Stochastic density dependence in population size of a benthic clonal invertebrate: the regulating role of fission

The influence of environmental variation on the demography of clonal organi sms has been poorly studied. I utilise a matrix model of the population dyn amics of the intertidal zoanthid Palythoa caesia to examine how density dep endence and temporal variation in demographic rates interact in regulating population size. The model produces realistic simulations of population siz e. with erratic fluctuations between soft lower and upper boundaries of app roximately 55 and 90% cover. Cover never exceeds the maximum possible of 10 0%, and the population never goes to extinction. A sensitivity analysis ind icates that the model's behaviour is driven by density dependence in the fi ssion of large colonies to produce intermediate sized colonies. Importantly , there is no density-dependent mortality in the model, and density depende nce in recruitment, while present, is unimportant. Thus it appears that the main demographic processes which are considered to regulate population siz e in aclonal organisms may not be important for clonal species.