Geographic distribution and diversity of free-living heterotrophic flagellates
ABSTRACT As yet, no consensus has emerged on the geographic distribution of free-living heterotrophic flagellates or on the overall diversity of the group. A survey of the literature on the distribution of flagellates from marine zones reveals that more than half the species have been reported from a single location. This suggests that these organisms are often endemic. In a series of original surveys of flagellates, about 40 per cent of the 350 species were reported from a single location, again suggestive of endemism. When the communities from these surveys are compared using the clustering algorithm in PRIMER, there is, in contrast, no evidence of endemism because the communities from geographic regions do not cluster together. Communities cluster on the type of habitat from which they were drawn, and this suggests that geographic location may play no part in the make-up of communities. The conflict of insights from information on species and information on communities creates uncertainty over the geographical distribution of flagellates. This is probably because the actual distribution of these organisms is obscured by factors extrinsic to their distribution, principally issues relating to under-reporting and to arguable species concepts. Our interpretation of available data is constrained by the morphological species concepts. Our interpretation is that there are not many species of heterotrophic flagellates (perhaps no more than 3,000) and most have a cosmopolitan distribution. We believe that there are assemblages of flagellates with distinctive taxonomic compositions, but that we are unable to describe these more precisely until we reduce the impact of factors which are external to the biology of the organisms but which influence our understanding of the structure of communities of heterotrophic flagellates.