Stability Analysis in Dynamics of Plant Herbivore System With Mating Induced Allee Effect

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1 IOSR Journal of Mathematics (IOSR-JM) e-issn: , p-issn: X. Volume 11, Issue 2 Ver. III (Mar - Apr. 215), PP Staility Analysis in Dynamics of Herivore System With Mating Induced Allee Effect Vijayalakshmi.S 1, Sahayajothi.S 2, Gunasekaran.M 3, * 1,2 Department of Mathematics, D.R.B.C.C.C. Hindu College, Chennai PG Department of Mathematics, Sri Suramaniya Swami Government Arts College, Tiruttani Astract: Insect herivores are hypothesized to e major factors affecting the ecology and evolution of plants. Earlier, plant-herivore models were phrased in terms of total vegetation iomass and total herivore population. Allee effect is an important dynamics phenomenon elieved to e manifested in several population process, notaly extinction and invasion. In this paper, a discrete-time plant-herivore model with mating induced Allee effect is investigated. We otain asymptotically stale conditions of the equilirium points which are suject to the Allee effect. The Allee effect which occurs on plant population is discussed y staility and numerical analysis. This study suggests that Allee effect has stailizing effect on -Herivore system. Keywords: -herivore system, Mating, Allee effect, Staility analysis, Equilirium points. I. Introduction Interactions etween plants and herivores have een studied y ecologists for many decades. Some ecological models, which are simple in mathematical expression, have een designed to study population temporal dynamics. In particular, the pioneering work in the field was initiated y May [18, 19]. Allee effect is a crucial phenomenon that has drawn considerale attention from ecologists [1, 3, 4, 6, 9, 15, and 2]. Various mechanisms related to Allee effect have een discussed as singular entities. It descries a positive interaction among individuals at low population sizes or densities, and these interactions may e critical for survival and reproductions. The population goes extinction elow a threshold and increases aove the threshold population density. Allee effect is therefore important in conservation of endangered and exploited species [13, 14, 16, and 21]. The Allee effect can e caused y any numer of causes, for example, mating etween the individuals of a species at low population densities. Other causes can e largely reduced defense against herivores, special trends of social dysfunction, etc. Some investigations have shown that Allee effect may e a destailizing factor in an ecological system [25]. But some papers have addressed the Allee effect with focus on the stailizing effect [12, 24, and 31]. Most studies on plants and animals have shown that Allee effect is common in nature [1, 2, 1, 22, and 23]. Darwin was the first of a long series of evolutionary otanists interested in mating system evolution [7, 8]. At the heart of this approach was the central role of floral iology and pollination process. The usual frame work for discrete-generation plant-herivore model [17, 3] has the form P t+1 = P t f 1 P t f 2 a, H t H t+1 = g 1 P t g 2 H t (1) P t - The density of edile plant iomass in generation t. H t - The population density of herivore at time t. f 2 a, H t - The effect of the herivore on the plant population growth rate with f 2 a, = 1 a - The amount of damage caused y herivore. g 1 P t - The function of plant density. g 2 H t - The non- linear function of herivore density. Many consumer-resource models assume a non-linear relationship etween resource population size and attack rate [3]. For plants and insect herivores, we similarly expect a non-linear functional relationship, due to herivore foraging time and satiation. The relationship is expressed in terms of plant iomass units rather than population size, ecause herivores are unlikely to kill entire plants. The growth function F(P t ) determines the amount of new leaves availale for consumption for the herivore in generation t. We assume that the herivores search for plants randomly. The area consumed is measured y the parameter a, i.e., a is a constant that correlates to the total amount of the iomass that an herivore consumes. The herivore has a one year life cycle, the larger a, the faster the feeding rate. After attacks y herivores, the iomass in the plant population is reduced to the following model which is reformulated from (1). P t+1 = F(P t )e ah t H t+1 = P t 1 e ah t (2) DOI: 1.979/ Page

