Growth and refuge location in continuous, modular organisms: experimental and computer simulation studies

Guilds of crustose bryozoans exhibited a range of growth outlines, varying from circular to elongate, and the stones on which they grew contained a range of refuge types, varying in size from a few mm² to a few hundred cm². These refuges, if encountered by the growing colonies of competitively subordinate species such as Electra pilosa L., enabled the latter to avoid competitive exclusion due to overgrowth mortality. Computer simulations suggested that, although modular organisms which are elongate are, in general, more likely to encounter spatial refuges than those with a different shape through vegetative growth, shape is less important than the size of the organisms themselves or the size and density of the spatial refuges. Moreover significant interactions between these 4 variables showed that they should be considered together and not in isolation from one another. Examples are given of variable growth forms in continuous, modular organisms from different taxa, including plants, and the importance of these predictive studies to refuge location by modular organisms is discussed.