frac{\alpha_{1}}{\gamma_{1}} &\frac{1}{2}\left(\frac{\beta_{1}}{\gamma_{1}}+\frac{\beta_{2}}{\gamma_{2}}\right) &0\\ \frac{1}{2}\left(\frac{\beta_{1}}{\gamma_{1}}+\frac{\beta_{2}}{\gamma_{2}}\right) &\frac{\alpha_{2}}{\gamma_{2}} &0\\ 0&0&\mu \end{array} \right), B_{1} = \left( \begin{array}{ccc} \frac{u^{*}d_{1}(w)}{\gamma_{1}} &0 &\frac{u^{*}d'_{1}(w)}{2\gamma_{1}}\\ 0 &\frac{v^{*}d_{2}(w)}{\gamma_{2}} &\frac{v^{*}d'_{2}(w)}{2\gamma_{2}}\\ \frac{u^{*}d'_{1}(w)}{2\gamma_{1}}&\frac{v^{*}d'_{2}(w)}{2\gamma_{2}}&\frac{Dw^{*}}{w^{2}} \end{array} \right). \end{equation} (4.10)

    It follows from (1.20) that

    \begin{equation} \begin{split} \left|\frac{\alpha_{1}}{\gamma_{1}}\right| > 0 \quad\text{and}\quad\left|\begin{matrix} \frac{\alpha_{1}}{\gamma_{1}} & \frac{1}{2}\left(\frac{\beta_{1}}{\gamma_{1}}+\frac{\beta_{2}}{\gamma_{2}}\right)\\ \frac{1}{2}\left(\frac{\beta_{1}}{\gamma_{1}}+\frac{\beta_{2}}{\gamma_{2}}\right) & \frac{\alpha_{2}}{\gamma_{2}} \end{matrix}\right| = \frac{\alpha_{1}\alpha_{2}}{\gamma_{1}\gamma_{2}}-\frac{1}{4}\left(\frac{\beta_{1}}{\gamma_{1}}+\frac{\beta_{2}}{\gamma_{2}}\right)^{2} > 0 \end{split} \end{equation} (4.11)

    as well as

    \begin{equation} |A_{1}| = \mu\left( \frac{\alpha_{1}\alpha_{2}}{\gamma_{1}\gamma_{2}}-\frac{1}{4}\left(\frac{\beta_{1}}{\gamma_{1}}+\frac{\beta_{2}}{\gamma_{2}}\right)^{2}\right) > 0, \end{equation} (4.12)

    which implies that the matrix A_{1} is positive definite as according to Sylvester's criterion. Similarly, we deduce from (1.21) that

    \begin{equation} \begin{split} \left|\frac{u^{*}d_{1}(w)}{\gamma_{1}}\right| > 0 \quad\text{and}\quad\left|\begin{matrix} \frac{u^{*}d_{1}(w)}{\gamma_{1}} & 0\\ 0 & \frac{v^{*}d_{2}(w)}{\gamma_{2}} \end{matrix}\right| = \frac{u^{*}v^{*}d_{1}(w)d_{2}(w)}{\gamma_{1}\gamma_{2}} > 0 \end{split} \end{equation} (4.13)

    as well as

    \begin{equation} \begin{split} |B_{1}| = \frac{u^{*}v^{*}w^{*}d_{1}(w)d_{2}(w)}{\gamma_{1}\gamma_{2}w^{2}}\left(D-\frac{u^{*}w^{2}|d'_{1}(w)|^{2}}{4\gamma_{1}w^{*}d_{1}(w)} -\frac{v^{*}w^{2}|d'_{2}(w)|^{2}}{4\gamma_{2}w^{*}d_{2}(w)}\right) > 0, \end{split} \end{equation} (4.14)

    which implies that the matrix B_{1} is positive definite. Thus there exist positive constants \kappa_{1} and \kappa_{2} such that

    \begin{equation} \begin{split} X_{1}A_{1}X_{1}^{T}\geq \kappa_{1}|X_{1}|^{2}\quad\text{and}\quad Y_{1}B_{1}Y_{1}^{T}\geq \kappa_{2}|Y_{1}|^{2} \end{split} \end{equation} (4.15)

    for all x\in \Omega and t > 0 . Let \varepsilon_{1}: = \min\{\kappa_{1}, \kappa_{2}\} , we have

    \begin{equation} \begin{split} \frac{\text{d}}{\text{dt}}\mathcal{E}_{1}(t)\leq-\varepsilon_{1}\int_{\Omega}|X_{1}|^{2}+|Y_{1}|^{2}dx\quad\text{for all}\;\;t > 0, \end{split} \end{equation} (4.16)

    which implies that (4.5) holds. The proof of Lemma 4.4 is complete.

    With the aid of Lemma 4.4, we shall give the following large time behavior of global solutions for system (1.11).

    Lemma 4.5. Let the assumptions of Theorem 1.2 hold. Then the global bounded solution of (1.11) converges to the coexistence steady state (u^{*}, v^{*}, w^{*}) given by (1.14), i.e.,

    \begin{equation} ||u(\cdot,t)-u^{*}||_{L^{\infty}(\Omega)}+||v(\cdot,t)-v^{*}||_{L^{\infty}(\Omega)}+||w(\cdot,t)-w^{*}||_{L^{\infty}(\Omega)}\rightarrow 0 \end{equation} (4.17)

    as t\rightarrow \infty .

    Proof. It follows from Lemma 4.4 and integration over (1, \infty) that

    \int_{1}^{\infty} \mathcal{F}_{1}(t) d t \leq \frac{\mathcal{E}_{1}(1)}{\varepsilon_{1}} < \infty.

    According to Theorem 1.1 and Lemma 4.1, the bounded solution u, v and w are Hölder continuous in \bar{\Omega} \times[t, t+1] with respect to t > 1 . Thus we conclude that \mathcal{F}_{1}(t) is uniformly continuous in (1, \infty) . Thus we infer from Lemma 4.3 that

    \begin{equation} \begin{aligned} \int_{\Omega}\left(u-u^{*}\right)^{2}dx+\int_{\Omega}\left(v-v^{*}\right)^{2}dx+\int_{\Omega}\left(w-w^{*}\right)^{2}dx\rightarrow 0 \end{aligned} \end{equation} (4.18)

    as t \rightarrow \infty . By the Gagliardo-Nirenberg inequality in two dimensions, there exists a C_{1} > 0 such that

    \left\|u-u^{*}\right\|_{L^{\infty}(\Omega)} \leq C_{1}\left\|u-u^{*}\right\|_{W^{1, 4}(\Omega)}^{\frac{2}{3}}\left\|u-u^{*}\right\|_{L^{2}(\Omega)}^{\frac{1}{3}}.