2 Staility Analysis in Dynamics of Herivore System With Mating Induced Allee Effect F P t - The amount of new leaves availale for consumption for the herivore in generation t. e ah t - Proaility of the plant escapes from the herivore. 1 e ah t - Proaility of the plant attacked y the herivore. Noting that the system 2 represents the dynamics of a system where the plant is attacked efore it has a chance to grow. II. The model Now we consider the system 2 when the plant population is suject to Allee effect [17, 26, 27, 28, 29, and 3] as follows: P t P t+1 = r e ah t 1 + P t H t+1 = P t 1 e ah t 3 P t - The term for mate-finding Allee effect. 1 + P t - The Allee effect constant. r - The intrinsic growth rate of the plant. Noting that the consequence of Allee effect is that to get rid of the hardness to find a mate (induced self- fertilization or pollinating agent) at low population density Fixed point and Local staility We now study the existence of fixed points of the system (3), particularly we are interested in the non-negative interior fixed point and we list all possile fixed points. i) E =, is trivial or extinction fixed point. ii) E 1 = r 1, is the axial or exclusion fixed point in the asence of the herivore (H=). iii) E 2 = P, H is the interior fixed point, where P X log X = and a( ) H log X = (4) a r where X =. 1+P III. The Dynamical ehavior of the model In this section, we investigate the local ehavior of the model 3 around each fixed point. The local staility analysis of the model 3 can e studied y computing the variation matrix corresponding to each fixed point. The variation matrix of the model at the state variale is given y P t+1 = F 1 P, H H t+1 = F 2 P, H for which the Jacoian matrix is given y J = J(P, H) = r e ah arp e ah 1+ P 2 1+ P (5) 1 e ah Pae ah The characteristic equation of Jacoian matrix can e written as 2 Tr (J) + Det (J) = where Tr is the trace and Det is the determinant of the Jacoian matrix J (P, H) which are defined as r e ah Tr = + 1+ P 2 Pae ah and Det = rape ah 1+P Pe ah 1+P 2 rape ah 1+P Pe ah Hence the model (3) is a Dissipative dynamical system if < 1 and Conservative 1+P 2 dynamical one if and only if rape ah 1+P Pe ah =. In order to study the staility of the fixed point model, 1+P 2 we first give the following theorem and lemma. Theorem: If P λ = λ 3 + B λ 2 + C λ + D= is the characteristic equation of the matrix then the following statements are true: a) If every root of the equation has asolute value less than one, then the fixed point of the system is locally asymptotically stale and the fixed point is called a sink. ) If at least one of the roots of the equation has asolute value greater than one, then the fixed point of the system is unstale and the fixed point is called a saddle. DOI: 1.979/ Page

3 Staility Analysis in Dynamics of Herivore System With Mating Induced Allee Effect c) If every root of the equation has asolute value greater than one, then the fixed point of the system is a source. d) The fixed point of the system is called hyperolic if no root of the equation has asolute value equal to one. If there exists a root of equation with asolute value equal to one, then the fixed point is called Nonhyperolic [11]. Preposition: 1 The fixed point E is locally asymptotically stale if r < 1, otherwise unstale. Proof: In order to prove the result, we estimate the Eigen values of the Jacoian matrix J at E is given y r J(E ) = The Eigen values of J at E are λ 1 r and λ 2 =. Thus E is stale if r < 1. If r > 1 then the fixed point E is unstale. Preposition: 2 The fixed point E 1 is stale if it satisfies the condition 1 r < a+ a Proof: In order to prove the result, we estimate the Eigen values of the Jacoian matrix J at E 1 is given y 1 a 1 r J(E 1 ) = r a r 1 The eigen values of J at E 1 are λ 1 = 1 a r 1 r 2 =. The point E 1 is locally asymptotically stale if 1 a r 1 < 1 and < 1, which implies that r > 1 a+ and r r a 1 is stale if 1 r< a+ a Lemma: If the Eigen values of the Jacoian matrix of the fixed point are inside the unit circle of the complex plane, the fixed point E 2 is locally stale. Using Jury s condition [5], the necessary and sufficient conditions for local staility of interior fixed points for 1,2 <1, are (i) 1+Tr(J)+Det(J)> (ii) 1 Tr(J)+Det(J)> (iii) Det(J) < Local Staility and Dynamical