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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