RANDOMNESS, SYNCHRONY AND POPULATION PERSISTENCE

The dynamics of populations whose life cycle includes a stage which is resistant to the external disturbances, is examined over a large range of time scales of the environmental change. Non-Markovian models show that when the disturbance and the resistant stage have comparable time scales, population persistance increases with increasing duration of disturbance; persistence in all harshly varying environments depends on the level of synchronization of the environmental and population processes. Population dynamics in fully periodic environments cannot approximate the dynamics in stochastic environments. An increasing number of sources of variation in the environment probably accounts for the increasing stability of population trajectories. Applications to empirical studies of population dynamics and life history strategies, as well as to parasite and pest control problems, are briefly discussed. Drugs and pesticides may be more effective when applied at variable intervals.