    Moreover, it follows from Lemma 4.2 that u(\cdot, t)-u^{*} is bounded in W^{1, 4}(\Omega) ; thus, we conclude from (4.18) that u(\cdot, t) \rightarrow u^{*} in L^{\infty}(\Omega) as t \rightarrow \infty . By the similar arguments for v and w , we derive (4.17). The proof of Lemma 4.5 is complete.

    Now, we give the convergence rate of the coexistence state (u^{*}, v^{*}, w^{*}) for System (1.11).

    Lemma 4.6. Let the assumptions of Theorem 1.2 hold; the global bounded solution (u, v, w) of (1.11) exponentially converges to the coexistence state (u^{*}, v^{*}, w^{*}) , i.e. there exist C > 0 and \lambda > 0 such that

    \begin{equation} ||u(\cdot,t)-u^{*}||_{L^{\infty}(\Omega)}+||v(\cdot,t)-v^{*}||_{L^{\infty}(\Omega)}+||w(\cdot,t)-w^{*}||_{L^{\infty}(\Omega)}\leq Ce^{-\lambda t} \end{equation} (4.19)

    for all t > T_{1} , where T_{1} > 0 is some fixed time.

    Proof. It follows from Lemma 4.5 that ||u-u^{*}||_{L^{\infty}(\Omega)}\rightarrow 0 as t\rightarrow \infty . Therefore, we apply L'Hôpital's rule to obtain

    \begin{equation} \lim\limits_{u\rightarrow u^{*}}\frac{u-u^{*}-u^{*}\ln\frac{u}{u^{*}}}{(u-u^{*})^{2}} = \frac{1}{2u^{*}}, \end{equation} (4.20)

    which implies that there exists a t_{1} > 0 such that

    \begin{equation} \begin{split} \frac{1}{4u^{*}}\int_{\Omega}(u-u^{*})^{2}dx\leq\int_{\Omega}\left(u-u^{*}-u^{*}\ln\frac{u}{u^{*}}\right)dx\leq\frac{3}{4u^{*}}\int_{\Omega}(u-u^{*})^{2}dx \end{split} \end{equation} (4.21)

    for all t > t_{1} . Similarly, we can find t_{2} > 0 satisfying

    \begin{equation} \begin{split} \frac{1}{4v^{*}}\int_{\Omega}(v-v^{*})^{2}dx\leq\int_{\Omega}\left(v-v^{*}-v^{*}\ln\frac{v}{v^{*}}\right)dx\leq\frac{3}{4v^{*}}\int_{\Omega}(v-v^{*})^{2}dx \end{split} \end{equation} (4.22)

    and

    \begin{equation} \begin{split} \frac{1}{4w^{*}}\int_{\Omega}(w-w^{*})^{2}dx\leq\int_{\Omega}\left(w-w^{*}-w^{*}\ln\frac{w}{w^{*}}\right)dx\leq\frac{3}{4w^{*}}\int_{\Omega}(w-w^{*})^{2}dx \end{split} \end{equation} (4.23)

    for all t > t_{2} . Let T_{1}: = \max\{t_{1}, t_{2}\} ; by means of the definitions of \mathcal{E}_{1}(t) and \mathcal{F}_{1}(t) , it follows from the second inequalities in (4.21)–(4.23) that there exists a C_{1} > 0 such that

    \begin{equation} C_{1}\mathcal{E}_{1}(t)\leq \mathcal{F}_{1}(t)\;\;\text{for all}\; \;t > T_{1}. \end{equation} (4.24)

    By Lemma 4.4, we derive

    \begin{equation} \mathcal{E}_{1}'(t)\leq -\varepsilon_{1} \mathcal{F}_{1}(t)\leq-\varepsilon_{1} C_{1}\mathcal{E}_{1}(t)\quad\text{for all}\;\;t > T_{1}, \end{equation} (4.25)

    which implies that there exist C_{2} > 0 and C_{3} > 0 such that

    \begin{equation} \mathcal{E}_{1}(t)\leq C_{2}e^{-C_{3}(t-T_{1})}\quad\text{for all}\;\;t > T_{1}. \end{equation} (4.26)

    Thus we deduce from the first inequalities in (4.21)–(4.23) that there exists a C_{4} > 0 such that

    \begin{equation} \begin{split} &\int_{\Omega}(u(x,t)-u^{*})^{2}dx+\int_{\Omega}(v(x,t)-v^{*})^{2}dx+\int_{\Omega}(w(x,t)-w^{*})^{2}dx\\ &\quad\leq C_{4}\mathcal{E}_{1}(t)\leq C_{2}C_{4}e^{-C_{3}(t-T_{1})}\;\;\text{for all}\;\;t > T_{1}. \end{split} \end{equation} (4.27)

    It follows from the Gagliardo-Nirenberg inequality in two dimensions, Lemma 4.2 and Lemma 3.2 that there exist positive constants C_{5} and C_{6} such that

    \begin{equation} \begin{split} &||u-u^{*}||_{L^{\infty}(\Omega)}+||v-v^{*}||_{L^{\infty}(\Omega)}+||w-w^{*}||_{L^{\infty}(\Omega)}\\ &\leq C_{5}\bigg(||u-u^{*}||_{W^{1,4}(\Omega)}^{\frac{2}{3}}||u-u^{*}||_{L^{2}(\Omega)}^{\frac{1}{3}} +||v-v^{*}||_{W^{1,4}(\Omega)}^{\frac{2}{3}}||v-v^{*}||_{L^{2}(\Omega)}^{\frac{1}{3}}\\& \quad+||w-w^{*}||_{W^{1,4}(\Omega)}^{\frac{2}{3}}||w-w^{*}||_{L^{2}(\Omega)}^{\frac{1}{3}}\bigg)\\ &\leq C_{6}\left(\int_{\Omega}(u-u^{*})^{2}dx+\int_{\Omega}(v-v^{*})^{2}dx+\int_{\Omega}(w-w^{*})^{2}dx\right)^{\frac{1}{6}}\\ &\leq C_{6}(C_{2}C_{4})^{\frac{1}{6}}e^{\frac{-C_{3}(t-T_{1})}{6}} \end{split} \end{equation} (4.28)

    for all t > T_{1} . The proof of Lemma 4.6 is complete.

    Proof of Theorem 1.2. The statement of Theorem 1.2 is a straightforward consequence of Lemma 4.6.

