Apparent global ubiquity of species in the protist genus Paraphysomonas

Evidence is presented for the ubiquity of protist species, Using the exampl e of protists that leave traces (siliceous scales) of their recent populati on growth, we show that most - perhaps all species in the genus Paraphysomo nas, are ubiquitous, Of the species recorded in surveys carried out worldwi de, we have identified 78% of their number in 0.1 cm(2) of sediment collect ed from a freshwater pond (total area 10(8) cm(2)) in England, Moreover, th e pond appears to act like a microcosm of aquatic environments in general, for species that are globally rare or abundant, are likewise rare or abunda nt in the pond. We assume that the rate of neutral migration to the pond is greatest for the globally abundant species, As these species are probably capable of growth in a broad range of conditions, they will more frequently encounter the environment they require for population growth, Thus globall y abundant species are also locally abundant in the pond - a pattern that w ill be amplified by periodic cyst production. Ubiquitous dispersal is proba bly driven by very high absolute abundance of individuals, and the water co lumn of the pond was estimated to support >10(14) Paraphysomonas individual s, Ubiquity will dampen rates of speciation, and the evidence presented her e indicates that global species richness of Paraphysomonas is indeed modest - perhaps close to what is already known.