Robert May ecologist

Photo: Hubble Telescope We have a catalog of all the celestial bodies our instruments can detect in the universe, but …

… we ignore how many living beings share the Earth with us

Census of Marine Life The known, the unknown and the knowable O’Dor & Gallardo 2005 Scientia Marina (modified from Falkowski & de Vargas 2004)

O’Dor & Gallardo Yarincick & O’Dor 2005 Scientia Marina 69 (Suppl 1)

The known: about 6000 species of prokaryotes about species of protists What is the unknown? How many “taxons” of microbes are there?

How much room for unknown taxons is there? 1. Numbers 2. Niches

1 cm prokaryotic cells

1 dm prokaryotic cells Most clone libraries

Yungas Nothofagus forest

1 m prokaryotic cells Venter’s study of Sargasso Sea

Equivalent to 2 x 10 6 km 2 of trees

1.4 x 10 9 km prokaryotic cells The whole ocean

1st Postulate: The number of microbial cells is enormous

Morse et al.: Nature More niches as size decreases due to fractal structure of nature

Lake Cisó (Girona) Purple sulfur bacteria H 2 S SO 4 e - CO 2 OM

Purple sulfur bacteria: Usually several species coexist in nature

Growth rate (h-1)

Percent of cells

DarkLight

2nd Postulate The number of potential niches is very large

Only a few thousand Hagström et al. Appl. Env.Microbiol. 68, 3628–3633 (2002). Perhaps two million Curtis et al. Proc. Natl Acad. Sci. USA 99, 10494–10499 (2002). How many taxons of bacteria are there in the sea?

The species difference between related communities suggests that the number of species of bacteria may be more than a THOUSAND MILLION. … speciation in bacteria is easy and extinction difficult, … giving a rate of speciation higher than the rate of extinction, … leading to an ever increasing number of species over time.

The abundance of individuals in microbial species is so large that dispersal is rarely (if ever) restricted by geographical barriers … global species number is relatively low AND COROLLARY (FICTION?) FACT

Science (2005) 310: 1878

3th Postulate: The number of microbial taxons is VERY large Range: 10 3 to 10 6 (perhaps even 10 9 ) taxons

T.L. Erwin 1991 ecologist Determining the number of species today is like reaching for the stars; there is no way with the data available today that we are even going to get reasonably close Photo: National Geographic

Biodiversity vs diversity Ramon Margalef (1997) Our Biosphere, Excellence in Ecology Series 10 Biodiversity is the dictionary Diversity is the words used in a book Ramon Margalef ecologist

Taxon number Individuals Diversity “Seed bank” Biodiversity = Diversity + “Seed bank”

Two kinds of taxons

Molecular techniques Taxon number Individuals Culture techniques Seed bank Diversity

Taxon number Individuals Diversity Difficult to know Biodiversity = Diversity (Knowable) + “Unknowable”

Diversity Seed bank BIODIVERSITY

How much room for species is there? 1. Numbers 2. Niches

All the marine bacterioplankton-derived 16S ribosomal DNA sequences … were analyzed When … dereplicated by using 97% similarity as a cutoff, 1117 unique ribotypes were found. We conclude that the apparent bacterioplankton species richness is relatively low.

Analysis of many clones from 10 sampling sites … dominant ribotypes were few (5 in average) and they were often already retrieved in previous analysis In contrast, a large part of each library was new or never found in previous studies… majority of rare ribotypes were specific to each location (I.e. endemic)..surprisingly low global diversity (around 2000 ribotypes)

T. Pommier, B. Canbäck, K. Hagman, L. Riemann, K. Simu, A. Tunlid & Å. Hagström (in preparation)

How much room for species is there? 1. Numbers 2. Niches

It is sufficient to estimate the area under the species-area curve for a given environment Number of spp can be calculated from the total number of individuals and the abundance of the most abundant members On a small scale: Oceans 160 per mL Soils per g On a large scale: Whole Oceans 2 x Tm Soils 4 x 10 6

Science (2005) 310: 502

Data from Rosenzweig et al. (1994) Genetics 137:903 Redrawn by Dykhuizen (1998) Ant. Van Leuuwen. 73:25