Past President's Address: Protistan Biogeography: Why All The Fuss?


  • 1Article based on a Past-President's address given at the annual meeting of the International Society of Protistologists held jointly with the Phycological Society of America at the Crowne Plaza Hotel In Providence-Warwick, RI, August 5–9, 2007.

Corresponding Author: David A. Caron, Department of Biological Sciences, University of Southern California, 3616 Trousdale Parkway, Los Angeles, California 90089-0371; e-mail:


ABSTRACT. Conflicting hypotheses regarding the distribution of protistan species on our planet have led to rather impassioned arguments in the recent literature, and heated discussions at scientific meetings. Both sides of this debate have mounted seemingly credible arguments for endemism on the one hand, or ubiquitous dispersal of protists on the other. At present, the controversy appears unending, perhaps because it is fueled by a convergence of unresolvable issues involving the enormous phylogenetic breadth of species presently encompassed by the term “protist,” the application of multiple species concepts to these taxa, the inability of extant techniques and technology to plumb the depths of microbial diversity in natural ecosystems, and a lack of knowledge regarding the relationship between dispersal rates and rates of evolution of protists. These issues have made it difficult to erect and test hypotheses concerning the distribution of protists. In the absence of definitive experimental or observational information, preconceived attitudes regarding protistan distributions have dominated the interpretation of the available data. On the positive side, the debate has led to the development and application of new approaches to the study of protistan diversity, and stimulated discussions involving how (and why) we define protistan species.