ECOLOGICAL AND HISTORICAL FACTORS IN FERN BIOGEOGRAPHY

Remarkable diversity in recognized endemic centres as well as noteworthy disjunct distributions have led students of the pteridophytes to seek historical explanations for these phenomena. A suite of distinctive attributes limit the array of possible explanations: most biogeographically significant are (1) the smaller number of species-range determinants, and (2) the substantial capacity for long-distance dispersal. These attributes constrain the train of events triggered by global events and culminating in the particular phylogenetic history of an evolutionary lineage. Fern biogeographers most often infer historical changes in habitat distribution predicated by climatic change from distribution patterns of phylogenetic lineages. Long-distance dispersal and vicariance are both prominent explanations for present-day disjunct distributions. Endemic centres develop in tropical wet-montane regions because of long-distance dispersal of species into the centres and retention of species in these ecologically diverse centres. Geographical rather than ecological isolation probably provides the isolation for evolutionary divergence in these species-rich regions.