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Turing instability and stationary patterns in a predator-prey systems with nonlinear cross-diffusions

Zijuan Wen

Author Affiliations

School of Mathematics and Statistics, Lanzhou University, Lanzhou, 730000, P.R. China

Boundary Value Problems 2013, 2013:155  doi:10.1186/1687-2770-2013-155

The electronic version of this article is the complete one and can be found online at: http://www.boundaryvalueproblems.com/content/2013/1/155


Received:6 September 2012
Accepted:16 June 2013
Published:1 July 2013

© 2013 Wen; licensee Springer

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

In this paper, we study a strongly coupled reaction-diffusion system which describes two interacting species in prey-predator ecosystem with nonlinear cross-diffusions and Holling type-II functional response. By a linear stability analysis, we establish some stability conditions of constant positive equilibrium for the ODE and PDE systems. In particular, it is shown that Turing instability can be induced by the presence of cross-diffusion. Furthermore, based on Leray-Schauder degree theory, the existence of non-constant positive steady state is investigated. Our results indicate that the model has no non-constant positive steady state with no cross-diffusion, while large cross-diffusion effect of the first species is helpful to the appearance of Turing instability as well as non-constant positive steady state (stationary patterns).

Keywords:
cross-diffusion; Holling type-II functional response; Turing instability; non-constant positive steady state; stationary patterns

1 Introduction

Let Ω be a bounded domain in <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M1','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M1">View MathML</a> with smooth boundary Ω. In this paper, we are interested in a strongly coupled reaction-diffusion equations with Holling type-II functional response

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M2','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M2">View MathML</a>

(1.1)

where ν is the unit outward normal to Ω. The two unknown functions <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M3','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M3">View MathML</a> and <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M4','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M4">View MathML</a> represent the spatial distribution densities of the prey and predator, respectively. The constants <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M5','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M5">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M6','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M6">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M7','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M7">View MathML</a> (<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M8','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M8">View MathML</a>), K, m and θ are all positive, and <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M9','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M9">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M10','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M10">View MathML</a> are nonnegative functions which are not identically zero. Moreover, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M5','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M5">View MathML</a> is the diffusion rate of the two species, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M6','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M6">View MathML</a> expresses the self-diffusion effect, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M7','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M7">View MathML</a> is called the cross-diffusion coefficient, K accounts for the carrying capacity of the prey, θ is the death rate of the predator, and m can be regarded as the measure of the interaction strength between the two species. In this model, the prey u and the predator v diffuse with fluxes

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M14','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M14">View MathML</a>

and

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M15','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M15">View MathML</a>

respectively. The cross-diffusion terms <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M16','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M16">View MathML</a> and <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M17','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M17">View MathML</a> can be explained that the prey keeps away from the predator while the predator moves away from a large group of prey. For more detailed biological meaning of the parameters, one can make some reference to [1-3].

The ODE system of (1.1)

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M18','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M18">View MathML</a>

(1.2)

has been extensively studied in the existing literature; see, for example, [4-6]. The known results mainly focused on the existence and uniqueness of a limit cycle. In [6], Rosenzweig argued that enrichment of the environment (larger carrying capacity K) leads to destabilizing of the coexistence equilibrium, which is the so-called paradox of enrichment. Cheng [4] first proved the uniqueness of limit cycle. Hsu and Shi [5] discussed the relaxation oscillator profile of the unique limit cycle and found that (1.2) has a periodic orbit if m is larger than a threshold value.

In mathematical biology, the classical prey-predator model (ODE system) reflects only population changes due to predation in a situation where predator and prey densities are not spatially dependent. It does not take into account either the fact that population is usually not homogeneously distributed, or the fact that predators and preys naturally develop strategies for survival. Both of these considerations involve diffusion processes which can be quite intricate as different concentration levels of predators and preys caused by different population movements. Such movements can be determined by the concentration of the same species (diffusion) and that of other species (cross-diffusion). In view of this, Shigesada, Kawasaki and Teramoto first proposed a strongly coupled reaction-diffusion model with Lotka-Volterra type reaction term (SKT model) to describe spatial segregation of interacting population species in one-dimensional space [3]. Since then the two-species SKT competing system and its overall behaviors continue to be of great interest in literature to both mathematical analysis and real-life modeling [7-10]. For the studies on biological models, since each model has rich and interesting properties and often describes complex biological process, it is very difficult to get some general conclusions for a class of mathematical models. So research in mathematical biology has often been performed by investigating a specific model, the focus of which is to discuss the influences of parameters on the behavior of species in the ecosystem. Thus, more and more attention has been recently focused on three or multi-species systems and the SKT model in any space dimension due to their more complicated patterns, and the SKT models with other types of reaction terms have also been proposed and investigated [11-19]. The obtained results mainly relate to the stability analysis of constant positive steady states and the existence of non-constant positive steady states (stationary patterns) [9,10,12-21], Turing instability [22,23], and the global existence of non-negative time-dependent solutions [7,8,11,24].

