POPULATION CYCLING IN SPACE-LIMITED ORGANISMS SUBJECT TO DENSITY-DEPENDENT PREDATION

We present a population model with density-dependent disturbance. The model is motivated by, and is illustrated with, data on the percentage of space covered by barnacles on quadrats of rock in the intertidal z one. The autocorrelation function observed indicates population cyclin g. This autocorrelation function is predicted qualitatively and quanti tatively by the detailed model we present. The general version of the model suggests the following rules regarding cycling in space-limited communities subject to density-dependent disturbances. These rules may apply to any space-limited community where a density-dependent distur bance reduces population densities to very low levels, like fire or wi nd for plant communities. We propose that the period of the cycle will be approximately equal to the time it takes the community to reach a critical density plus the average time between disturbance events when the density is above that critical density. The cycling will only be clear from autocorrelation data if the growth process is relatively co nsistent, there is a critical density (which the sessile organism reac hes and passes) above which the probability of disturbance increases r apidly, and the time to reach the critical density is at least twice t he average time between disturbance events.