A Discrete Numerical Scheme of Modified Leslie-Gower With Harvesting Model

Recently, exploitation of biological resources and the harvesting of two populations or more are widely practiced, such as fishery or foresty. The simplest way to describe the interaction of two species is by using predator prey model, that is one species feeds on another. The Leslie-Gower predator prey model has been studied in many works. In this paper, we use Euler method to discretisize the modified Leslie-Gower with harvesting model. The model consists of two simultanious predator prey equations. We show numerically that this discrete numerical scheme model is dynamically consistent with its continuous model only for relatively small step-size. By using computer simulation software, we show that equlibrium points can be stable, saddles, and unstable. It is shown that the numerical simulations not only illustrate the results, but also show the rich dynamics behaviors of the discrete system.


INTRODUCTION
For many years, the predator-prey relationship has been the most popular topics in mathematical modelling.One of the model is known as Leslie-Gower predator-prey model.It was introduced by [1] and written as follow.) where () represents the density of the prey at time t with intrinsic growth rate  1 ; while () represents the density of the predator at time t with intrinsic growth rate  2 . 1 and  2 are the strength of competition among individuals of the prey and predator respectively.The main difference between Leslie-Gower model and Lotka-Volterra that is in Leslie-Gower model carrying capacity of the predator is proportional to the number of prey [2].Since then, the model has been modified by numerous experts, such as [3] and [4].
Finite difference has been used to discretize the continous model to find its numerical solution approximation.The common method is Euler Method [5].This technique has been applied to various models, for instance [6], [7] , [8] , and [9].It is found that the obtained discrete model may show rich dynamics.However, divergent approximation may be occur.Hence, stepsize plays an important role to avoid inconsistency of the model.

A Discrete Numerical Scheme of Modified Leslie-Gower With Harvesting Model
Riski Nur Istiqomah Dinnullah 43

Numerical Discretization and Its Equilibria
The model we use in this paper is written as follow.
where H and P represent the density of the prey and predator in time t respectively.In this model, we also assume that 0 <   <   ,  = 1,2 to control the density of the prey and predator.
We are now derive the discrete version of the (2).Applying Euler scheme to the first equation of ( 2) leads us to the following form: Applying Euler scheme to the second equation of ( 2) leads us to the following form: Combining ( 3) and (4) leads us to the following system: Having found the discrete version, the next step is find the equilibria of (5).Suppose that ( * ,  * ) is the equilibrium of ( 5), then we have Since step-size ℎ > 0 then we have that is either A Discrete Numerical Scheme of Modified Leslie-Gower With Harvesting Model Riski Nur Istiqomah Dinnullah 44 On the other hand we have since h > 0 then we have that is either By looking at (8) and (12), we have the first equilibrium, that is Next, by substituting (8) to (13) we have the second equilibrium, that is The third equilibrium is found by substituting (12) to (9), that is The last equilibrium is found by solving ( 9) and ( 13), that is where .

Figure 1. Numerical Solution Approach 𝐸 2
In Figure 1, we use (0.5; 0.2) as the initial condition and step-size ℎ = 0.1.We found that the numerical solution approach the  2 = (0,3).From this simulation, we can infer that the equilibrium point  2 is stable for relatively small step-size.

Figure 2. Numerical Solution of Second Simulation
In Figure 2, we use (0.1; 0.1) as the initial condition.We found that the numerical solution is close to  4 but never reach the point.From the simulation, we can conclude that  4 is an unstable equilibrium.

Figure 3. Numerical Solution of Third Simulation
In Figure 3, we use (0.01; 0.01) as initial condition.We found numerically that  1 is an unstable equilibrium while  2 is a stable equilibrium.

A Discrete Numerical Scheme of Modified Leslie-Gower With Harvesting Model
Riski Nur Istiqomah Dinnullah 47

CONCLUSION
From this paper, a discrete numerical scheme of modified Leslie-Gower with harvesting model has been investigated.We use Euler-method to discretisize the model.We found four equilibrum points with their properties.The  1 ,  3 , and  4 are unstable equilibrium, while  2 is the stable one.It is shown that the discrete model is dynamically consistent with its continuous model only for relatively small step-size h.Further works, especially about stability-analysis need to be considered.Furthermore, the discrete model may show complex dynamical behaviors, such as bifurcation and chaos phenomenon.

Figure 4 .
Figure 4. Numerical Solution of The Fourth Simulation