The role of diffusion in the modeling of many biological processes has been extensively studied. Starting with Turing’s seminal work [25], diffusion and cross diffusion have been observed as causes of the spontaneous emergence of ordered structures, called patterns, in a variety of nonequilibrium situations. Diffusion-driven instability, also called Turing instability, has also been verified empirically in some chemical and biological models [26-28]. For the system with cross-diffusion, we can know that this kind of cross-diffusion may be helpful to create non-constant positive steady-state solutions for the predator-prey system, for example [9,10,16]. Recently, the authors of [22] discussed a two-species Holling-Tanner model with simple linear cross-diffusion

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M19','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M19">View MathML</a>

and showed that under some parameters the positive equilibrium is stable for a diffusion system while unstable for a cross-diffusion system, which implies that cross-diffusion can induce the Turing instability of the uniform equilibrium. In [23], Xie investigated a class of strongly coupled prey-predator models with four Holling-type functional responses:

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M20','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M20">View MathML</a>

The results indicated that diffusion and cross-diffusion in these models cannot drive Turing instability. However, diffusion and cross-diffusion can still create non-constant positive solutions for the models.

As for reaction-diffusion system of (1.2), the diffusive predator-prey equations with no self- and cross-diffusion (<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M21','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M21">View MathML</a> in (1.1)) under Neumann boundary value conditions have also been investigated (see, for example, [29-33]). Ko and Ryu [29] obtained some results on the global stability of the constant steady state solutions and the existence of at least one non-constant equilibrium solution. Medvinsky et al.[30] used this model as a simple mathematical model to investigate the pattern formation of a phytoplankton-zooplankton system, and their numerical studies show a rich spectrum of spatiotemporal patterns. The discussion in [32] shows this system possesses complex spatiotemporal dynamics via a sequence of bifurcation of spatial nonhomogeneous periodic orbits and spatial nonhomogeneous steady state solutions. In [31], Peng and Shi proved the non-existence of non-constant positive steady state solutions. Recently, the existence, multiplicity and stability of positive solutions for the weakly coupled equations in (1.1) with Dirichlet boundary conditions were investigated in [33].

From the above introductions, one can learn that few studies have been conducted into the occurrence of Turing instability for a strongly coupled reaction-diffusion system with nonlinear cross-diffusion terms in the literature. Motivated by a series of pioneering works such as [9,10,16], we are interested in the instability induced by cross-diffusion and the stationary patterns of strongly coupled model (1.1). The aim of this paper is to discuss Turing instability and establish the existence of non-constant positive steady states of system (1.1). The methods we employed are the classical linearization method and the Leray-Schauder degree theory. However, while performing a priori estimates and stability analysis, we must try a new method and techniques to solve difficulties caused by nonlinear cross-diffusion terms <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M22','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M22">View MathML</a> and <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M23','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M23">View MathML</a>. Nonlinear cross-diffusion terms also add complexity of computation of characteristic equations. Moreover, this paper focuses on the influence of nonlinear cross-diffusion terms on the appearance of Turing instability, and the discussion shows that large cross-diffusion coefficient of the first species is helpful to the appearance of Turing instability as well as non-constant positive steady state.

