Download File - International Census of Marine Microbes

Geographic variations in microbial cytometric diversity
William Li
Bedford Institute of Oceanography
Canada
William Li reviewed some of the recent reports in the literature that address issues
surrounding microbes and spatial scaling.
He pointed out that a compilation of extant
microbes listed in textbooks might fall short of a true census because the concept of species is
problematic. Bill outlined recent studies on soil fungi and salt marsh bacteria in which the
taxa-area relationships were used to extrapolate from local to regional scales. The slopes of
these relationships were low, indicating that taxonomic richness is not greatly dissimilar at
different scales, suggesting a ubiquitous distribution of many microbes. However, more
recent studies of bacteria in water-filled treeholes and of phytoplankton in limnetic and marine
systems indicate that the slopes are much higher in non-contiguous habitats. In other words,
diversity at local scales may not be easily extrapolated to the global scale. The taxa-area issue
remains unresolved for marine microbes. Bill suggested that Alan Longhurst’s concept of the
biogeochemical provinces in the ocean might be one way to focus our census efforts. This
approach has been used to scale up primary production from the regional to the global scale.
For the census of marine microbes, it therefore seems worthwhile to understand the patterns
and mechanisms that relate microbial diversity to primary production.
Spatial scaling of microbial soil fungi
“The taxa-area relationship … was relatively flat (slope z=0.074) … This suggests that despite high local
diversity, microorganisms may have only moderate regional diversity.” (Green et al. 2004 Nature 432:747-750).
Spatial scaling of salt marsh sediment bacteria
“The z-values for bacteria … are among the lowest … for any organisms, suggesting that turnover of bacterial
taxa at these spatial and taxonomic scales may be lower than that of most other organisms.” (Horner-Devine et
al. 2004 Nature 432:750-753).
Spatial scaling of bacteria in water-filled treeholes
“Bacterial genetic diversity in this system increased with increasing island size according to the familiar
species-area power law (Fig. 1A). The slope z of the relationship (z = 0.26) is indistinguishable from published
values for larger organisms (Fig. 1B). The data show that area size strongly influences the diversity of these
microbial communities.” (Bell et al. 2005 Science 308:1884).
Spatial scaling of phytoplankton (laboratory cultures to oceans)
“Phytoplankton species richness thus scales smoothly and consistently from laboratory microcosms to the
world’s oceans, with 74% of the observed variance in S being attributable to variations in ecosystem surface
area alone. z-value = 0.134 ” (Smith et al. 2005 PNAS 102:4393-4396).
Spatial scaling of small organisms – are they ubiquitous? - maybe
“Both a and b-components of species diversity are size-dependent: there are many more species in smaller
size classes in any one local community, but at a global scope the situation changes drastically.” (Azovsky
2000. Web Ecology 1:28-34)
Spatial scaling of small organisms – are they ubiquitous? – maybe not
“Physical population isolation may be more common than is currently appreciated, as the ability to detect
isolation clearly depends upon the resolving power of the genetic marker(s) used and the habitats and
organisms examined.” (Papke and Ward 2004)
Biogeochemical provinces: a basis for examining geographic variation
Longhurst (1995) Ecological Geography of the Sea. Academic Press
10
-2
-1
Areal primary production (g C m d )
Biogeochemical provinces: a possibility to scale diversity through production?
1
NWCS
GFST
ARCT
BPLR
NASE
NASW
0.1
0.01
0.1
1
10
Area (106 km2)
data of Longhurst et al. (1995) Journal of Plankton Research 17:1245-1271
100
Biogeochemical provinces: a possibility to scale diversity through production?
NWCS
GFST
ARCT
BPLR
NASE
NASW
-1
Primary production (Gt C y )
10
1
P = 0.43 A0.46
0.1
0.1
1
10
Area (106 km2)
data of Longhurst et al. (1995) Journal of Plankton Research 17:1245-1271
100
“Diversity is a unimodal function of biomass or productivity” (Irigoien et al.)
Diversity is maximum at intermediate levels of biomass or productivity because of nutrient or food
limitation at low levels, and selective grazing or predation at high levels.
(Irigoien et al. 2004 Nature 429:863-867)
Cytometric richness is maximum at intermediate biomass
Cytometric richness (S)
200
ALL z<200m
NWCS
z<20m
GFST z<20m
NWCS
z<20m
ARCT z<20m
GFST
z<20m
BPLR z<20m
ARCT
NASE z<20m
BPLR
NASE upwelling
z<20m
z<20m
NASWupwelling
NASE
z<20m
z<20m
NASW z<20m
150
100
50
0
10-4
10-3
10-2
10-1
100
Chlorophyll (mg m-3)
data of Li (2002) Nature 419:154-157
101
102