Uncertainty in ecological catastrophe

The dynamics of spatial pattern in a prey-predator system is studied by applying the lattice model of position-fixed reaction. This system exhibits a phase transition between a phase where both prey and predator survive, and a phase where predators are extinct. This phase transition or catastrophe is brought about by very small disturbances, for example, the prey population abruptly increases, even though the reproduction rate of prey slightly decreases. It is, therefore, found that the catastrophe has both properties of phase transition and indirect effect. If such a catastrophe occurs in real ecosystems, it is hopeless to determine the origin of the catastrophe.