The paper is organized as follows. In Section 2, we discuss the stability of a positive equilibrium point for ODE and PDE systems and then obtain sufficient conditions of the appearance of Turing pattern. The results imply that cross-diffusion <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M24','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M24">View MathML</a> has a destabilizing effect, which is helpful to the occurrence of Turing instability. In Section 3, we obtain a priori upper and lower bounds for the positive steady states problem of (1.1) in order to calculate the topological degree. In Section 4, the non-existence of non-constant positive steady state for (1.1) with vanished cross-diffusions is discussed. In Section 5, we establish the global existence of non-constant positive steady state of (1.1) for suitable values of cross-diffusion coefficient <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M24','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M24">View MathML</a> and then show that large cross-diffusion effect <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M24','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M24">View MathML</a> can create non-constant positive steady states.

2 Turing instability driven by cross-diffusion

Denote <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M27','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M27">View MathML</a>. It is known from [31] that problem (1.1) has a unique positive equilibrium

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M28','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M28">View MathML</a>

if and only if

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M29','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M29">View MathML</a>

(2.1)

Moreover, problem (1.1) has a trivial equilibrium <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M30','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M30">View MathML</a> and a semi-trivial equilibrium <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M31','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M31">View MathML</a>.

We first investigate the stability of positive equilibrium for a reaction-diffusion system.

Lemma 2.1Suppose that<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M32','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M32">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M33','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M33">View MathML</a>. Then the positive equilibrium<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34">View MathML</a>of (1.1) is uniformly asymptotically stable.

Proof For simplicity, we denote <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M35','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M35">View MathML</a> and

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M36','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M36">View MathML</a>

Then problem (1.1) can be rewritten as

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M37','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M37">View MathML</a>

(2.2)

The linearization of problem (2.2) at the positive equilibrium <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34">View MathML</a> is

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M39','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M39">View MathML</a>

(2.3)

where <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M40','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M40">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M41','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M41">View MathML</a>. Here

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M42','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M42">View MathML</a>

It is easy to verify that <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M43','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M43">View MathML</a> if <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M44','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M44">View MathML</a>.

Let <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M45','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M45">View MathML</a> be a set of eigenpairs for −Δ in Ω with no flux boundary condition, where <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M46','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M46">View MathML</a> , and let <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M47','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M47">View MathML</a> be the eigenspace corresponding to <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M48','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M48">View MathML</a> in <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M49','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M49">View MathML</a>, let <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M50','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M50">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M51','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M51">View MathML</a>, be an orthonormal basis of <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M47','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M47">View MathML</a>. Let

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M53','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M53">View MathML</a>

Then we can do the following decomposition:

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M54','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M54">View MathML</a>

(2.4)

For each <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M55','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M55">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M56','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M56">View MathML</a> is invariant under the operator <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M57','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M57">View MathML</a>. Then problem (2.3) has a non-trivial solution of the form <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M58','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M58">View MathML</a> (<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M59','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M59">View MathML</a> is a constant vector) if and only if <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M60','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M60">View MathML</a> is an eigenpair for the matrix <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M61','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M61">View MathML</a>.

The characteristic equation of the matrix <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M62','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M62">View MathML</a> is given by

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M63','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M63">View MathML</a>

Notice that

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M64','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M64">View MathML</a>

where

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M65','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M65">View MathML</a>

Obviously, if <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M33','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M33">View MathML</a>, then <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M67','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M67">View MathML</a> and so <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M68','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M68">View MathML</a>. Thus, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M69','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M69">View MathML</a>. It follows from Routh-Hurwitz criterion that the two roots <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M70','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M70">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M71','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M71">View MathML</a> of <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M72','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M72">View MathML</a> have both negative real parts for all <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M55','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M55">View MathML</a>.

In order to obtain the local stability of <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M74','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M74">View MathML</a>, we need to prove that there exists a positive constant δ such that

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M75','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M75">View MathML</a>

(2.5)

Let <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M76','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M76">View MathML</a>, then

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M77','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M77">View MathML</a>

Notice that <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M78','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M78">View MathML</a> as <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M79','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M79">View MathML</a>. We can calculate that

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M80','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M80">View MathML</a>

By Routh-Hurwitz criterion, the two roots <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M81','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M81">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M82','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M82">View MathML</a> of <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M83','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M83">View MathML</a> have both negative real parts. Then we can conclude that there exists a positive constant <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M84','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M84">View MathML</a> such that <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M85','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M85">View MathML</a>. By continuity, we see that there exists <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M86','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M86">View MathML</a> such that the two roots of <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M87','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M87">View MathML</a> satisfy <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M88','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M88">View MathML</a> for all <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M89','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M89">View MathML</a>. Then <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M90','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M90">View MathML</a> for all <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M89','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M89">View MathML</a>. Let

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M92','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M92">View MathML</a>

Then (2.5) holds true. The theorem is thus proved. □

Similarly, we can also learn, by the proof of Lemma 2.1, a series of stability results about the positive equilibrium for problem (1.1) with different cross-diffusion cases.