    In this subsection, we shall study the stabilization of the semi-trivial steady state (\overline{u}, 0, \overline{w}) or (0, \widetilde{v}, \widetilde{w}) for some parameters cases. Since the methods of the proofs of Theorem 1.3 and Theorem 1.4 are very similar, we only give the proof of Theorem 1.3 for brevity. To do this, let us introduce the following functionals

    \begin{aligned} \mathcal{E}_{2}(t) = &\frac{1}{\gamma_{1}}\int_{\Omega}\left(u-\overline{u}-\overline{u}\ln \frac{u }{\overline{u}}\right)dx+\frac{1}{\gamma_{2}}\int_{\Omega}vdx \\ &+\int_{\Omega}\left(w-\overline{w}-\overline{w}\ln \frac{w}{\overline{w}}\right)dx,\\ \end{aligned}

    and

    \begin{aligned} \mathcal{F}_{2}(t) = &\int_{\Omega}\left(u -\overline{u}\right)^{2}dx+\int_{\Omega}v^{2}dx+ \int_{\Omega}\left(w-\overline{w}\right)^{2}dx\\ &+\int_\Omega {{{\left| {\frac{{\nabla u}}{u}} \right|}^2}}dx+\int_\Omega {{{\left| {\nabla w} \right|}^2}}dx, \end{aligned}

    where \overline{u} = \frac{\mu(\gamma_{1}-\theta)}{\alpha_{1}\mu+\gamma_{1}}\; \; \text{and}\; \; \overline{w} = \frac{\alpha_{1}\mu+\theta}{\alpha_{1}\mu+\gamma_{1}} .

    Lemma 4.7. Let the conditions of Theorem 1.3 hold. Then there exists a positive constant \varepsilon_{2} independent of t such that

    \begin{equation} \begin{aligned} \mathcal{E}_{2}(t) \geq 0 \end{aligned} \end{equation} (4.29)

    and

    \begin{equation} \begin{aligned} \frac{\text{d}}{\text{dt}} \mathcal{E}_{2}(t) \leq-\varepsilon_{2} \mathcal{F}_{2}(t)-\frac{1}{\gamma_{2}}(\theta-\gamma_{2}\overline{w}+\beta_{2}\overline{u})\int_{\Omega}vdx \;\;\;{for\; all\; t > 0 }. \end{aligned} \end{equation} (4.30)

    Proof. Let

    \begin{array}{l} J_{1}(t): = \frac{1}{\gamma_{1}}\int_{\Omega}\left(u-\overline{u}- \overline{u}\ln \frac{u}{\overline{u}}\right)dx, \\ J_{2}(t): = \frac{1}{\gamma_{2}}\int_{\Omega}vdx, \\ J_{3}(t): = \int_{\Omega}\left(w-\overline{w}-\overline{w}\ln \frac{w }{\overline{w}}\right)dx, \end{array}

    then \mathcal{E}_{2}(t) can be represented as

    \mathcal{E}_{2}(t) = J_{1}(t)+J_{2}(t)+J_{3}(t)\quad\text{for all}\;\;t > 0.

    Firstly, we can prove the nonnegativity of \mathcal{E}_{2}(t) for all t > 0 by the similar arguments used in Step 1 in Lemma 4.4. For brevity, we omit the details here. Now, we shall prove (4.30). By a series of simple calculations, we get

    \begin{equation} \begin{aligned} \frac{\text{d}}{\text{dt}} J_{1}(t) & = -\frac{\overline{u}}{\gamma_{1}}\int_{\Omega}\frac{d_{1}(w)|\nabla u|^{2}}{u^{2}}dx-\frac{\overline{u}}{\gamma_{1}}\int_{\Omega}\frac{d'_{1}(w)\nabla u\cdot\nabla w}{u}dx\\&\quad +\int_{\Omega}(u-\overline{u})(w-\overline{w})dx-\frac{\alpha_{1}}{\gamma_{1}}\int_{\Omega}(u-\overline{u})^{2}dx\\&\quad -\frac{\beta_{1}}{\gamma_{1}}\int_{\Omega}(u-\overline{u})vdx, \end{aligned} \end{equation} (4.31)

    where we have used the fact that \theta = \gamma_{1}\overline{w}-\alpha_{1}\overline{u} .

    Similarly, we can derive

    \begin{equation} \begin{aligned} {\frac{\text{d}}{\text{dt}}} J_{2}(t) & = -\frac{\alpha_{2}}{\gamma_{2}}\int_{\Omega}v^{2}dx-\frac{\beta_{2}}{\gamma_{2}}\int_{\Omega}v(u-\overline{u})dx\\&\quad +\int_{\Omega}v(w-\overline{w})dx-\frac{1}{\gamma_{2}}(\theta-\gamma_{2}\overline{w}+\beta_{2}\overline{u})\int_{\Omega}vdx, \end{aligned} \end{equation} (4.32)

    and

    \begin{equation} \begin{aligned} \frac{\text{d}}{\text{dt}} J_{3}(t) & = -D\overline{w}\int_{\Omega}\frac{|\nabla w|^{2}}{w^{2}}dx- \int_{\Omega}(w-\overline{w})(u-\overline{u})dx-\int_{\Omega}(w-\overline{w})vdx\\&\quad-\mu\int_{\Omega}(w-\overline{w})^{2}dx, \end{aligned} \end{equation} (4.33)

    where we have used the fact that \mu = \overline{u}+\mu \overline{w} . Thus it follows from (4.31)–(4.33) that

    \begin{equation} \begin{aligned} \frac{\text{d}}{\text{dt}} \mathcal{E}_{2}(t)& = -\frac{\alpha_{1}}{\gamma_{1}}\int_{\Omega}(u-\overline{u})^{2}dx -\frac{\alpha_{2}}{\gamma_{2}}\int_{\Omega}v^{2}dx-\mu\int_{\Omega}(w-\overline{w})^{2}dx\\&\quad -\left(\frac{\beta_{1}}{\gamma_{1}}+\frac{\beta_{2}}{\gamma_{2}}\right)\int_{\Omega}(u-\overline{u})vdx-\frac{\overline{u}}{\gamma_{1}}\int_{\Omega}\frac{d_{1}(w)|\nabla u|^{2}}{u^{2}}dx\\&\quad-D\overline{w}\int_{\Omega}\frac{|\nabla w|^{2}}{w^{2}}dx-\frac{\overline{u}}{\gamma_{1}}\int_{\Omega}\frac{d'_{1}(w)\nabla u\cdot\nabla w}{u}dx\\ &\quad-\frac{1}{\gamma_{2}}(\theta-\gamma_{2}\overline{w}+\beta_{2}\overline{u})\int_{\Omega}vdx\\ &: = -\int_{\Omega}X_{2}A_{2}X_{2}^{T}dx-\int_{\Omega}Y_{2}B_{2}Y_{2}^{T}dx-\frac{1}{\gamma_{2}}(\theta-\gamma_{2}\overline{w}+\beta_{2}\overline{u})\int_{\Omega}vdx, \end{aligned} \end{equation} (4.34)

    where X_{2} = (u-\overline{u}, v, w-\overline{w}) and Y_{2} = \left(\frac{\nabla u}{u}, \nabla w\right) , as well as

    \begin{equation} A_{2} = \left( \begin{array}{ccc} \frac{\alpha_{1}}{\gamma_{1}} &\frac{1}{2}\left(\frac{\beta_{1}}{\gamma_{1}}+\frac{\beta_{2}}{\gamma_{2}}\right) &0\\ \frac{1}{2}\left(\frac{\beta_{1}}{\gamma_{1}}+\frac{\beta_{2}}{\gamma_{2}}\right) &\frac{\alpha_{2}}{\gamma_{2}} &0\\ 0&0&\mu \end{array} \right), B_{2} = \left( \begin{array}{ccc} \frac{\overline{u}d_{1}(w)}{\gamma_{1}} &\frac{\overline{u}d'_{1}(w)}{2\gamma_{1}}\\ \frac{\overline{u}d'_{1}(w)}{2\gamma_{1}}&\frac{D\overline{w}}{w^{2}} \end{array} \right). \end{equation} (4.35)

