are studying the dynamics of populations of the intertidal mussel
Mytilus californianus, a dominant species of the intertidal
zones of the North American continent. This species is found in
narrow bands in shore sites of moderate to high wave exposure.
The predators of M. californianus are the sea star, Pisaster
ochraceus, in the low intertidal Pacific Northwest, and the
spiny lobster, Panulirus interruptus, in Southern California.
We are interested in how zonation occurs in the intertidal zone
and what controls the levels of zonation.
model a region of the intertidal zone as an open system (Figure 1).
We assume a constant input of mussel larvae which settle onto
the substrate. Mussels grow asymptotically towards a terminal
size. Mussels die due to non-predatory mortality or they are consumed
by predators. Predators immigrate into the system at a constant
rate and emigrate from the system at a rate that decreases with
the amount of prey being consumed. As mussels increase in size
they become more resistant to predation. In the spatially-explicit
models, the recruitment of mussel larvae is enhanced by the presense
of surrounding mussels and the vulnerability of a mussel to predation
decreases with the size of its neighbors.
have developed a multiple model approach to the study of predation
in benthic communities. Four classes of models have been developed
and analyzed: (1) an analytical “mean field” approximation
consisting of ordinary differential equations (ODE),
(2) a stochastic birth-death (SBD)
version of the mean field ODE model, (3) a spatially-explicit
cellular automata (CA)
model, and (4) a spatially-explicit agent-based model (ABM).
A set of model parameters values are common to all four model
types. Comparison and cross-validation can be made among models
in order to take advantage of the strengths and that each has