Lemma 2.2Suppose that<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M32','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M32">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M94','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M94">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M95','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M95">View MathML</a>. The positive equilibrium<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34">View MathML</a>of (1.1) is unstable if<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M97','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M97">View MathML</a>and

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M98','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M98">View MathML</a>

for some<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M55','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M55">View MathML</a>, whereas it is uniformly asymptotically stable if<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M100','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M100">View MathML</a>.

Lemma 2.3Suppose that<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M32','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M32">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M102','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M102">View MathML</a>. Then the positive equilibrium<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34">View MathML</a>of (1.1) is uniformly asymptotically stable for disappeared cross-diffusion.

Lemma 2.4Suppose that<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M32','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M32">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M105','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M105">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M106','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M106">View MathML</a>. Then the positive equilibrium<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34">View MathML</a>of (1.1) is uniformly asymptotically stable.

Now we consider the case when <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M108','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M108">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M109','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M109">View MathML</a>. For simplicity, denote

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M110','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M110">View MathML</a>

Then

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M111','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M111">View MathML</a>

We thus have the following result.

Lemma 2.5Suppose that<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M32','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M32">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M108','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M108">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M109','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M109">View MathML</a>. The positive equilibrium<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34">View MathML</a>of (1.1) is unstable if<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M116','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M116">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M117','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M117">View MathML</a>and

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M118','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M118">View MathML</a>

for some<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M55','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M55">View MathML</a>, whereas it is uniformly asymptotically stable if<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M120','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M120">View MathML</a>, or<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M116','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M116">View MathML</a>and<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M122','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M122">View MathML</a>.

Now we consider the corresponding ODE system. Let <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M123','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M123">View MathML</a> be a positive solution of (1.2). It is easy to show that <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M124','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M124">View MathML</a> and <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M125','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M125">View MathML</a> are both well posed. Similar to the proof of Lemma 2.1, we can get the following stability result.

Lemma 2.6Assume that<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M32','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M32">View MathML</a>. The positive equilibrium point<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34">View MathML</a>of (1.2) is locally asymptotically stable. In particular, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34">View MathML</a>is globally asymptotically stable if<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M129','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M129">View MathML</a>.

Proof According to the proof of Lemma 2.1, we can easily obtain local asymptotical stability of <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M130','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M130">View MathML</a> for ODE system (1.2).

Define the following Lyapunov function:

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M131','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M131">View MathML</a>

where ρ is a positive constant to be determined. Obviously, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M132','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M132">View MathML</a>, and <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M133','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M133">View MathML</a> if <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M134','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M134">View MathML</a>. We compute the derivative of <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M135','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M135">View MathML</a> for system (1.2):

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M136','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M136">View MathML</a>

It is easy to demonstrate that <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M137','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M137">View MathML</a> if <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M138','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M138">View MathML</a>. On the other hand, we can choose <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M139','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M139">View MathML</a> and then <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M140','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M140">View MathML</a>. Then we get

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M141','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M141">View MathML</a>

By the Lyapunov-LaSalle invariance principle [34], <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M130','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M130">View MathML</a> is globally asymptotically stable. So the proof of Lemma 2.6 is completed. □

Based on the above discussion, we now can establish some sufficient conditions for the occurrence of Turing instability induced by cross-diffusion. Our main result in this section is the following theorem.

Theorem 2.7Assume that<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M32','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M32">View MathML</a>. The stability of the constant equilibrium<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34">View MathML</a>is stable for the ODE dynamics (1.2) while unstable for the PDE dynamics (1.1) if one of the following two conditions is fulfilled:

(C1) <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M94','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M94">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M97','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M97">View MathML</a>, and<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M147','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M147">View MathML</a>for some<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M55','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M55">View MathML</a>,

(C2) <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M109','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M109">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M116','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M116">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M117','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M117">View MathML</a>, and<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M152','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M152">View MathML</a>for some<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M55','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M55">View MathML</a>.