    It follows from (1.20) that

    \begin{equation} \begin{split} \left|\frac{\alpha_{1}}{\gamma_{1}}\right| > 0 \quad\text{and}\quad\left|\begin{matrix} \frac{\alpha_{1}}{\gamma_{1}} & \frac{1}{2}\left(\frac{\beta_{1}}{\gamma_{1}}+\frac{\beta_{2}}{\gamma_{2}}\right)\\ \frac{1}{2}\left(\frac{\beta_{1}}{\gamma_{1}}+\frac{\beta_{2}}{\gamma_{2}}\right) & \frac{\alpha_{2}}{\gamma_{2}} \end{matrix}\right| = \frac{\alpha_{1}\alpha_{2}}{\gamma_{1}\gamma_{2}}-\frac{1}{4}\left(\frac{\beta_{1}}{\gamma_{1}}+\frac{\beta_{2}}{\gamma_{2}}\right)^{2} > 0 \end{split} \end{equation} (4.36)

    as well as

    \begin{equation} |A_{2}| = \mu\left( \frac{\alpha_{1}\alpha_{2}}{\gamma_{1}\gamma_{2}}-\frac{1}{4}\left(\frac{\beta_{1}}{\gamma_{1}}+\frac{\beta_{2}}{\gamma_{2}}\right)^{2}\right) > 0, \end{equation} (4.37)

    which implies that the matrix A_{2} is positive definite as according to Sylvester's criterion. Similarly, we deduce from (1.23) that

    \begin{equation} \begin{split} \left|\frac{\overline{u}d_{1}(w)}{\gamma_{1}}\right| > 0 \quad\text{and}\quad |B_{2}| = \frac{\overline{u}\overline{w}d_{1}(w)}{\gamma_{1}w^{2}}\left(D-\frac{\overline{u}w^{2}|d'_{1}(w)|^{2}}{4\gamma_{1}\overline{w}d_{1}(w)}\right) > 0, \end{split} \end{equation} (4.38)

    which implies that the matrix B_{2} is positive definite. Thus there exist positive constants \iota_{1} and \iota_{2} such that

    \begin{equation} \begin{split} X_{2}A_{2}X_{2}^{T}\geq \iota_{1}|X_{2}|^{2}\quad\text{and}\quad Y_{2}B_{2}Y_{2}^{T}\geq \iota_{2}|Y_{2}|^{2} \end{split} \end{equation} (4.39)

    for all x\in \Omega and t > 0 . Let \varepsilon_{2}\in (0, \min\{\iota_{1}, \iota_{2}\}) ; we obtain

    \begin{equation} \begin{split} \frac{\text{d}}{\text{dt}}\mathcal{E}_{2}(t)\leq-\varepsilon_{2}\int_{\Omega}|X_{2}|^{2}+|Y_{2}|^{2}dx -\frac{1}{\gamma_{2}}(\theta-\gamma_{2}\overline{w}+\beta_{2}\overline{u})\int_{\Omega}vdx\quad\text{for all}\;\;t > 0, \end{split} \end{equation} (4.40)

    which implies that (4.30) holds. The proof of Lemma 4.7 is complete.

    With the help of Lemma 4.7, we shall give the following stabilization of the semi-trivial steady state (\overline{u}, 0, \overline{w}) for System (1.11).

    Lemma 4.8. Let the assumptions of Theorem 1.3 hold. Then the global bounded solution (u, v, w) of (1.11) converges to the semi-trivial steady state (\overline{u}, 0, \overline{w}) given by (1.24), i.e.,

    \begin{equation} ||u(\cdot,t)-\overline{u}||_{L^{\infty}(\Omega)}+||v(\cdot,t)||_{L^{\infty}(\Omega)}+||w(\cdot,t)-\overline{w}||_{L^{\infty}(\Omega)}\rightarrow 0 \end{equation} (4.41)

    as t\rightarrow \infty .

    Proof. The proof of this lemma is similar to that of Lemma 4.5; here we omit the details.

    Now, we give the convergence rate of the semi-trivial steady state (\overline{u}, 0, \overline{w}) for System (1.11).

    Lemma 4.9. Let the assumptions of Theorem 1.3 hold; then, there exist positive constants C and \lambda such that:

    (a) when \theta = \gamma_{2}\overline{w}-\beta_{2}\overline{u} , then

    \begin{equation} ||u(\cdot,t)-\overline{u}||_{L^{\infty}(\Omega)}+||v(\cdot,t)||_{L^{\infty}(\Omega)}+||w(\cdot,t)-\overline{w}||_{L^{\infty}(\Omega)}\leq C(1+t)^{-\lambda}\;\;\text{for all}\;\; t > T_{2}; \end{equation} (4.42)

    (b) when \theta > \gamma_{2}\overline{w}-\beta_{2}\overline{u} , then

    \begin{equation} ||u(\cdot,t)-\overline{u}||_{L^{\infty}(\Omega)}+||v(\cdot,t)||_{L^{\infty}(\Omega)}+||w(\cdot,t)-\overline{w}||_{L^{\infty}(\Omega)}\leq Ce^{-\lambda t}\;\;\text{for all}\;\; t > T_{2}, \end{equation} (4.43)

    where T_{2} > 0 is some fixed time.

    Proof. Let

    \begin{equation} \mathcal{F}_{2}^{*}(t): = \int_{\Omega}\left(u -\overline{u}\right)^{2}dx+\int_{\Omega}v^{2}dx+ \int_{\Omega}\left(w-\overline{w}\right)^{2}dx, \end{equation} (4.44)

    then it follows from Lemma 4.7 that there exists a \varepsilon_{2} > 0 such that

    \begin{equation} \begin{aligned} \frac{\text{d}}{\text{dt}} \mathcal{E}_{2}(t) \leq-\varepsilon_{2} \mathcal{F}_{2}^{*}(t)-\frac{1}{\gamma_{2}}(\theta-\gamma_{2}\overline{w}+\beta_{2}\overline{u})\int_{\Omega}vdx \;\;\;\text{for all t > 0 }. \end{aligned} \end{equation} (4.45)

