COEXISTENCE OF BANKSIA SPECIES IN SOUTHWESTERN AUSTRALIA - THE ROLE OF REGIONAL AND LOCAL PROCESSES

60 of the 75 Banksia species are confined to southwestern Australia wh ere five or six species often coexist. We explored the role of regiona l species richness, niche differentiation, and habitat specialization in structuring banksia assemblages. The diversity of growth forms and categories of seed production and response to fire were assessed in ac tual assemblages at 40 sites throughout southwestern Australia. Divers ity indices at each site were compared with those from null communitie s assembled on the basis of the abundance and sociability of taxa in r egional species pools. The relationship between local and regional spe cies richness suggests that processes at the scale of 100-m(2) quadrat s limit local richness and therefore coexistence. However, there was n o consistent evidence that taxa are differentiated by growth form or r egeneration strategy. No particular biological profile makes a banksia adept at coexisting with a wide range of other taxa. Habitat speciali zation is an important factor contributing to lower local richness tha n would be predicted from niche differentiation of taxa in regional po ols. There is recent empirical evidence of several mechanisms whereby the number of coexisting banksias is increased beyond the limits sugge sted by simple niche theories. Variability in the fire regime also pro vides a mechanism for maintaining local species richness because diffe rent fires favour recruitment of different taxa.