Nonequilibrium phase transition in a lattice prey-predator system

We study a lattice model of a prey-predator system. Mean-field approximatio n predicts that the active phase, i.e., one with a finite fraction of preys and predators, is a generic phase of this model. Moreover, within this app roximation the model exhibits quasi-oscillations resembling Lotka-Volterra systems. However, Monte Carlo simulations for a one-, two-, and three-dimen sional versions of this model do not support this scenario and predict that at a certain value of some parameter the model enters the absorbing state, i.e., a state where the entire population of predators dies out and the mo del is invaded by preys. Simulations for the one-dimensional version indica te that the transition into the absorbing state belongs to the directed per colation universality class. (C) 2000 Elsevier Science B.V. All rights rese rved.