The form of an organism is often closely linked to its function, and this relationship may be particularly important in organisms where individual form is highly flexible due to the repeated iteration of minute multicellular modules. In many modular taxa, including the bryozoans discussed in this thesis, each module is able to function as largely independent units; an individual module can feed independently, has a separate gut, and has the potential to reproduce. These characteristics mean that the number of modules in a bryozoan colony, and hence its size, is a reasonably accurate measure of the colony’s ability to both capture resources and to produce sexually developed larvae. Size is therefore a more appropriate measure of colony demography than age, the criterion traditionally used for unitary organisms. However, processes that can complicate the demography of modular organisms such as colony damage, fission or fusion also mean that the age structure of the component modules in a colony or fragment remains an important predictor of colony functioning, interacting with the effects of colony size. (For complete abstract open document)