    We deduce from Lemma 4.8 that ||u(\cdot, t)-\overline{u}||_{L^{\infty}(\Omega)}+||v(\cdot, t)||_{L^{\infty}(\Omega)}+||w(\cdot, t)-\overline{w}||_{L^{\infty}(\Omega)}\rightarrow 0 as t\rightarrow \infty . Hence, we apply L'Hôpital's rule to obtain

    \begin{equation} \lim\limits_{u\rightarrow \overline{u}}\frac{u-\overline{u}-\overline{u}\ln\frac{u}{\overline{u}}}{(u-\overline{u})^{2}} = \frac{1}{2\overline{u}}, \end{equation} (4.46)

    which implies that there exists a t'_{1} > 0 such that

    \begin{equation} \begin{split} \frac{1}{4\overline{u}}\int_{\Omega}(u-\overline{u})^{2}dx\leq\int_{\Omega}\left(u-\overline{u}-\overline{u}\ln\frac{u}{\overline{u}}\right)dx \leq\frac{3}{4\overline{u}}\int_{\Omega}(u-\overline{u})^{2}dx \end{split} \end{equation} (4.47)

    for all t > t'_{1} . Similarly, we can find t'_{2} > 0 satisfying

    \begin{equation} \begin{split} \frac{1}{4\overline{w}}\int_{\Omega}(w-\overline{w})^{2}dx\leq\int_{\Omega}\left(w-\overline{w}-\overline{w}\ln\frac{w}{\overline{w}}\right)dx \leq\frac{3}{4\overline{w}}\int_{\Omega}(w-\overline{w})^{2}dx \end{split} \end{equation} (4.48)

    for all t > t'_{2} .

    By using the fact that \lim_{s\rightarrow 0}\frac{s}{s^{2}+s} = 1 , it follows from ||v(\cdot, t)||_{L^{\infty}(\Omega)}\rightarrow 0 as t\rightarrow \infty that there exists a t'_{3} > 0 such that

    \begin{equation} \begin{split} \frac{1}{2}\int_{\Omega}v^{2}+vdx\leq\int_{\Omega}vdx\leq\frac{3}{2}\int_{\Omega}v^{2}+vdx \end{split} \end{equation} (4.49)

    for all t > t'_{3} .

    (a) When \theta = \gamma_{2}\overline{w}-\beta_{2}\overline{u} , (4.45) can be turned into

    \begin{equation} \begin{aligned} \frac{d}{d t} \mathcal{E}_{2}(t) \leq-\varepsilon_{2} \mathcal{F}_{2}^{*}(t) \;\;\;\text{for all t > 0 }. \end{aligned} \end{equation} (4.50)

    Let T_{2}: = \max\{t'_{1}, t'_{2}, t'_{3}\} ; by means of the definitions of \mathcal{E}_{2}(t) and \mathcal{F}_{2}^{*}(t) , it follows from the second inequalities in (4.47) and (4.48) that there exist positive constants C_{1} and C_{2} such that

    \begin{equation} \begin{split} \mathcal{E}_{2}(t)&\leq \frac{3}{4\gamma_{1}\overline{u}}\int_{\Omega}(u-\overline{u})^{2}dx+\frac{1}{\gamma_{2}}\int_{\Omega}vdx+\frac{3}{4\overline{w}}\int_{\Omega}(w-\overline{w})^{2}dx\\ &\leq C_{1}\left(\int_{\Omega}(u-\overline{u})^{2}dx\right)^{\frac{1}{2}}+C_{1}\left(\int_{\Omega}v^{2}dx\right)^{\frac{1}{2}}+ C_{1}\left(\int_{\Omega}(w-\overline{w})^{2}dx\right)^{\frac{1}{2}}\\ &\leq C_{2}(\mathcal{F}_{2}^{*}(t))^{\frac{1}{2}}, \end{split} \end{equation} (4.51)

    for all t > T_{2} , where we have used Hölder's inequality and the boundedness of (u, v, w) asserted by Theorem 1.1. Thus, we deduce from (4.50) that

    \begin{equation} \mathcal{E}_{2}'(t)\leq-\frac{\varepsilon_{2}}{C_{2}^{2}}\mathcal{E}_{2}^{2}(t)\quad\text{for all}\;\;t > T_{2}, \end{equation} (4.52)

    which implies

    \begin{equation} \mathcal{E}_{2}(t)\leq \frac{C_{3}}{t-T_{2}}\quad\text{for all}\;\;t > T_{2}, \end{equation} (4.53)

    with some positive constant C_{3} . Hence we infer from the first inequalities in (4.47)–(4.49) that there exists a C_{4} > 0 such that

    \begin{equation} \begin{split} &\int_{\Omega}(u-\overline{u})^{2}dx+\int_{\Omega}v^{2}dx+\int_{\Omega}(w-\overline{w})^{2}dx\\ &\quad\leq C_{4}\mathcal{E}_{2}(t)\leq \frac{C_{3}C_{4}}{t-T_{2}}\;\;\text{for all}\;\;t > T_{2}. \end{split} \end{equation} (4.54)

    It follows from the Gagliardo-Nirenberg inequality in two dimensions, Lemma 4.2 and Lemma 3.2 that there exist positive constants C_{5} and C_{6} such that

    \begin{equation} \begin{split} &||u-\overline{u}||_{L^{\infty}(\Omega)}+||v||_{L^{\infty}(\Omega)}+||w-\overline{w}||_{L^{\infty}(\Omega)}\\ &\leq C_{5}\bigg(||u-\overline{u}||_{W^{1,4}(\Omega)}^{\frac{2}{3}}||u-\overline{u}||_{L^{2}(\Omega)}^{\frac{1}{3}} +||v||_{W^{1,4}(\Omega)}^{\frac{2}{3}}||v||_{L^{2}(\Omega)}^{\frac{1}{3}}\\& \quad+||w-\overline{w}||_{W^{1,4}(\Omega)}^{\frac{2}{3}}||w-\overline{w}||_{L^{2}(\Omega)}^{\frac{1}{3}}\bigg)\\ &\leq C_{6}\left(\int_{\Omega}(u-\overline{u})^{2}dx+\int_{\Omega}v^{2}dx+\int_{\Omega}(w-\overline{w})^{2}dx\right)^{\frac{1}{6}}\\ &\leq C_{6}(C_{3}C_{4})^{\frac{1}{6}}(t-T_{2})^{-\frac{1}{6}} \end{split} \end{equation} (4.55)

    for all t > T_{2} .

    (b) When \theta > \gamma_{2}\overline{w}-\beta_{2}\overline{u} , let T_{2}: = \max\{t'_{1}, t'_{2}, t'_{3}\} ; by means of the definitions of \mathcal{E}_{2}(t) and \mathcal{F}_{2}^{*}(t) , it follows from the second inequalities in (4.47) and (4.48) that there exists a positive constant C_{7} such that

    \begin{equation} \begin{split} \mathcal{E}_{2}(t)\leq C_{7}\left(\mathcal{F}_{2}^{*}(t)+\int_{\Omega}vdx\right), \end{split} \end{equation} (4.56)

    for all t > T_{2} .

