Abstract Study of perturbation experiments is crucial for conservation biology. We carry out Monte Carlo simulations on finite-size lattices composed of n species ( n ≤ 4). The value of mortality rate m of top predator is altered to a higher or lower level, and a fluctuation enhancement (FE) is explored. Here FE means an uncertainty in population dynamics. It is found for n ≥ 2 that FE is observed, when m is decreased. Namely, when we protect the top predator, its population dynamics becomes very difficult to predict.