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)

www.icm.csic.es/scimar

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

The known:about 6000 species of

prokaryotesabout 80000 species of

protistsWhat is the unknown?

How many “taxons” of microbes are there?

How much room for unknown taxons is there?

1. Numbers2. Niches

1 cm3 105 prokaryotic cells

1 dm3 108 prokaryotic cells

Most clone libraries

Yungas

Nothofagus forest

1 m3 1011 prokaryotic cells

Venter’s study of Sargasso Sea

Equivalent to 2 x 106 km2 of trees

1.4 x 109 km3

1029 prokaryotic cells

The whole ocean

1st Postulate:

The number of microbial cells is enormous

Morse et al.: NatureMore niches as size decreases due to

fractal structure of nature

Lake Cisó (Girona)

Purple sulfur bacteria

H2S SO4

e-

CO2 OM

Purple sulfur bacteria:Usually several species

coexist in nature

Growth rate

(h-1)

102030405060708090024681012Van Gemerden (1974)C.vinosumC.weisseiTime (days)6 hours light / 6 hours dark

Percent of cells

00,10,20,30,40,50,6-50050100150200Van Gemerden (1974)C.vinosum SulfideC.weissei SulfideC.vinosum SulfurC.weissei SulfurTime (h)

Dark Light

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 communitiessuggests 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 lowAND COROLLARY (FICTION?)

FACT

Science (2005) 310: 1878

3th Postulate:

The number of microbial taxons is VERY large

Range: 103 to 106 (perhaps even 109) taxons

T.L. Erwin 1991ecologist

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 Margalefecologist

Taxon number

Individuals

Diversity

“Seed bank”

Biodiversity = Diversity + “Seed bank”

Two kinds of taxons

Molecular techniques

Taxon number

Individuals

Culture techniques

Seed bankDiversity

Taxon number

Individuals

Diversity

Difficult to know

Biodiversity = Diversity (Knowable) + “Unknowable”

Diversity

Seed bankBIODIVERSIT

Y

How much room for species is there?

1. Numbers2. Niches

All the marine bacterioplankton-derived 16S ribosomal DNA sequences … were analyzedWhen … 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 analysisIn 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. Numbers2. Niches

It is sufficient to estimate the area under the species-area curve for a given environmentNumber 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 6400-38000 per g

On a large scale: Whole Oceans 2 x 106 1 Tm Soils 4 x 106

Science (2005) 310: 502

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