    By combining (4.45) with (4.56), we have

    \begin{equation} \begin{aligned} \frac{\text{d}}{\text{dt}} \mathcal{E}_{2}(t) \leq-\frac{\varepsilon_{2}}{C_{7}} \mathcal{E}_{2}(t)-\frac{1}{\gamma_{2}}(\theta-\gamma_{2}\overline{w}+\beta_{2}\overline{u}-\gamma_{2}\varepsilon_{2})\int_{\Omega}vdx \;\;\;\text{for all}\; t > T_{2} . \end{aligned} \end{equation} (4.57)

    Since \theta > \gamma_{2}\overline{w}-\beta_{2}\overline{u} , then we can select \varepsilon_{2}\leq \frac{1}{\gamma_{2}}(\theta-\gamma_{2}\overline{w}+\beta_{2}\overline{u}) such that

    \begin{equation} \begin{aligned} \frac{\text{d}}{\text{dt}} \mathcal{E}_{2}(t) \leq-\frac{\varepsilon_{2}}{C_{7}} \mathcal{E}_{2}(t)\;\;\;\text{for all}\; t > T_{2} , \end{aligned} \end{equation} (4.58)

    which means that there exist C_{8} > 0 and C_{9} > 0 satisfying

    \begin{equation} \mathcal{E}_{2}(t)\leq C_{8}e^{-C_{9}(t-T_{2})}\quad\text{for all}\;\;t > T_{2}. \end{equation} (4.59)

    Thus we deduce from the first inequalities in (4.47)–(4.49) that there exists a C_{10} > 0 such that

    \begin{equation} \begin{split} &\int_{\Omega}(u-\overline{u})^{2}dx+\int_{\Omega}v^{2}dx+\int_{\Omega}(w-\overline{w})^{2}dx\\ &\quad\leq C_{10}\mathcal{E}_{2}(t)\leq C_{8}C_{10}e^{-C_{9}(t-T_{2})}\;\;\text{for all}\;\;t > T_{2}. \end{split} \end{equation} (4.60)

    It follows from the Gagliardo-Nirenberg inequality in two dimensions, Lemma 4.2 and Lemma 3.2 that there exist positive constants C_{11} and C_{12} such that

    \begin{equation} \begin{split} &||u-\overline{u}||_{L^{\infty}(\Omega)}+||v||_{L^{\infty}(\Omega)}+||w-\overline{w}||_{L^{\infty}(\Omega)}\\ &\leq C_{11}\bigg(||u-\overline{u}||_{W^{1,4}(\Omega)}^{\frac{2}{3}}||u-\overline{u}||_{L^{2}(\Omega)}^{\frac{1}{3}} +||v||_{W^{1,4}(\Omega)}^{\frac{2}{3}}||v||_{L^{2}(\Omega)}^{\frac{1}{3}}\\& \quad+||w-\overline{w}||_{W^{1,4}(\Omega)}^{\frac{2}{3}}||w-\overline{w}||_{L^{2}(\Omega)}^{\frac{1}{3}}\bigg)\\ &\leq C_{12}\left(\int_{\Omega}(u-\overline{u})^{2}dx+\int_{\Omega}v^{2}dx+\int_{\Omega}(w-\overline{w})^{2}dx\right)^{\frac{1}{6}}\\ &\leq C_{12}(C_{8}C_{10})^{\frac{1}{6}}e^{\frac{-C_{9}(t-T_{2})}{6}} \end{split} \end{equation} (4.61)

    for all t > T_{2} . The proof of Lemma 4.9 is complete.

    Proof of Theorem 1.3. The statement of Theorem 1.3 is a direct consequence of Lemma 4.9.

    In this subsection, we are devoted to discussing the asymptotic stability of the prey-only steady state (0, 0, 1) under some suitable parameters conditions. To do this, let us denote the following functionals

    \begin{aligned} \mathcal{E}_{3}(t) = &\frac{1}{\gamma_{1}}\int_{\Omega}udx+\frac{1}{\gamma_{2}}\int_{\Omega}vdx+\int_{\Omega}\left(w-1-\ln w\right)dx\\ \end{aligned}

    and

    \begin{aligned} \mathcal{F}_{3}(t) = \int_{\Omega}u^{2}dx+\int_{\Omega}v^{2}dx+ \int_{\Omega}\left(w-1\right)^{2}dx+\int_\Omega {{{\left| {\nabla w} \right|}^2}}dx, \end{aligned}

    we can derive the following estimates of \mathcal{E}_{3}(t) and \mathcal{F}_{3}(t) .

    Lemma 4.10. Let the conditions of Theorem 1.5 hold. Then there exists a \varepsilon_{3} > 0 independent of t such that

    \begin{equation} \begin{aligned} \mathcal{E}_{3}(t) \geq 0 \end{aligned} \end{equation} (4.62)

    and

    \begin{equation} \begin{aligned} \frac{\text{d}}{\text{dt}} \mathcal{E}_{3}(t) \leq-\varepsilon_{3} \mathcal{F}_{3}(t)-\frac{1}{\gamma_{1}}(\theta-\gamma_{1})\int_{\Omega}udx -\frac{1}{\gamma_{2}}(\theta-\gamma_{2})\int_{\Omega}vdx \;\;\;{for\; all\; t > 0 }. \end{aligned} \end{equation} (4.63)

    Proof. By the similar arguments as in the proofs of Lemma 4.4 and Lemma 4.7, we can derive (4.62) and

    \begin{equation} \begin{aligned} \frac{\text{d}}{\text{dt}}\mathcal{E}_{3}(t)& = -\frac{\alpha_{1}}{\gamma_{1}}\int_{\Omega}u^{2}dx -\frac{\alpha_{2}}{\gamma_{2}}\int_{\Omega}v^{2}dx-\mu\int_{\Omega}(w-1)^{2}dx\\&\quad -\left(\frac{\beta_{1}}{\gamma_{1}}+\frac{\beta_{2}}{\gamma_{2}}\right)\int_{\Omega}uvdx-D\int_{\Omega}\frac{|\nabla w|^{2}}{w^{2}}dx\\&\quad-\frac{1}{\gamma_{1}}(\theta-\gamma_{1})\int_{\Omega}udx-\frac{1}{\gamma_{2}}(\theta-\gamma_{2})\int_{\Omega}vdx\\ &\leq-\frac{\alpha_{1}}{\gamma_{1}}\int_{\Omega}u^{2}dx -\frac{\alpha_{2}}{\gamma_{2}}\int_{\Omega}v^{2}dx-\mu\int_{\Omega}(w-1)^{2}dx -\frac{D}{K_{0}^{2}}\int_{\Omega}|\nabla w|^{2}dx\\&\quad-\frac{1}{\gamma_{1}}(\theta-\gamma_{1})\int_{\Omega}udx-\frac{1}{\gamma_{2}}(\theta-\gamma_{2})\int_{\Omega}vdx, \end{aligned} \end{equation} (4.64)

    where we have used the fact that w\leq K_{0} = \max\{||w_{0}||_{L^{\infty}(\Omega)}, 1\} . Let \varepsilon_{3}\in \left(0, \min\{\frac{\alpha_{1}}{\gamma_{1}}, \frac{\alpha_{2}}{\gamma_{2}}, \mu, \frac{D}{K_{0}^{2}}\}\right) ; we obtain

    \begin{equation} \begin{split} \frac{\text{d}}{\text{dt}}\mathcal{E}_{3}(t)\leq-\varepsilon_{3}\mathcal{F}_{3}(t) -\frac{1}{\gamma_{1}}(\theta-\gamma_{1})\int_{\Omega}udx-\frac{1}{\gamma_{2}}(\theta-\gamma_{2})\int_{\Omega}vdx, \end{split} \end{equation} (4.65)

    for all t > 0 . The proof of Lemma 4.10 is complete.

