Of the>2000 eukaryote taxa recorded, those identified to species level with
sufficient associated geographical information were allocated to size classes,
and the percentage of cosmopolitan species calculated for each size class. The
curve that emerged for Priest Pot (Fig.9.4) appeared fairly smooth, apart from
the low value datapoint marking the smallest size class (arrow), which was
almost certainly a consequence of undersampling worldwide. Most species in
that size class were chrysomonads, and species-level identification requires
electron microscopy and other specialized techniques. Nevertheless, 43 of the
50 species of the flagellated chrysomonadParaphysomonasknown worldwide
were recorded from Priest Pot.Testing the theory of cosmopolitan distribution
Cryptic protist diversity exceeds the diversity of ‘active’ species,
and the habitat selects
Ubiquitous dispersal of free-living microbial eukaryotes implies that a large
species richness will exist wherever life is possible. This will rarely be obvious,
however, because most microbial species are usually encysted or in some other
cryptic, inactive state, waiting for the arrival of conditions that support popu-
lation growth. However, with patience and experimental manipulation (e.g.
Finlay, Esteban & Fenchel,1996a; Fenchelet al., 1997) it is usually possible to
coax these cryptic species to excyst and grow so that they become detectable.
The limited information available indicates that the ‘seedbank’ of cryptic
species richness can be very diverse. In order to investigate this, we examinedFigure 9.4The proportion
of eukaryote species at
Priest Pot that are
cosmopolitan, arranged in
logarithmic size classes.
The principal taxa
contributing to the upper
shoulder of the curve are
protozoa, gastrotrichs,
rotifers, ostracods,
nematodes and
cladocerans. The main
taxa in the lower part of
the curve are triclads,
molluscs, aquatic insects
and leeches. Adapted from
Finlay and Fenchel (2004 ).172 B. J. FINLAY AND G. F. ESTEBAN