Remark 2.8 The Turing instability refers to ‘diffusion driven instability’, i.e., the stability of the constant equilibrium changing from stable for the ODE dynamics, to unstable for the PDE dynamics. Lemma 2.4 and Theorem 2.7 imply that cross-diffusion <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M24','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M24">View MathML</a> has a destabilizing effect, which is helpful to the occurrence of Turing instability. Moreover, we can see that sufficiently large cross-diffusion <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M24','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M24">View MathML</a> can guarantee <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M94','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M94">View MathML</a> and <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M116','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M116">View MathML</a>, even <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M97','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M97">View MathML</a> and <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M117','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M117">View MathML</a> under a proper parameter condition. So large cross-diffusion effect <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M24','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M24">View MathML</a> can induce Turing instability.

3 Prior bounds for the positive steady states of the PDE system

The corresponding steady state problem of (1.1) is

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M161','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M161">View MathML</a>

(3.1)

In this section, we give a priori positive upper and lower bounds for positive solutions to the elliptic system (3.1). For this, we need to make use of the following two results.

Lemma 3.1 (Maximum principle [9])

Let<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M162','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M162">View MathML</a>and<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M163','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M163">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M164','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M164">View MathML</a>.

(1) If<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M165','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M165">View MathML</a>satisfies

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M166','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M166">View MathML</a>

and<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M167','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M167">View MathML</a>, then<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M168','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M168">View MathML</a>.

(2) If<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M165','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M165">View MathML</a>satisfies

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M170','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M170">View MathML</a>

and<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M171','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M171">View MathML</a>, then<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M172','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M172">View MathML</a>.

Lemma 3.2 (Harnack inequality [35])

Let<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M165','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M165">View MathML</a>be a positive solution to<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M174','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M174">View MathML</a>with<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M175','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M175">View MathML</a>subject to the homogeneous Neumann boundary condition. Then there exists a positive constant<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M176','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M176">View MathML</a>such that

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M177','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M177">View MathML</a>

In this paper, we assume that the classical solution is in <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M178','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M178">View MathML</a>. The results of upper and lower bounds can be stated as follows.

Theorem 3.3 (Upper bound)

For any positive classical solutionwof (3.1), there exist two positive constants<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M179','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M179">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M8','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M8">View MathML</a>, such that

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M181','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M181">View MathML</a>

Proof Problem (3.1) can be rewritten as

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M182','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M182">View MathML</a>

(3.2)

Let <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M183','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M183">View MathML</a> be a point such that <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M184','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M184">View MathML</a>. Applying Lemma 3.1 to the first equation in (3.2) yields <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M185','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M185">View MathML</a> and

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M186','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M186">View MathML</a>

Denote <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M187','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M187">View MathML</a>. Let <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M188','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M188">View MathML</a> be a point such that <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M189','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M189">View MathML</a>. Since

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M190','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M190">View MathML</a>

from Lemma 3.1, we can obtain <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M191','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M191">View MathML</a> and

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M192','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M192">View MathML</a>

This completes the proof. □

Theorem 3.4 (Lower bound)

Suppose that<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M193','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M193">View MathML</a>. For any positive classical solutionwof (3.1), there exists a positive constant<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M194','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M194">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M8','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M8">View MathML</a>, such that

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M196','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M196">View MathML</a>

Proof Since the inequalities

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M197','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M197">View MathML</a>

Harnack inequality in Lemma 3.2 shows that there exist two positive constants <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M198','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M198">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M8','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M8">View MathML</a>, such that

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M200','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M200">View MathML</a>

Thus,

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M201','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M201">View MathML</a>

By the same way, we have

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M202','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M202">View MathML</a>

On the other hand, by integrating the second equation in (3.1), we have <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M203','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M203">View MathML</a>, which implies that there exists a point <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M204','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M204">View MathML</a> such that <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M205','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M205">View MathML</a>, i.e.,

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M206','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M206">View MathML</a>

So <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M207','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M207">View MathML</a> and

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M208','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M208">View MathML</a>

