Pacific Mycogeography: An Appraisal

Abstract

Biogeographers often stress the importance of considering all biotic groups when searching for generalizations about the distribution of organisms in space and time. Biotas consist of associated and coevolved organisms, strictly dependent or interdependent, yet having different life histories and dispersal capabilities. Data derived from studies of such associations should more rigorously test biogeographical scenarios calling for either dispersion* or migration* as the mechanism responsible for disjunct distributions. Despite frequent references to the potential significance of data awaiting discovery, especially within the realm of microorganisms, and complaints about chronic inadequacy of data provided by anyone group of organisms individually, few biogeographers have ventured from the well-trodden tracks of zoo- and phytogeography into the microbial underworld or sought cooperation of workers in these more 'peripheral' disciplines. Consistently neglected are the Fungi which are now widely acknowledged to represent the third major Kingdom of land-based organisms. As obligate carbon heterotrophs, the fungi have been intimately linked with plants throughout their long history, and are a potentially rich source of phytogeographical data because the association is often sufficiently close and specialized to impose restrictions on the freedom of movement of components either individually or in partnership. The evolution of the now dominant groups of phytotrophic fungi is probably linked with, and parallels the rise to dominance of, the angiosperms. However, the history of the Fungi extends beyond that of the angiosperms and is often marked by morphological and ecological stability of low-ranking taxa since the Mesozoic or earlier (Pirozynski 1976). The fossil history of fungi is still fragmentary but, as records accumulate, fungal data may offer clues to phylogenetic and geographical relationships between extinct and extant angiosperms, as well as between the angiosperms and their precursors. Why, then, have fungi been almost totally ignored by biogeographers? Several legitimate factors, as well as some misconceptions, have contributed to the situation. The major obstacle to the pursuit of mycogeography is our still poor understanding of phylogenetic relationships within the fungi. Hierarchies of taxa based on biological relatedness are the fundamental units of biogeography. Mycological taxa are more typological than zoological or botanical, more open to different interpretations and consequently less reliable as biogeographical units.