Original articles
A delayed fractional order food chain model with fear effect and prey refuge

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Abstract

A delayed fractional-order prey–predator system with fear (felt by prey) effect of predator on prey population incorporating prey refuge has been proposed. We consider a three species food chain system with Holling type I functional response for the predator population including prey refuge. The existence and uniqueness of the system is studied along with non-negativity and boundedness of the solutions of proposed system. Next, local stability of the equilibria has been studied for both delayed and non-delayed systems. We have also established that the non delayed system is globally stable under some parametric restrictions. Finally we have discussed the Hopf bifurcation due to time delay and other parameters both theoretically and numerically by the help of MATLAB and MAPLE.

Introduction

Food chain models are very popular in the field of biomathematics. Several researchers have analyzed ecological models based on at least three trophic levels [23], [27]. The study of a mathematical model should be based on at least three trophic levels such that more focus can be made on complex behavior demonstrated by deterministic models comprised of three or more trophic levels [37]. Practically, different three species systems have become the center of significant attention in its own right. Researchers have drawn their attention on food chain system of waste-bacteria-ciliates in waste treatment process [23]. Recently, many researchers are also working on three species system in fractional order system [2], [16]. In this work, we have concentrated on fractional order system on three species model.

Fractional differential equation is a modern concept and this is a part of abstract mathematics. Fractional order system has the effect of existence of time memory but this effect is absent in integer order system. Fractional order derivative is correlated to the entire time domain for a biological process while integer order derivative indicates a change of certain trait at particular time [35]. There are few works on fractional order delay in recent years [16], [38], [47], so we have drawn our attention to develop a delayed fractional order system with different prey–predator interaction.

The fear of predator on prey affects the anti-predator defenses and reduces the reproduction rate of prey. Many researchers propose the effect of predation based on direct intake of prey by predators, there is a straightforward corroboration that the fear of predators is as important as direct consumption [3]. Many creatures have faced predation threat and have shown different kinds of anti-predator responses like change in habitat usage, foraging behaviors, vigilance and physiological changes [3], [5], [36], [45], [48]. Nowadays many researchers are developing mathematical models based on fear effect [3], [7], [28], [31], [49], [51].

A refuge is renowned for protecting a constant fraction of prey from predation. The behavior of hiding of prey may stabilize the predator–prey dynamics and the prey refuges are protected from predation. A refuge is an idea in biology and ecology, where an organism acquires protection from predation by hiding themselves in a region where they are isolated or inaccessible for predation. The existence of refuges has an important role on the coexistence of prey and predators [29], [41], [42], [46]. There are some empirical and theoretical works that analyze the influence of prey refuge [6], [8], [24], [39], [43], [44].

Motivation: The ecology of fear admits that predators behave both ways in affecting prey populations with knock-on effects down the food chain. Predators kill prey, which affects prey populations. However, predators also terrify prey who exhibit a variety of anti-predator defenses to avoid being predated on the other hand prey refuges create food crisis for predators [50]. There are many works that have been done on prey–predator dynamics incorporating prey refuge and fear effect [19], [51]. The effect of fear vastly impacts on prey’s feeding which has effects down the food chain strongly. The previous works on prey–predator interaction incorporating prey-refuge and fear effect have been based on classical integer order system. In spite of enormous amount of works focused on fractional differential equation and dynamical systems, there are remain many challenging open problems. Motivated by the recent works [2], [6], [8], [19], [38], [47], [51], we have constructed our model by considering the both responses fear and refuge in a delayed Caputo fractional order food chain model. This is due to that fact that fractional order system is more precise for the explanation of memory and hereditary properties of the system compared with an integer order system [13], [20], [34]. The objectives of this paper are as follows:

  • 1.

    To investigate the impacts of prey refuge in food chain system.

  • 2.

    To investigate the impacts fear effect in food chain system.

  • 3.

    To study the impacts of gestation time delay in food chain system.

Brief overview: We have organized our work in several stages. Initially, we have formulated a three species food chain model incorporating prey refuge and fear effect with gestation time delays in Section 2. We have also considered the case without gestation time delay. Section 3 deals with the introductory theories. Section 4.1 contains the equilibrium points of both non-delayed and delayed systems and their feasibility criteria. In Section 4.2, we have studied the existence and uniqueness of the non-delayed system which assures the existence and uniqueness of the delayed system. Further, non-negativity and boundedness have also been established theoretically in Section 4.3. Next, we have analyzed local and global stability of the non-delayed system in Sections 4.4 Local stability analysis of non delayed system, 4.5 Global asymptotic stability respectively. In Section 5, we have studied delayed system and established local stability criterion and also studied the Hopf bifurcations with respect to the gestation time delay. The remaining sections (6–7) contain numerical simulations and conclusions of the whole work respectively.

Section snippets

Formulation of model

Our aim is to formulate a food chain model incorporating fear effect and prey refuge. Before demonstrating the fear effect in our model, let us assume that the prey population (X) maintains a logistic growth in absence of predation and effect of fear. The logistic growth of prey (X) can be split up into three portions; reproductive rate (R), natural death rate (D), and density dependent death rate due to intraspecific competition (I). We have the following ODE with respect to the time T: dXdT=RX

Introductory theories

In this section we have recalled some important theories which are helpful for our further analysis. Our model is based on Caputo fractional differential equations and we have recalled some basic definitions, Mittag-Leffler function and some conditions for stability of equilibrium in this section.

Definition 1

[33], [35]

The fractional order derivative in Caputo sense with order ε>0 for a function fCn([t0,+),R) is denoted and defined as: t0CDtεf(t)=1Γ(nε)t0tf(n)(s)(ts)εn+1ds,whenε(n1,n),nN t0CDtεf(t)=dndtnf(t)

Analysis of non delayed model (2.4)

In this section, we have discussed about the non delayed system (2.4). The various equilibria of systems (2.3), (2.4) are mentioned in Section 4.1. The uniqueness and boundedness of the solutions of systems (2.3), (2.4) have been discussed in Sections 4.2 Existence and uniqueness, 4.3 Non negativity and boundedness of solutions respectively. The local stability and global stability of our proposed non-delayed system (2.4) have been performed in Sections 4.4 Local stability analysis of non

Analysis of delayed system (2.3)

The system (2.3) and system (2.4) have same set of equilibrium points. The conditions for existence, uniqueness, boundedness, nonnegativity obtained for system (2.4) also hold for system (2.3). The stability criterion is different for delayed system (2.3) due to gestation time delay τ and we have observed Hopf bifurcations in certain interval of τ and outside this region the solutions are asymptotically stable. The following lemma is required before analyzing the delayed fractional order

Numerical simulations

In this section, numerical simulations have been performed using Adams–Bashforth–Moulton Predictor–corrector method [11], [12] and the scheme developed by Ivo Petras to validate the theoretical results established in the previous sections. In addition, the effects of fractional order, time delay and prey refuge on the stability of the equilibrium points have been presented. We are more interested in the stability of coexistence equilibrium E3 rather than trivial E0, axial E1 or predator free

Conclusions

In this study, we have investigated a fractional order food chain model with refuge in presence of time delay and fear effect on the prey. First, we have discussed the fractional order model without time delay. It is observed that the system is locally and globally asymptotically stable under restricted parametric conditions. Numerically, it is found that no bifurcation occurs for our chosen parametric values. It is also observed that periodic nature of the solutions increases when the order of

Acknowledgments

The authors are grateful to the anonymous referees, Prof. Laura Gardini, Editor-in-Chief, for their careful reading, valuable comments and helpful suggestions, which have helped them to improve the presentation of this work significantly.

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