INDIVIDUAL BASED SIMULATIONS OF THE DIRECT AND INDIRECT EFFECTS OF LIMPETS ON A ROCKY SHORE FUCUS MOSAIC

Ecological models that include spatial processes can produce complex p atterns in space and time. However, the ecological relevance of such b ehaviour remains unclear. Previous work has generally focused on syste ms where the dynamics of simulated species are closely linked. We pres ent a stochastic spatial model for an open system where species are on ly weakly or indirectly linked. The principal interaction, that limpet s reduce the local probability of Fucus recruitment, was defined empir ically. Fucus abundance at large scales could be approximated without resorting to a spatially explicit model. However, the behaviour of ind ividual limpets at intermediate densities could alter Fucus abundance and small scale spatiotemporal pattern. By altering small scale patter n, in simulations, limpets could also affect the population densities of poorly dispersing species dependent on Fucus cover. Increasing the temporal variability of limpet or Fucus populations at large scales le d to correlated dynamics at different spatial scales in simulations. T here was little correlation between scales in time series taken from t he field. This weak correlation between scales suggests that local eff ects, such as those associated with individual limpet grazing, are imp ortant in the dynamics of a real system. Development and testing of th e model are facilitated because predictions apply to clearly definable temporal and spatial scales.