ehavior around interior fixed point E 2 We now investigate the local staility of interior fixed point E 2. The Jacoian matrix (5) at E 2 has the form J(E 2 ) = ra 2 2 X a +XlogX 2 X ralogx a +XlogX logx Its characteristic equation is 2 Tr(J(E 2 )) + Det(J(E 2 )) =. (7) where Tr(J(E 2 )) = = B ra logx a+logx 1 and Det(J(E 2 )) = = B a +X logx 2 2. By Lemma, using formulas of Tr and Det, the interior fixed point is locally stale if we find that the inequality (i) is equivalent to 1+B 1 +B 2 > which implies that B 1 +B 2 > 1, the inequality (ii) is equivalent to B 1 B 2 <1, the inequality(iii) is equivalent to B 2 <1. For the interior fixed point E 2 the roots of eq. (7) are 1,2 = B 1 ± B B2 2 B B 2 < 2. ra 2 2 logx X a +XlogX 2 +. Both eigen values are locally asymptotically stale if B 1 + B B 2 < 2 and B 1 IV. Numerical Analysis In this section, we numerically descrie our analytical results otained in the former sections y using MATLAB programming. We present the time series graphs for the plant-herivore system with Allee effect. In particular, we illustrate the stailizing effects of Allee function on plant population. Fig.1, Fig.2 and Fig.3 (See Appendix) shows the time series graphs for Herivore, and DOI: 1.979/ Page (6)

4 Staility Analysis in Dynamics of Herivore System With Mating Induced Allee Effect -Herivore populations respectively, when a=.45, =15.4, P =.2 and H =.25. These diagrams are consistent with the analytical results otained in the former sections. V. Discussion and Conclusion Ecological facts lead us to the importance of an Allee effect on population dynamics. In this paper we studied such an effect on plant population. By comining mathematical and numerical analysis, we have shown the impact of Allee effect on plant population on the staility of the positive equilirium point for a discretetime plant-herivore system. As it is expressed y many researchers, the impact of the Allee effect on the staility population models can show different dynamics which strictly depend on the assumptions of the corresponding model. Hence, it is not surprising that while Allee effect is a destailizing force for some models, for some others it might e a stailizing force. As we analyze in this study for our plant-herivore model, Allee effect has a stailizing force. Furthermore, we conclude from numerical analysis that, for some fixed parameter values, Allee effect changes the staility of the positive equilirium points from unstale to stale position. In this paper, we have studied the Allee effect on the plant population. However, it may e very complicated structure when the herivore population (or, oth plant and herivore population) is suject to an Allee effect in the system. In the future studies, it would e very interesting to improve such structures. References [1]. Allee, W.C., 1931.Animal Aggregations: A study in General Sociology. University of Chicago Press, Chicago. [2]. Amarasekare, P., Interactions etween local dynamics and dispersal: insights from single species models. Theor. Popul. Biol. 53, [3]. Andrew M. Kramer, Brain Dennis, Andrew M. Liehold, John M.Drake., 29. The evidence for Allee effects.popul.ecol.51: [4]. 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5 & Herivore Herivore Staility Analysis in Dynamics of Herivore System With Mating Induced Allee Effect Dr M Gunasekaran received B.Sc.,M.Sc., and M.Phil., in Mathematics from Bharathidasan University, Tiruchirapalli, Tamil Nadu in 1989, 1991 and 1992 respectively. He completed his Ph.D degree in Mathematics-Zoology from University of Madras, Chennai. He is a Professor of Mathematics with 23 years of teaching experience and now he is working in Sri SuramaniyaSwamy Government Arts College, Tiruttani. His areas of research are Drug designing, Mathematical models in Prey-Predator system, -Herivore system and Queuing system. He has pulished 15 international journals, presented 7 research papers in various National and International Conferences. He has supervised 15 M.Phil., scholars in the area of various Queuing models. He has also given invited talks in National and International conferences in his specialized areas. Appendix: Herivore Fig.1 series graph for Herivore population (a=.45; =15.4;p =.2,H =.25) Fig.2 series graph for population (a=.45; =15.4;p =.2,H =.25) 6 5 Herivore Fig.3 Series graph of -Herivore system (a=.45; =15.4; Po=.2, Ho=.25) DOI: 1.979/ Page