    With the help of Lemma 4.10, we shall give the following stabilization of the prey-only steady state for System (1.11).

    Lemma 4.11. Let the assumptions of Theorem 1.5 hold. Then the global bounded solution of (1.11) converges to the prey-only steady state (0, 0, 1) , i.e.,

    \begin{equation} ||u(\cdot,t)||_{L^{\infty}(\Omega)}+||v(\cdot,t)||_{L^{\infty}(\Omega)}+||w(\cdot,t)-1||_{L^{\infty}(\Omega)}\rightarrow 0 \end{equation} (4.66)

    as t\rightarrow \infty .

    Proof. The proof of this lemma is similar to that of Lemma 4.5; here we omit the details.

    Now, we give the convergence rate of the prey-only steady state (0, 0, 1) for System (1.11).

    Lemma 4.12. Let the assumptions of Theorem 1.5 hold; then there exist positive constants C and \lambda such that:

    (a) when \gamma_{i} = \theta , i = 1, 2 , then

    \begin{equation} ||u(\cdot,t)||_{L^{\infty}(\Omega)}+||v(\cdot,t)||_{L^{\infty}(\Omega)}+||w(\cdot,t)-1||_{L^{\infty}(\Omega)}\leq C(1+t)^{-\lambda}\;\;{for \;all}\;\; t > T_{3}; \end{equation} (4.67)

    (b) when \gamma_{i} < \theta , i = 1, 2 , then

    \begin{equation} ||u(\cdot,t)||_{L^{\infty}(\Omega)}+||v(\cdot,t)||_{L^{\infty}(\Omega)}+||w(\cdot,t)-1||_{L^{\infty}(\Omega)}\leq Ce^{-\lambda t}\;\;{for\; all}\;\; t > T_{3}, \end{equation} (4.68)

    where T_{3} > 0 is some fixed time.

    Proof. Let

    \begin{equation} \mathcal{F}_{3}^{*}(t): = \int_{\Omega}u^{2}dx+\int_{\Omega}v^{2}dx+ \int_{\Omega}\left(w-1\right)^{2}dx, \end{equation} (4.69)

    then it follows from Lemma 4.10 that there exists a \varepsilon_{3} > 0 such that

    \begin{equation} \begin{aligned} \frac{\text{d}}{\text{dt}} \mathcal{E}_{3}(t)\leq-\varepsilon_{3} \mathcal{F}_{3}^{*}(t)-\frac{1}{\gamma_{1}}(\theta-\gamma_{1})\int_{\Omega}udx-\frac{1}{\gamma_{2}}(\theta-\gamma_{2})\int_{\Omega}vdx \;\;\;\text{for all t > 0 }. \end{aligned} \end{equation} (4.70)

    By using the facts that \lim_{s\rightarrow 0}\frac{s}{s^{2}+s} = 1 and \lim_{s\rightarrow 1}\frac{s-1-\ln s}{(s-1)^{2}} = \frac{1}{2} , it follows from ||u(\cdot, t)||_{L^{\infty}(\Omega)}+||v(\cdot, t)||_{L^{\infty}(\Omega)}+||w(\cdot, t)-1||_{L^{\infty}(\Omega)}\rightarrow 0 as t\rightarrow \infty , as asserted in Lemma 4.11 that there exists a T_{3} > 0 such that

    \begin{equation} \begin{split} \frac{1}{2}\int_{\Omega}u^{2}+udx\leq\int_{\Omega}udx\leq\frac{3}{2}\int_{\Omega}u^{2}+udx \end{split} \end{equation} (4.71)

    and

    \begin{equation} \begin{split} \frac{1}{2}\int_{\Omega}v^{2}+vdx\leq\int_{\Omega}vdx\leq\frac{3}{2}\int_{\Omega}v^{2}+vdx \end{split} \end{equation} (4.72)

    as well as

    \begin{equation} \begin{split} \frac{1}{4}\int_{\Omega}(w-1)^{2}dx\leq\int_{\Omega}\left(w-1-\ln w\right)dx \leq\frac{3}{4}\int_{\Omega}(w-1)^{2}dx \end{split} \end{equation} (4.73)

    for all t > T_{3} .

    (a) When \gamma_{i} = \theta , i = 1, 2 , (4.70) can be simplified as

    \begin{equation} \begin{aligned} \frac{\text{d}}{\text{dt}} \mathcal{E}_{3}(t) \leq-\varepsilon_{3} \mathcal{F}_{3}^{*}(t) \;\;\;\text{for all t > 0 }. \end{aligned} \end{equation} (4.74)

    By means of the definitions of \mathcal{E}_{3}(t) and \mathcal{F}_{3}^{*}(t) , it follows from the second inequality in (4.73) that there exist positive constants C_{1} and C_{2} such that

    \begin{equation} \begin{split} \mathcal{E}_{3}(t)&\leq \frac{1}{\gamma_{1}}\int_{\Omega}udx+\frac{1}{\gamma_{2}}\int_{\Omega}vdx+\frac{3}{4}\int_{\Omega}(w-1)^{2}dx\\ &\leq C_{1}\left(\int_{\Omega}u^{2}dx\right)^{\frac{1}{2}}+C_{1}\left(\int_{\Omega}v^{2}dx\right)^{\frac{1}{2}}+ C_{1}\left(\int_{\Omega}(w-1)^{2}dx\right)^{\frac{1}{2}}\\ &\leq C_{2}(\mathcal{F}_{3}^{*}(t))^{\frac{1}{2}}, \end{split} \end{equation} (4.75)

    for all t > T_{3} , where we have used Hölder's inequality and the boundedness of (u, v, w) asserted by Theorem 1.1. Thus we deduce from (4.74) that

    \begin{equation} \mathcal{E}_{3}'(t)\leq-\frac{\varepsilon_{3}}{C_{2}^{2}}\mathcal{E}_{3}^{2}(t)\quad\text{for all}\;\;t > T_{3}, \end{equation} (4.76)

    which implies

    \begin{equation} \mathcal{E}_{3}(t)\leq \frac{C_{3}}{t-T_{3}}\quad\text{for all}\;\;t > T_{3}, \end{equation} (4.77)

    with some positive constant C_{3} . Hence we infer from the first inequalities in (4.71)–(4.73) that there exists a C_{4} > 0 such that

    \begin{equation} \begin{split} &\int_{\Omega}u^{2}dx+\int_{\Omega}v^{2}dx+\int_{\Omega}(w-1)^{2}dx\\ &\quad\leq C_{4}\mathcal{E}_{3}(t)\leq \frac{C_{3}C_{4}}{t-T_{3}}\;\;\text{for all}\;\;t > T_{3}. \end{split} \end{equation} (4.78)