Now we need to prove v has a positive lower bound. Suppose on the contrary that <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M209','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M209">View MathML</a> does not hold. Then there exists a sequence <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M210','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M210">View MathML</a> with <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M211','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M211">View MathML</a> such that the corresponding nonnegative solution <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M212','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M212">View MathML</a> of (3.1) with <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M213','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M213">View MathML</a> satisfies

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M214','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M214">View MathML</a>

and then

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M215','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M215">View MathML</a>

(3.3)

We may assume, by passing to a subsequence if necessary, that as <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M216','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M216">View MathML</a>,

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M217','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M217">View MathML</a>

By (3.1) and the <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M218','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M218">View MathML</a> regularity theory of elliptic equations, we can conclude that <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M219','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M219">View MathML</a> for any <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M220','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M220">View MathML</a>. Then, for <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M221','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M221">View MathML</a>, by Sobolev embedding theorem, we have <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M222','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M222">View MathML</a>. It follows, by passing to a subsequence if necessary, that <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M212','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M212">View MathML</a> converges uniformly to the nonnegative function <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M224','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M224">View MathML</a> in <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M225','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M225">View MathML</a> as <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M216','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M216">View MathML</a>. Then

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M227','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M227">View MathML</a>

By (3.3), we note that <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M228','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M228">View MathML</a>. Moreover, since

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M229','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M229">View MathML</a>

we have

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M230','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M230">View MathML</a>

Multiplying the above equation by <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M231','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M231">View MathML</a> and then integrating the resulting equation over Ω, we can obtain

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M232','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M232">View MathML</a>

Thus, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M233','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M233">View MathML</a> and then <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M234','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M234">View MathML</a> as <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M216','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M216">View MathML</a>. At the same time, we consider the integral equation

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M236','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M236">View MathML</a>

However, since <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M237','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M237">View MathML</a> as <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M216','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M216">View MathML</a>, we can conclude that <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M239','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M239">View MathML</a> is positive or negative as n is large enough. It is a contradiction. □

4 Non-existence of non-constant positive steady states

The aim of this section is to investigate the non-existence of non-constant positive steady states of problem (1.1) with no cross-diffusion.

Theorem 4.1Let<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M102','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M102">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M241','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M241">View MathML</a>. Then there exists a positive constant<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M242','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M242">View MathML</a>such that problem (1.1) has no non-constant positive steady state provided that<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M243','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M243">View MathML</a>.

Proof For any <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M244','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M244">View MathML</a>, denote <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M245','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M245">View MathML</a>. Assume that <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M35','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M35">View MathML</a> is a positive solution of (3.1) with <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M102','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M102">View MathML</a>. Multiplying the two equations in (3.1) by <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M248','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M248">View MathML</a> and <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M249','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M249">View MathML</a>, respectively, and integrating the results over Ω by parts, we can obtain

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M250','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M250">View MathML</a>

where ϵ is the arbitrary small positive constant arising from Young’s inequality.

Similar to the proof of Lemma 3.3 and Lemma 3.4, we can conclude that

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M251','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M251">View MathML</a>

It follows from the Poincaré inequality that

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M252','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M252">View MathML</a>

Since <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M253','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M253">View MathML</a> if

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M254','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M254">View MathML</a>

we may choose ϵ sufficiently small and <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M255','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M255">View MathML</a> sufficiently large such that <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M256','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M256">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M257','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M257">View MathML</a>. Thus, we can conclude that <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M258','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M258">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M259','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M259">View MathML</a>. Then the proof is completed. □

5 Existence of non-constant positive steady states

In this section, we shall use the Leray-Schauder degree theory to develop a general setting to establish the existence of stationary patterns for system (1.1). Denote

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M260','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M260">View MathML</a>

where C is a positive constant whose existence is guaranteed by Theorems 3.3 and 3.4.

