PREDICTING DISPERSAL SPECTRA - A MINIMAL SET OF HYPOTHESES BASED ON PLANT ATTRIBUTES

1 The dispersal mode adopted by a plant species is frequently associat ed with other attributes of the plant and its habitat. In this paper w e review these associations and present a set of hypotheses which, whe n considered together, make a probabilistic prediction of the dispersa l mode adopted by a plant species. When applied to a species list, the hypotheses can be used to generate a prediction of its dispersal spec trum, i.e. the percentages of different dispersal modes that have been adopted. 2 The formulation of such a set of hypotheses has several pu rposes: (i) to summarize existing knowledge about dispersal adaptation s and their interrelations with other attributes of plants and their h abitats; (ii) to couch that knowledge in such a way that falsifiable p redictions can be made; (iii) to arrive at provisional conclusions abo ut which factors are the most important in shaping the evolution of di spersal mode in different plants or different environments. 3 The revi ew of relationships between dispersal mode and other attributes of pla nts and their habitats lead to the following provisional conclusions; (i) seeds larger than 100 mg tend to be adapted for dispersal by verte brates while those smaller than 0.1 mg tend to be unassisted; most see ds, however, are between 0.1 and 100 mg, and in this range all of the dispersal modes are feasible; (ii) plant growth form and stature (some times in relation to the canopy height of the vegetation) seem to excl ude certain dispersal modes; (iii) the availability of specific disper sal vectors seems rarely to be an important determinant of dispersal m ode; (iv) attributes of the physical environment also seem rarely to b e important, except indirectly through their influence on plant statur e and seed size.