Models of open populations with space-limited recruitment: extension of theory and application to the barnacle Chthamalus montagui

1. Barnacles are a good model organism for the study of open populations wi th space-limited recruitment. These models are applicable to other species with open supply of new individuals and resource limitation. The inclusion of space in models leads to reductions in recruitment with increasing densi ty, and thus predictions of population size and stability are possible. 2. Despite the potential generality of a demographic theory for open space- limited populations, the models currently have a narrow empirical base. In this study, a model for an open population with space-limited recruitment w as extended to include size-specific survival and promotions to any size cl ass. The assumptions of this model were tested using data from a pan-Europe an study of the barnacle Chthamalus montagui Southward. Two models were con structed: a 6-month model and a periodic annual model. Predicted equilibria and their stabilities were compared between shores. 3. Tests of model assumptions supported the extension of the theory to incl ude promotions to any size class. Mortality was found to be size-specific a nd density independent. Studied populations were open, with recruitment pro portional to free space. 4. The 6-month model showed a significant interaction between time and loca tion for equilibrium free space. This may have been due to contrasts in the timing of structuring processes (i.e. creating and filling space) between Mediterranean and Atlantic systems. Integration of the 6-month models into a periodic annual model removed the differences in equilibrium-free space b etween locations. 5. Model predictions show a remarkable similarity between shores at a Europ ean scale. Populations were persistent and all solutions were stable. This reflects the apparent absence of density-dependent mortality and a high adu lt survivorship in C montagui. As populations are intrinsically stable, obs ervations of fluctuations in density are directly attributable to variation s in the environmental forcing of recruitment or mortality.