Since the determinant <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M261','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M261">View MathML</a> is positive for all non-negative w, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M262','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M262">View MathML</a> exists and <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M263','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M263">View MathML</a> is positive, thus w is a positive solution of system (3.1) if and only if

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M264','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M264">View MathML</a>

(5.1)

where <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M265','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M265">View MathML</a> is the inverse of <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M266','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M266">View MathML</a> in X, subject to the homogeneous Neumann boundary condition. Since <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M267','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M267">View MathML</a> is a compact perturbation of the identity operator, the Leray-Schauder degree <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M268','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M268">View MathML</a> is well defined if <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M269','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M269">View MathML</a> for any <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M270','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M270">View MathML</a>. Further, we calculate

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M271','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M271">View MathML</a>

We recall that if <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M272','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M272">View MathML</a> does not have any pure imaginary or zero eigenvalue, the index of the operator Ψ at the fixed point <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34">View MathML</a> is defined as <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M274','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M274">View MathML</a>, where r is the total number of eigenvalues of <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M272','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M272">View MathML</a> with negative real parts (counting multiplicities). Then the degree <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M268','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M268">View MathML</a> is equal to the sum of the indexes over all solutions to equation <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M277','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M277">View MathML</a> in <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M278','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M278">View MathML</a>, provided that <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M279','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M279">View MathML</a> on <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M280','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M280">View MathML</a>.

In order to calculate r, we employ the eigenspaces of −Δ. Using the decomposition (2.4) we investigate the eigenvalues of matrix <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M281','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M281">View MathML</a>. First, we know <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M282','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M282">View MathML</a> is invariant under <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M281','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M281">View MathML</a> for each <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M284','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M284">View MathML</a> and each <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M285','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M285">View MathML</a>, i.e., <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M286','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M286">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M287','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M287">View MathML</a> for any <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M287','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M287">View MathML</a>. Hence, μ is an eigenvalue of <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M281','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M281">View MathML</a> on <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M282','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M282">View MathML</a> if and only if it is an eigenvalue of the matrix

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M291','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M291">View MathML</a>

So <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M281','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M281">View MathML</a> is invertible if and only if, for any <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M55','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M55">View MathML</a>, the matrix <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M294','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M294">View MathML</a> is non-singular. Denote

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M295','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M295">View MathML</a>

We notice that if <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M296','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M296">View MathML</a>, then for each <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M297','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M297">View MathML</a>, the number of negative eigenvalues of <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M281','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M281">View MathML</a> on <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M282','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M282">View MathML</a> is odd if and only if <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M300','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M300">View MathML</a>. In conclusion, we have the following result.

Lemma 5.1Assume that, for each<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M55','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M55">View MathML</a>, the matrix<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M302','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M302">View MathML</a>is non-singular. Then

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M303','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M303">View MathML</a>

According to the above lemma, we should consider the sign of <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M304','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M304">View MathML</a> in order to calculate <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M305','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M305">View MathML</a>. Since

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M306','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M306">View MathML</a>

and <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M307','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M307">View MathML</a>, we only need to consider the sign of <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M308','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M308">View MathML</a>. A direct calculation shows

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M309','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M309">View MathML</a>

where

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M310','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M310">View MathML</a>

Let <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M311','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M311">View MathML</a> and <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M312','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M312">View MathML</a> be the two roots of <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M313','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M313">View MathML</a> with <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M314','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M314">View MathML</a>. Then

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M315','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M315">View MathML</a>

So the signs of <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M316','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M316">View MathML</a> and <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M317','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M317">View MathML</a> are identical. Perform the following limits:

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M318','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M318">View MathML</a>

where

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M319','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M319">View MathML</a>

Then we have the following result.

Lemma 5.2Assume that<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M32','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M32">View MathML</a>. Then there exists a positive constant<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M321','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M321">View MathML</a>such that for any<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M322','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M322">View MathML</a>, the two roots<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M311','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M311">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M312','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M312">View MathML</a>of<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M313','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M313">View MathML</a>are all real and satisfy

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M326','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M326">View MathML</a>

(5.2)

Moreover, we can conclude that

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M327','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M327">View MathML</a>

(5.3)

Now we establish the global existence of non-constant positive solution to (3.1) with respect to the cross-diffusion coefficients <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M24','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M24">View MathML</a>, as the other parameters are all fixed positive constants.

Theorem 5.3Assume that the parameters<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M329','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M329">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M255','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M255">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M331','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M331">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M332','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M332">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M333','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M333">View MathML</a>, K, Mandθare all fixed and satisfy<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M243','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M243">View MathML</a>, <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M193','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M193">View MathML</a>and

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M336','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M336">View MathML</a>

(5.4)

Let<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M337','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M337">View MathML</a>be given by the limit in (5.2). If<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M338','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M338">View MathML</a>for some<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M339','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M339">View MathML</a>and the sum<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M340','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M340">View MathML</a>is odd, then there exists a positive constant<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M321','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M321">View MathML</a>such that, if<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M342','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M342">View MathML</a>, problem (1.1) has at least one non-constant positive steady state.