    It follows from the Gagliardo-Nirenberg inequality in two dimensions, Lemma 4.2 and Lemma 3.2 that there exist positive constants C_{5} and C_{6} such that

    \begin{equation} \begin{split} &||u||_{L^{\infty}(\Omega)}+||v||_{L^{\infty}(\Omega)}+||w-1||_{L^{\infty}(\Omega)}\\ &\leq C_{5}\bigg(||u||_{W^{1,4}(\Omega)}^{\frac{2}{3}}||u||_{L^{2}(\Omega)}^{\frac{1}{3}} +||v||_{W^{1,4}(\Omega)}^{\frac{2}{3}}||v||_{L^{2}(\Omega)}^{\frac{1}{3}}\\& \quad+||w-1||_{W^{1,4}(\Omega)}^{\frac{2}{3}}||w-1||_{L^{2}(\Omega)}^{\frac{1}{3}}\bigg)\\ &\leq C_{6}\left(\int_{\Omega}u^{2}dx+\int_{\Omega}v^{2}dx+\int_{\Omega}(w-1)^{2}dx\right)^{\frac{1}{6}}\\ &\leq C_{6}(C_{3}C_{4})^{\frac{1}{6}}(t-T_{3})^{-\frac{1}{6}} \end{split} \end{equation} (4.79)

    for all t > T_{3} .

    (b) When \gamma_{i} < \theta , i = 1, 2 , by means of the definitions of \mathcal{E}_{3}(t) and \mathcal{F}_{3}^{*}(t) , it follows from the second inequalities in (4.71)–(4.73) that there exists a positive constant C_{7} such that

    \begin{equation} \begin{split} \mathcal{E}_{3}(t)\leq C_{7}\left(\mathcal{F}_{3}^{*}(t)+\int_{\Omega}udx+\int_{\Omega}vdx\right), \end{split} \end{equation} (4.80)

    for all t > T_{3} .

    By combining (4.70) with (4.80), we derive

    \begin{equation} \begin{aligned} \frac{\text{d}}{\text{dt}} \mathcal{E}_{3}(t)\leq-\frac{\varepsilon_{3}}{C_{7}} \mathcal{E}_{3}(t)-\frac{1}{\gamma_{1}}(\theta-\gamma_{1}-\varepsilon_{3}\gamma_{1})\int_{\Omega}udx-\frac{1}{\gamma_{2}}(\theta-\gamma_{2} -\varepsilon_{3}\gamma_{2})\int_{\Omega}vdx \end{aligned} \end{equation} (4.81)

    for all t > 0 . Since \gamma_{i} < \theta , i = 1, 2 , we can select \varepsilon_{3}\leq \min\left\{\frac{1}{\gamma_{1}}(\theta-\gamma_{1}), \frac{1}{\gamma_{2}}(\theta-\gamma_{2})\right\} such that

    \begin{equation} \begin{aligned} \frac{\text{d}}{\text{dt}} \mathcal{E}_{3}(t) \leq-\frac{\varepsilon_{3}}{C_{7}} \mathcal{E}_{3}(t)\;\;\;\text{for all t > T_{3} }, \end{aligned} \end{equation} (4.82)

    which means that there exist C_{8} > 0 and C_{9} > 0 satisfying

    \begin{equation} \mathcal{E}_{3}(t)\leq C_{8}e^{-C_{9}(t-T_{3})}\quad\text{for all}\;\;t > T_{3}. \end{equation} (4.83)

    Thus we deduce from the first inequalities in (4.71)–(4.73) that there exists a C_{10} > 0 such that

    \begin{equation} \begin{split} &\int_{\Omega}u^{2}dx+\int_{\Omega}v^{2}dx+\int_{\Omega}(w-1)^{2}dx\\ &\quad\leq C_{10}\mathcal{E}_{2}(t)\leq C_{8}C_{10}e^{-C_{9}(t-T_{3})}\;\;\text{for all}\;\;t > T_{3}. \end{split} \end{equation} (4.84)

    It follows from the Gagliardo-Nirenberg inequality in two dimensions, Lemma 4.2 and Lemma 3.2 that there exist positive constants C_{11} and C_{12} such that

    \begin{equation} \begin{split} &||u||_{L^{\infty}(\Omega)}+||v||_{L^{\infty}(\Omega)}+||w-1||_{L^{\infty}(\Omega)}\\ &\leq C_{11}\bigg(||u||_{W^{1,4}(\Omega)}^{\frac{2}{3}}||u||_{L^{2}(\Omega)}^{\frac{1}{3}} +||v||_{W^{1,4}(\Omega)}^{\frac{2}{3}}||v||_{L^{2}(\Omega)}^{\frac{1}{3}}\\& \quad+||w-1||_{W^{1,4}(\Omega)}^{\frac{2}{3}}||w-1||_{L^{2}(\Omega)}^{\frac{1}{3}}\bigg)\\ &\leq C_{12}\left(\int_{\Omega}u^{2}dx+\int_{\Omega}v^{2}dx+\int_{\Omega}(w-1)^{2}dx\right)^{\frac{1}{6}}\\ &\leq C_{12}(C_{8}C_{10})^{\frac{1}{6}}e^{\frac{-C_{9}(t-T_{3})}{6}} \end{split} \end{equation} (4.85)

    for all t > T_{3} . The proof of Lemma 4.12 is complete.

    Proof of Theorem 1.5. The statement of Theorem 1.5 is a direct consequence of Lemma 4.12.

    The author is grateful to the editor and three anonymous referees for their valuable comments, which greatly improved the exposition of our paper. The author is also deeply grateful to Professor Renjun Duan for the support and friendly hospitality in CUHK. The work was partially supported by the National Natural Science Foundation of China (Grant Nos: 11601053, 11526042), Natural Science Foundation of Chongqing (Grant No. cstc2019jcyj-msxmX0082), Chongqing Municipal Education Commission Science and Technology Research Project (Grant No. KJZD-K202200602), China-South Africa Young Scientist Exchange Project in 2020, The Hong Kong Scholars Program (Grant Nos: XJ2021042, 2021-005) and Young Hundred Talents Program of CQUPT from 2022–2024.

    The author declares that there is no conflict of interest.



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