Proof By Lemma 5.2, there exists a positive constant <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M321','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M321">View MathML</a> such that, if <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M342','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M342">View MathML</a>, (5.3) holds and

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M345','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M345">View MathML</a>

(5.5)

We will prove that for any <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M342','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M342">View MathML</a>, (1.1) has at least one non-constant positive steady state. The proof will be fulfilled by contradiction. Suppose on the contrary that the assertion is not true for some <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M347','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M347">View MathML</a>. Let <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M24','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M24">View MathML</a> be fixed as <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M349','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M349">View MathML</a>.

For <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M350','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M350">View MathML</a>, define

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M351','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M351">View MathML</a>

and

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M352','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M352">View MathML</a>

and then consider the problem

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M353','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M353">View MathML</a>

(5.6)

Then w is a non-constant positive steady state of (1.1) if and only if it is a non-constant positive solution of problem (5.6) for <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M354','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M354">View MathML</a>. It is obvious that <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34">View MathML</a> is the unique constant positive solution of (5.6) for any <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M356','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M356">View MathML</a>. From (5.1), we know that for any <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M350','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M350">View MathML</a>, w is a positive solution of problem (5.6) if and only if

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M358','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M358">View MathML</a>

It is obvious that <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M359','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M359">View MathML</a>. Theorem 4.1 indicates that <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M360','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M360">View MathML</a> only has the constant positive solution <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34">View MathML</a> in <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M362','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M362">View MathML</a>. A direct calculation shows that

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M363','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M363">View MathML</a>

In particular,

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M364','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M364">View MathML</a>

Here <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M365','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M365">View MathML</a>. Moreover, we already know that

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M366','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M366">View MathML</a>

(5.7)

and <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M307','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M307">View MathML</a>.

For <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M354','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M354">View MathML</a>, by (5.3), (5.5) and (5.7), we have

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M369','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M369">View MathML</a>

Thus, 0 is not an eigenvalue of the matrix <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M302','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M302">View MathML</a> for all <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M371','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M371">View MathML</a>, and

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M372','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M372">View MathML</a>

is odd. It follows from Lemma 5.1 that

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M373','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M373">View MathML</a>

(5.8)

For <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M374','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M374">View MathML</a>, we have

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M375','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M375">View MathML</a>

(5.9)

from Theorem 4.1.

On the other hand, by Theorems 3.3 and 3.4, there exists a positive constant M such that for all <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M350','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M350">View MathML</a>, the positive solution of (5.6) satisfies <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M377','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M377">View MathML</a> and <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M378','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M378">View MathML</a> on <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M379','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M379">View MathML</a>. By the homotopy invariance of the topological degree, we can obtain

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M380','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M380">View MathML</a>

(5.10)

Now, by our supposition, both equations <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M381','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M381">View MathML</a> and <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M360','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M360">View MathML</a> have only the constant positive solution <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M34">View MathML</a> in <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M384','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M384">View MathML</a>. Thus, by (5.8) and (5.9),

<a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M385','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M385">View MathML</a>

which contradicts (5.10). The proof is completed. □

Remark 5.4 Condition (5.4) may be fulfilled if m is much larger than K, and K is rather small in comparison with m and θ. Moreover, the conclusion in Theorem 5.3 coincides with the discussion in Section 2. So we know that large cross-diffusion effect <a onClick="popup('http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M24','MathML',630,470);return false;" target="_blank" href="http://www.boundaryvalueproblems.com/content/2013/1/155/mathml/M24">View MathML</a> is helpful to the formation of stationary patterns.

Remark 5.5 The results of Theorems 2.7, 4.1 and 5.3 show that large cross-diffusion effect of the first species can create not only Turing patterns but also stationary patterns (non-constant positive steady states).

Competing interests

The author declares that she has no competing interests.

Acknowledgements

The author is supported by the Tianyuan Youth Foundation of NSFC (No. 11026067) and the National Natural Science Foundation of China (No. 11201204). The author appreciates the referee for the helpful comments and suggestions.

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